computer simulation of the monostable multivibrator

COMPUTER SIMULATION OF THE MONOSTABLE MULTIVIBRATOR USING PSPICE E. B. Emoricha*, H. B. de Pedro, J. B. Magallanes, Electronics Group Department of Physics MSU-Iligan Institute of Technology, 9200 Iligan City *Presentor

ABSTRACT Monostable multivibrators have attracted some attention in the progressive industry of electronics because of its promising use. There had been several theoretical analyses on the circuit just to study its operational characteristics. The non-triviality and the complexity of the existing analyses can be surmounted by simulating some reliable computational models. In this study, the monostable multivibrator circuit is simulated by optimizing the use of the software package PSPICE. The operation of one-shot is being analyzed taking some considerations of its components. The voltages of the primary components of the one-shot are plotted versus time using the Orcad-PSPICE A/D Lite EDITION. The results are then compared to that of published electronic analysis.

I. INTRODUCTION Computer analysis of an electronic system has two approaches: using language such as BASIC, C, FORTRAN and the other approach is to use a software package, for example, GNUCAP, CIRCUIT MAKER, and SPICE [1]. This study employs PSPICE to analyze a multivibrator circuit. Multivibrators are oscillators that produce digital signals. There are three different kinds of multivibrator circuits, namely the astable multivibrator also called freerunning signal or clock signal, bistable multivibrator or flip-flop (latch), and the monostable or one-shot multivibrator that either generates single pulse or series of clock pulses. The bistable multivibrator has two stable states. It remains in one of the states until a trigger is applied [2]. The one that is being simulated in this study is the monostable multivibrator circuit. Monostable or one-shot is a multivibrator which produces a single pulse that stays high or low for a fixed amount of time that depends on external resistors and capacitors of the one-shot. This device is used to delay, reshape, and/or eliminate mechanical switch bounce [3]. Retriggerable one-shots allow the one-shot to be fired while the output is still activated. That means that one shot starts the timing cycle over

if another trigger occurs while the output is already high. A non-retriggerable one-shot cannot be retriggered while the output is activated. For this one-shot the output must complete its cycle, return to its resting state and then be triggered again. The aim of this paper is to illustrate the basic operation of the monostable multivibrator. There are several analyses that have been done using this monostable multivibrator circuit. But such analyses are purely theoretical that needs knowledge on some principles of the electronic network analysis (i.e., Kirchoff’s Rule, Thevenins and Norton’s Theorem). 1.1 The PSPICE PSPICE is a simulation package that models the behavior of a circuit containing analog and digital devices. It runs both basic and advanced analyses. Basic, for example, DC sweep and other DC calculations, AC sweep and Noise, and Transient and Fourier analyses. Parametric and Temperature, and the Monte Carlo Sensitivity/worst – case are the advanced analyses [4].

1.2 Why PSPICE? Amongst the available simulation programs, PSPICE is chosen because of the following reasons: a. It is widely used in the electronic industry. b. It allows the mixing of the digital and analog parts. c. It is easy to familiarize and use. d.It gives access to the libraries developed by the manufacturers. e. The software was first made available to us from the NIIGATA UNIVERSITY of JAPAN by the department. The PSPICE that is being used is the student version from Japan and the one available from the distributor (PSPICE A/D Lite Version 9.2). The simulation program is limited only to 64 nodes and 10 transistors but all the other features are made available. II. EXPERIMENTAL DETAILS Before the simulation starts, the researcher first does some familiarization of the software package. The circuit is redrawn; nodes are identified and labeled in logical order. The network is then converted into codes and is entered into the computer in an input file. 2.1 The Circuit Diagram of the Monostable or One-Shot Multivibrator

2.2 The Codes for Simulation Monostable Multivibrator Circuit ********************************* ***** Subcircuit Description ***** **************************************** .subckt uA741 1 2 3 4 5 ********** Include here the u741 ******** ********** circuit description ********** .ends uA741 ***************************************** ********* Main Circuit ********** ***************************************** *********

Power Supplies

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Vcc 5 0 DC +15V Vee 6 0 DC -15V **** input trigger signal + circuit **** Vtrig 7 0 PWL(0, +15V 10us, +15V10.01us, + 0V 60us, 0V 60.01us, +15V 10ms, + +15V 10.00001ms, 0V 10.090ms, 0V + 10.09001ms, +15V 1s, +15V) C2 7 4 0.1uF R4 4 0 100k D2 2 4 D1N4148 *** Monostable Multivibrator Circuit **** Xopamp1 2 1 5 6 3 uA741 R1 2 0 1k R2 2 3 9k R3 1 3 50k C1 1 0 0.1uF D1 1 0 D1N4148 *********

