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Basic Electronics

1.1 Resistance It is the property of substance which opposes the flow of current through it. In any substance there are limit number of free electrons as charge which are agent for current flow. So no. of electrons in given substance determines the flow of current. As already mentioned there are limit number of electrons as free electrons so it cause to limit the flow of current .This limitation represents the property to oppose the flow of current. The resistance is essential electrical property of element or substance through which we can control the flow of control and we can be able to use electrical and electronic device as we want. For example we can change the speed of FAN by changing the different value of resistance in the path from the current source to device. The resistance is abbreviated by letter “R”, and its unit is OHM or .The symbol of resistor is

Resistance is expressed by given formula, R= where is resistivity of given element or substance, l –length of substance or wire, A – cross sectional area of the substance or wire. According to the OHM’s law the resistance is formulated by formulae, R= where V is potential difference or voltage, I is current flow through resistor. This law states that the current flow is directly proportional to voltage if resistance is constant. So the resistor is linear device as in any fixed resistor current increases linearly with increment of voltage. Resistor, its types, its combination formula and applications RESISTORS

the

the the the

It is basically electrical component which has property of opposing the flow of current through it. The resistors are of many types regarding to its construction, application, etc. symbol of resistor is or and is abbreviated by letter R. the basic unit of resistor is ohm. Resistor is the component made of different composition and materials to fulfill the property of resistance or to limit definite amount of flow of current. Written By Ir. Shanta Maharjan

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Basic Electronics

Resistors can be divided in many different types by construction (composition), use or applications. Types by construction 1. Fixed resistor: fixed resistors are those resistors whose resistance is fixed or cannot change once it is manufactured. 1.1 Carbon resistor: this is most common resistor made of carbon clay composition with tinned connecting leads. It is low power rating resistors and available of 0.1 watt to 2 watts maximum. Tolerance of this type of resistance is 5% to 20%. This type of resistor creates the noise during the electron passing from one particle to another particle so is it is less used where low noise is required. It is low cost device so it is most common and economical in application. 1.2 Carbon film and metal film resistor: It is constructed by film deposited technique of depositing a thick film of resistive material (pure carbon and some metals) on to an insulating glass ceramics and other insulating substrate in the manner depicted. Metal film resistors can range in the value up to 10000MOhm and much smaller than wire wound resistors..It exhibits the tolerance of 1%. 1.3 Wire sound resistor-It is made of long wire wounded around insulating cylindrical core .the wire is made of 60% copper and 40% nickel. It is used where high power resistor is required .It is found power rating or 5 watts to 200 watts. Tolerance of this type resistor is also low only up to 10%.In precision construction the tolerance is decreased up to 0.0005%. 1. Variable resistors. Variable resistor means the resistors whose value can be changed as required. We can change the value of resistance by changing length of the resistive plate used for resistor. 1.1 Carbon deposited potentiometer or variable resistor: Here the middle terminal which can swing from first terminal to last terminal. The output is taken from the middle terminal and another anyone terminal. The value of POT is found some mega ohms.

Written By Ir. Shanta Maharjan

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Basic Electronics

1.2 Wire wound variable resistor. It is similar in function with POT. The wire wound type is used where high power rating resistors are required. Series and parallel combination of resistors We need to combine the resistors in series and parallel (shunt) to achieve different values as in manufacture the standard values of resistors only manufactured. Same ways we need to calculate total value of resistors for calculating different other values for example to find current, voltages. 1. Series combination For series combination the total value is calculated by simply adding number resistors which are in series. As, R total=R1+R2+ …+R n 2. Parallel combination: The total resistance of shunt resistors is given by the formula: = Applications Although the resistors are used to limit current flow, its application in electronics is various as function at particular cases. 1. To limit currant at given path of current flow as controlling speed of AC/DC motors. 2. To divide voltage: Since the voltage source is constant for full given circuit, it needs to divide the voltage for different component with different voltages. It can be done with different voltage dividing shunt, series methods. 3. To change time constant-In many circuits where the charge, discharge works as wave shaping, triggering etc the resistor act as time delay so it is used in time domain circuits. 4. Resistors are also used to control the capacitance by controlling voltage so it is used for filtering, tuning etc (in TV).


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Basic Electronics

Inductance Inductance is property of substance which can store the charge by virtue of magnetic flux coupling in changing current across it. The stored charge as voltage, which is opposite of source voltage cause of reducing the resulting voltage and reduces the flow of current through it. It can be redefined that it is the property of physical substance which tends to oppose the change of current through it. As the current changes the magnetic flux produced by current in inductor or device crosses itself and induces a electromotive force (emf).It is opposite of source voltage in polarity so it reduce the resulting voltage and in result the current flow through decreases. The opposing voltage increases with the rate of change of current. So high frequency current it opposes more current so it is expressed in property of inductance. For DC the inductance is zero as there will not develop any back emf as no magnetic flux induces in inductor. Inductor, its types, series-parallel combination, applications

Inductor Inductor as device is coil (rounded) conductive wire which is used an inductive device. The main concept of inductor is the magnetic flux which when in round shaped accumulates in small space so the magnetic flux density increases and inducement of magnetic flux also increases. By formula the inductance is expressed as, L= where 0 is permeability of free space, 0 is relative permeability of core material, N no. of turns; A-area of one turn, l- is length of coil. The inductance is expressed by letter “L” and unit is Henry. The symbol of inductor is


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Basic Electronics

Inductor as constant resistor for constant frequency is called inductive reactance and formulated by formula, X L =2 In terms of changing current the inductance can be defined as, L= where the inductance increases with the high change in current.

Types of inductors: By using purpose 1. Fixed inductor: those inductors which are fixed shape and not any changing facility of change the inductance is called fixed inductors. 2. Variable inductors: in these type inductors the one of parameters as length, area, no. of turns of coil, core changeable. Mostly the core of inductor is varied to change the inductance of inductor for different inductances. BY core 1. Air core: this type of coil with no core which is called air core. The air core is with very low inductance at range of 0.1 . 2. Iron core: here is used the core of soft magnetic irons or laminated iron plates. It increases the inductance up to 50 H which is very high value. Transformers are example of iron core. By frequency range 1. Filter chokes: It is for purpose of very low frequency range 50-60 Hz. It is used in power supply AC/DC smoothing. This type of inductor should be high inductance as 50 H etc. 2. Audio frequency chokes: this type of chokes is used to filter in the audio range electronic circuits as in radio-amplifiers etc. 3. Radio frequency chokes: it is used in radio transmission-reception, modulation where very low inductances are reauired.Mostly small air core inductors are used in radio frequency range applications.

Series and Parallel combination 1. Series combination The inductors in series connection are similar to resistors as given below. L total=L1+L2+…+L n 3. Parallel connection: Its parallel connection also same as resistor as 4. =


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Applications 1. It is used as DC smoothing purpose is power supply. 2. It is used in tuning the frequency channel in receiver. 3. It is also used in oscillator to generate frequency. 4. is used as filter to pass definite range of frequency

Capacitance When two conductive plates are separated with insulation between them the device can accumulate charge. But charging and discharging takes time so when there is changing voltage the process of charging, discharging oppose the change in voltage across it. This property of tending oppose the change in voltage is called capacitance. The capacitance is abbreviated with C and measured in Farad. The symbol of the capacitance is

The value of capacitance with charge and voltage is given by C= It means if 1 coulomb of charge accumulate for 1 volt then it is called 1 farad of capacitance is the given value of capacitor. If it is 2 farad then the charge should be double for 1 volt unit. In the case of reactance the capacitive reactance is X c= Capacitance of a capacitor may also be defined in terms of its property to oppose the change of voltage in the circuit. In that case, C= where i- is charging current, rate of change of voltage When the rate of change or high frequency voltage is given then the capacitance is increased. According to construction the capacitance can be defined as, C=K where K is dielectric constant of material used between the plates,A effective area of plates and d distance between the plates. The construction of inductor is given below.


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Types of capacitor 1. Ceramic capacitor: It is most used type as it is cheap. It is made of ceramic composition. Its value available from 100pF to 0.1 The tolerance may be from 20% to 100% as its vale depends upon the temperature, given voltages etc. 2. Paper capacitor: In this type the capacitor is made of paper as insulator and conductive metallic paper also used as conductive metallic paper. It is small and cheapest one. The available value is from 500pF to 50 The tolerance is 20%. 3. Film capacitor: The film capacitor is made of thin plastic as insulator as Mylor, Teflon or Polyhelene. So it is high reliable and low tolerance of 5%.It can work up to 200 C. The value available in construction is from 500pF to 10 It can work up to high voltage 1000 volts. 4. Mica capacitor: Mica is transparent, high dielectric strength mineral that is easily formed into uniform sheets as thin as 0.0025mm.It has high breakdown voltage and is almost totally chemically inert. It posses very small leakage current .Available capacitance ranges 1pF to 0.1 4. Electrolytic capacitor: To gain high capacitance it is made from some special chemical soaked paper as insulator. This chemical makes the two plates as positive and negative terminals so it is strongly noticed one to connect correct polarity with voltage source. Similarly the user not should not exceed the rated value of voltage, if not it will explode. It can be found the values of certain farad to 50 thousand . 5. Variable capacitors: there are many types of variable capacitors. The most used variable capacitor is gang capacitor which has air insulation, used in radio receiver tuning. It rotates in axis and change the effective area for capacitance. The series and parallel combinations Written By Ir. Shanta Maharjan

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1. Series combinations: In this connection the value is added as the parallel form of resistors as, = 2. In parallel connection the total value will be, C total=C1+C2+…+C n Applications 1. As inductor the capacitors are also used for filters. 2. Used in signal shaping circuits. 3. Used tuning, oscillating etc. 4. Voltage dividing application

1.2 Voltage and current source In any electric and electronic circuit there should be source either voltage or current source. A source is to supply power to load which is connected with it. Almost all power supplies in circuits are voltage source as electrical power house mains voltage, battery voltage. But there are some sources as solar cell where actually source is current created by the solar energy.

So source can be divided in two types as voltage source and current source. Voltage source: Any source which produces voltage output continuously is known as voltage source. The voltage source may be AC or DC source. DC voltage source: this source is the constant same polarity source of voltage. The connecting lead voltage polarity remains same at all time of supplying voltage. If the connecting lea d is positive then it remains only positive and same in the case of negative. The examples of constant DC source are batteries, cells, DC generators. Written By Ir. Shanta Maharjan

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Basic Electronics

When a load is connected with load sources the current flow from the positive terminal to load and load to negative terminal of the source. The flow of current is in only one direction so it is called direct current. Since a battery or DC source is originated in some materialistic medium it consists an internal resistance. So the real output from the source is somehow lower than the real source. When a batter source is used and with time being the battery voltage decreases as the internal resistance increases.

When RL is connected with the source voltage with source the load current will be IL= Same as the terminal voltage will be V terminal= V source-IL. R in AC voltage source: AC voltage source is the device from which the load gets alternating voltage. It means the terminal voltage periodically changes from negative to positive and again to negative and so for all time of using. The examples of AC sources are AC mains, some oscillators etc. The internal resistance equivalent source resistance is called internal impedance as for DC components. The circuit given for AC source is given by circuit.

Here IL= Same as terminal voltage is V terminal=VS- IL. Z in


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Current source: It is the constant current source that supplies current to a load even if its impedance varies. The symbolic representation of such an ideal source is given below.

When we talk about the ideal current source the load should not open as in open circuit the current does not flow. There is not ideal current source as the voltage may exist. A practical current source can be represented with an parallel impedance Zin..

The shunt resistance is called internal impedance of the source and accounts for the fall in output current with the increase in the load impedance. If a load impedance ZL is connected across the output terminals, the current source supplied by the source will be different from IS. The current supplied by the source will be divided itself between two branches –one made of the source internal impedance ZL external to the source. The Load current IL being equal to In practical term the larger the internal impedance Z in comparing to load impedance ZL the smaller is the ratio and better it operates as a constant current source.

1.2.1 Current Controlled Dependent Voltage Source


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The current-controlled dependent voltage source as shown above, produces a voltage proportional to the current, ix, in a different branch of the network. The transresistance, ρ, in ohms is multiplied by i x in amps to produce the dependent source voltage in volts. Unlike the two previous examples, we cannot simply designate the controlling branch by its nodes. Since there could be multiple branches carrying very different currents between any pair of nodes, we must explicitly identify the branch of the controlling current. Eventually, we will be able to do this with any type of element. However, the only reliable method of doing this at present is to use an independent voltage source as an ammeter to report the current of the controlling branch to the dependent source. Usually, this means you must insert a zero-valued independent voltage source in series with the branch containing the controlling current so that the controlling current enters the positive terminal of the independent voltage source. However, if there happens to be an independent voltage source that monitors the controlling current you can use it. If necessary, use a minus sign to get the right polarity.

1.2.2Current Controlled Dependent Current Source

The current-controlled dependent current source produces a current proportional to the controlling current, ix, flowing in a different branch. The current gain, β, is Written By Ir. Shanta Maharjan

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dimensionless. Designating the control scheme is similar to setting up the currentcontrolled dependent voltage source previously discussed. We must use a voltage source connected in series with the controlling element so that the controlling current enters the positive terminal of the independent voltage source used as an ammeter. If no voltage source is needed for its voltage, we use a zero-valued voltage source as shown in the figure.

1.2.3 Voltage Controlled Voltage Source

In the above figure, we find the dependent source whose positive terminal is designated as "n+" and whose negative terminal is designated as "n-." The controlling voltage is a branch voltage at some other circuit location. In this case, the positive terminal of the controlling branch is designated as "nc+" while the negative terminal is designated as "nc-" The "gain" of the dependent voltage source is , a dimensionless quantity. For example, if vx happened to be 16.0 volts while  = 4, then node "n+" would be at 64.0 volts higher potential than node "n-."

1.2.4 Voltage Controlled Current Source


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In the above voltage-controlled dependent current source a current equal to times vx flows from node "n+" through the source and out node "n-." γ is called the transconductance and has the dimensions of Siemens (inverse ohms). For example, if the controlling branch voltage, vx , equals 6.0 volts and the transconductance, γ, is 0.25 Siemens, the current produced by the dependent source is 1.5 amps.

Kirchhoff’s voltage and current law Kirchhoff’s current Law Kirchhoff’s voltage law states that the algebraic sum of current at any node or point is zero. It means the incoming current and outgoing current always equal.

Mathematically, or I in = I out For above figure, iin1+iin2=iout1+iout2+iout3 Kirchhoff’s voltage Law Kirchhoff’s voltage Law states that the algebraic sum of the products of currents and resistance in all parts of the network is equal to the algebraic sum of the emf in the circuit. source=V distribute


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V=I1R1+I2R2+...+I n .R n Example

Find the current through the R3. For loop of V1, I1.R1+I1.R2+ (I1+I2) R3=V1 Or 50 I1+150 I1+ (I1+I2)100=5 Or, 200 i1+100 I1+ 100 I2 =5 Or, 300 I1 +100I2=5…..eq.(1) For loop V2, I2.R5+I2.R4+ (I1+I2) R3=V2 Or, 50 I2+20I2+100 I1+100I2=4 Or, 100I1+170I2=4…..eq. (2) Multiplying eq.2 by 3, 300I1+510I2=12…..eq.3 Comparing eq.1 and 3 300 I1 +100I2=5…..eq. (1) - (300I1+510I2=12)…..eq.3 -410I2=-7 Or, I2=7/410=0.017 Amp. Putting this value to equation 1 300 I1 +100I2=5 I1= (5-100x0.017)/300 = (5-1.7)/300 =3.3/300 =0.011 amp. Written By Ir. Shanta Maharjan

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The resultant current through the R3 is I= I1-I2= 0.017-0.011=0.006 amp =6mA.

