Nov 30, 2007 ... Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1.
Tesis adalah hakmilik ... Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor
Falsafah dan Sarjana ... Objektif projek ini adalah sebagai alat komunikasi
dimana apabila isyarat .... A modern communications system in first.
PSZ 19:16(Pind.1/97)
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS♦ JUDUL:
VOICE COMMUNICATION USING RF SESI PENGAJIAN: 2007/2008
MOHD SAIFUL EFFENDI BIN MUSTAPA ALBAKRI
Saya
(HURUF BESAR) mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( √ )
√
SULIT
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972)
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
________________________________ (TANDATANGAN PENULIS) Alamat Tetap: 27, JALAN CEMPAKA 29,
TAMAN CEMPAKA, 68000 AMPANG, SELANGOR Tarikh
: 30 NOVEMBER 2007
CATATAN:
*
**
________________________________ (TANDATANGAN PENYELIA) EN. CAMALLIL BIN OMAR (Nama Penyelia)
Tarikh
: 30 NOVEMBER 2007
Potong yang tidak berkenaan.
Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
♦
Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).
"I declare that I have assessed this thesis and in my opinion, it is suitable in terms of scope and quality for the purpose of awarding a Bachelor Degree in Electrical Engineering (Electronics)”.
Signature
: ………………………………..
Supervisor Name
: EN CAMALLIL BIN OMAR
Date
: 30 NOVEMBER 2007
VOICE COMMUNICATION USING RF
MOHD SAIFUL EFFENDI BIN MUSTAPA ALBAKRI
This thesis is submitted as a part of fulfillment the requirements for the degree of bachelor of Electrical Engineering (Electronic)
Faculty of Electrical Engineering Universiti Teknologi Malaysia
NOVEMBER 2007
ii
"I declare that this thesis entitled “Voice Communication Using RF” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree ”
Signature
: ……………………………...........................
Author
: MOHD SAIFUL EFFENDI BIN MUSTAPA ALBAKRI
Date
: 30 NOVEMBER 2007
iii
Specially dedicated to My beloved parents, brothers and sisters who have encouraged, guide and inspired me throughout my journey in education
iv
ACKNOWLEDGEMENT
Praise be to Allah S.W.T the Most Gracious, the Most Merciful, whose blessing and guidance have helped me through my thesis smoothly. Peace and blessing of Allah be upon our Prophet Muhammad S.A.W who has given guidance to mankind.
I would like to take this opportunity to express my deepest gratitude to my beloved supervisor of this project, Mr. Camallil Bin Omar who has relentlessly and tirelessly assisted me in completing this project. He has given me support and insight in doing this project and has patiently listened and guided. My thanks also go to my family who has given me support throughout my academic years.
I also would like to express my gratitude to my friends for their co-operation during doing this project. I also wish acknowledgement to the people who give support directly or indirectly to the project. Once again, thank you very much.
v
ABSTRACT
The aim of the project is to develop a miniaturized low power FM transmitter and FM receiver that can be used as equipment for helping in the communication system such as room monitoring. The overall module should be miniature to enable portability. By using the wireless microphone people can speak anywhere instead of speaking in one place. Frequency modulation (FM) has several advantages over the system of amplitude modulation (AM) used in the alternate form of radio broadcasting. The most important of these advantages is that FM system has a greater freedom from interference and static. A well-design FM receiver is not sensitive to such disturbances when it is tuned to an FM signal of sufficient strength. Also, the signal-to-noise ratio in an FM system is much higher than that of an AM system. FM broadcasting stations can be operated in the very high frequency bands at which AM interference is frequently severe; commercial FM radio stations are assigned frequencies between 88 MHz to 108 MHz and will be the intended frequency range of transmission. The objectives of this project is to use as a communication equipment where when the signal (voice) captures by the FM transmitter and transmit through the receiver by tuning the frequency in the range of FM frequency which not being used by other radio station.
vi
ABSTRAK
Matlamat projek ini adalah bertujuan untuk membina alat pemancar FM berkuasa rendah dan penerima FM(radio) yang boleh digunakan sebagai alat yang boleh membantu di dalam sistem komunikasi. Secara keseluruhan, modul ini akan dibina sebagai alat yang mudahalih iaitu mudah diubah kedudukannya. Dengan menggunakan mikrofon tanpa wayar, pengguna boleh bercakap di mana-mana sahaja di dalam satu tempat. Terdapat beberapa kelebihan dalam sistem FM berbanding AM iaitu FM banyak digunakan di dalam penyiaran radio. FM juga mempunyai kebebasan dalam gangguan hingar serta statik. Nisbah hingar FM juga lebih tinggi berbanding AM di mana gangguan hingar AM lebih tinggi. Siaran stesen radio FM adalah dari 88Mhz sehingga 108Mhz dan ini akan dijadikan sebagai frekuensi pancaran. Objektif projek ini adalah sebagai alat komunikasi dimana apabila isyarat suara berjaya diterima oleh alat pemancar FM dan dipancar kepada penerima tersebut ditala frekuensinya dalam lingkungan frekuensi FM iaitu 88Mhz sehingga 108Mhz dan boleh digunakan oleh mana-mana stesen radio.
vii
TABLE OF CONTENT
CHAPTER
1
2
TITLE
PAGE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENT
vii
LIST OF FIGURES
xi
LIST OF TABLES
xii
LIST OF ABBREVIATION
xiii
LIST OF APENDICES
xv
INTRODUCTION 1.1
Review
1
1.2
Objectives
2
1.3
Scope of project
2
1.4
Outline of the thesis
3
LITERATURE REVIEW 2.1
Background
4
2.2
Communications theory
5
2.2.1
6
Transmitter
2.2.2 Receiver
6
2.2.3
7
Noise
viii 2.3
2.4
3
Modulation
7
2.3.1
7
Description of modulation
2.3.2 Need for modulation
8
2.3.3
9
Frequency modulation
2.3.4 Derivation of FM equation
13
Demodulation
14
2.4.1
14
Phase Lock Loop (PLL)
2.5
Power amplifier
16
2.6
The resonant circuit
18
2.6.1 Parallel resonant circuit
18
METHODOLOGY 3.1
Low Power FM Transmitter
19
3.2
Discrete components
20
3.2.1
20
3.3
3.4
Electret microphone
3.2.2 Capacitor
21
3.2.3
Inductor
22
3.2.4
Resistor
24
Amplifier
25
3.3.1
Class A
26
3.3.2
Class AB
27
3.3.3
Class B
28
3.3.4
Class C
29
Design under consideration
30
3.4.1
One transistor design
30
3.4.2
Two transistor design
31
3.5
Final layout design
32
3.6
FM Receiver
33
3.6.1 Introduction
33
3.6.2
Theory
34
3.6.3
Noise in FM receiver
35
3.6.4 Design FM receiver
37
3.6.5
38
FM receiver circuit
ix
3.7
3.6.6
Description of FM receiver circuit
39
3.6.7
Active IF filter
41
3.6.8
Final layout design
42
Audio Amplifier
42
3.7.1 Introduction
43
3.7.2
Analysis of LM386 chip
44
3.7.3
Additional gain
45
3.7.4
High gain and filtering
45
3.7.5 Discussion
4
5
47
RESULTS AND ANALYSIS 4.1
Analysis results
48
4.2
Final FM transmitter circuit
50
4.3
Final FM receiver circuit
51
4.4
Final audio amplifier circuit
52
4.5
Final hardware design
53
4.6
Discussion
54
CONCLUSION AND RECOMMENDATION 5.1
Chapter overview
55
5.2
Conclusion
55
5.3
Recommendation for the future work
56
REFERENCES
57
APPENDICES A
58
APPENDICES B
59
x
LIST OF FIGURE
FIGURE NO.