Model Statements

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.model D1N4148 DIs=0.1p Rs=16 CJO=2p + Tt=12n Bv=100 Ibv=0.1p) ********** Analysis Requests ************ .IC V(3)=+15V .TRAN 1ms 2ms 0ms *********** Output Requests

***********

.PLOT TRAN V(7) V(3) V(2) V(1) .Probe .End

Figure 1.Circuit Diagram of the One-Shot

The first line of the code is the name of the circuit followed by the subcircuit description of the u741. The subcircuit description of the u741 can be made available by the software library or by the internet. The trigger signal is a PWL (Piecewise Linear Source) with a height of 15 volts. The model statement that is available is

the model of the diode that is being used. It is available in the library of the simulation package. The command line .IC fixes the node voltage of node 3 to 15 volts over the entire bias point analysis. The line .TRAN prompts PSPICE to run transient analysis from 0 to 2ms. The output request .PLOT commands PSPICE to create a plot of the signal in the .OUT file for .TRAN analysis. .PROBE directs PSPICE to write the results of the transient simulation of the voltages at nodes 7, 3, 2, and node 1 in a format that the Probe graphics post-processor can read. III. RESULTS and DISCUSSIONS Assuming that the circuit at first is at stable state, and then the initial voltage Vo is equal to 15 volts (trace is shown using the output voltage V3).

Figure 3. Voltages at node 1, C1 and D1 Note that the trace of the voltage at node 1 is the same trace to that of the diode 1 and capacitor 1. Also, the voltage at node 2 is shown by the Figure 4.

Figure 2. Trace of the Output Voltage If we would have the trace of the voltage V1(refer to Figure 3), notice that the capacitor charges toward -15 volts but it stops to -1.5007 volts. That is because at that point the u741 returns back 14.613volts.

Figure 4. Voltage at node 2 In the operation of the one shot as it is shown in the traces, upon applying the pulse the u741 switches to -15 volts. D1 became reversed biased so as the C1 is no longer clamped to its initial condition but charges toward -15 volts with time constant,RC. At this point V2 sits at F -Vout that is -13.090 volts. When the voltage C1 equals the voltage -1.5007 volts, the u741 comparator back to 14.613 volts (output voltage). The voltage across C1 settles down to 567.201 volts.

Education, PCASTRD, to the MSU-IIT and to the Physics Department who in one way or another helped in this research. Also, to the Niigata University for the simulation program being used in this study. REFERENCES

Figure 5: Voltage at C1, V trig, Vout Figure 5 is the superimpose traces of the voltages at the capacitor one, trigger voltage and the output voltage. The pulse width at the midpoint of the waveform (refer to Figure 2) is equal to 750.793us (subtract 791.950us and 41.157us.). In the published analyses of the circuit, in the stable state of the circuit the output voltage is equal to the trigger voltage. The voltage at node 1 is equal to the voltage across the capacitor and must be approximately equal to 0.7 volts. And the pulse width is given by the formula: T= R3 C1 ln {1+ (0.7/Vout)/(1-L)} where L= R1/(R1 + R2 ), from which one had obtained T= 0.754855 ms. IV. CONCLUSION In the operation of the one shot there exists a quasi-stable state at certain time. The quasi stable state is determined by the R-C network and the threshold. The PWL is used to trigger the circuit to switch to a quasi-stable state. The R-C circuit causes the circuit to return to its stable state. By comparison, there exists a significant difference between the obtained data to that obtained by the electronic circuit analysis. The difference that occurred is due to some approximations in the calculation of the analysis. ACKNOWLEDGMENTS The researchers would like to express their deepest gratitude to the Commission on Higher

[1] Boylestad, R., and L. Nashelsky. 1992. Electronic Devices and Circuit Theory New Jersey: Prentice-Hall, Inc. [2] http://www.seas.smu.edu [3] http://www.hcc.hawaii.edu [4] PSPICE A/D online manual [5] Faissler, W. L., An Introduction to Modern Electronics, John Wiley & Sons, Inc [6] National Semiconductor Company. National Operational Amplifiers Databook.1995