1.3.1 Superposition Theorem This theorem states that the individual effect on any circuit or network is equal to total effect in the form of current and voltages. In other word the theorem can be expressed as, “ the current or voltage of any component of a network with two or more voltage sources is the Algebraic sum of the current or voltage caused by each source acting independently.” Example: Find the current flow through the R3 using superposition theorem.

A. To apply the superposition theorem first we calculate the effect of E2 ,


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1. Now find the total resistance, = The total resistance is, R1,2,3=R1,3+R2=7.5+20=27.5 ohm 2. Current through the total circuit, IT=E2/RT=12/27.5=0.436 amp 3. Voltage across the R2, VR2=IR2xR2=ITxR2=0.436x20=8.72V 4. Voltage across the shunt R1,3, VR1,R3=ITxR1,3=0.436x7.5=3.28V 5. Current through R3, I’R3=VR1,R3/R3 =3.28/30=0.11amp B. To apply the superposition theorem first we calculate the effect of E1,

1. Now find the total resistance, = The total resistance is, R1,2,3=R2,3+R1=12+10=22 ohm 2. Current through the total circuit, IT=E1/RT=6/22=0.273 amp 3. Voltage across the R1, VR2=IR1xR1=ITxR1=0.273x10=2.73 V 4. Voltage across the shunt R1,3; VR2,R3=ITxR2,3=0.273x12= 3.27 V 5. Current through R3, I’’R3 = VR2,R3/R3 =3.27/30=0.11amp C. Total effect of E1 and E2 in R3 for current is(as the direction of current is same), IR3= I’R3+ I’’R3=0.11amp+0.11amp=0.22 amp


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1.3.2 Thevinin’s Theorem This theory is applied in terms of network as source for given load. Here all networks without load is considered as source and internal resistance of source to the load. It replaces the network with mathematical equivalent and a total equivalent of resistor as internal resistor in series with the source. Basically this theory is applied in transistorized voltage divider concepts. Here is the example of thevinins with schematic diagram,

1. Remove the RL as open circuit as figure and Remove the source and leaving the internal resistance of source. Calculate I, V and R thevinins.

Since all resistances are series with respect to source so, 1.1 ITH=E/ (R1+R2+r i) Written By Ir. Shanta Maharjan

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1.2 VCD=VTH=ITHxR2=R2XE/ (R1+R2+ri) 1.3 R TH=? To find the thevinins resistance the source is short circuit and keep the internal resistance as shown in figure above. Now see the circuit from the A, B there will be shunt of R2 with R1 and r i, so the thevinins resistance will be, RTH=R2// (R1+ri) = 1.4 Thevinins equivalent circuit and current flow through the load.

IL= This theory is valid even for the linear networks which have a non linear load as transistors.

1.3.3 Norton Theorem It is similar theorem as Thevinins and expressed that the network in similar circumstances can also be represented by a current generator shunted by an internal conductance. It shows the difference between the thevinins and Norton theory and can be said it is alternative method to Thevinins theorem. Norton Theory is stated as follows: 1. Any two terminal active network containing voltage sources and resistances when viewed from its output terminals is equivalent to constant current source and a parallel resistance. The constant current is equal to current which would flow in a short circuit placed across the terminals and parallel resistance is parallel resistance is the resistance of the network when viewed from these open circuit terminals after all voltages and current sources have been removed and replaced by their internal resistances. 2. Another useful generalized form of this theorem is as: the voltage between any two points in a networks is equal to ISC X Ri where ISC is the short circuit current between the two points and Ri is the resistance of the network as viewed from these points with all voltage sources being replaced by their internal resistances (if any) and current sources replaced by open circuits. Example: find the current through the R3 using Norton theorem. Written By Ir. Shanta Maharjan

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1. Short circuit is lunched between A and D, A and F. In this way the short circuit current can be found as,

Here Isc=

where G1 and G2 are branch conductance.

2.To find the internal resistance ,the conductance is taken as series, Gi=G1+G2+G3 Or, Ri=1/Gi=1/ G1+G2+G3 Now find the Voltage across the R3 is VAB= ISC x RI =( G1+G2+G3 3. The current through the R3 is I3=VAB/R3

1.4 Filter Filter is in electronics for selection or rejection or attenuation of given range of frequency from input to desired output. Filter is applied in different applications as:  Tuning desired channel or desired range of frequency.  Reject noises and spikes  Reject unwanted range of frequency There are basically four types of filters 1. High pass filter 2. Low pass filter 3. band pass filter 4. band stop filter 1. High Pass filter High Pass filter means the filter which passes the upper range of frequency from given frequency margin. Generally hum sounds and other low frequency noises are rejected by this type of filter. High Pass filter can be made of simply a capacitor in series to input as given below.


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The capacitor in series provides reactance decrease with the increment of the frequency by formula, XC =1/ (2. .F.C).So the current pass through the capacitor is high with the high frequency and high voltage is dropped across the resistor. So it acts as high pass filter. Graphically the High pass filter can be represented by given figure.

The high pass is from the cutoff frequency which means the out before the cutoff is not passed to output and after the cutoff is full of input. But it is ideal case only, in practical the figure is little different as given below.

In practical the cutoff value is determined by the point where the 0.707 of peak value of output amplitude. 2. Low pass filter Low pass filter is just opposite of high pass filter. Low pass filter is used to pass basically the main signal frequencies which is mainly low frequency as audio frequency, cardio pulses etc.


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In this case the capacitor acts as low reactance for high frequency to the ground but for low frequency it becomes high reactance so it passes to load or output. The equation same but applied as parallel for input.

3. Band stop A band stop filter is the filter which to reject proper band of frequency range as shown in figure. It means it passes well the frequency beyond and below range comparing the band stop range. This type of frequency filter is used to stop definite range of noise, IF range which is to be processed further in radio, television etc. A Band stop filter is designed with LC tank circuit with series to signal source as given below.


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4. Band pass A band pass filter is opposite to band stop filter which passes different range of frequency and rejects all the above and below range comparing to given range. The best example of the band pass filter tuned frequency in tuning purpose, IF band pass filter in radio receiver. The circuitry of the band pass filter is the L-C tank circuit parallel to source signal as given below.

These filters are called passive filters. Nowadays there are used mostly active filters with op-amps (operational amplifiers).Active filters have advantages of impedance matching for source and loads. Same way active filter can avoid using of inductors for band pass and pass stop filters. The filter design in active filter is much easier than passive filters without changing load effect and gain of amplifiers. Here is one example of active filter and its filtering property.


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Above diagram is low pass active filter. It has gain of amplitude with respect to frequency is given by following formula. |

|= √

The operation of the low pass filter can be verified from the gain magnitude equation, 1. For very low frequency i.e. f=f H ; Vout/Vin Vd then Vo=(R/(R+rd))*Vs-((R/(R+rd)*Vd *when R>>rd, then V0=Vs-Vd If Vd= 0.7V for silicon then the Vout =Vs-0.7V.It is shown by figure.


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Half wave rectifier with RC filter

As the diode passes the current through it ,the charges as electrons starts to charge the capacitor during which the voltage across the capacitor is not seen direct across it as it charges slowly comparing to the applied voltage increment at capacitor. The slowness depends upon the value of capacitance and internal resistance of diode. When the voltage across the capacitor reaches maximum and tends to decrease the capacitor starts to discharge through the load resistor. In this case the decrement not occurs as in decreasing the supply voltage but it slows to discharge according to value of load resistor and capacitor. It means the time period constant of charging and discharging is higher than the time period of input sine wave. So this property makes the output voltage is in smoothing or more linear than previous pulsating which can be shown by given figure. It makes more smoothed dc output as,


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Some important factors of rectifier 1. Peak current-The instantaneous voltage applied to rectifier is Vs=Vsmax sinwt The instantaneous current i=Imax sinwt for 0Vbe and Re >> R th. Relationship between α , β, γ Here; α = IC / IE ; β = IC / IB ; γ = IE / IB Relation between α & β α = IC / I E = IC / (I c+ I B) 1/ α = (I c + I B) / IC = 1 + IB / IC = 1+ ( 1/ β ) 1/ α = (β +1) / β α = β / (β +1) ………………………… 1 β = IC / I B = IC / (IE – IC) 1/ β = (I E – IC) / IC = (IE / IC ) – 1 = (1/α) –1 1/ β = (1– α) / α β = α / (1– α) ………………………… 2 Relation between β & γ β = γ –1 …………………………….. 3 γ = β + 1…………………………….. 4 Relation between γ And α α = (γ – 1) / γ ……………………… 5 γ = 1 / (1– α) ……………………….. 6 Current relationship with α, β, γ IC= β IB = α IE = (β /1+β) IE = α IB /(1– α)……… 7 IE= IC/α = (1– β / β) IC = γ IB / (γ – 1)…………… 8 IB= IC/β = IE (1+ β) = (1–α) IE = IC /(γ – 1)……… 9 The three currents in the transistor always make relationship I E : IB : IC ……………………………………. 10 Or, 1: 1–α: α………………………………………11 Or, 1+β: 1: β………………………………………12 Or, γ: 1: γ – 1………………………………………13


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3.4.1 Bipolar transistors as switch Transistors are various used as switch as it can be switched 1. Very fast ( more than 109 times per second) 2. Can be used as automatic switching Application  Flip flop pulse generation  Digital electronics switching and logic  Automatic lamp, detector circuit Condition for switching 1. Full saturation for Switch ‘ON’

2. Cut off for Switch OFF Circuit diagram for switching

Simply transistor as switch is used in common emitter- self bias mode (no dc bias at Base-emitter) Operation: 1. In normal condition or no base input voltage, the base emitter junction barrier is no forward biased so IC cannot flow. So collector base remains high reverse biased and VCE is high or VCE = VCC In conclusion; IC ~ 0 Written By Ir. Shanta Maharjan

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2. When high positive input; the Base & emitter is forward biased and flow current IB. It makes the high current IC to flow or, IC = I C max . In this case IE is also maximum. But VCE goes to near zero as Base- collector reverse resistance becomes near to zero. So voltage across V CE ~ 0. In conclusion; V CE = 0; IC = IC (max) Calculation: At Switch off:V CE = VCC – ICRC = VCC – (0).RC Or, V CE = VCC …………………. 1 Switch on:IC = IC set. (Max) = VCC / RC ………………….. 2 IB = IC / β (set.) = (VCC / RC). (1/ β) …………… 3 IB = (VHIGH – VBE) / RB ………………………….. 4 Or, RB = (VHIGH – V BE) / IB = = (V HIGH – V BE ) / (β RC / VCC) (from eq. 2) Or, RC = (V CC. RB) / (β (VHIGH – V BE))…………………………. 5 In this way the calculation shows we can design a switching circuit with its given biasing .From formula we can find out RB and RC.


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3.5 MOSFET (metal oxide silicon field effect transistor) MOSFET is also transistor but the main difference between them is there is no flow of current from input to output as happens in the transistor base emitter circuit. So the input signal power is theoretically not require or not dissipated. All other functions of MOSFET are same as application. The main principle of MOSFET is the electric field created by input to the channel of charge flow path. When the input at Gate is positive it can attract electron as negative charge from substrate silicon to channel. Similarly when there is negative signal at gate it can attract holes at channel path. The increment or decrement of gate input voltage cause to control the current flow through the channel which similar to control the current flow across the collector to emitter in transistor. The schematic diagram of MOSFET is given below.

Here the MOSFET is fabricated in P-substrate for making depletion type MOSFET for N-channel MOSFET. Construction of N-channel MOSFET: In this MOSFET the Source semiconductor is made of highly doped n-type semiconductor then the channel internally created as lightly doped, then the Drain is again highly doped N-semiconductor as shown in figure N+ as highly doped and only N is lightly doped. From Source and Drain is taken metallic contact and taken leads as output terminals. In the case of Gate there is crated an insulation layer of SiO2 and over that a metallic layer is developed. The lightly doped n channel insulating layer and metallic layer cause a sandwiched where the terminal thorough the metallic layer is taken as Gate terminal. Working principle, characteristic To make the MOSFET working the proper biasing is required which is given in following diagram.


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G

Here the Gate is supplied first highly negative voltage; in this case the metallic plate accumulates the negative charge. This negative charge creates electric field which repels the electrons of N-channel and there may no flow of charge or electron from source to drain which is called pinch off voltage of gate voltage. But when there is decreased negative voltage to gate then the electron at channel increases and consequently the source to drain flow of electron increases. It means the drain increases with less negative at Gate. In this function the electrons of n-channel is deployed so this mode of function is depletion type MOSFET. But if we change the supply at Gate with positive then the action is reversed. So the positive at gate attract more electrons from P-substrate so the electrons are enhanced and more current starts to flow through the channel. This type of action is expressed with enhance type MOSFET. Here is the characteristic curve of output characteristics curve as well as transfer characteristic curve.

Here when the VG is extremely negative then there is zero ID but when it decreases the Id increases.


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Even at zero gate voltage a significant current flows. After that at positive at gate the enhanced mode provides again more current. In enhanced type MOSFET there will not be any channels so PMOS conducts only When the gate is negative, NMOS conducts only when the gate is positive.

3.5.2 CMOS and CMOS as NOT Gate CMOS is the abbreviated name of complementary metal oxide silicon field effect transistor. The name complementary is for pack of two opposite MOS as NMOS and PMOS providing desired function. NMOS as N drain and N source but there is not any channel as the NMOS and PMOS for complementary MOS or CMOS should be enhanced type. The NMOS needs positive at gate for enhancing the electrons to conduct current from source to drain. The PMOS needs negative at gate to enhance holes at channel way to flow the charges through it. So with this opposite combination it can work as different logic functions and other functions which are valuable in electronics. The basic CMOS circuit is given below.


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CMOS as inverter or NOT logic gate Here is going to explain the CMOS as NOT gate for which we should understand first NOT gate function. It is logic where when given input HIGH gives output LOW and when the input is LOW then output will be HIGH. The HIGH in digital is +5V and the LOW is 0 volt. The supply for the gates are also equivalent 5V.It means we give the inputs HIGH or LOW as binary 1 or 0. Now we explain the function of NOT gate with given circuit.