TITLE
2.1
Block diagram of communication system
2.2
Block diagram for voice communication
PAGE 5
using RF
6
2.3
Antenna calculation
10
2.4
Frequency modulation spectrum
11
2.5
Example waveform frequency modulation
13
2.6
Block diagram of PLL
15
3.1
Electret microphone
20
3.2
Self-made equation
23
3.3
Frequency calculation
23
3.4
Class of power amplifier
25
3.5
Class A voltage and current waveform
26
3.6
Class A circuit diagram
26
3.7
Load line of class A amplifier
27
3.8
Class AB voltage and current waveform
28
3.9
Class B voltage and current waveform
28
3.10
Class C voltage and current waveform
29
3.11
Class C circuit diagram
29
3.12
Load line of class C amplifier
29
3.13
One transistor design
30
3.14
Two transistor design
31
3.15
Final layout design
32
3.16
he slot noise generator frequency plan
36
3.17
The TDA7000 as a Variable Capacitor Tuned FM Broadcast Receiver
38
xi 3.18
IF filter of the TDA7000
41
3.19
Measured response of the IF filter
42
3.20
FM receiver circuit
42
3.21
LM386 schematic
44
3.22
Audio amplifier circuit
46
3.23
Voltage gain
46
4.1
Graph supply current vs voltage
49
4.2
Power output vs supply voltage
49
4.3
Final FM transmitter circuit
50
4.4
Waveform from transmitter when no speaking
50
4.5
Final FM receiver circuit
51
4.6
PCB layout for FM receiver
51
4.7
Audio amplifier circuit
52
4.8
PCB layout for audio amplifier
52
4.9
Final hardware design for voice Communication using RF
53
4.10
FM receiver hardware
53
4.11
FM Transmitter hardware
53
xii
LIST OF TABLES
TABLE NO. 3.1
TITLE Gives a standard overview of the types of resistors used and their specification
3.2
PAGE
24
Comparison of peak possible efficiency for different operation classes of power amplifiers.
26
3.3
Mixer slot noise level
34
4.1
Supply current and output current
48
xiii
LIST OF ABBREVIATIONS
RF
-
Radio Frequency
MHz
-
Megahertz
PA
-
Power Amplifier
Fc
-
Frequency Carrier
I
-
Current
R
-
Resistance
Z
-
Impedance
C
-
Capacitor
L
-
Inductor
Fo
-
Resonant frequency
Q
-
Quality factor
FM
-
Frequency modulation
AM
-
Amplitude modulation
PM
-
Phase modulation
N
-
Number of turns in coil
L
-
Length of coil
A
-
Cross sectional area of coil
β
-
Current gain
xiv
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Datasheet TDA7000
58
B
Datasheet LM386
59
CHAPTER 1
INTRODUCTION
1.1
Review
Frequency modulation (FM) is the method of varying a carry wave’s frequency proportionally to the frequency of the other signal especially in the case of the human voice. If we compared to the other transmission method like amplitude modulation (AM) vary the amplitude of the carrier wave according to an input signal. Frequency modulation (FM) has several advantages over the system of amplitude modulation (AM) used in the alternate form of radio broadcasting. The most important of these advantages is that an FM system has greater freedom from interference and static. FM broadcasting stations can be operated in the very high frequency bands at which AM interference is frequently severe; commercial FM radio stations are assigned frequencies between 88Mhz to 108Mhz and will be the intended frequency range of transmission. In this project we will discuss upon the usage of frequency modulation (FM) where this method brings many advantages compared to other method. In this project also, we will discuss how FM receiver can be build from one chip and can hear the radio from other frequency using this method.
2 1.2
Objectives
This project has a number of main objectives. They are: •
To design and build low power transmitter over the FM frequency and allows the transfer of the voice over the certain distance to a FM tuner
•
To design and build FM receiver so that voice from transmitter can be heard when we tuned the frequency.
•
To facilitate the user that they can speak without any wiring interference in the certain distance.
•
To learn, understand and gain new knowledge about FM transmitter and FM receiver.
1.3
Scope of project
The scopes of this project are listed below: 1) Study about the theory to develop this system: •
Principle communication
•
Frequency modulation (FM)
•
Radio frequency
•
Wireless communication
•
The components that being used for this project
2) Design the suitable circuit that can apply to achieve the objective. •
Electrets microphone
•
Small signal amplifier
•
Power amplifier
•
FM receiver
•
Audio amplifier
3 1.4
Outline of the thesis
This thesis is organized into 7 chapters, leading through fundamental of FM transmitter. This thesis will also concentrate on the theory and procedure in designing FM transmitter, receiver and audio amplifier. Chapter 1 gives the brief introduction on frequency modulation as well as the application of the FM transmitter.
In chapter 2, the introduction briefly describes the frequency modulation theory, the advantages of the FM and the derivation of the FM voltage equation. It also explain on the technical terms that associated in the FM and also explaining briefly on the capture effect and the modulation effect or the modulation factor of FM and also the FM demodulation.
In chapter 3, we discuss more about the low power FM transmitter, FM receiver and audio amplifier. In this chapter also, the theory that briefly described of this three part included. The design procedure and design specification are presented in this chapter. The final layout for transmitter, receiver and audio amplifier will also present in this chapter.
Chapter 4 deals with the results and analysis obtained from the experiments. In chapter 5 devoted to a conclusion of the project. Recommendation for future implementation also presented.
CHAPTER 2
LITERATURE REVIEW
2.1
Background The comparatively low cost of equipment for a frequency modulation (FM)
broadcasting station, resulted in rapid growth in the years following World War II. Within three years after the close of the war, 600 licensed FM stations were broadcasting in the United States and by the end of the 1980s there were over 4000. Similar trends have occurred in Britain and other countries. This is because of crowding in the amplitude modulation (AM) broadcast band and the inability of standard AM receivers to eliminate noise, the tonal fidelity of standards stations is purposely limited.
FM does not have these drawbacks and therefore can be used to transmit music reproducing the original performance with a degree of fidelity that cannot be reached on AM bands. FM stereophonic broadcasting has drawn increasing numbers of listeners to popular as well as classical music, so that commercial FM stations draw higher audience ratings than AM stations. FM is the method of varying a carrier wave’s frequency proportionally to the frequency of another signal, in our case the human voice. This compares to the other most common transmission method, AM. AM broadcasts vary the amplitude of the carrier wave according to an input signal. Standard FM broadcasts are based in the 88 – 108 MHz range; otherwise known as the RF or Radio Frequency range. However, they can be in any range, as long as a receiver has been tuned to demodulate them.
5 2.2
Communications theory
In a broad sense, the term communication refers to sending, receiving and processing of information by electronic means. Communications started with wire telegraphy in the eighteen forties, developing with telephony some decades later and radio at the beginning of last century. A modern communications system in first concerned with the sorting, processing and sometimes storing of information before its transmission. The actual transmission then follows, with further processing and the filtering of noise. Finally for the reception, this may include processing steps such as decoding, storage and interpretation.
In order to become familiar with this system, it is necessary first to know about amplifier and oscillators, the building blocks of all electronic processes and equipment. With these as a background, the everyday communications concepts of noise, modulation and information theory, as well as the various systems themselves, may be approached. The communications system exists to convey a message. This message comes from the information source.
Figure 2.1 : Block diagram of communication system
6 .2.2.1 Transmitter Transmitter is required to process and possible encode the incoming information so as to make it suitable for transmission and subsequent reception. Eventually, in a transmitter, the information modulates the carrier; i.e. is superimposed on a high-frequency wave. The actual method of modulation varies from one system to another. Modulation may be high level, and the system itself may be amplitude modulation, frequency modulation, pulse modulation or any variation or combination of these, depending on the requirements.
2.2.2
Receiver There are great varieties of receivers in communication system, since the
exact form of a particular receiver is influenced by a great many requirements. Among the more important requirements are the modulation system used. As stated initially, the purpose of a receiver and the form of its output influence its construction as much as the type of modulation system used. The output of a receiver may be fed to a loudspeaker, video display unit, various radar displays, television or computer. In each instance different arrangements must be made, each affecting the receiver design. Note that the transmitter and receiver must be in agreement with the modulation and coding methods used and also timing or synchronization in some system.
Transmitter
Receiver
Figure 2.2: Block diagram for voice communication using RF
7 2.2.3 Noise
Noise may be defined in electrical terms as any unwanted introduction of energy tending to interfere with the proper reception and reproduction of transmitted signals. Many disturbances of and electrical nature produce noise in receivers, modifying the signal in an unwanted manner. In radio receivers, noise may produce unwanted pulse or perhaps cancel out the wanted ones. Noise can limit the range of systems, for a given transmitted power. It affects the sensitivity of receivers by placing a limit in the weakest signals that can be amplified. It may sometimes even force a reduction in the bandwidth of a system.
There are numerous ways of classifying noise. It may be subdivided according to type, source, effect, or relation to the receiver, depending on circumstances. It is most convenient here to divide noise into two broad groups; noise whose sources are external to the receiver and noise created within the receiver itself. External noise is difficult to treat quantitatively and there is often little that can be done about it, short of moving the system to another location. Internal noise is both more quantifiable and capable of being reduced by appropriate receiver design. Because noise has such a limiting effect and also because it is often possible to reduce its effects through intelligent circuit use and design, it is more important for all those connected with communications to be well informed about noise and its effects.
2.3
Modulation
2.3.1
Description of Modulation The point to modulation is to take a message-bearing signal and superimpose
it upon a carrier signal for transmission. Modulation is the process of shifting the frequency of a signal so that the resulting signal is in a desired frequency band. This is done by using a high frequency carrier signal to transmit a lower frequency information signal. In other words, the information signal modulates the carrier signal to the desired frequency. Two common types of modulation are Amplitude
8 Modulation (AM) and Frequency Modulation (FM). A third type, Phase Modulation (F M or PM) is very similar to FM and is often used to mean the same as FM. For case of transmission carrier signal are generally high frequency for severable reasons: •
For easy (low loss, low dispersion) propagation as electromagnetic waves
•
So that they may be simultaneously transmitted without interference from other signals
•
So as to enable the construction of small antennas ( a fraction, usually a quarter of the wavelength)
•
So as to be able to multiplex that is to combine multiple signals for transmission at the same time.
2.3.2
Need for Modulation
There is an even more important argument against transmitting signal frequencies directly; all sound is concentrated within the range from 20Hz to 20 kHz, so that all signals from different sources would be hopelessly and inseparably mixed up.
In order to separate the various signals, it is necessary to convert them all to different portions of the electromagnetic spectrum. Each must be given its own frequency location. This also overcomes the difficulties of poor radiation at low frequencies and reduces interference. Once signals have been translated, a tuned circuit is employed in the front end of the receiver to make sure that desired section of the spectrum is admitted and all unwanted signals are rejected. The tuning of such a circuit is normally made variable and connect to the tuning control, so that the receiver can select any desired transmission within predetermined range such as the very high frequency (VHF) broadcast band used for frequency modulation.
Although this separation of signals has removed a number of difficulties encountered in the absence of modulation, the fact still remain that unmodulated carriers of various frequencies cannot by themselves be used to transmit intelligence.
9 An unmodulated carrier has constant amplitude, a constant frequency and a constant phase relationship with respect to some reference. A message consists of ever varying quantities. Speech, for instance, is made up of rapid and predictable variations in amplitude (volume) and frequency (pitch). Since it is impossible to represent these two variables by a set of three constant parameters, an unmodulated carrier cannot be used to convey information. In a continuous-wave modulation system (amplitude or frequency modulation) one of the parameters of the carrier is varied by the message. Therefore at any instant its deviation from the unmodulated value (resting frequency) is proportional to the instantaneous amplitude of the modulating voltage and the rate at which this deviation takes place is equal to the frequency of this signal. In this fashion, enough information about the instantaneous amplitude and frequency is transmitted to enable the receiver to recreate the original message.
2.3.3
Frequency Modulation There are two fundamental types of communication systems: baseband
systems and passband systems. In baseband systems, signals are transmitted without any changes to their frequencies. Passband communication systems, on the other hand shift the frequency spectrum of signal to a new frequency location, the carrier frequency. The human voice has strong components with frequencies of the order of 1 kHz and less. Transmitting such a signal using electromagnetic waves with a baseband system would lead to a number of problems. These problems include: 1)
Antenna length.
In order for an antenna to efficiently radiate energy, it must be longer than ?/10, where ? is the wavelength of the radio waves. From the relation between frequency and wavelength, it can be seen that λ=c/f Where f is the frequency of the signal and c is the speed of light. For a 1 kHz signal,
10
Thus, for efficient radiation of energy, and antenna for this system must be 30 km in length. Such an antenna would be very difficult and expensive to implement.
Figure 2.3: Antenna calculation The design and positioning of the antenna is as crucial as the module performance itself in achieving a good wireless system range. The following will assist the designer in maximizing system performance. The antenna should be kept as far away from sources of electrical interference as physically possible. If necessary, additional power line decoupling capacitors should be placed close to the module. The antenna ‘hot end’ should be kept clear of any objects, especially any metal as this can severely restrict the efficiency of the antenna to receive power. Any earth planes restricting the radiation path to the antenna will also have the same effect. Best range is achieved with either a straight piece of wire, rod or PCB track @ _ wavelength (7cm @ 868MHz). Further range may be achieved if the _ wave antenna is placed perpendicular in the middle of a solid earth plane measuring at least 10cm radius. In this case, the antenna should be connected to the module via some 50 ohm characteristic impedance coax.
11 2. Interference.
If two signals were to be transmitted over baseband in the same geographic region, they would interfere with each other, and both signals would be distorted.
3. Signal Efficiency.
Signals transmitted in baseband have a lot of noise and interference associated with them, which results in lower signal efficiency and poor signal propagation. In order for radio communication to be feasible these problems need to be dealt with, and the solution is to shift the frequency of the transmitted signals to a higher frequency.
Figure 2.4: Frequency Modulation (FM) Spectrum
12 An important component in modulation and radio frequency devices is the mixer or multiplier. In most circuits designers strive for linearity, but mixers and multipliers work on non-linearity. As the name implies, a multiplier uses non-linear circuit components, usually diodes, to multiply two signals together. The result is a slew of harmonics and other frequencies arithmetically related to the frequencies of the original waveforms. A more specific type of multiplier is called a mixer. A mixer is made especially to produce only the sum and difference of the root frequencies. Mixers are most usually though of as operating on sinusoidal signals so an example of the output of a mixer fed with two frequencies, fc & fo, would look like: cos ( 2πƒct ) x cos ( 2πƒot ) = cos ( 2π [ƒc + ƒo ] t ) + cos ( 2π [ƒc – ƒo ] t ) Example frequency wave:
13
Figure 2.5: Example waveform of frequency modulation
2.3.4
Derivation of FM Equation
As was done with AM, a mathematical analysis of a high-frequency sine wave, modulated by a single tone or frequency, will be used to yield information about the frequency components in an FM wave, FM power relations, and the bandwidth of an FM signal. From the definition of frequency deviation, an equation can be written for the signal frequency of an FM wave as a function of time ƒsignal = ƒc + kƒeM (t) = ƒc + kƒEM sinωM t And substitution of δ = kƒ × EM ƒsignal = ƒc + δ sinωM t
But what does this equation indicate? It seems to be saying that the frequency of the transmitter is varying with time. This brings up the same type of problem that was observed when we looked at a time display of AM and then performed a mathematical analysis in an attempt to determine its frequency content. With AM, the signal appeared to be a sine wave that’s amplitude was changing with time. At the time, it was pointed out that a sine wave, by definition, has constant peak amplitude, and thus cannot have peak amplitude that varies with time. What about the sine wave’s frequency? It also must be a constant and cannot be varying with time. As was the case with AM, where it turned out that our modulated wave was
14 actually the vector sum of three sine waves, a similar situation is true for FM. An FM wave will consist of three or more frequency components vector ally added together to give the appearance of a sine wave that’s frequency is varying with time when displayed in the time domain. A somewhat complex mathematical analysis will yield an equation for the instantaneous voltage of an FM wave of the form shown here:
eFM (t) = Ec sin (ωct + mƒsinωMt) 2.4
Demodulation
2.4.1
Phase-Locked Loop (PLL)
A phase-locked loop (PLL) is a closed loop frequency control system based on the detection of phase difference between the input and the output signals of the controlled oscillator. The oscillator is constantly adjusted to match phase and thus lock on the frequency of an input signal. In addition to locking a particular frequency, a PLL can be used to generate a signal, modulate or demodulate a signal, reconstruct a signal with less noise, or multiply and divide a frequency. PLLs are used in wireless communication very often, especially where the signals are transferred by frequency modulation or phase modulation. They can also be used on amplitude modulation. The PLL is the best frequency demodulator because it can remove noise and interference with its low-pass filter and its highly linear output can faithfully reproduces the original modulating signal.