In this circuit the input is given low or grounded the input but the respective voltage between the source and gate is VSGP=-5V for Q p so the gate act as negative at gate of Q p. This negative of gate to PMOS causes to attract holes to channel way and a current flow at saturation through the Q p. It makes the V dd of +5V will transfer to V0 so V0=+5V. Now for QN or NMOS the relative voltage between the source and gate, VSGN=0v and no enhance action of electron is not created at channel way so no charge flow occurs. It means the V O remains same +5V or no current flow to ground. The both NMOS and PMOS act here to create HIGH at output with low input. And it satisfies the half function of NOT gate when input is LOW or 0V then output is HIGH or Vo=+5V Now for when the input is HIGH or +5V, the circuit is given,


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Here when the input is HIGH then relative voltage between source to gate for PMOS as VSGP=0V so the zero gate voltage cause no creation of holes at channel way so no charge flow occurs and the V0 remains 0V. For NMOS or QN the VSGN= +5v So the QN is in conduction mode but there is no any bias in drain of QN which is in this condition is V0 and V0=0V.So there will be output as V0 will be zero. In this way the CMOS here act as high input to LOW output or when there is 1 in input the output is 0. The advantage of CMOS as gate in both cases is that the actual current flow through the CMOS to ground will not occur for both HIGH and LOW inputs. The very few of current may flow as leakage current so power consumption is very low

3.3 Differential Amplifier Differential Amplifier is the amplifier which provides difference of voltage after amplification from two associated amplifiers. If two different small voltages are to be compared then the differential amplifiers are employed. In differential amplifier the two inputs or required one input with respect to another reference level of voltage it amplifies the difference with high magnified amplitude so we can distinguish the difference as calibrated to any measuring device or to any controlling device. Here is basic diagram of differential amplifier and its working function.

In this circuit the transistors Q1 and Q2 are identical and the R c1 and Rc2 are equal value. Same as the V cc for both transistors are from single supply and emitter is connected together and grounded. This means the transistor gain is same so if there is given equal V 1 and V2 then Vc1 and Vc2 outputs are also equal. So if we take outputs from this output terminal directly then we will Written By Ir. Shanta Maharjan

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get zero voltage. The calculative analysis of differential amplifier can be as following for different conditions. Condition1 If Vb1=Vb2, then, Ie1=Ie2=I tot/2 as I tot=Ie1+Ie2 Same as, V ce =V cc-Ic* R c = V ccRc = V ccRc The differential voltage V d=Vce1-Vce2=0 Condition 2 When V b1 is grounded and Vb2 is increased, in this condition if V b1 =1V then Vbe1=0.7V.In this situation the V e=Vb1-Vbe=1-0.7=0.3V This V e=0.3 act as reverse bias to Q2 transistor so it doesn’t conduct and Vce2=Vcc and Vce1=V ccRc Voltage V d= Vce1-Vce2= V cc-(V ccR c) =Rc Conclusion In all conditions the differential amplifier works where the difference voltage will be denoted by So Vd= Vce1-Vce2= Rc Condition3 V b1 =-1V and Vb2=0 or grounded. Now, V be1= V b1-(-0.7) V =-1+0.7=-0.3V So the V e=V1-Vbe1=-1-(-0.3) =-0.7V It makes the Q2 transistor conduct as it fulfills the correct .Where as the Q1 with negative will not conduct so, Vce1=V cc andVce2=V ccRc So the difference value


Rc.

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3.2.1

Model

Modeling of a transistor is also defining of function of transistor with different input signal level and frequencies and analyzing it’s all factors which affect the signal with basic parameters in terms of resistance, voltage, capacitance and current. Here is given a basic equivalent diagram of transistor for T model.

Here in diagram the dc biasing is shortage as it doesn’t, change the voltage across the supply at ideal case. In this circuit the Vbe as input voltage of signal and all parameters of output is compared according to this signal. So this is called voltage controlled current source modeling. It means the Vbe as controller to change the IC. Here in diagram is the resistance between input terminals to the base of transistor. As we know Vbe and then Ib= ----Eq. 1 The collector current Ic can be derived from the formula transconductance which symbolized by gm where gm= and Ic=gm*Vbe ----Eq.2 From these two equations we can derive the value of Ie as given way. Ie=Ic+Ib = gm*Vbe+ =

(1+gm* )

= Here the is gm* rπ can be proved by following relationships. gm*Vbe= gm* rπ *ib as from ib=Vbe/rπ and Vbe= ib *rπ from above relationship eq. 2 Ic= gm* rπ *ib = gm* rπ = gm* rπ


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Explanation of π model The above relationship can be expressed in π model by given expression.

Here the base connection is related to emitter with Vbe signal and the current flow ib across the rπ .It changes the output current Ic as main source current in terms of gm*Vbe which means the Ic depends upon the conductance gm occurred by Vbe so this model is voltage of input controlling output current source. Here the Ie is given by normally as expressed in equation = In the case of the π model for current controlled current source the circuit will be

Here the Ic is expressed with Ib which is Ic controlled with Ib .It can be taken from relationship from = In wide π model the model can be expressed by following diagrams.

Here the extra parameters are added for more real modeling. The C and r are capacitance and between the Base to Collector .same as the C is capacitance between the base and emitter. The r0 is the resistance between the Collectors to Emitter.


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3.2.2 T model The T model is similar expression but more simple and some time more relevant expression. Here is basic diagram for T model.

In this model the current voltage Vbe controlled current source is given. Here Ib is defined by given calculation. So Ib=Ie-Ic = =

(1- gm*re)

=

(1-

here

equals gm*re by given calculation **

=

=

=

gm*re =

(1-

= In the case of current controlled current source diagram is below.

Here Ic is expressed with term


where

= .

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3.4.2 Transistor as logic circuit Transistor as logic circuit means transistor can be used as logic gate which is called TTL (transistor transistor logic) circuit. Transitory is then fabricated in silicon chip as SSI (small scale integrated) circuit to construct logic gates as AND, OR, NAND, NOR and so. Many memory chips in the form of flip-flop logic memory, and many digital counters, encoders, decoders, ADC, DAC etc. are made of transistor logic gates. Simply the transistor as common emitter mode configuration also act as NOT gate which we can see understand from transistor function in amplification.

In this circuit when the transistor base is with zero volt or logic “0” then the transistor does not conduct and we can see through the formula that the output at Vce is hgh, Vcc=Ic*Rc+Vce When the transistor does not conduct, it means the Ic flow is zero in this case the above formula becomes, Vce(output)=Vcc or 5V which is logic “1” Same way when there is logic “1” or 5V at base of transistor, then the transistor gets sufficient voltage to drive the transistor and there the transistor conducts in saturation or Ic is maximum. In this case the resistive property of transistor from collector to base and emitter is so low comparing to Rc so most of voltage drop across the Rc. But as the resistance between the collector and emitter is very low so the V ce becomes very low at mill volts so it can be considered as OV or logical “o”. In this way the transistor in this condition work as logical NOT gate. With the help this NOT gates, many other logic gates and logical functions can be achieved. Here is another logic gate circuit made by transistor which is often used as NOT gate in practical and more reliable gate than previous explained.


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Condition 1(high input) 1. When high input in emitter it makes the transistor Q1 base emitter reverse but base collector becomes forward bias as diode so the current flow from source. 2. This current cause to have voltage to drive the Q2 and it flows the current through the Q2 and decreases voltage across the Q2. 3. As the voltage at collector at Q2 is decreased, the decreased voltage cannot drive the transistor Q4 as the diode at emitter makes more voltage need to drive the Q4.So Q4 is cutoff and no current flow through the Q4. 4. In the case of Q3 the transistor will get supply source through the Q2 conducted so it conducts. Since it conducts its voltage at collector becomes less and it in turn supply source to base of Q5 very few and Q5 is in cutoff. Conclusion: the Out Put is logic “0” for logic “1” in input. Condition2 (LOW INPUT) 1 .Since low at emitter the base to emitter conduct as diode and the base to collector becomes reverse bias so the Q2 remains cutoff as it does not get base voltage through the Q1. 2. As the Q2 is cutoff the voltage at collector of Q2 is high so it drives Q4 with high voltage which easily overcomes the voltage dropper diode and transistor Q4.so it passes source voltage to collector of Q5.. 3. In this case the collector of Q3 will not get collector voltage from the Q2 so it (Q3) remains cutoff. As its collector has no voltage it cannot drive the Q5 so Q5 also remains cutoff and the voltage at collector of Q4 remains the source voltage as high voltage. It may decreased as Vout= Vcc-Vbe-Vdiode or 5-0.7-0.7=3.4V which is still derived as logic “1”.


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4. Operational Amplifier An operational amplifier is the hypothetical invention for all purpose of electronic circuits in single device as integrated circuit( IC).And it became a versatile semiconductor IC as amplifier, Instrumentational differentiator, mathematical operation add, subtract, integrator, differentiator, summing, filter, oscillator etc. The name operational amp is given from its ability to work as mathematical operations as add, subtract and so. So OP-AMP is designed with number of semiconductor devices as diodes, transistors, semiconductor resistors-capacitors in single chip as IC. The µA series of 741 and LM 338 are the examples of opamps. Symbol and description Here is the symbol of op-amp and its terminal functions

In this symbols the Terminal 1, 5, 7 are not used practically. The terminal 2 is for inverting terminal which inverts the terminal 2 input as if positive is given the output will be negative and if negative then o/p will be positive. Same as if there is given sinusoidal signal the output will be 180 phase shift. The terminal 3 is the non inverting which same voltage and phase as in input. The terminal 7 is for positive bias as Vcc and terminal 4 is for negative supply as Vee as in transistor supply. Now output is taken from terminal 6. The basic advantages of op-amp: 1. The voltage a current gain can be controlled from externally with resistors ratio easily. 2. It has high gain up to tens of thousands. 3. The input power is practically negligible or no practically current flow from outer circuit to op-amp. 4. The op-can amplify micro volt range. 5. It can take both negative and positive signal. 6. It can give both negative and positive voltage output. 7. Easy to design as filter, oscillator amplifier, differential amplifier. 8. It can be used mathematical calculation as adding, subtract, integrating, differentiating. Written By Ir. Shanta Maharjan

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Ideal and practical properties of op-amp Ideal 1. Differential or open loop gain or amplification is infinity. A= but practically up to A=100000 2. Input impedance is infinity. in= but practically at mega ohms. So, very negligible current will flow through op-amp. 3. Output impedance zero. Zo/p=0 but practically very few ohms. So the changing load or adding many loads also effect very low. 4. Virtual ground between the two input terminals. As the voltage at the inputs are negligible. 5. It has ability to direct coupling with precious section and next section. 6. It has flat frequency response for all frequencies.

4.1.1Virtual ground concept As we know that the output voltage is not possible more than maximum voltage applied in given circuit so the output of more practical op-amp is +15V or -15V. So as we mentioned the gain of practical op-amp is almost 100000.The lowest possible input voltage may be of 15V/100000=150 . In this way the 150 is very small to bias 15 voltages so it can be considered as zero voltage. And this concept leads to Vi/p 0 which in result it act as ground or short circuited to ground (because we consider ground as zero potential).But in case ofu grounding the potential as short circuit it must flow maximum current but here the current is zero so not actual short but there is like open circuit and no current flow as the input impedance is infinity so input current to op-amp is zero. So this phenomenon is called virtual ground. Where Vin at near op-amp terminal is zero. And Iin at input terminal of op-amp is zero.


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4.1.2 Op-amp Model As diode and transistor, the op-amp can be also transformed in model to define its basic function and operation. If we take only the op amp itself the op as its basic characteristics we van express as given way.

Here the inputs are connected with input resistance which is theoretically infinity. The difference voltage developed across the infinity resistance Is amplified by op- amp by A times. So the output before the output impedances is AVD. But the output impedance is very low or zero the all output is taken out from output terminal. In practical the gain of amplifier is controlled by input resistance and feedback resistance so the simple practical circuit is given by following diagram and its model is also given in side.

In this diagram the feedback and input resistors are given in equivalent circuit .All other parameters are same to previous op-amp. The equivalent model foe different circuit is different according to components added with it. The possible output range for all models can be expressed by given diagram.


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4.1.3 Inverting OP-AMP

In inverting op-amp the input voltage is given to inverting input and non inverting terminal is grounded. A feedback circuit is added from RF to inverting terminal. In this way the calculation for deriving the gain or output is given like this. We Know the input current as total current is equal to IF and IB . As, Iin=IF+IB----1 But since the IB is zero the equation becomes, Iin=IF-------2 By Ohms law the above current can be rewritten, = -------3 We know the open gain of op-amp V0=A(V1-V2) The V2= (As V1 is grounded or V1=0)-----4 The value of V2is put in eq. 3 = The gain with feedback is Af=

=-

As the gain of op-amp is 100000 which is very high so AR1>> (R1+R2) And Af= =- = Or, Vo= Vin The equation gives the gain of inverting op-amp and output of op-amp which depends upon the ratio of feedback resistor and input resistor R1.Same way the sign “-“ indicates the inversion output comparing to the input signal or voltage.


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4.1.4 Non-Inverting OP-AMP The inverting op-amp circuit is given below.

In this circuit the input is given to non-inverting terminal and feed-back is given to inverting terminal as shown in figure. From above diagram we can write, VIN=V1 And V2=I*R1= xR1 From open loop amplification,V0=A(V1-V2) Putting value of V1 and V2, Vo=A(V1xR1) Vo=

-

Or

=

Vo= Same as above the gain of 100000 then the AR1>> R1+Rf so R1+Rf can be ignored So V0= Vo=

X

Vo=(1+ ) X =Af=( 1+ ) From this equation we can conclude that the gain is similar to inverting but the output is same polarity of input as the output sign is positive. Written By Ir. Shanta Maharjan

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4.1.5 Integrating OP-AMP This circuit is for mathematical integration with respect to time. If we provide any signal it integrates the signal. As the sine wave is given in input the output is integration as cosine. The basic integration circuit is given below.

From above diagram we can write, Iin=IB+Ic Iin =Ic ----1 (As IB=0 ) From the capacitive current flow equation for current and voltage, Ic=C d Applying the relation in eq. 1 =Cf As V2 is virtual ground and equals to zero so, =Cf Integrating both sides ∫ Or, V0=

∫

=C f (-V0)

∫

This equation shows the output is integration of input with time period constant R f and C f.


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4.1.6 Differentiating OP-AMP It is very similar to integrating but its function is just opposite differentiating. Here the capacitor is in series with the input signal. It is shown below.

Its same relationship as previous that Ic= IB +If Ic =If ----1 (As IB=0 ) Providing same relationship of voltage and current for capacitor Ic =C d And applying to equation 1 C1 = As V2=0 due to virtual ground, then C1 = Vo =- C1Rf From this equation the input is proved as differentiation of input signal.


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4.1.7 Summing OP-AMP The summing amplifier means summing or algebraic sum of the all input to the outputs. The circuit altogether same to inverting op-amp but there may many inputs to the main inverting input. he circuit for summing op amp is given below.

From above diagram we can find different currents flowing through each resistor I1= ; I2= ; I3= ; If= By applying Kirchhoff’s law, I1+ I2+I3+ If=0 So applying previous values, + + - =0 Or V0=-( + or V0=-(K1V1+ K2V2+ K3V3) If value chosen for R1=R2=R3=Rf then, V0=-(V1+ V2+ V3) The formula derives the algebraic sum of all inputs.


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4.2.1 Basic feedback theory and negative –positive feedback The concept feedback means taking some part of output voltage or current into the input. This process is variously used in electronics for different purposes as 1. Stability 2. Automatic gain control 3. Automatic frequency control 4. Reducing noise 5. Oscillation or frequency generation Here is basic diagram of feedback theory.