A PLL is made up of three parts: phase comparator, a voltage-controlled oscillator (VCO), and a low-pass filter. These three parts are connected to form a close loop negative frequency feedback system. The phase comparator, in the simplest sense, is a mixer. A block diagram of a PLL is shown figure 2.6
15
Figure 2.6 : Block diagram of PLL With no frequency applied to the PLL system, the error voltage (Ve(t)) at the output of phase comparator is zero. The output voltage of low-pass filter (Vd(t)) is also zero, which makes the VCO to operate at a set frequency f0 called center frequency. When an input signal is applied to the PLL system, the phase comparator compares the frequency and the phase with the frequency and phase of VCO, and generates the error voltage with the frequency and phase difference between the input signal and the VCO. The error voltage is then filtered by the low-pass filter and applied to the control input of the VCO. Vd(t) varies in order to reduce the difference of the frequency between the signal input and VCO. When the frequency of VCO is quite close to that of the input signal, the closed-loop nature of PLL immediately forces VCO to lock the frequency with the signal input.
So when the PLL is locked, the VCO frequency is almost exactly same as signal input except for a finite phase difference. The change of input frequency causes a phase or frequency shift and produces an error voltage which forces the VCO to track the input and reduce the difference between the input and the output to be zero. If there is no input, the output is the free-running frequency of the VCO.
The lock range of a PLL is the range of frequencies over which a PLL is able to track an initially locked input frequency. If the input signal leaves the lock range, the PLL will be unable to follow it frequency and returns to run at its free-running frequency. This is known as becoming unlocked.
16 The capture range of a PLL is the limit of frequencies over which a PLL will accept and lock onto an input signal starting from the unlocked or free-running condition. Generally the capture range is narrower than the lock range and it makes the PLL look like a bandpass filter. The loop filter also determines how fast the input signal can change and still keep lock. The narrower the loop filters bandwidth, the smaller the allowable phase error. This makes the response slower and the capture range narrower.
2.5
Power Amplifier
The circuit is classic push-pull. The input transformer provides balanced drive to the gates through a balanced matching network. The gates are kept at ground potential by resistors on each side of the transformer secondary, although a single resistor at the secondary center tap would work as well. The output signals from each drain go through identical matching networks to a simple coax balun. The powdered iron coil form on the output balun lowers the loss which would otherwise be inherent in the longer piece of coax required to obtain the minimum necessary common mode impendence.
The power amplifier takes the energy drawn from the DC power supply and converts it to the AC signal power that is to be radiated. The efficiency or lack of it in most amplifiers is affected by heat being dissipated in the transistor and surrounding circuitry. For this reason, the final power amplifier is usually a Class-C amplifier for high power modulation systems or just a Class-B push-pull amplifier for use in a low-level power modulated transmitter. Therefore the choice of amplifier types depends greatly on the output power and intended range of the transmitter.
The main characteristics of an amplifier are linearity, efficiency, output power, and signal gain. In general, there is a trade off between these characteristics. For example, improving amplifier’s linearity will degrade its efficiency. Therefore knowing the importance degree of each one of these characteristics is an essential step in designing an Amplifier. This can be jugged based on the application. As an
17 example high output power Amplifier is used in the transmitter side of a transceiver, whereas high linear amplifier used in the receiver side. An amplifier is said to be linear if it preserves the details of the signal waveform, that is to say, V0(t) = A .Vi(t) where, Vi and Vo are the input and output signals respectively, and A is a constant gain representing the amplifier gain. But if the relationship between Vi and Vo contains the higher power of Vi, then the amplifier produces nonlinear distortion. The amplifier’s efficiency is a measure of its ability to convert the dc power of the supply into the signal power delivered to the load. The definition of the efficiency can be represented in an equation form as
η
=
Signal power delivered to load DC power supplied to output circuit
For an ideal amplifier, the efficiency is one. Thus, the power delivered to the load is equal to the power taken from the DC supply. In this case, no power would be consumed in the amplifier. In reality, this is not possible, especially in high frequency realm of RF circuits. In many high frequency systems, the output stage and driver stage of an amplifier consumed power in the amplification process. The gain of the amplifier (G) is equal to the magnitude of the output signal (Xo) over the magnitude of the input signal (Xi) as shown in the equation.
G can be voltage, current, or power gain depending on the application.
To describe the theory behind power amplifier designs in depth. First we will investigate the operation classes of amplifiers, certainly class A, AB, B and C, D, E and F. Then the properties of power amplifiers are discussed, certainly the output power, efficiency, gain, linearity and stability.
18 2.6
The resonant circuit At the previous section, we looked briefly about the frequency modulation.
All these components will be the basic building blocks used in any radio frequency section of any transmitter and receiver. What makes them very important is there response at certain frequency. At high frequency the inductors impedance becomes quite high and the capacitor’s impedance drops. At high low frequency the impedance of an inductor is small and the impedance of a capacitor is quite high. The resistor in theory maintains its resistive impedance at low and high impedance. ωc = 1/ (√ LC) At a certain frequency the capacitor’s impedance will equal that of an inductor. This is called the resonant frequency and can be calculated by letting the impedance of a capacitor to that of the inductor’s and then solving for ω (angular velocity in radians per seconds) and then finding the resonant frequency Fc (it is normally represented Fo), but in relation to FM it essentially represents the oscillator carrier frequency in Hertz.
2.6.1
Parallel resonant circuit FM radio stations operate on frequencies between 88 and 108 MHz. The
variable capacitor and your self-made inductor constitute a parallel LC circuit. It is also called a tank circuit and will vibrate at a resonant frequency which will be picked up your pocket FM radio. In tank circuits, the underlying physics is that a capacitor stores electrical energy in the electric field between its plates and an inductor stores energy in the magnetic field induced by the coil winding. The mechanical equivalent is the energy balance in a flywheel; angular momentum (kinetic energy) is balanced by the spring (potential energy). Another example is a pendulum where there's a kinetic versus potential energy balance that dictates the period (or frequency) of oscillations. Given your variable capacitor ranges from 4 to 34 pF, your tank circuit will resonant between 66 and 192 MHz, well within the FM radio range.
CHAPTER 3
METHODOLOGY
3.1
Low Power FM Transmitter
Frequency Modulation (FM) is the method of varying a carrier wave's frequency proportionally to the frequency of another signal, in our case the human voice. This compares to the other most common transmission method, Amplitude Modulation (AM). AM broadcasts vary the amplitude of the carrier wave according to an input signal. Standard FM broadcasts are based in the 88 - 108 MHz range; otherwise known as the RF or Radio Frequency range. However, they can be in any range, as long as a receiver has been tuned to demodulate them.
Thus the RF carrier wave and the input signal can't do much by themselves, they must be modulated. That is the basis of our transmitter. An example is useful to illustrate what is actually going on. If we were to broadcast a 100MHz signal and tune a radio into that frequency, we would hear nothing. That 100MHz signal has locked or captured that spot and simply produces a DC value. Now if we were to move the incoming signal +/-100KHz in either direction at a frequency of 1000Hz, then we would hear a 1000Hz signal on the radio. If we only moved +/-10Khz then the sound from the radio would be 1/10th the original in loudness. Thus the rate or frequency at which we change the RF carrier produces the audible frequency that we hear, and the further from the main RF carrier we move, the louder the output will be. This is the basis of all FM transmitters. We will now look at how this is achieved by examining the basic circuit.
20 3.2
Discrete Components
3.2.1
Electret microphone
A microphone is an example of a transducer a device that changes information from one to another. Sound information exists as patterns of air pressure; the microphone changes this information into patterns of electric current. The two most commonly used are the magneto-dynamic and the variable condenser microphone. The electret microphone belongs to the condenser microphone family. The powering requirements of the electret microphone are handled by incorporating a self-polarised or electrer capacitor element within the microphone. If and ordinary capacitor of good quality is taken and induce a voltage across it, the capacitor will become charged. Then remove the voltage the capacitor will retain its charges, quite often for a long time. The electret is specially designed capacitor that will hold charged definitely. This means that the manufacturer can charge the electret during the process of constructing the microphone, a step that eliminates the polarizing voltage requirement of the condenser mike. The major disadvantage of electrets is that they lose their charge after a few years and cease to work.
An electret microphone has two pins which connect to the positive and negative leads of a battery. As shown in the drawing below, one looks at the bottom of the electret microphone. The pad that physically touches the microphone's casing connects to the battery's negative lead.
Figure 3.1 : Electret Microphone
21 3.2.2
Capacitor The voltage across capacitor lags the current through it by 90 degree,
applying the same logic to the capacitor as was used for the inductor, the reason for this lag in voltage is that the voltage is proportional to the integral of current entering the capacitor. Capacitors as mentioned before are made up of two conducting plates with dielectric in between. The most important factors when choosing a capacitor are: 1)
Leakage resistance
2)
Polarized
3)
Temperature Coefficient
There are six types in choosing capacitor: 1.
Silver Mica These capacitors have excellent stability and a low temperature coefficient,
and are widely used in precision RF tuning application
2.
Ceramic Types These low cost capacitors offer relatively large values of capacitance in a
small low-inductance package. They often have very large and non-linear temperature coefficients. They are best used in applications such as RF and HF coupling or decoupling or spike suppression in digital circuits, in which large variations of value are of little importance.
3.
Electrolytic Types These offer large values at high capacitance density; they are usually
polarized and must be installed the correct way round. Aluminum foils types have poor tolerances and stability and are best used in low precision applications such as smoothing filtering coupling and decoupling in audio circuits.
22 4.
Tantalum types Offer good tolerance, excellent stability, low leakage, low inductance and a
very small physical size, and should be used in applications where these feature are positive advantage.
5.
Poly types Of the four main poly types pf capacitors, polystyrene gives the best
performance in terms the overall precision and stability. Each of the others (polyester, polycarbonate and polypropylene) gives a roughly similar performance and is suitable for general-purpose use. ‘Poly’ capacitors usually use a layered ‘Swiss-roll’ form of construction. Metallised film types are more compact that layered film-foil types but have poorer tolerance and pulse ratings than film-foil types. Metallised polyester types are sometimes known as ‘green-caps’
6.
Trimmer capacitors Polypropylene capacitors are ideal variable capacitors, a fact due to the
polypropylene dielectric having a high insulation resistance with a low temperature coefficient. The polypropylene variable capacitor comes in a 5mm single turn package, which is suitable for mounting directly on to a PCB. The typical range of capacitance involved would be from 1.5pF to 50pF.
3.2.3
Inductor There are two types of inductors that can be discussed, and they are: 1.
Manufactured inductor When choosing an inductor from a manufacturer, the core in the coil and the over all Q factor will have to be taken into account. The core should preferably be made of soft ferrite, which will in turn minimize the energy losses of the inductor and therefore increase the Q factor. The ferrite core can be adjusted to gives a slight change in inductance
23 2.
Self made inductor Inductors can be easily wound around air-cored formers; there are a number a various manufactured air cored formers on the market. Self made inductors are very useful when a particular inductance is desired. The self made inductor can be calculating by the equation below:
Figure 3.2 : Self made equation
The specific frequency f generated is now determined by the capacitance C and inductance L measured in Farads and Henry respectively
Figure 3.3 : Frequency calculation
24 3.2.4 Resistor Fixed and variable resistors from the basic components in any electronic circuit; therefore they shall be the first component that will look at, followed by capacitors and lastly inductors. The three main factors when choosing a resistor for an intended application, which are;
1.
Tolerance
2.
Power rating
3.
Stability
Table 3.1 : Gives a standard overview of the types of resistors used and their specification
Max Value Tolerance
Thick Film 1 ±1% to ±5
Metal Film 10 ±1% to ±5
Carbon Film 10 ±1% to ±5
Wire wound 22 ±1% to ±5
Power rating
0.1 to 1 Watt
0.125 to 0.7W
0.125 to 2W
2.5W
Temperature
±100 to 200ppm/OC
±50 to 200ppm/OC
0 to 700ppm/OC
±30 to 500ppm/OC
Stability
Very Good
Very Good
Very Good
Very Good
Typical used
Accurate work
Accurate work
General
Low values
coefficient
purpose
25 3.3
Amplifier Amplifier is one of the most important factors to design the FM transmitter
circuit. This is because when the voice through out from electret microphone, the signal is very small. So, amplifier must include in the circuit to amplify the signal.
Amplifiers are classified according to their circuit configurations and methods of operation into different classes such as A, B, AB, C, D, E and F. These classes range from entirely linear with low efficiency to entirely non-linear with high efficiency. Choosing the bias point of an RF Power Amplifier can determine the level of performance ultimately possible with that PA. In certain applications, it may be desirable to have the transistor conducting for only a certain portion of the input signal.
The comparison of PA bias approaches evaluate the trade-offs for: Output Power, Efficiency, Linearity, or other parameters for different applications. The propose of a good dc bias design is to select the proper quiescent point or Q-point and hold the quiescent point constant over variations in transistor parameter and temperature. The reason is that the choice of q-point greatly influences the linearity, power handling and efficiency. In addition, as can be seen further, the choice of optimal q-point is limited by a safety region which prevent the transistor from being heated badly and damaged.
Figure 3.4 : Class of power amplifier
26 Table 3.2 : Comparison of peak possible efficiency for different operation classes of power amplifiers.
3.3.1 Class A The most simplistic way to distinguish the amplifiers classes is the conduction angle. Class-A amplifiers have a conduction angle of θC=2π; Class-AB amplifiers have a conduction angle of π< θC 60 dB down, and worst-case harmonics were >30 dB down. Since the front end provides reasonable selectivity, oscillator harmonics should not affect receiver performance.
3.6.3 Noise in FM Receiver
The purpose of the slot noise generator is to evaluate the front-end performance of an FM receiver that will be operating in a metropolitan area with strong signals. Because of front-end nonlinearities, the locally strong signals may add artifacts to a frequency occupied by a weak station. A repeatable figure of merit had to be found to measure the front-end nonlinearities. Two-tone inter modulation testing does not adequately measure high-order inter modulation distortion. One measurement method is the use of over-the-air stations. However, if the antenna is moved in any way, or if atmospheric conditions change, results are no longer valid. Also, it would be difficult to find an empty space in the FM band with sufficient bandwidth to add a test signal. A second method is the combination of the output of 50 small FM transmitters, all modulated with different program material. However, unless this is done with extreme care, the transmitters could intermodulate, filling the test slot with noise. In addition, this is a rather complex measurement method. A third approach is to generate noise over the entire FM band with a narrow deep slot placed in the noise at the center of the FM band. The ratio of noise in and out of the slot is defined as the noise power ratio. However, generating a slot in the noise with the required 1% bandwidth with steep skirts would be difficult. One approach might be to generate
36 the noise at baseband, bandpass it from 2 to 10 MHz, and mix it up to the frequency of interest. Mixing and amplifying must be linear so as not to add noise in the slot.
A noise power ratio of greater than 50 dB might be achievable. In fact, such a device was successfully constructed, with a measured slot noise depth of –30 to – 58 dB, depending on the spectrum analyzer used, and with a spectrum analyzer bandwidth of 300 kHz (random noise is generated from 0 to 15 MHz). A block diagram and a schematic of the slot noise generator are shown in Figure 3.16. Next, it is bandpassed from 2 to 10 MHz. The 2 MHz filter edge defines the width of the slot and the 10 MHz filter edge keeps noise out of the image frequency. Two filters were implemented to avoid slot noise depth problems. The signals were mixed up to 98 MHz using +17 dBm LO mixers. The two signals were then amplified and combined. A second combiner allows the addition of a test signal in the slot. In the frequency plan shown in Figure 3.16, the baseband noise is down 3 dB at 2 and 10 MHz and down 60 dB at 1.5 and 17 MHz. Noise is mixed up to 97.35 MHz and 98.85 MHz for a center frequency of 98.0 MHz. Figure 3.16 shows a slot noise width at about 2 MHz with a depth of about 56 dB using a Tektronix 7L14 or 2712. All slot noise testing was done with a spectrum analyzer bandwidth of 300 kHz.