Here in diagram the Vin is amplified and we get output with gain A times with respect to Vin. As, Vout=A* ( Vin ) In feedback system the Vout is attenuated in feedback block as attenuator so that only a part or portion could be taken from the full output. So the Vf the fraction of output is again given to input of amplifier or op-amplifier. Now the feedback factor is given by the 𝛽= In this way the input will be changed now as Vinf= Vin+ Vf Or V inf= Vin 𝛽 Same way the Vout also change with the feedback. Since the gain is same for feedback amplifier the output will be now, Vout=A (Vinf) =A (Vin 𝛽 Written By Ir. Shanta Maharjan

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Here the actual output depends upon type of feed back as the feedbacks are two types. If the feedback adds with the input then it is called positive feedback. In negative feedback there the input is reduced by the negative feedback. If we consider here the negative feedback then the output will be Vout=A (Vin 𝛽 Or Vout=A Vin

) 𝛽

)

Or Vout(1+ 𝛽)=A Vin Or 𝛽) Here the voltage gain is with feedback. For Positive feedback the gain will be 𝛽) Here the factor 𝛽 or 𝛽 will take role for feedback system. In many cases the negative feedback system is used as it provides good stability. But in the case of positive feedback, it is used as oscillator for producing continues wave frequency. The basic function of feedback visually can be given by following diagram.


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4.2.1Concept of stability Stability is the term for working any circuit which can work same ability even changing the outer parameters as changing temperature, ageing the components, changing or replacing the components etc. We cannot practically control the outer changing but we can have such controlling additional circuit which can sense the change and manage the circuit in same as usual .The Stability is gained only by the negative feedback only. The factor stability can be derived as given, A f= (here the 𝛽 Is taken very high than the unity so 1 is ignored)t This equation shows that the overall gain of feedback amplifier is independent to amplification of circuit. And the feedback circuit provided feedback factor takes role as changing its value to maintain the gain Af same.

4.2.2 Oscillator Oscillator is the electronic circuit which produces continuously the frequency or variations of voltage or current with time. The shape of frequency may be varied as sine wave, square wave, rectangular wave, triangular wave etc. But the frequency rate is same along the time. Oscillator is key function for all communication as carrier frequency, local oscillator frequency. In digital a clock pulse is essential for all process of digital logical functions. In TV it creates the scanning properly by saw tooth waves. So the oscillator and its stability of generation of same frequency and shape is very important for proper function of electronic circuit. It is already mentioned that the oscillation is the voltage variations periodically with time. For this input, as DC supply voltage where oscillating circuit converts the DC supply to oscillating frequency. The main concept of oscillating is the reactive electrical device as capacitor and inductor which reacts the change in voltage and current. So charging discharging process and inducing emf is the key function of oscillation. Here is the basic function of oscillation generation.


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In this diagram the capacitor is charged by battery and switched off. Then the capacitor discharges through the inductor. The Inductor then induces emf so it act as source and it starts to charge the capacitor but in reverse form. After charging the capacitor it again discharges through the inductor but in reverse emf. So this time the capacitor is charged again in reverse to previous. In this way it continues to act. But At every time when current passes through the inductor the pure resistance act as to reduce the current so the emf induces in the inductor reduces. Same way when the capacitor charges the capacitive leakage also cause to decrease of charged so the voltage developed across the capacitor decreases .In this way each time the voltage and current decreases and the oscillation amplitude decreases so at some time the oscillation damped to zero. This damping oscillation has frequency of Fosc= √

Using this concept the LC oscillator is developed. The damping is decreased by fulfilling the loss of resistive in inductor and leakage in capacitor with the help of positive feedback. In positive feedback same amount of lose is voltage feedback (VF) to the LC tank and continuous wave is achieved as shown in diagram.

For continuous wave generation following condition should meet.


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From this diagram we can conclude that, A v= V0=Av x VF------eq1 VF=𝛽 V0 From eq.1 V0=𝛽 Av x VF Or V0(1-𝛽 Av)=0 Since V0 is not equal to zero, then And ( 𝛽 Av) = 0 And for proper oscillation the criteria is 𝛽 Av =1. This is the criteria that the (𝛽 Av) should be 1 and which is positive feedback.


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4.3.1 SQUARE WAVE GENERATION USING OP-AMP

Here the op-amp act as comparator which means it gives out as difference between the two input terminals. The main principle is based on the capacitor charging from the output voltage. And during charging the comparisons of two terminals exceed and the voltage output position changes from high state to low and vice-versa. Here are given steps of wave generation. 1. When there is positive the Z1 act normal diode and Z2 act as reverse bias and zener voltage develops across the Z2 as Vz2.Same as if Negative output then the Z1 conduct as develops negative voltage across the Zz1.This zener diodes ensured the fixed amplitude voltage of pulse. 2. The feedback taken from Vout is 𝛽 V0ut or form above equation =𝛽 and V positive feedback= 3. Actual input to two terminals is: Vin = Vc4. When the Vin is positive as comparator the input at inverse is more positive that non inverse terminal so the output will be negative. Vice-versa will be for negative input or negative at inverting terminal which gives positive output voltage. 5. At instant Vin< 0 or positive Vout so the capacitor starts to charge exponentially from Vout constant voltage of Vz2.the time period for charging is Written By Ir. Shanta Maharjan

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Rf C. This charging continues up to voltage level of Vc=feedback back voltage V positive feedback at non inverting terminal or 𝛽 = Vz2.At this point the two terminals voltage equals and the Vout becomes zero. 6. In the process of being zero output the Positive charge Vc gets positive voltage to inverting terminal so it provides Positive Output voltage instantly in which time period the negative charge is discharged as recovery time. 7. Since the output is now positive the capacitor starts to charge with the positive output .The charge with same time period up to feedback voltage. The output voltage remains positive equal to voltage drop across the Vz1. 8.When the positive charging Cv equal to voltage feed back then the momently the output is should be zero but since the capacitor charge voltage positive and zero output causes (which makes non-inverting terminal is zero for that moment) the output instantly goes to negative high voltage equal to voltage drop across the Z1. 7. Now the point 5 repeats to charge the capacitor. 8. In this way the Vout is rectangular pulse with same time period. The diagram of Capacitor voltage charge Vc and pulse of output is given below.


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4.3.2 Op-Amp Triangular Generator The triangular wave generator is the simply the integrating circuit after the square wave op-amp pulse generator. We should know that the square wave in a integrating capacitor converts into triangular wave by Function of charging and discharging the square wave. The diagram for triagulat wave circuit is given below

As the triangular generator is given the input of square wave the function integration is given by the formula ∫ For stable triangular development the condition 5C2R4 > T/2.Where T is the period of square wave.


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4.3.3 Wein Bridge OP-AMP oscillator Since the oscillation is bassed in wein developed bridge ,the osilltor named as bridge oscillator.the concept of wein bridge also the RC charging discharging function which changes the output variation and the positve feedback provides continues oscillation generation.Here is the diagram for wein Bridge oscillator.

Here the Z1 term for series combination R1 and C1 and Z2 for shunt R2 and C2. The Z1=R1+Xc1=R1+ Z2=

+

=

=

Here the output voltage V0, V0=V2=I*(Z1+Z2) V1=I*Z2


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The feedback factor 𝛽

=

-----1

The oscillator will oscillates at a frequency which makes phase shift of zero. Therefore Wosc may be determined by equating the imaginary term of equation to zero. W2 osc = Usually R1, R2 and C1 C2 are chosen equal so W2 osc = W osc= F osc = -----2 The equation shows the value of RC determines which frequency is being generating through the op-amp. The minimum gain required for oscillation is taken from the above formula by substituting the value of eq. 2 to 1.The value of minimum voltage gain to be for normal oscillation is the 3 time which means the Av=3 or the feedback factor which is reciprocal of gain should be 𝛽 Then the 𝛽 Av =1 condition for oscillation is met by A v = 3.So the𝛽 .So Av=3x1/3=1 which is required condition for oscillation. Here from the diagram we can easily say that the voltage across the Z4 is the negative feedback. And the Z4can be placed as thermistor so that it improves the stability with change in temperature. Wien Bridge is used to produce the triangular wave which can be changed to sine wave by diode-resistor network.


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5.1 Communication system Introduction Communication System is the modern communication such as radio, TV, Internet, mobile communication etc. All these communications are called electronic media. Nowadays all commercial welfare e-commerce, entertainment, medical- tele operation etc are also going on with communication. So the knowledge of such communication skills is essential now for education in any fields. The electronic communication means the communication between the two places or two or more persons by exchanging the data, information, audio video materials etc transmitting receiving and processing through electronic media. From telephone to huge networking internet all are now electronic media and this world or people of this world cannot survive now without electronics communication. The basic advantages of electronic media over other Medias or communications are: 1. very fast within second we can contact now any persons of the world.(mobile communication) 2. We can talk face to face via video chatting. 3. We can share huge information via internet. 4. We can save our data in internet. 5. For medical purpose also the operations can even take through tele communications. 6. Very reliable and wide versatile functions can be done through the communication. 7. It is becoming so cheap than other communication. The simplest communication system is given below. INFORMATION

TRANSMITTER

CHANNEL

RECEIVER

DESTINATION

* DATA

*ENCODING

*WIRELESS

*DECODING

*DATA

*AUDIO

*MODULATION

*COAXIAL

*DEMODULATIO N

*AUDIO

*VIDEO

*FIBEROPTICS

*VIDEO

The main aim of the communication is to send the information to destination part. The information may be any form as audio sound, video pictures and text Written By Ir. Shanta Maharjan

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type data etc. The data and other information are mostly available in the form of analog type. First the information should be sensed by different transducers and sensors to convert in the electrical form signal. The signal in should be amplified in sufficient level so that it could be encoded or modulated. In transmitter part there should be the signal to prepare for transmission. So the signal should be either encoded or modulated and amplified. Then it may be transmitted directly through the cable or may be radiated by transmitter by antenna. The channel means the medium through which the signal is transmitted. Coaxial cable, fiber-optics are now used as signal transmission by wire. In the case of wireless the electromagnetic waves act as carrying signal from transmitter to receiver. In channel there may be added many noises as well as disturbances. It may take some distortions also in medium. But the fiber optics media is reliable where least noise and distortions occurs. In receiver part first the signal is tuned and filtered hen it is demodulated or decoded (for digital system) and processed to convert the signal in analog original form. In destination the data are converted in the form which the human being can understand as data, audio and video as it is kept in transmitter part. Speakers, TV, monitors are the destinations for communication system.


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5.2 Wireless communication Since the communication by wire is not possible for distant places as well as it is very expensive to connect the all users through the wires for each communications. So wirelesses became essential for electronic communication where the information can be sent any part of world and far to earth to even to moon and so. The examples of wireless communications are AM radio, FM radio, TV, dish TV , TELEX etc. In radio communication as wireless communication the signal is transmitted via electromagnetic waves which travel itself to any distant with the speed of light. Here is basic block diagram for radio or wireless communications.

Oscillator

Signal

RF amplifier

RF Power output Modulation

Amplifier

In wireless communications the essential part is the modulation where the low frequency signal should be converted into high frequency which provides possibility of short practicable antenna length and it provides the many channels in same place. So in radio analog communication the modulation is done as amplitude modulation, frequency modulation, pulse modulation etc. In modulation there should be generated high frequency carrier as local oscillator. It is mostly done in crystal oscillator. The generated frequency is amplified and mixed with the modulating information signal in the power amplifier output. In Written By Ir. Shanta Maharjan

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modulation process for example for amplitude modulation the amplitude of the carrier high frequency according to the amplitude or the information signal. The modulated signal is then transmitted through the appropriated antenna. In general the antenna length should be half of the wave length of the targeted carrier frequency. When the modulated signal is transmitted through the antenna the signal is converted in the electromagnetic wave. The electromagnetic wave can travel through the air, vacuum directly so it is kept in height. RF amp+tuner

MIXER

IF amp and demodulator

signal amp

Ocillator

In receiving part the signal is converted to electrical signal as the magnetic field of the electromagnetic wave cross the conductor of antenna. The signal is tuned as desired channel and amplified in the RF amplifier. In mixer th signal is mixed with the local oscillator frequency and we tune the difference frequency between them as intermediate frequency (IF frequency).It is done to improve the quality of receiving signal as definite single frequency. Then the signal is demodulated to original signal and sent to audio amplifier. After that the signal is sent to drive speaker which converts the electrical signal to acoustic sound.


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5.3.1 Antenna Antenna is the special metallic structure to transmit or receive the electromagnetic field with optimum power. The basic concept of transmitting the electromagnetic wave is the electrodynamics of electric and magnetic field along conductor. In each the length of quarter of wave length there is occurred magnetic field as shown below.

The antenna as conductor behaves as capacitive and inductive device. When current flow across the conductor the two ends far from centre accumulates the charges and act as capacitor and electric field is developed across it .Similarly the inductive effect is developed across the conductor as there will develop magnetic field . The capacitor C and inductor L act as resonant for given frequency. For the length the current distribution is shown as above. Similarly for the current distribution is high at centre as the impedance is low at centre. And voltage distribution is high at ends as the impedance is very high at ends. In this condition the maximum electromagnetic field is developed across the antenna. So the given length is maximum efficiency for electromagnetic radiation for related frequency with the proper wave length. For the antenna the length can be calculated by given formula. E= sin where E-magnitude of field strength R-distance at which the strength measured L-length of antenna I-Current amplitude


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The angle of the axis of wire and point of maximum radiation But in practical to fabricate an antenna for operation at 175.25 MHz for NTV we can calculate above equation and should be multiplied by 0.95 as the coefficient of travelling in air medium. It can be calculated by the simple equation also, as L= = = As the length should be reduced by 0.95 for the air medium then the length will be =86.6x 0.95=82.27cm For non resonant antennas the radiation pattern is with lobes and not efficient to transmit at distant places. The shape of the antenna is different for different communications systems. For AM radio transmission the Marconi type antenna is used in vertically to reduce the size of the antenna again quarter by grounding the antenna and mirroring form ground. For short wave AM radio the antennas are used as longitudinal antennas using the wire suspended in two wall support horizontally .In radio receiving the telescopic and loop antennas are used for both low frequency AM and shortwave radio. For FM transmission mostly used dipole antenna but since the FM is used as local area transmission the antenna for receiving is mostly not so much necessary as special antenna. The same AM antenna work sufficient for FM receiving also. For TV transmission the dipole antenna is used but for receiving there are used yagi-uda antenna as it is directive and high gain than dipole antenna. For satellite broadcasting TV channels as DISH channels there are used disk antenna with wave guide. In mobile communication wave guides are used to receive by mobile stations. For special purpose there are used different antennas as batwing, turnstile, logperiodic, quad antennas, conical, helical antenna etc.


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5.3.2 Electro-magnetic wave (EMW) and propagation

Since the electromagnetic field is actually comes out from the source of electrons electric and magnetic field which when in same alignment gives significant effect as in capacitor and inductor. When the current flow through the opening end as in antenna it releases the electric and magnetic in each changing current as waves in the ponds. The combined electromagnetic field which is released to air or any medium is called electro-magnetic wave or field. Since these two fields are perpendicular as in origin in an electron the field travelling also in perpendicular as it develops across the antenna. The electromagnetic field is in spherical form. The length of the sphere from origin is the amplitude and which also denotes frequency along the z-axis. In this way we can conclude that the direction of the electric field, magnetic field and propagation are perpendicular to each other. The spherical wave fronts can be shown as below.

The density is inversely proportional to square of the distance from the source .This inverse square law which means the power reduce of one quarter at every doubling of distance. It can be derived as, = Written By Ir. Shanta Maharjan

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Where, In

at r from an isotropic source Pt=transmitted power terms of impedance the characteristics impedance

Z=√ =√

of

ir

is

=377 .

This impedance is found in centre of antenna dipole for resonant frequency.

5.3.3 Propagation The propagation of electromagnetic wave means the ways of transmitting the EMW throughout the atmosphere. The wave transmitting depends upon the atmosphere construction, temperature and ground of earth. When we want to transmit the EMW throughout the earth the propagation would be in the very high frequency range. According to the way of propagation there are basic ways of propagation which is given bellow. 1. Ground wave-Since the ground itself conductive the ground wave propagation the propagation should be vertical polarized which means the electric wave should be vertical to earth surface. When the Wave travels through the surface the wave is diffracted and inclines with the surface so it travels even further than line of sight. Most of medium and short wave AM radios are propagated in ground waves. For High frequency the loss is high so it is not preferred through the ground wave.

2. Sky wave-In sky wave the wave is travelled through the air of atmosphere . If two transmitted and receiving are is line of sight then it is called line of sight communication. The TV and FM radio are propagated in line of sight communication.


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In the case of long distance the propagated EMW toward the up sky with certain angle the EMW is reflected by different layers as D, E, F1, F2 of ionospheres and travel back to surface of earth as shown below.

In the case of more than 30 MHz and the angle up propagation is more than 300 the propagated frequency penetrate the atmospheric level and travel to space which used for satellite communication.


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5.5 Fiber optics Fiber optics is the medium through which the signal is transmitted from one place to other place by means of optical fiber. It is one type of quartz which is purified and made thread like to pass the light from one end to another end of the fiber.

Here is the basic optical diagram of fiber.

The quartz rod having under gone the modified chemical vapor deposition process is now placed vertically in a drawing tower where is further heated 22000 F and drawn downward by means of computer controlled melting and drawing process which produces fine ,high quality thread approximately 125 in diameter and about 6.5 KM in length. Here the optically pure core centre is 8 . Then the core is surrounded by less optically pure quartz called the cladding. The cladding is approximately 117 Then the silicone and buffer is covered over cladding. The metallic hard structure is applied for protection of fiber core. Then lastly polymer is used a soft protection of cable. The basic concept of optical fiber is the reflection in core fiber throughout all length. The reflection is caused as the reflection index of core is higher than the cladding reflection index.


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Optical fiber communication

In fiber optic communication the signal is processed and transmitted through the LED or laser. The light emitted by LED is transmitted through the optical fiber. In receiving part the light is converted into electrical signal by photo diode or photo transistor. Then it is processed to convert once again in original signal. The beam splitters are used to tap the signal to other communication centers. The repeaters are to compensate the loss of the optical signal in every distance of 1000ft. or so. In repeater the signal is similar to receiver it is received by optical device as photodiode or phototransistor. The mode of operation can be done by following modes.


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The basic advantages of optical fiber communication 1. It safe from electric shocks, disturbances. 2. It is safe from oxidization. 3. It is practically noise free in-between media. 4. So fast communication as the bandwidth for communication in 50-100 gigahertz. 5. It is practically not affected by environment, temperature. 6. More than 100000 voice channels are available. 7. The digital communication rate is excess of 2000Mbytes/s. 8. Very reliable output with very least distortion. 9. The loss or attenuation is very low so repetition is required for 1000ft distance.

5.4.1 Internet Internet is latest technology of communication as it has connected billions of people through the computer. It provided people unlimited privilege to use communication for their personal and social life. All business, education is now totally relying on Internet. So internet is defined as worldwide computer platform through which we can communicate as radio, TV, audio-video information, text materials, direct chatting, visual chatting etc. How INTERNET works? Internet is virtual connection between all attached computer through the many severs as service providers. When one computer of one place wants to contact it may need to pass many networks to reach desired computer destination. For example if one run yahoo mail, he should type yahoo address as target address and he also should type his username and password. This information first goes to local Internet service provider (ISP) and through it goes to national major service provider as NTA of Nepal and so. This sends the information to continental service provider via satellite antenna for example Singapore station who has their satellite in space. When the Singapore gets the request of connecting the Yahoo main service provider is in US so it connects the target via satellite. If we want to contact any people of world we can contact him by his address of e-mail ,mobile set ,local telephone with the help of service provider for example AOL as America on line.


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The computer when wants to connect any website he should code the address of the target website address and with it also its own address sent to local ISP. The ROUTER which connects the sender computer to server and server decides to send the route to send the datagram (data of sender and target) through the router. If it is intercontinental target then it should mostly transmit the signal satellite dish antenna to target space satellite antenna and again take back to the earth station .From earth station it is sent to ISP and routed to targeted website or targeted computer. Since the signal transmitted through the air or line cable the signal is modulated so a modulator and demodulator (MODEM) is required to convert the signal in original digital signal from modulated signal or it needs to modulate the digital signal before transmit the signal through the communication medium. The basic characteristics and properties of INTERNET 1. The internet has speed of sending and receiving the information which is called up link and down link which is measured by kilo, mega and gega byte per second. The good ISP with good connection via fiber optics can link the website with gega byte. The PSTN can have from 128Kbytes to some Mega bytes. When we browse number of websites the bandwidth of kilo, mega are shared. 2. It can provide different tasks at same time as chatting, down loading, direct talking, film TV direct observing etc. 3. All people can have their website and can share their data forever. With email address the user can send their information from any part of world to anywhere and same way receive. 4. Almost all information of world can be shared and downloaded in the wide network which may contain every PCs of world, servers. 5. Now e-commerce, e-education, online education, e-banking and most of jobs can be done through the world wide waves Written By Ir. Shanta Maharjan

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5.4.2INTRANET Internet is the communication network which plays central role for all PCs, laptops, internet accessing mobiles network world wide as a whole. But intranet is related to a group of computers which are members of organization host by dedicated server and share information among them. The intranet members also use all infrastructure of internet and communicate through the internet. The difference is that a firewall is created between public internet users as that the members of intranet only use or share the materials of intranet, it means the intranet use some typical passwords, user names to enter the intranet which is accepted by intranet server. There many intranet servers well known for intranet, one of them is face book, yahoo, Google etc. To become member of face book we should fill the form given by the organization and we should have accepted user name and pass word. Once we are member when we want to enter in the organization we should have corrected enter given user name and pass word. Then only we have authorize to use all privilege provided by given server of organization. Some intranet is free to enter but some needs to pay membership fee. Same as some intranet website needs special identity for being membership. The common thing of internet and internet is that both of them run on top of TCP/IP and HTTP. But intranet filters nonmembers, or illegal access through firewalls.We should notice that all intranets are logically or only virtually “internal” to an organization. Physically they are open and once they can contact with many other intranet organizations and public websites. All above explanations can be expressed through the given diagram.

Advantages of intranet 1. it is more flexibility, high efficiency, low cost networking than client server networking. 2. It is based in Internet protocols so accessibility is worldwide. Written By Ir. Shanta Maharjan

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3. Through intranet one easily advertises worldwide we attractive hope page and information. 4. It can handle multimedia data effort fully. 5. Low administration and system cost configuration. Disadvantage-It is however only virtually internal so some bad user can hack firewall pass words and it can destroy, steal valuable data, and so need to be care full.


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6.1 Number system, binary arithmetic Number system is the expression of a set of values used to represent quantity. The quantity is symbolized as digits and the value depends upon symbol and position of symbol. There are different number systems which explains up to what it can valued by single symbol as decimal can count up to 9 then for further counting there is required repeat symbol two digit as 10, 11, 12…Each system is based on radix as decimal is based on base 10.So all quantity more than single digit should be multiplied by 10 according to its position as, 234=2x102+3x101+4x100 Here the 10 is base or radix for decimal system. Similarly all system is based on the given radix. Here is some systems and its radix. 1. Binary system where we can have only two symbols 0 and 1tem.So two symbol will have radix 2.Now expressing its value as in decimal system it will be, (101)2= 1x22+0x21+1x20 2. Octal system: Its upper count is 0 to 7 but symbols are 8 so the radix is 8. (341)8=3x82+4x81+1x80 3. Hexadecimal System-its counting is up to 15 from 0 so the radix is 16. Here the symbol beyond 9 as for 10 used A, 11=B, 12=C, 13=D, 14=E and 15=F. 4. The above systems are well known and used in digital electronics but we can have any number system and used the radix. Since human use mostly the decimal system and the electronic digital system use binary system here is going to compare between these two number systems. DECIMAL BINARY DECIMAL BINARY 0 0 11 1011 1 1 12 1100 2 10 … … 3 11 255 11111111 4 100 65536 1111111111111111 5 101 6 110 7 111 8 1000 9 1001 10 1010


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Conversion between numbers 1. Decimal to binary: Ex.(36)10=( )2 ? 2 36 reminder 0 2 18 2 2 2 2

9 4 2 1 0

0 1 0 0 1

Least significant bit(LSB)

Most significant bit(MSB)

Ex.(36)10=(100100)2 2. Binary to Decimal Ex. (10111)2= ( )10 ? (10111)2= 1x24+0x23+1x22+1x21+1x20 =16+0+4+2+1 =23 Answer (10111)2= (23)10 3. Octal to Binary Ex. (361)8= ( ) 2 ? Octal No. 3 Binary value 011 Answer (361)8= (011110001)2 4. Binary to Octal Ex. (110111010)2= ( ) 8 ? Binary 110 Octal 6 Ans. (110111010)2= (672)8 5.hexadecimal to Binary Ex. (3A1)16= ( ) 2 ? Hexa No. 3 Binary value 0011 Answer (361)8=(001110100001)2 Written By Ir. Shanta Maharjan

6 110

1 001

111 7

010 2

A 1010

1 0001

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6.Binary to Hexadecimal Ex. (110111010110)2= ( )16 ? Binary 1101 1101 Hexa D D Ans. (110111010110)2= ( DD6)16 7.Hexadecimal to decimal Ex. (B14)16= ( ) 10 ? HEXA no. B 1 2 Weifhed bit 16 161 Weifhted value 256X11 16X1 Solved 2816 16 multiplication SUM of weight=2816+16+4=2836 (B14)16= ( 2836 ) 10 8.Octal to hexadecimal Ex. (237)8= ( )16 ? Octal 2 3 Binary 010 011 convert to 4-bit for hexadecimal 010 011 111 = 0 010 011 11 00 = 2 3 C = (23C)16

0110 6

4 160 1X4 4

7 111

Addition and Subtraction of Binary system 1. Addition Ex. (1111)2+ (1010)2 1 1 + + 1 1 1 1 +1 0 1 0 1 1 0 0 1 Ans. (11001)2 2. Subtraction Ex. (1101)2-(1011)2 10 1 1 0 1 -1 0 1 1 0 0 1 0 Written By Ir. Shanta Maharjan

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6.2 LOGIC GATES LOGIC GATES are the basic fundamental component used in digital electronics to construct all digital functions as counters, encoder, decoder, MUX, DEMUX, mathematical operations as add to divide, logical functions, microcontrollers, microprocessors etc. The term gate is used to describe the set of the basic electronic components as diode transistors MOSFETs etc. The logic is the true result for given circumstances or conditions. In daily life we use logic but it is high level so we cannot use or so complex this logic to make the machines to work as we want. So the digital logic which we can apply simply as it has only two conditions of ON and OFF and through it all complex logic can be apply with series of logic conditions of 1 as ON and 0 as OFF. We can give reverse logic also as the 1 for OFF and 0 for ON which doesn’t differ the logic system. When we have to convert the equivalents of ON and OFF or 1 and 0 to electrical form it is considered as +5 volts as 1 and 0 volt as 0. A logic applies a truth with given logic input as 1 and 0 and called truth table. There are basic seven fundamental logic gates as NOT, AND, OR, NAND, NOR, XOR, X-NOR. The basic gates are actually NOT, AND and OR gate from which all other gates can be constructed easily. However as component gate NAND gates are called fundamental gates which can be used construct the all other gates in it-self without help of other gates. Here are the gates, its symbol, Boolean expression, truth table and explanation of logic. NOT gate The NOT gate means inverting the given input. The gate has only one input and one output. If we give input high as 1 then the output is low and vice versa. The symbol, truth table electrical equivalent is given below.

The Boolean expression algebraically formula is Y= ̅ Written By Ir. Shanta Maharjan

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AND GATE It is the gate which gives output 1 or high when all inputsw are high otherwise the output is 0 or low.

The Boolean formula is Y=A.B NAND GATE NAND gate is combination of AND gate and NOT gate as,

The specific symbol for NAND gate is The Boolean algebra expression is Y= ̅̅̅̅̅ It performs logical multiplication.

OR gate It is compose of two or more inputs and single output and performs logical addition.

The boolian expression is Y= A+B Written By Ir. Shanta Maharjan

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NOR gate It is the combine gate of NOT gate with OR gate.

The Boolean expression is Y=̅̅̅̅̅̅̅̅ EX-OR gate The exclusive OR gate is for such condition when the inputs should be one of them 1 but another should be 0, as shown in truth table.

The Boolean algebra for EX-OR gate is Y=A ̅ It is made of AND and OR gate and NOT gate.

̅B=A

EX-NOR GATE It is the EX-OR gate with NOT gate here are given its symbol and truth table.

The Boolean expression is Y=A.B + ̅ . ̅ = A Written By Ir. Shanta Maharjan

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Boolean addition multiplication and laws, rules 1. 0+0=0 2. 0+1=1 3. 1+1=1 4. A+B=B+A 5. AB=BA 6. A+ (BC) = (A+B) (A+C) 7.̅̅̅̅̅̅̅̅̅ ̅ ̅ 8. ̅̅̅̅̅= ̅ ̅ 9. A+0=A 10. A+1=1 11. A.1=A 12. A.0=0 13. A+A=A 14. A+ ̅ 15. A.A=A 16. A. ̅ 17. A+AB=A 18. A+ ̅


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6.3.1 MUX (Multiplexer) It is the digital circuit used to select one of given data from two or more data as selection or serially. This type of function is used in many applications as in telephone exchange system, CCTV channel selection etc. The basic diagram of MUX is given below.

Here the S0 and S1 is data selector and D0toD3 are en data. The MUX has one output Y. If there is 16 input data then the no. of selector should be 4 . The data selection truth table is given below. S0 S1 Y 0 0 D0 O 1 D1 1 0 D2 1 1 D3 This truth table shows when there are selectors with 0 and 0,the data output will be D0,same as when the selectors are with 1,1 then data output will be D3. The logic gate realization for MUX is given below.

In this diagram there is used NOT gates to convert the S0 and S1 for getting input of inverse as ̅ and ̅ . The upper AND gate is used to take data output of D0 which is fulfill by the logic of inputs D0. ̅ ̅̅̅̅ .It means when the ̅ ̅̅̅̅ are 1 and 1 then the data signal can Written By Ir. Shanta Maharjan

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be possible to come out from that AND gate. So in this condition the D0 will be output as logic that if D0=1 or 0 the output will be same 1 or 0. But in this condition other AND gates outputs are insured zero as the condition meets only for above condition or the other AND gates outputs are no meaning as resultant for selection of data. This process is true for each NOT gates. So this circuit is for MUX.