Figure 3.16: The slot noise generator frequency plan
37 3.6.4
Design FM Receiver The almost total integration of an FM radio has been prevented by the need
for LC tuned circuits in the RF, IF, local oscillator and demodulator stages. An obvious way to eliminate the coils in the IF and demodulator stages is to reduce the normally used intermediate frequency of 10.7MHz to a frequency that can be tuned by active RC filters, the op amps and resistors of which can be integrated. An IF of zero deems to be ideal because it eliminates spurious signals such as repeat spots and image response, but it would not allow the IF signal to be limited prior to demodulation, resulting in poor signal-to-noise ratio and no AM suppression. With an IF of 70kHz, these problems are overcome and the image frequency occurs about halfway between the desired signal and the center of the adjacent channel. However, the IF image signal must be suppressed and, in common with conventional FM radios, there is also a need to suppress interstation noise and noise when tuned to a weak signal. Spurious responses above and below the center frequency of the desired station (side tunings), and harmonic distortion in the event of very inaccurate tuning must also be eliminated.
The new circuit is the TDA7000 which integrates a mono FM radio all the way from the aerial input to the audio output. External to the IC are only one tunable LC circuit for the local oscillator, a few inexpensive ceramic plate capacitors and one resistor. The TDA7000 dramatically reduces assembly and post-production alignment costs because only the oscillator circuit needs adjustment during manufacture to set the limits of the tuned frequency band. The complete FM radio can be made small enough to fit inside a calculator, cigarette lighter, key-ring fob or even a slim watch. The TDA7000 can also be used as receiver in equipment such as cordless telephones, CB radios, radio-controlled models, paging systems, the sound channel of a TV set or other FM demodulating systems.
38 3.6.5 FM receiver Circuit
Figure 3.17: The TDA7000 as a Variable Capacitor-Tuned FM Broadcast Receiver
39 3.6.6 Description of the FM receiver circuit
The circuit diagram of the complete mono FM radio. An experimental printed-wiring board layout is given in Figure. Special attention has been paid to supply lines and the positioning of large-signal decoupling capacitors. The functions of the peripheral components of Figure 3.17 not already described are as follows: C1 – Determines the time constant required to ensure muting of audio transients due to the operation of the FLL. C2 – Together with R2 determines the time constant for audio de-emphasis (e.g., R2C2 = 40ms. C3 – The output level from the noise generator during muting increases with increasing value of C3. If silent mute is required, C3 can be omitted. C4 – Capacitor for the FLL filter. It eliminates IF harmonics at the output of the FM demodulator. It also determines the time constant for locking the FLL and influences the frequency response. C5 – Supply decoupling capacitor which must be connected as close as possible to Pin 5 of the TDA7000. C7 to C12, C17 and C18 – Filter and demodulator capacitors. The values shown are for an IF of 70kHz. For other intermediate frequencies, the values of these capacitors must be changed in inverse proportion to the IF change. C14 – Decouples the reverse RF input. It must be connected to the common return via a good quality short connection to ensure a low-impedance path. Inductive or capacitive coupling between C14 and the local oscillator circuit or IF output components must be avoided.
40 C15 – Decouples the DC feedback for IF limiter/amplifier LA1. C19 and C21 – Local oscillator tuning capacitors. Their values depend on the required tuning range and on the value of tuning capacitor C20. C22, C23, L1, L2 – The values given are for an RF bandpass filter with Q = 4 for the European and USA domestic FM broadcast band (87.5MHz to 108MHz). For reception of the Japanese FM broadcast band (76MHz to 91MHz), L1 must be increased to 78nH and L2 must be increased to 150nH. If stopband attenuation for high level AM or TV signals is not required, L2 and C22 can be omitted and C23 changed to 220pF. R2 – The load for the audio output current source. It determines the audio output level, but its value must not exceed 22kW for VCC = 4.5V, or 47kW for VCC = 9V.
The figure 3.17 shown that the TDA7000 consists of a local oscillator and a mixer, a two-stage active IF filter followed by an IF limiter/amplifier, a quadrature FM demodulator, and an audio muting circuit controlled by an IF waveform correlation. The conversion gain of the mixer, together with the high gain of the IF limiter/amplifier, provides AVC action and effective suppression of AM signals. The RF input to the TDA7000 for –3dB limiting is 1.5mV. In a conventional portable radio, limiting at such a low RF input level would cause instability because higher harmonics of the clipped IF signal would be radiated to the aerial. With the low IF used with the TDA7000, the radiation is negligible. To prevent distortion with the low IF used with the TDA7000, it is necessary to restrict the IF deviation due to heavily modulated RF signals to ±15kHz. This is achieved with a frequency-locked loop (FLL) in which the output from the FM demodulator shifts the local oscillator frequency in inverse proportion to the IF deviation due to modulation.
41 3.6.7 Active IF filter
The first section of the IF filter (AF1A) is a second-order low-pass SallenKey circuit with its cut-off frequency determined by internal 2.2kW resistors and external capacitors C7 and C8. The second section (AF1B) consists of a first-order bandpass filter with the lower limit of the passband determined by an internal 4.7kW resistor and external capacitor C11. The upper limit of the passband is determined by an internal 4.7kW resistor and external capacitor C10. The final section of the IF filter consists of a first-order low-pass network comprising an internal 12kW resistor and external capacitor C12. The overall IF filter therefore consists of a fourth-order low-pass section and a first-order high-pass section. Design equations for the filter are given in Figure 3.18. Figure 3.19 shows the measured response for the filter.
Figure 3.18: IF filter of the TDA7000
42
Figure 3.19 : Measured response of the IF filter
3.6.8 Final layout design
Figure 3.20: FM receiver circuit Figure 3.20 shows the final design for receiving human speech from the transmitter circuit. This FM receiver circuit operated across the commercial bandwidth (88MHz to 108MHz). This design was conclude after considering all basic design. This circuit output must connect to audio amplifier circuit to hear at the speaker.
43 3.7
Audio Amplifier
3.7.1
Introduction The previous section, we have discussed the theory about amplifier. In this
chapter, we will described more about audio amplifier. This amplifier must insert in the output of FM receiver circuit to hear the human speech at the speaker. This audio amplifier circuit, we used the LM386 chip as the main of the circuit. The LM386 must be one of the most popular audio output amplifiers among radio amateurs, despite having been around for a long time. It can be obtained in both dual-in-line and surfaces mount packages and outputs 325 mW in the standard version that runs from 4-12 Volts supply voltage. Its voltage gain of 46 dB is in many cases too little, especially in direct conversion receivers. When I built the Pixie 2 with the LM386 audio stage, it struck me how the sensitivity of the receiver was limited by the audio gain. I asked myself if it would be possible to increase the gain and add some filtering without in a simple way, and the result is a gain of more than 70 dB and an audio bandwidth of a few hundred Hz by only adding 3 resistors, 1 capacitor and an inductor.
44 3.7.2
Analysis of the LM386 chip
Figure 3.21 : LM386 schematic The basic LM386 amplifier is used without any feedback between pins 1, 5, and 8. The standard way for getting a larger gain is to connect a large capacitor (say 10 µF) between pins 1 and 8. In either case, the voltage gain equation is:
Here Z1-5 and Z1-8 are the impedances between the respective pins. This equation describes the feedback path from the output to the emitter of the input stage, where the factor 2 is due to the differential input stage. Z1-5 must also include the built-in 15k resistor which is in parallel to external circuitry, and likewise Z1-8 should include the built-in 1.35k resistor. Thus, without external components, it has a gain of = + · =) 1350 150 / (15 2 k Av 20 or 26 dB and with a large capacitor between pins 1 and 8 it has a gain of 200 150 / 15 2 = · = k Av or 46 dB. The application note of the LM386 suggests a bass boost by connecting 10k in series with 33nF between pins 1 and 5 with pin 8 open, while a common set of values among radio amateurs is in the order of 2.2k and 4.7nF. The effect is a roll-off at frequencies above 1-2 kHz. The effect can be analyzed with the gain equation above by inserting 2.2e3 + 1/(j2πf4.7e-9) in parallel to the 15k internal feedback resistor. I use Matlab for this kind of analysis.