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6.3.2 DEMUX The DEMUX is the invert action of MUX where the INPUT is only one but the input is distributed in number of OUTPUTs as desired or selection. So the diagram is

The truth table for selection of output for DEMUX is: S0 S1 X 0 0 D0 O 1 D1 1 0 D2 1 1 D3 When the data selection is 0 and 1 for S0 and ̅̅̅̅ Then the data of input X comes out from D1.Same to other conditions the output will be data output from input. The realization circuit for DEMUX is:

The DEMUX works according to the AND gate which gives output as the condition meets as shown in outputs for each data output. For example if the condition X. ̅ ̅̅̅̅ .Then the output will appear at D0 .Same to other outputs for different conditions.


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6.3.3 ENCODER Encoder is the logic circuit which converts the given value of quantity to digital equivalent. For example if we push the keyboard button of 9 the key board encoder converts it to proportion digital binary values. In this case the 9 will appear as 1001. Here is the diagram for ENCODER.

In this encoder when we choice any values it convert in 4 bits. Here the most significant bit is D and least is A. So for 9 the D=1,C=0,B=0 and A=1. This is realized by following circuit.

Here the logic OR gate is used for logic output. The trick here is used that D output for most significant can be high or 1 only when the digital number at D for values 8 and 9 as 1000 and 1001. The left as MSB high only in 8 and 9 so the input for D as in OR gate only from 8 and 9 as shown above. In this way if we push 8 the D will be 1 as 1000 and but the all other outputs C, B, A is low as there is no where 8 inputs to other OR gates.Another example for A output high the possible conditions are

pushing 1,3,5,7,9 as all have digital value at LSB(least significant bit) most right bit high 1 as 1=0001 3=0011, 5=0101,7=0111,9=1001.


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Now for example we push 6 then the 0110 so D=0, C=1, B=1 and A=0. It means the B and C OR gates get value 6 and these gates give high but other gates D and A will give low or O as they didn’t get input from 6 switch. The truth table for encoder is decimal D C B A 1 0 0 0 1 2 0 0 1 0 3 0 0 1 1 4 0 1 0 0 5 0 1 0 1 6 0 1 1 0 7 0 1 1 1 8 1 0 0 0 9 1 0 0 1


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6.3.4 DECODER It is the opposite function of encoder. It means when the binary coded digits are given in decoder circuit the output will provide high or 1 at given value quantity. So if the binary value 1001 is given the output of 9 should be switched or high 1. The symbolic diagram for decoder is:

The truth table for decoder is given below. D C B A Y 0 0 0 1 1 0 0 1 0 2 0 0 1 1 3 0 1 0 0 4 0 1 0 1 5 0 1 1 0 6 0 1 1 1 7 1 0 0 0 8 1 0 0 1 9 From above truth Table we can conclude, ̅ ̅ ̅+ ̅ ̅ ̅ C ̅ ̅+ ̅ C ̅ + ̅ C ̅+ ̅ C Y= ̅ ̅ ̅ ̅̅ The realization of decoder is given below.


̅̅̅̅̅C

̅̅̅

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In this realization the value of decimal is satisfies only when the AND gate condition meets and one AND gate at a time only becomes satisfied condition. If 1001 is the binary value then only the ninth AND gate only gives output high and all other gives output low.


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6.5.1 Combinational circuits A combinational logic circuit means a functional logic for a definite purpose of two or more logic gates. If say all digital circuits are combinational circuit. Here is an example of logic AND - OR logic.

In this AND-OR logic may have 16 different inputs and one output. Each AND gate individually provides its product of inputs. When even one high output of one AND gate, the output will be high as the next is OR gate. The Boolean algebra expression for this logic is given below.

We can evaluate the output equation by substituting into the various combination of input variables values .For example, A=1,B=1,C=1 and D=0, Y=AB+CD=1.1+1.0=1+0=1 Similarly many logic combinational circuits can be construct analysis in same way


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6.5.2 SUM of PRODUCT The sum of product form explains the product of two or more variables or their complements is the simply the function the AND function of those variables. The Product of two variables is AB and product of three variables are ABC and so on. So a sum of product expression is two or more AND functions OR together . It means the output of four variables in this form is AB+CD. The one of the example is given below.

Here the sum of product form is A ̅ + ̅ The another example `of SOP is,


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6.5.3 Product of Sum (POS) The Product of sum can be thought of as the dual of the sum of products. It is terms of logic functions, the AND of two or more OR functions. For instance, (A+B)(B+C) is a product of sums expression .The example of POS is given below.

This form lends itself to straight forward implementation with logic gates because it involves simply ANDing two or more OR terms.


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6.5.4 K-MAP (Karnaugh Map) It provides a systematic method for simplifying a Boolean expression and if properly used will produce simplest sum of product expression possible. The format of two three and four variable Karnaugh map is given.

The Plotting of K-Map is given below. For two variables, AB +A ̅

Here co-ordinate of AB and A ̅ are put the value 1.Smae plotting is done according to co-ordinate. For three variables, ABC +A ̅ C +A ̅ ̅ ,

Same way for four variables, ABCD +A ̅ CD +A ̅ ̅ ̅


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Grouping cells The grouping is done in the cases when there are 1s in horizontally and vertically with nearby 1s.Ex.1

EX.2The grouping is possible between above and below 1s.

Example for complete function for expression, X= A ̅ C + ̅ C + ̅ ̅ C + ̅ ̅ ̅ + ̅̅

The solution for K-map Four of 1s appearing in adjacent cells can be grouped. The remaining one is absorbed in an overlapping group. Step1.In this way we can give solution for two 1s as, ̅ . ̅ ̅ .C as the same vertical horizontal variables multiplies and the above ̅ common is added, the now the simplify ̅ ̅ ̅ Remains as common in both products For the case of ̅ so So we can put the value as output for given 1s is ̅ Step 2For four 1s the solution taken same way as above, ̅ ̅ C. ̅ ̅ . A ̅ C .A ̅ ̅ = ̅ as all other A and C products are equal 0 for ̅A =0 and C ̅̅̅=0. 3. Adding results of 1s as adding of results. Written By Ir. Shanta Maharjan

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So the overall output is ̅ + ̅

6.6.1 Latch It is digital circuit for maintaining a particular logic condition. A latch consists of a feedback loop it prevents changes from high to low, or vice versa resulting from external causes. In other word it is simple circuit for storing a logic element 1 or 0. All latches are bitable device and keep the value by means of feedback. The difference between the flip-flop and latch is method of changing their state of store. It means there is different method for changing the store value of 1 to 0 or o to 1.

S-R Latch The S-R latch is simply two gates function for example two NAND gates with feedbacks of output to one another gates input as shown in figure.

To understand easily the given circuit is used as to make the both input low operation.

The latch has two inputs ̅ and ̅ and same as two outputs, Q and ̅ We will start by assuming both inputs and Q output are high. In this case the Q output back toward input G2 is high but the inverter converts to LOW so the actual input to G2 is LOW. In this case both two inputs are actual low so the output of OR gate is LOW as ̅ First the truth table is given below. Inputs Outputs Comments ̅ R Q 0 0 1 0 No change ,latch remains in present state 0 1 0 1 Latch sets 1 0 1 0 Latch resets 1 1 1 1 Invalid condition Written By Ir. Shanta Maharjan

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1. When the inputs S and R are “low” then ̅ and ̅ “high” in this condition the Q will be “high” and ̅ will be low as described above. 2. When the̅̅̅ goes to “low” due to S goes “high” and ̅ is same “low”, then the condition is called SET as S is “High” from outside inter. In this condition the Q is “1” or “high” and it is referred as SET. The condition remains SET even changing momentarily S is changed its condition from “low” to “high” which means real “low” in ̅ .To change this condition the R should be “high” so that ̅ will be “low”. 3. In this third condition the ̅ is “low” and “low” at ̅̅̅ ,the G2 is forced the ̅ to “High” or “1”, as there are inputs to G2 or gate “1” and “0” and for OR gate the output is “1”. Now the G2 of High 1 is fed back to G1 and reversed to 0 by invertors so the G1 changes its position from “1” to “0” as the real inputs to OR gate is “low” from ̅̅̅ from inverter so output Q is “0” which is called RESET condition. The condition of ̅ remains “High” or “1” even when the R changes its condition from low to high. It means R “low” makes the ̅ “high” but the real Inputs of G2 will be 1 from ̅ and feedback from low output Q is changed by inverter “High” so the ̅ is “high” again. In this way the Q also remains same “LOW”. 4. But in the condition but high at S and R the ̅ and ̅ will be “low”, both gates G1 and G2 are forced to output high for both Q and ̅ It happens as both the G1 and G2 gets simultaneously and which makes the inputs 1 and 0 for both G1 and G2 so the outputs for OR gates will be “1”. This condition is not desirable as we have conceptually the Q and ̅ are complementary. So we say it INVALID CONDITION. 5. Conclusion : (a ) In each condition the Q and ̅ should be complementary .If Q=1 then ̅ = “0” and if Q= “0” then ̅ = “1”. (b) When the latch is set it means the condition of Q= “1” and this condition can be changed only when the R goes LOW or ̅ is High. Same way the RESET condition can be changed by S to High or ̅̅̅ is LOW.


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6.6.2 Flip flop Flip flop is also a form of latch which also keeps the memory of “1” or “0” in its output as in Latch. But the flip flop has additional clock pulse input with other two inputs. So it is also called synchronous bitable device. The term synchronous is for condition that the state of output only changes at specified point on a triggering input called clock designated as control pulse. In each possible edge of the triggering pulse only provides the possibility of changes of output state. Here is the basic diagram of RS flip-flop. S

Q

C ̅ R

The basic truth table for R-S flip is also same as given below. Inputs Outputs Comments ̅ ̅ ̅ Q 1 1 1 0 No change ,latch remains in present state 0 1 0 1 Set condition 1 0 1 0 Reset condition 0 0 1 1 Invalid condition The logical function of real R-S flip flop is given below gates. The each conditions are explains with individual operation with different inputs. Condition 1. SET CONDITION where Q= “1” and ̅ = “0”.

For SET condition the S= “1” and R= “0”.When control 1 pulse of positive edge goes then as shown above action occurs. a) In G1 gate the both inputs are “1” so the G1 as NAND gate provides o/p of 0.When the “O” is applied to inverter it is changed to “1”. This “1” is to the input of OR gate so it is sure that the o/p will be one in any case whether Written By Ir. Shanta Maharjan

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another input to OR gate G3 is “1” or “0”.So the G3 o/p as Q will be “1” which is set condition. b) In G2 gate gets input “0” and from control it gets “1” positive edge. As “1” and “O” input to NAND gate it gives output “1”. Them this o/p is given to inverter so it is changed to “0”.The another input is feedback from Q which is sure “1” so inverted to 0 by inverter nearby G4.So G4 gets both inputs “0” and gives the OR gate G4 Low or “0”.this value is ̅ Condition 2.RESET, R= “1” and S= “0” This condition is opposite of SET condition so easily can imagine that the value of Q and ̅ will be interchanged. Here the basic action of RESET with logic values.

a) In G2 gate the both inputs are “1” so the G1 as NAND gate provides o/p of “0”.When the “O” is applied to inverter it is changed to “1”. This “1” is to the input of OR gate so it is sure that the o/p will be one in any case whether another input to OR gate G4 is “1” or “0”. So the G4 o/p as ̅ will be “1” which is set condition. b) In G1 gate gets input “0” and from control it gets “1” positive edge. As “1” and “O” input to NAND gate it gives output “1”. Them this o/p is given to inverter so it is changed to “0”.The another input is feedback from ̅ which is sure “1” so inverted to 0 by inverter nearby G3.So G3 gets both inputs “0” and gives the OR gate G3 Low or “0”.this value is C0NDITION 3. “No Change”, where the value of Q and ̅ will remains no change It means it keeps its remaining value with no change for S= “0” and R= “0” Here is diagram with function for NO Change condition. No change condition for Q= “0” and ̅


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a) The G1and G2 both gets the input high from control and “0” from S and R so the both will NAND gates will have o/p of “1”.Now for G3 as “1” is from G1 is inverted so one input for G3 will be “0”.The next input will be taken previous value ̅ so inverted value will be “0”.In this way both values will be “0” so the output of G3 as Q will be previous value “0”. b) In the case of G4 the one value from NAND gate will converted to “0” by inverter to G4.But another input is fed back from Q= “0” so its inverted value will be “1”.In G4 when inputs of “1” and “0” will provide “1” o/p as ̅ The same process repeats for the previous value for Q= “1” and ̅ .The logic values are given below for this condition but explanation is not given as the function is similar but gate function of G3 and G4 is interchanged.

CONDITON 4 “NOT valid VALUE” It is condition when S= “1” and R= “1”.It is undesired condition which does not give required function as digital circuit and not usable. so the predicted values should be either Q= “1” when ̅ or Q= “0” when ̅ The condition of not valid logic operation is given below.

As the both inputs to G1 and G2 are “1” the both outputs are “0” which creates the inverter to “1” in both OR gates. So it is insured that the output of OR gate is high for both G3 and G4 which we consider invalid for digital function. Written By Ir. Shanta Maharjan

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6.6.3 D-flip-flop D- flip-flop is changed form of S-R flip flop as which has only one input and outputs are as usual. This flip flop is used to store single data bit “1” or “0”.The basic diagram of D-flip flop is given below.

The truth table for D flip flop is given below. Inputs Outputs Comments ̅ C Q 1 0 1 Set condition 0 1 0 Reset condition 1. When the input D is high or “1” then the R is inverted so the R is low or “0”. The real input is D= ”1” and R=”0” and when the C is positive going high then it is SET condition so the D input is stored in Q as high or “1”.Same way when the input is low or “0” then the data at Q will be reset and Q= “0”.So at set, “1” is stored and at Reset the “0” is stored. In this way data storing the value of Q follows the value of D. The timing diagram of D-flip flop is given below.

The data storing occurs when positive going pulse from the control pulse. Unless until the control pulse is not given the previous data remains unchanged even the data at D changed. Above timing diagram shows the storing data of “1” and “0” with control pulse.


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6.6.4 J-K master slave flip-flop In Master Slave flip-flop the same flip is repeated and the first flip flop is called master and the second one is called slave. The first flip flop dictates the second one. The output is similar to simple flip-flop. In J-K flip-flop the input is rename by J-k .The another difference is the output of q is given to G2 AND gate. Same as the output ̅ Here is diagram and truth table of master and slave J-K flip-flop.

Inputs

Outputs ̅ Q 1 0 0 1 1 0 1 1

Comments

K 1 1 Invalid condition 0 1 Reset condition 1 0 set condition 0 0 No change ,latch remains in present state Function In this flip-flop the functions are similar to S-R flip-flop, but the outputs of master flip-flop is given to slave to ensure again to achieve the output same. Here the master is clocked or controlled by positive going pulse where as the inversed negative pulse is applied control to slave flip flop. The outputs of the slave are feedback to J-K inputs such that the input is like locked. By truth table act same as before at both J= “1” and K= “1” the condition is not valid as the output is toggled in high which is not desirable. In the case of J= “0”, K=”0” the data in Q and ̅ are unchanged. In the case J= “1” and K= “0” the flip is Set and Q= “1” will stored, where as the ̅ In the opposite case J= “0” and K= “1” will reset the previous value of “1” in Q to new value of J= “0” to Q= “0”. Written By Ir. Shanta Maharjan

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6.7.1 Sequential circuits

The Combinational circuits are such logic circuit which gives environment for inputs of memory, retrieving it from memory and provides outputs. In inputs there may be different inputs as data, instruction .So the inputs of I1,I2..,Im are inputs to the combinational logic required for proper operation of the circuit. At any given time the memory is in state called the present state will advance to a next state on a clock pulse as determined by condition on the excitation lines (Y1, Y2,…, Y p).The present step of the memory is represented by the state variables (Q1,Q2,…,Q x ).These state variables along with the inputs determine the system outputs (O1,O2,…,On).


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6.7.2 Shift register counters A shift register is basically a shift register with the serial output connected back to serial input in order to produce serial sequences. These devices are often classified as counters because they exhibit a specified sequence of states. Here is simple three bit shift register counter with its logic circuit and timing diagram.

Truth table Clock pulse QA QB QC 0 0 0 0 1 1 0 0 2 1 1 0 3 1 1 1 4 1 1 1 5 0 1 1 6 0 0 1 In this circuit shift register is used of D-flip flop. In first clock pulse the FFA gates triggering and the output will be “1” as another input of FFA is from ̅ is “1” as in initial the Q is “0”.So the output of FFA of QA is “1” or “high”. But for FFB its clock pulse is with “0” as the moment of clock pulse and the output QB is “0”. Same for QC, which is also “0” as D input is “zero”. For next clock pulse the QA is still “1” as the input clock pulse and input ̅ also “high” “1”.In this moment the QB will be “high” as this moment the clock pulse and input QA both are “high”. But the QC is still “low”. For third clock pulse the QC will be “high” but this time even the ̅ will be “high” or not changed. In 4th clock pulse the position of ̅ will be changed to “0” as inverter of Q .This is due to “high” input from QC and clock pulse. In 5th clock pulse the change in ̅ is feedback to FFA so the QA is now goes to “low”. To become QA “high” the ̅ should be “high”. It will occur only at 9th clock pulse. Written By Ir. Shanta Maharjan

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So the pulse is counted in order of CBA or Qc QB QA, where A is least significant bit and C is most significant bit. In this counter the outputs are Qc QB QA. In this way the counting is 001,011 and 111 .After that the count will be 011,001,000. Again it starts to count in order 001,011 and 111.

7.1 Instrumentation System It is the process through which we measure any desired fix or variable value of physical quantity. The physical quantity may be sound, optical, heat, physical length movement, electrical and magnetic values. There are various methods of instrumentation or measurement system, some of which are given below. Mechanical instrumentation-It provides mechanical quantity or values with mechanical sensing and indicating .For example “Bordew Pressure gauge” measures gas pressure with spring needle deflection from pressure leaf plate. Electric instrumentation-In this system the physical quantity is first converted to electric quantities as resistance, voltage, capacitance, current, frequency, phase etc. These physical quantities are processed and displayed through the magnetic deflection in analog millimeters’ and indicators. Electronic instrumentation: Most of the modern instrumentation now uses electronic instrumentation as it can measure very high precision and reliable measuring. The electronic sensors and electronic processing and electronic display or controlling systems cause the electronic instrumentation popular in many industrial and household uses. Beyond that this system can provide fast and flexible response, memorable easy handling low cost device and mounting. The examples of electronic instruments are digital multimeters, oscilloscope, spectrum analyzer, strain gauge etc. It helps to find the mechanism faults, process behaviors research outputs, design etc. This system includes sensors, Instrumentational amplifiers as comparators, amplification, feedbacks etc. The electronic instrumentation can be shown in block diagram as given.


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7.2 Transducer /Sensors It is defined as a device which provides a usable outputs in response to a specified measurand or physical quantity. In normal condition the output is electrical quantity and the physical quantity may contain not only quantity but property and condition being measured. The sensors are mostly sensing device to convert the physical quantity to convert equivalent electrical signal. All sensors are transducers as it converts one from of energy to another. But some transducer are not sensors as it doesn’t senses the signal but it may display the quantity or reproduce the signal in original or understandable form as speakers, CRT TV etc. The sensors play a vital role in function of electronics, controls and automation and in all fields of science and technology. Types of sensors/transducers Type 1The sensors are available in all categories on the basis of energy generated or received. 1.Electrical:Charge,current,voltage,resistance,inductance,capacitance,dielectric constant, polarization, frequency, electric field, dipole moment and so on. 2.Mechanical:Length,volume,forfce,pressure,accelaeration,torque,mass,flow,aco ustic intensity, and so on. 3. Thermal: Temperature, heat flow, entropy, state of matter. 4. Magnetic: Field intensity, flux density, permeability, magnetic moment etc. 5. Radiant-optical: optical intensity, phase, reflective index, refraction, absorbent, transmittance, wavelength, Doppler Effect 6. Chemical : concentration, composition, oxidation, reaction rate, pH and like. Type 21. Passive sensor: It is the sensor which does not need power supply as parameters resistor, capacitor and inductors are called passive sensors. 2.2 Active sensor: Active sensors are those sensors which needs electric supply as photo diode, LDR etc. Type 3:Modern sensor Nowadays many modern sensors are used as transducers as micro-electromechanical sensors, CMOS image sensors, displacement and motion detectors, biosensors. Same as Coriolis, magnetic and Ultrasonic flow meters, photoelectric, proximity, Hall Effect, infrared, integrated analog and digital sensors, radar based level sensors are considered as modern sensors.


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7.3 Oscilloscope It is a precision electronic instrument which can apply all electronic, electrical phenomena of given circuit and used to design, research, experiments. It helps to understand the real activity of circuit. Here is listed the functions which can be used to measure or display. 1. AC/DC voltage, current 2. Signal current flow pattern 3. Frequency and phase of signal 4. Rise and fall time of signal. 5. Comparison of two signals and its patterns. 6. Analyze the signal positions, wavelengths.TV satellite signals. Simple block diagram and brief working concept

The main concept of oscilloscope is the CRT which can convert the electron flow into visual form. The vertical amplifier amplifies the signal which increases the amplitude and it in vertical deflection as electrical field strength which makes the electron beam to swing vertically. If there is not horizontal swing it will create the vertical line at centre line of oscilloscope graph face plate. In the case or horizontal the time base generator is to swipe the input signal in horizontal way so a saw tooth wave is generated by time base generator. With time varying in the saw tooth wave we can create the wave shape long or short horizontally. If the time is short of saw tooth wave then wave length will be lengthened and vice versa. The calibration is made accordingly with the time base selector. With the help of the horizontal sweep pulse as saw tooth save the vertical changing of signal is spread over the screen. And we can see the full signal of amplitude wise changing vertical signal in vertical and horizontal wave. If the changing of signal is fixed then we can see the signal as fixed shape. And if there is not any signal, even though the horizontal signal is present and a horizontal line is Written By Ir. Shanta Maharjan

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appeared in centre as zero level. In this way the signal appeared on screen. The triggering signal is given to horizontal from vertical to synchronize the signal from left to right movement of electron beam. The delay circuit is used in vertical section to match the timing of vertical and horizontal at the deflection plates as the time delay occur in horizontal section of more processing than vertical so the vertical signal is delayed as much as delayed in horizontal section. Here are given the methods of measuring different parameters of signals. 1. DC voltage When we provide DC voltage the Oscilloscope selector should be in DC range. The dc voltage line is appeared on the graph represented plate. The line appeared above the reference level is counted. If the selector voltage level is two and the appeared level is three then the DC voltage is 6. 2. Frequency

The signal amplitude V p=p is measured signal covered appearance of above peak to bottom peak and multiplied by the indication of voltage level selector. In the case of frequency the horizontally covered time period as blocks and multiplied by time indicator selector. If the 4 blocks are covered and time period is 5mS, then the time period will be 20mS and converted it to frequency is reciprocal so f=1/t =1/20mS =50Hz


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7.4 Strain Gauge Strain is the parameter of mechanical force applied on the surface of the metal or anybody. In many cases the strain to be measured for almost of mechanical functions. So, strain gauge is used to measure precisely the given measurand. The strain gauge is the device or instrument to measure the strain. There are various types of strain gauges and applied for different condition .In any case the strain gauge is applied on the surface. According to the its different principle there are different gauges as 1. Resistive 2. Capacitive 3. Electromagnetic 4. Piezo- electric 5. Semiconductor type. Strain Gauge of resistive type is still popular as its simple and effective so here are going to explain resistive type. The resistive strain gauge is based on the property of resistance of material which is defined by the formula, R= In strain the w ire network as conductive resistance is applied and due to function of strain the length of the conductive wire is changed or increased so the resistance of the wire is increased which is proportional to strain.


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If the wire is uniformly stressed along its length then and the stress is given by then [

]

The sensitivity factor of strain gauge is expressed by the formula; =1+2 + By construction the strains are two types 1. Wire type, 2.Foil type

The strain gauge can be instrumented in Wheatstone bridge format with Instrumentational amplifier. It gives precision output with reliable output. It is shown by following figure,


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In Wheatstone bridge the V a = V b so the relationship is Simplifying it,

=

After Instrumentational amplifier the output will be, V o=

7.5 DMM (digital multimeter) Digital multimeter is now common instrument to measure various electrical parameters to measure AC/DC voltage, current, résistance, capacitance, inductance, frequency, diode-transistor and IC testing. Since it has high precision measuring, reliable, stable, long durable, more security, it has taken almost all applications over classical analog meters. Since it displays in alphanumerical values its response is fast and easy readable and automatic the selection of ranges. The digital multimeters may have small range circuit to high precision according to price and application. But the basic block diagram is same for all digital multimeters.


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The Selection of parameter and basic attenuation and rectification for AC, current source providing for resistance measuring is similar to analog measuring. From ADC to display circuit is real digital circuitry which provides digital display. In ADC as analog to digital convertor the quantity Measuring is selected range as given way.

After this section the range voltage equivalent to all parameters are converted to digital binary bits. The digital binary bits are counted by counter so it provides fixed binary value. Now the binary value is decoded in either seven segment display or other displays so it could be converted in human understandable digits. Specifications of digital multimetersRanges Written By Ir. Shanta Maharjan

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1. DC voltage up to 1kv 2. AC ,, ,, 750V 3. Dc current ,, 10 amp 4. AC ,, ,, 10 amp 5. Resistance up to 200Mohm Basic accuracy 1. For DC 0.5% 2. For AC 1% 3. For DC current 1% 4. For 1.2 % for AC current 5. .for resistance 0.8% Display: 5 digits

7.2 Regulated power supply Regulated DC power supply is applied in many in many electronic appliances. Normal unregulated powers supplies are avoided in many cases as it creates own noises and the stability of working will be not proper for high precision equipments as in digital devices. In regulated power supply the output will be same for high range even the input voltage and output load is changed. The basic block diagram of regulated power supply is given below.


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In this block diagram the mains 220V AC supply is step down, rectified and smoothed as DC voltage but it is unregulated as its output voltage changes with Change in mains voltage and change of load also changes the output voltage. The regulating circuit senses the change in voltage. The amount of changing is fed back to regulating transistor and controls the conduction of transistor which in result the output is kept constant. The basic regulating poser supply is given below.

In this circuit the change of voltage causes to change the voltage in o/p circuit as error voltage. This error voltage is amplified in error amplifier and it controls the regulating amplifier in conduction as it changes the base voltage to regulating transistor. When the input is increased the error voltage also increases and it is amplified in determined gain. The error voltage at base of error amplifier makes the amplifier more conduction so the collector voltage of this amplifier is reduced. As the collector voltage is decreased this same terminal as base to regulating transistor is reduced so the transistor conduction in same proportion as the input voltage is increased. So the output voltage remains same as unchanged. The vice versa process repeats for decreasing the input voltage. Power supply regulation parameters 1. Load regulation: The load regulation factor is the change in o/p voltage at no load and full load. Llr=(Vln-Vlf)/Vlf where Vlf full load voltage and Vln -no load voltage 2. Minimum load resistance-It is power delivery at its full load current at rated voltage is referred to as a minimum load resistance, RL=


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3. Source or mains line regulation: It is regulation of source at high input and low input. LSR=(VHI-VLI)/Vnominal load –o/p in percentage. 4. O/p Impedance-The o/p impedance should be zero or some milliohms so that the changing load doesn’t change the o/p voltage. 5. Ripple rejection-The supply should reject ripples from ac input. It is very low at regulated power supply.

7.3.1 Remote control It is electronic equipment through which other electronic devices can be operated from distance. Now a days the remote control are used for various purposes from TV,DVD player, household door , box ,car to internet control medical surgery, satellite path control etc. There are various types of remote controls as wire linked remote control, ultrasound wireless control, optical infrared control and electromagnetic radio wave wireless controls. Due to advance technology and far distance cover radio wave remote control is used widely for most of applications. But for reasonable shot distance the infrared remote control is used as household remote controls. Basic block diagram and function of infrared wireless remote control is given below.


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In keypad all functions are listed as bottoms for switching given function. When we switch a function, the related switch is closed and the related input of microprocessor is got triggered. The microprocessor which is already programmed takes this action and converted to some 8 bit control bits as coding. In further these codes are modulated in certain high frequency 160 to 220 kHz. For high 1 logic it is frequency modulated or keyed to 220 KHz and for low logic 0 it is modulated by 160 KHz. Then it is send to infrared drover which is amplified to drive the infrared LED. Then it sent to LED to convert the signal in infrared light waves which is invisible to human. The infrared signal is received by photodiode or photo transistor. It converts it to electrical signal and converted to binary train of high- low as coded in transmitter as function of FM demodulation. The coded binary signals are decoded in microprocessor and it is switched desired function of electronic functions for example channel selection in TV etc.

7.3.2Character display Character display is the display of alpha-numerical display which is used in many indicators as in many device display system in CD players, radio tuning, control display in photocopy machines etc. In many advertisements in city –markets also display big lettering in alphabetical and numerical display units. Modern display system gives flow of information in cyclic order, same as we see the scrolling news, advertisements etc in TV. The concept of the character display is similar to 7-segment display. But for alphanumerical display unit is much more complex and if say it a scrolling it takes still more complex. A basic block diagram of character display is shown below.


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When we type any letter it is recognized by microprocessor in the form of digital binary 8 to 16 bit codes. And it is sent to memory unit for storing the data. Then we manipulate the data for display methods, timing, repeating etc through the logic unit. Once both of function and data is stored we can start to display the character. The data is taken from memory unit and run as given by the logic the microprocessor provides the digital data in same order and timing as mentioned by logic and it is decoded by alphanumerical decoder to glow the units of alphanumerical LEDS or LCD panel. The sample of alphanumerical panels is given below.

7.3.3 Audio-video system Audio video system means all electronic systems which represents audio and video signal from converting these signals to electrical signals and Written By Ir. Shanta Maharjan

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processing and reproducing these signal to original form of audio and video signals. The basic functions of audio systems are given below by block diagram and fundamental terminologies.