45 3.7.3
Additional gain The LM386 data sheet says “Gain control can also be achieved by
capacitively coupling a resistor from pin 1 to ground.” The effect of a low value resistor here is to decrease feedback and increase gain. JF1OZL has measured the gain with various resistors and by going as low as to a 3.3 ohms resistor, he got 74 dB. In this case, the feedback consists of a division between the Z1-5 and the Z1-gnd impedances, indicating that the gain is found from the equation of an inverting feedback amplifier:
The approximation is in the case that the open-loop gain, Ao, is much larger than the closed-loop gain, Av,2. This will give a gain of 15000/3.3 = 4546 = 73.2 dB which is close enough to JF1OZL’s measurement. Such a high gain requires careful circuit layout with attention to ground loops and proper decoupling, or the amplifier will oscillate. I have measured a gain of over 80 dB in a well decoupled circuit, but then the amplifier is at the verge of self-oscillation.
3.7.4
High Gain and Filtering The two ideas above can be combined in order to get both a high gain and
high frequency roll-off. Further, if the circuit between pin 1 and ground is a series resonance circuit, the bandpass characteristic can be made even sharper. An inductor of 1 mH will resonate with the 100 µF capacitor at about 500 Hz and is fine. The problem now is that the gain will drop so much at the higher frequencies that it gets below the value of 9 which is the stability limit for the LM386. To limit the attenuation at high frequencies, the inductor has to be paralleled with a resistor and a value of 220 ohms or less seems to be adequate. A potentiometer in series with the inductor makes the gain variable. The resulting schematic is shown in Figure 3.22
46
Figure 3.22: Audio amplifier circuit
Figure 3.23: Voltage gain
47 3.7.5 Discussion I tried different LM386-N1’s in this circuit and found that the peak gain of the highest curve would vary. Another chip with date code 99 gave 2 dB more gain, while a third one with date code 92 had 7 dB lower gain. I also tried a surface mount LM386-M1 dated 93 which had 5 dB less gain. In all cases, the gain at 1 kHz hardly changed at all. Also, the peak gain is sensitive to output load. The peak value of the highest curve would fall by 8 dB with a 32 ohm load, while hardly changing at all at 1 kHz. These results suggest that the gain, Av,2 depends on the open-loop gain, and that the open-loop gain varies from batch to batch.
The muting of the amplifier by means of pin 7, is still possible, but only if pin 7 is connected to Vcc. Grounding of pin 7 will only mute the amplifier in the basic 26 and 46 dB circuits, while the amplifier of Figure 3.22 will instead output a lowlevel low frequency noise. I also tried to find the gain equation for the circuit in Figure 3.22 and my guess was Av = Av,1 + Av,2. However, this equation overestimates gain by something like 8 dB except for the peak of the highest curve. Maybe some readers who are more into the inner workings of this amplifier can come up with a better equation.
In summary, addition of a few components to the basic LM386 amplifier results in a response which is fine for CW reception with a peak in the 500 Hz range. The amplifier also has enough gain for a direct conversion receiver with a passive mixer like the Pixie 2, that it in many cases it can drive a loudspeaker. Hopefully, the circuit can benefit other direct conversion receivers also.
CHAPTER 4
RESULT AND ANALYSIS
4.1
Analysis Results
The y-axis of the spectrum analyzer measures the power of the output wave mili-decibels; the formula for converting either way from mili-watts to mili-decibels are given below; PdBm = 10 log 10 ( PmW) All measures were taken with the 20Ω impedance onto the end of the probe to ensure the matching of the 50Ω transmission line to the output impedance of the oscillator. Table 4.1 Supply
voltage Supply current
Output Power
Output Power
(V)
(mA)
(dBm)
(mW)
9
8.37
8.1
6.457
8
7.31
7.1
5.129
7
6.24
6.0
3.982
6
5.23
3.5
2.239
5
4.27
1.88
1.542
4
3.33
-1.42
0.721
The table 4.1 shows the supply current and output power as a result of the dc supply of the battery decreased during continuous operation over 18 hours.
49
supply current(mA)
Supply Current vs Supply voltage 9 8 7 6 5 4 3 2 1 0
8.37 7.31 6.24 5.23 4.27 3.33
9
8
7
6
5
4
supply voltage(v)
Figure 4.1 Power output vs Supply voltage
Output power (mW)
7
6.457
6
5.129
5 4
3.982
3 2.239
2
1.542
1
0.721
0 9
8
7
6
5
4
Supply voltage (v)
Figure 4.2 From the two graphs above, it can be easily seen that hat the supply current decreases linearly as the supply voltage supplied by the battery decreases, also the output power is decreases as voltage supply to the transmitter decreases. The typical voltage input from the battery source will be 9.2V in the first 30 minutes of operation decreasing to the 8.8V to 7V band in the next 14 hours of continuous operation decreasing to the 7V to 4V band of operation in the following 6 hours. This last band of voltage operation produced fairly low levels of transmission. The middle band 7 to 8.8V emitted a very strong transmission indeed, which lasted for 14 hours, this is the main features that make the battery such a popular battery for intensive dc supply to radio receiver because of this stable transmission over a long period of time can be sustained.
50 4.2
Final FM transmitter circuit
Figure 4.3 Figure 4.3 shows the final layout design for FM transmitter. This circuit was created in the ISIS software. For the information, this circuit was operated in 88MHz. So, the receiver that we build must tuned to 88MHz for operating.
Figure 4.4 : Waveform from transmitter when no speech
51 4.3
Final FM receiver circuit
Figure 4.5 Figure 4.5 shows the final layout design for FM receiver. This circuit was created in the ISIS software. This circuit can operated in the range 88MHz to 108MHz. So either than hear the voice from transmitter, we can hear other radio station.
Figure 4.6: PCB layout for FM receiver
52 4.4
Final Audio amplifier circuit
Figure 4.7: Audio amplifier circuit
Figure 4.8: PCB layout for audio amplifier
53 4.5
Final hardware design
Figure 4.9: Final hardware design for voice communication using RF
Figure 4.11: FM Transmitter hardware Figure 4.10: FM receiver hardware
54 4.6
Discussion The design chosen was low powered and tunable to different frequency. The
parts used are very common and the circuit is very easily constructed. The circuit was firsts build on strip board and worked rather well without applying any real effective RF techniques, all which had to be adhered to was to keep the leads short and compact the circuitry as much as possible. The PCB as expected performed exceedingly well, but more of an better attempt had to be made in matching the antenna and shielding the RF section from the output as the PCB layout was a lot more efficient in radiating power out. Unwanted Electro-magnetic radiation had to be stopped from destructively interfering with the carrier modulation. To keep the design simple and easy to construct it was decided to just wrap household cling-film electrically protecting the circuitry from the aluminum foil that was used to electromagnetically shield the RF stage. In design this circuit, it’s very important to make sure that the coil must design so that the output frequency must in the range from 88MHz to 108MHZ. From that, calculation can be made from the equation: fc = 1 / 2π √ LC From this equation, frequency can be calculated when inductance (coil) and capacitance have been calculate from the circuit.
CHAPTER 5
CONCLUSION AND RECOMMENDATION
5.1
Chapter Overview
During the development of this project, several shortcomings of the project were noted. Hence, there are still rooms for improvement. This chapter highlights some of the flaws of this project and suggestions for future improvement.
5.2
Conclusion
This project involved the development of software and hardware design of low power of FM Transmitter and FM Receiver. This project can be considered succeed and meet the design specification requirement although their distance cannot achieve that we want.
To approach a project like this a parallel path has to be taken in regards to the theory and the practical circuitry, for a successful conclusion in any project the paths must meet, and this only happens when they are fully understood. This is why a good grounding in the basics of communication theory and analogue design must be achieved before ever approaching a project like this. To start off looking at block diagrams of basic transmitter was a must, even if it seemed abstract and obscure the underlying meaning of each block can be found out one by one. This is made the overall project challenging and rewarding.
56 5.3
Recommendation for the future work
Below are some recommendation and suggestion to any person intending to undertake a project of Voice Communication using RF for further improve on the performance of the developed device.
The main area of instability is in the oscillator part of the circuit. Shielding the oscillator helped in part to counteract this. After learning a lot from this project, there would have been a few things that could have been done to the final design to improve its performance.
1) Avoiding using too much solder lead. This will cause an increased on characteristics of impendence. 2) Follow the oscillator with the buffer amplifier to reduce the effects of loads changes. 3) Build FM receiver using digital switch. Not tuning the frequency. 4) Use negative temperature coefficients to compensate for typically positive-temperature-coefficient tuned circuit. 5) Build this project for long distance to communicate.