In audio section the system starts from microphones as it converts audio acoustic signal into electrical signal. There are many microphones as moving coil, condenser, ribbon, electrets microphones etc. In amplifier the tone control, volume controls are also associated. Now if it is to transmit through radio wave, it is modulated as AM and FM and transmitted through antenna. If it is just amplifier then it is further amplified .In the case hi-fisystems the signals from microphones are separately amplified and noise reduction systems are employed for high quality sounds. Then it is given to speakers to produce the sound. In the case of magnetic recording it is given audio head and recording take place in magnetic tape. If it is to be recorded in compact disk it is digitalized, compressed in MPEG system and send to CD laser recording block where the CD is optically recorded in pit and flats. Nowadays the signals are communicated through the internet which is done with MODEM and computer with local ISP to international network system. In the case of telephony it is done through the wire cable, wireless and optical fiber through the local, central exchange system to Written By Ir. Shanta Maharjan

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international exchange network. In mobiles the audio signal is similarly received even through the satellites. The video system is similar to audio system but its communication via TV system, video cassettes and communicated through the different systems as given below. a

In video system the picture information is first converted to video electrical signal by CRT camera or CCD camera. This signal is encoded in well-known TV systems as PAL, SECAM or NTSC. In TV system they are modulated as VSB or FM modulation then it is transmitted through the antenna. The transmitted signal is received by receiver and demodulated, decoded and reproduced through the CRT TV receiver or LCD panel. If we need to record then it is recorded in magnetic video cassette tapes. Nowadays the video signal recorded in CD as optical recording for which it is again compressed and formatted in MPEG or DVD format. For internet the DVD system is again connected with computer and shared the message with the networks.


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7.3.4 Data Logging Data logging is the method of recording sensor measurements over a period of time. Typically in robotics you will not need a data logger. But there are times when you may need to analyze a complex situation, process large amounts of data, diagnose an error, or perhaps need an automated way to run an experiment. For example, you can use a data logger to measure force and torque sensors perform current or power use measurements, or just record data for future analysis. A data logger can be defined as, “an electronic device that records data over time or in relation to location either with a built instrument or sensors or via external instruments and sensors." Data loggers, or data recorders as they are sometimes called, encompass a range of products including software and hardware. We specialize in stand-alone devices that can record information electronically from internal or external sensors or other equipment that provides digital or serial outputs. Parts of a Data Logger Typically, data loggers are very simple devices that contain just three basic parts: 1) A sensor (or sensors) measures an event. Anything can be measured. Humidity, temperature, light intensity, voltages, pressure, fault occurrences, etc. 2) A microcontroller then stores this information, usually placing a time-stamp next to each data set. For example, if you have a data logger that measures the temperature in your room over a period of a day, it will record both the temperature and the time that temperature was detected. The information stored on the microcontroller will be sent to a PC using a UART for user analysis. 3) And lastly the data logger will have some sort of power supply, typically a battery that will last at least the duration of the measurements. Key features of the data loggers we provide include: 

Stand-alone operation - The data loggers are normally configured with a PC although some models can be configured from the front panel. Once configured they don't need the PC to operate. Many of the loggers can be started and stopped via a button or external switch. Also, all of the loggers we provide have built-im memory for measured data - see #3 below.


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



Support for multiple sensor types - We offer data loggers with both dedicated input types (thermocouple, RTD, humidity, voltage, etc.) and universal input loggers that allow the input channels to be configured for specific sensor by the user, either through software or configuration switches. Local data storage- All of the data logger we provide have local data storage, so all of the measured data is stored within the logger for later transfer to a PC .Software provided with the loggers allows measured data to be easily downloaded to a PC for analysis and archiving. Automatic data collection - Our data loggers will collect data at regular intervals, 24 hours a day 365 days a year if necessary. You don't need to rely on a person or a PC to take a measurement.

When we choose data logging following factors should be mentioned.          

Automatically collect data Minimize measurement errors Reduce personnel costs Automatically generate alarms on out of limit conditions More reliable than PC/MS Windows Permanent electronic record Easier to analyze data Battery powered for remote sites or critical applications Easy to set-up Makes data available to many users


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7.3.5 Clock counter measurements Clock counter measurements are common for many physical parameters. In this clock counter the sensed voltage are converted in numerical values with the help of clock pulse counters. There are many clock counter measurements for example, ramp counter, integration op-amp counter, count up measurements, successive counting measurements. Here is given one simple example of count up clock counter measurements.

1.Initially a DC voltage from the sensor which is going to measure its value Is applied to comparator and the output of the comparator is negative as the input is given from the inverting terminal is positive and non inverting terminal is zero in first moment. 2. The negative high output of the comparator provides the 8-bit counter is to start count with start high and clock pulse is passed out to output. 3. The first bit clock pulse as output is given to decoder and 8-bit D/A convertor. 4. The first bit is decoding in Decoder for 7-segment display and display unit will show 1. 5. 4.The D/A convertor convert the 1 bit to analog voltage level and it is given to positive terminal to compare with given DC voltage to inverting terminal.


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6. Since the inverting terminal is Higher than non-inverting the so the output will be again and it allows the counter to pass the next bit. 7. It is again decoded in decoder and will show 2 by the decoder. 8. The second bit also converted to analog value and compared to input in comparator. 9. The process continues until the comparator is equal and it gives the output of comparator is zero. It stops the counter to pass the clock pulse. 10. Last bit in output of the counter is decoded in decoder which is equivalent value of the input signal of DC level. In this way a clock counter cam measure any DC level voltage measurements.


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Numerical examples CHAPTER 1. SOURCE 1. Conversion of voltage source to current source

Soln-IS= = and having same resistance across the current source. So the circuit will be,

2. Conversion of current to voltage source

Soln-Voc=Is x Rs=4x25=100V and resistance will be is series with same value.

3. Find the current in 25 ohm resistor of given circuit using conversion method

Converting the current in voltage source, Voc1=Is1xRs1=10x 5=50 V Voc2=Is2xRs2=5x 10=50 V Now the figure will be,

The current will be, I= = =100/40=2.5 AMP.


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Kirchhoff’s Law Problem: Find the current through the R3 of following circuit

Since the supply of 30V and 50V are in reverse connection and I2 is more than I1 the voltage across the 500 0hm will be (I2-I1) R3, so when the circuit individually taken using Kirchhoff’s voltage law. 1. Circuit Across R1,R2 and 30V I1.R1+ (I2-I1) R3=E1 Or, 100 I1+500(I2-I1) =30 Or, -400 I1+500 I2=30…… Eq.1 2. Circuit Across R2,R3 and 50V, I2.R2+ (I2-I1) R3=E2 Or, 200 I2+ (I2-I1)500=50 Or, 700 I2-500I1=50 Or, -500 I1 + 700 I2=50……Eq.2 3. Eq.1 multiply by 5 and eq. 2 by 4 and subtracting eq. 1 and eq.2 -2000 I1+2500I2=150 - (2000 I1 + 2800 I2=200) -300 I2=-50 Or, I2=50/300=0.167amp 4. Value of I2 is applied at eq.1 -400 I1+500 I2=30 -400 I1+500x0.167=30 I1= (30-83.33)/400=53.33/400=0.133 5. Current through the R3= I2-I1=0.167-0.133=0.034A=34 mA Voltage across the R3, 0.034 x 500 =17V


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Example2 (Kirchhoff’s law) Problem: Find current in all branches

Soln1. in the loop fcdef, 11 i2+6(i1+i2) =30+10 Or, 6i1+8i2=40…..Eq.1 2. in the loop abcfa, 2i1+4i1-11i2+6i1=20-30 Or, 12i1-11i2=-10…..Eq.2 3. Multiplying eq. 1 by 2 and subtracting with eq.2 12i1+16i2=80 - (12i1-11i2=-10) 27i2=100 I2=100/27=3 amp 4. Applying i2 in eq.1 6i1+8x3=40 Or, i1=16/6=2.66


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Superposition theorem Example: Problem-Two ac sources each of the internal resistances 20 ohms are connected in parallel across a resistance load. If the generated emf are 50V and are 900 out of phase with each other determine the current which will flow in the 10 ohm resistor and in each generator.

Soln1.For E1 acting alone,

I1=E1/R eq=

=50/26.7=1.88Amp

Same as IR1 is, IR1=1.88x 2.For E2 acting alone,

I2=E2/R eq=j50/26.7=1.88 IR2=1.88x20/30=j1.25 A 3. Mutual current at R3, Written By Ir. Shanta Maharjan

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IR3= IR1+ IR2=1.25 +j1.25 A=1.77 A

Thevinins Theorem

Problem: 1. Determine the current through the 40 ohm resistor in given circuit. RT=30+ 2. When the 40 ohm resistor is open then the mesh formed by the voltage sources and 10 ohm and 20 ohm resistors, I= 3. Open circuit voltage VTH=25-0.33x20=25-6.6=18.4 V

4. Current through the 40 ohm resistor is, IL=


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Norton Theorem

Problem: Find the current flow through the resistor across the A and B without source using Norton theorem. Soln1. Equivalent resistance of circuit from the A and B to source, RT= 2. Total current from sources considering the A and B are shorted, ISC=I1+I2+I3= 3. Current through the 25 resistor is, I=


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Diode

Problem 1: if supply voltage is 10 V and resistor is 1Kohm, then find the load line, operating point of given circuit. Solution: 1. To find the maximum current, Where v D =0, I D (max)=V/RS=10/1x103=0.01 A 2. To find the voltage across the diode, ID=0, V D (max) =VS=10V 3. The Operating point of the circuit is, ID= (VS-VD)/RS= (10-0.7)/1x103=9.3/1x103=0.0093 A VD=0.7V


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Problem 2 Find the currents I1 , I2and VS of following circuit

After all diodes voltage across the diodes are represented by potentials as shown below.

1. 2. 3. 4.

Voltage across the X point cannot exceed more than the 1.4V. So the VS=1.4-VD1=1.4-0.7=0.7 As the VS and VD1 equals to 1.4V so D1 doesn’t conduct. But D2 and D3 conducts and I1 and I2 equals. So, I1=I2 = (5-1.4)/1=3.6 mA


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ZENER DIODE

Problem A Zener diode rated 10V.40mA can be considered as ideal where R z =0, calculate RL, IL. Solution: 1. The current through series resistor is: IS= (60-10)/1x103=60mA 2. When IZ=0 or zener diode is open then the all current flow through the load resistor, and the load resistor will be, VL=I X R L (min) = Or, RL (min) =250ohm 3. RL is maximum when I z is 40mA, IL=60-40=20mA So the R L (max) =10/20x10-3=0.5x103=500 ohm.


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Transistor1

Find Ic, RC and load line with the load line, if the current gain is 100and RC=1K,RB=10K 1. Finding the value of IB, VBB=IB*RB+VBE Or, 5V=5x103xIB+0.7V Or, IB= (5-0.7)/10x103 Or, IB=0.43 mA 2. Finding the value of IC, Gain 𝛽= =100, Or, IC=100x0.43x10-3 Or, IC=0.0043 A 3. Finding the value of VCE=VCC-ICRC Or, VCE=10-0.0043x1x103=10-4.3=5.7V 4. Finding Imax for load line. (When VCE=0) I max=VCC/RC=10/1x103=10mA 5. Vce(max)=VC C when the IC=0 So load line and operating point is:


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Transistor2.

Find the value of IB,VCE ,IC if RC=2K,gain =50, RB=100K, VCC=12V 1. Finding IB a) using Kirchhoff’s law, VCC=I’CXRC+IBRB+VBE VCC=(IC+IB)RC+ IBRB+VBE as Since the IB too small then I’C= IC+IB=IC VCC= 𝛽 IB)RC+ IBRB+VBE


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IB=

=56.5

2. Finding IC, IC= 𝛽 IB=50x56.5 =2.83 mA 3. Finding VCE VCC=I’CRC+VCE=ICXRC+VCE(as I’C VCE=VCC- ICXRC =12V-2.83x10-3x2x103 =6.35V

)

Transistor 3

The two relevant equations are Vcc=ICxRC+VCE VCC=IBXRB+VBE


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Transistor 5

Find IE ,IC if R1=2K, R2=12K,VCC=20V,RC=100 ohm, 1.Finding the value of Rth and Vth I thevinins= =20/14=1.42 mA R thevinins=

=1.71 Kohm

V thevinins= I thevinins*R2= R2=1.42 x10-3x12x3=17 2. Finding IB, VTH=IBxRth+VBE Or, IB=(VTH-VBE)/RTH=(17-0.7)/1.71x103=9.5 mA 2. Finding IC, IC= 𝛽 3. Finding VCE,


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VCE=Vcc-IcxRC=20-0.095x0.1x103=10.5V

Clipping circuit

If the signal of ac is 10V,RS=100 ohm, VDC=2V,RL=1Kohm,thew find the output voltage with shape of output signal. 1. Finding output of positive half signal, a) The diode is reversed biased so all current passes through the load and series resistor, Is=V ac / R s+ R L=10V/1100ohm=0.009A Output voltage=I s x RL=0.009x1x103=9Vp 2. In the case of negative half cycle, a) The diode is forward biased but a dc bias of 2 volt opposes the forward bias so up to 2.7V flow through the load. The output voltage will be till 2.7 is, Output current=7.3/1100=0.006 Output Voltage=0.006x1x103=6V b) the voltage beyond the 2.7 V the diode conducts so the current flow through the diode and not flow through the load resistor so the output voltage is zero.


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Clamping circuit

When there is positive half, the diode doesn’t conduct until 0.7v to overcome the potential barrier of diode. So till 0.7 V it is passed through the load resistor which means it is appeared in output. This voltage is not developed across the capacitor as voltage drop across load resistor as it is high resistor value When the input positive exceeds 0.7V then the diode starts to conduct and the current flow through the diode to charge the capacitor up to 5-0.7V=4.3V. When there starts the negative half cycle the supply voltage adds with charged voltage of capacitor so the two supply voltage of capacitor and supply voltage adds and there will be 4.3V+5V=9.3V.This voltage is developed across the load resistor as this time the diode is fully reversed biased and no flow of current through it. So the load resistor voltage is the negative voltage of 9.3 V. The signal shape remains same but it is shifted down upper 0.3V and lower 9.3V as negative side. In this way the signal is clamped down. If we want to shift it upper clamp we should change the diode in opposite way. If we want to shift in some high voltage range we should add battery in series to block the supply voltage.


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K-map Reduce the following function to its minimum sum of product form.

X= ̅ ̅ ̅ ̅ + ̅ ̅ C ̅ A ̅ ̅ ̅ + ̅ CD+ A ̅ C ̅ x=0,2,8,7,8,10=0000(0),0010(2),1000(8),0111(7),1000(8),1010(10) The ̅ CD, is converted to f0ur digit as below and it becomes 7,8 where the 8 is repeated so can take only one 8. Now, 1.Equalizing the equation to four variables for ̅ CD, X= ̅ ̅ ̅ ̅ + ̅ ̅ C ̅ A ̅ ̅ ̅ + ̅ CD(B+ ̅ + A ̅ C ̅ ̅ X= ̅ ̅ ̅ ̅ + ̅ ̅ C ̅ A ̅ ̅ ̅ + ̅ CDB+̅̅̅̅̅̅̅̅ + A ̅ C ̅ or Plotting the K-map,

2.After filling the K-map we factored by angles to one factor and near by vertical two 1s are factorized or grouped in another factor as shown above, a) the corners groups, ̅ ̅ ̅ ̅ ̅ ̅C ̅ A ̅C ̅ A̅ ̅ ̅ As A and ̅ in product so cancels, As there is only ̅ it remains, As there is B and ̅ so it cancels, As there is only ̅ so it remains, The resulatant will be ̅ ̅

b)vertical group, ̅ CDB+̅̅̅̅̅̅̅̅̅̅̅ ̅ ̅ CD as not cancelled but B is cancelled. Written By Ir. Shanta Maharjan

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C) the resultant will be, X= ̅ CD+ ̅ ̅ 3. realization of this in gates,


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