58
APPENDIX A Datasheet TDA7000
INTEGRATED CIRCUITS
DATA SHEET
TDA7000 FM radio circuit Product specification File under Integrated Circuits, IC01
May 1992
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
GENERAL DESCRIPTION The TDA7000 is a monolithic integrated circuit for mono FM portable radios, where a minimum on peripheral components is important (small dimensions and low costs). The IC has an FLL (Frequency-Locked-Loop) system with an intermediate frequency of 70 kHz. The i.f. selectivity is obtained by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency. Spurious reception is avoided by means of a mute circuit, which also eliminates too noisy input signals. Special precautions are taken to meet the radiation requirements. The TDA7000 includes the following functions: • R.F. input stage • Mixer • Local oscillator • I.F. amplifier/limiter • Phase demodulator • Mute detector • Mute switch QUICK REFERENCE DATA 2,7 to 10 V
Supply voltage range (pin 5)
VP
Supply current at VP = 4,5 V
IP
typ.
R.F. input frequency range
frf
1,5 to 110 MHz
8 mA
Sensitivity for -3 dB limiting (e.m.f. voltage) (source impedance: 75 Ω; mute disabled)
EMF typ.
1,5 µV
EMF typ.
200 mV
Signal handling (e.m.f. voltage) (source impedance: 75 Ω) A.F. output voltage at RL = 22 kΩ
Vo
PACKAGE OUTLINE 18-lead DIL; plastic (SOT102HE); SOT102-1; 1996 July 24.
May 1992
2
typ.
75 mV
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
Fig.1 Block diagram.
May 1992
3
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
RATINGS Limiting values in accordance with the Absolute Maximum System (IEC 134) Supply voltage (pin 5)
VP
max.
12 V
Oscillator voltage (pin 6)
V6-5
Total power dissipation
see derating curve Fig.2
Storage temperature range
Tstg
Operating ambient temperature range
Tamb
VP−0,5 to VP + 0,5 V −55 to +150 °C 0 to + 60 °C
Fig.2 Power derating curve.
D.C. CHARACTERISTICS VP = 4,5 V; Tamb = 25 °C; measured in Fig.4; unless otherwise specified PARAMETER
SYMBOL
Supply voltage (pin 5)
MIN.
TYP.
MAX.
UNIT
VP
2,7
4,5
10
V
IP
−
8
−
mA
Supply current at VP = 4,5 V Oscillator current (pin 6)
I6
−
280
−
µA
Voltage at pin 14
V14-16
−
1,35
−
V
Output current at pin 2
I2
−
60
−
µA
Voltage at pin 2; RL = 22 kΩ
V2-16
−
1,3
−
V
May 1992
4
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
A.C. CHARACTERISTICS VP = 4,5 V; Tamb = 25 °C; measured in Fig.4 (mute switch open, enabled); frf = 96 MHz (tuned to max. signal at 5 µV e.m.f.) modulated with ∆f = ± 22,5 kHz; fm = 1 kHz; EMF = 0,2 mV (e.m.f. voltage at a source impedance of 75 Ω); r.m.s. noise voltage measured unweighted (f = 300 Hz to 20 kHz); unless otherwise specified. PARAMETER
SYMBOL
MIN.
TYP.
MAX.
UNIT
Sensitivity (see Fig.3) (e.m.f. voltage) for −3 dB limiting; muting disabled
EMF
−
1,5
−
µV
for −3 dB muting
EMF
−
6
−
µV
for S/N = 26 dB
EMF
−
5,5
−
µV
EMF
−
200
−
mV
S/N
−
60
−
dB
at ∆f = ± 22,5 kHz
THD
−
0,7
−
%
at ∆f = ± 75 kHz
THD
−
2,3
−
%
AMS
−
50
−
dB
RR
−
10
−
dB
V6-5(rms)
−
250
−
mV
Signal handling (e.m.f. voltage) for THD < 10%; ∆f = ± 75 kHz Signal-to-noise ratio Total harmonic distortion
AM suppression of output voltage (ratio of the AM output signal referred to the FM output signal) FM signal: fm = 1 kHz; ∆f = ± 75 kHz AM signal: fm = 1 kHz; m = 80% Ripple rejection (∆VP = 100 mV; f = 1 kHz) Oscillator voltage (r.m.s. value) at pin 6 Variation of oscillator frequency ∆fosc
−
60
−
kHz/V
S+300
−
45
−
dB
S−300
−
35
−
dB
∆frf
−
± 300
−
kHz
B
−
10
−
kHz
Vo(rms)
−
75
−
mV
at VP = 4,5 V
RL
−
−
22
kΩ
at VP = 9,0 V
RL
−
−
47
kΩ
with supply voltage (∆VP = 1 V) Selectivity A.F.C. range Audio bandwidth at ∆Vo = 3 dB measured with pre-emphasis (t = 50 µs) A.F. output voltage (r.m.s. value) at RL = 22 kΩ Load resistance
May 1992
5
Philips Semiconductors
Product specification
FM radio circuit
Fig.3
TDA7000
A.F output voltage (Vo) and total harmonic distortion (THD) as a function of the e.m.f. input voltage (EMF) with a source impedance (RS) of 75 Ω: (1) muting system enabled; (2) muting system disabled.
Conditions:
0 dB = 75 mV; frf = 96 MHz. for S + N curve: ∆f = ± 22,5 kHz; fm = 1 kHz. for THD curve; ∆f = ± 75 kHz; fm = 1 kHz.
Notes 1. The muting system can be disabled by feeding a current of about 20 µA into pin 1. 2. The interstation noise level can be decreased by choosing a low-value capacitor at pin 3. Silent tuning can be achieved by omitting this capacitor.
May 1992
6
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
Fig.4 Test circuit; for printed-circuit boards see Figs 5 and 6.
May 1992
7
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
Fig.5 Track side of printed-circuit board used for the circuit of Fig.4.
Fig.6 Component side of printed-circuit board showing component layout used for the circuit of Fig.4.
May 1992
8
Philips Semiconductors
Product specification
FM radio circuit
TDA7000
PACKAGE OUTLINE DIP18: plastic dual in-line package; 18 leads (300 mil)
SOT102-1
ME
seating plane
D
A2
A
A1
L
c e
Z
w M
b1
(e 1) b
b2 MH
10
18
pin 1 index E
1
9
0
5
10 mm
scale DIMENSIONS (inch dimensions are derived from the original mm dimensions) UNIT
A max.
A1 min.
A2 max.
b
b1
b2
c
D (1)
E (1)
e
e1
L
ME
MH
w
Z (1) max.
mm
4.7
0.51
3.7
1.40 1.14
0.53 0.38
1.40 1.14
0.32 0.23
21.8 21.4
6.48 6.20
2.54
7.62
3.9 3.4
8.25 7.80
9.5 8.3
0.254
0.85
inches
0.19
0.020
0.15
0.055 0.044
0.021 0.015
0.055 0.044
0.013 0.009
0.86 0.84
0.26 0.24
0.10
0.30
0.15 0.13
0.32 0.31
0.37 0.33
0.01
0.033
Note 1. Plastic or metal protrusions of 0.25 mm maximum per side are not included. OUTLINE VERSION
REFERENCES IEC
JEDEC
EIAJ
ISSUE DATE 93-10-14 95-01-23
SOT102-1
May 1992
EUROPEAN PROJECTION
9
Philips Semiconductors
Product specification
FM radio circuit
TDA7000 The device may be mounted up to the seating plane, but the temperature of the plastic body must not exceed the specified maximum storage temperature (Tstg max). If the printed-circuit board has been pre-heated, forced cooling may be necessary immediately after soldering to keep the temperature within the permissible limit.
SOLDERING Introduction There is no soldering method that is ideal for all IC packages. Wave soldering is often preferred when through-hole and surface mounted components are mixed on one printed-circuit board. However, wave soldering is not always suitable for surface mounted ICs, or for printed-circuits with high population densities. In these situations reflow soldering is often used.
Repairing soldered joints Apply a low voltage soldering iron (less than 24 V) to the lead(s) of the package, below the seating plane or not more than 2 mm above it. If the temperature of the soldering iron bit is less than 300 °C it may remain in contact for up to 10 seconds. If the bit temperature is between 300 and 400 °C, contact may be up to 5 seconds.
This text gives a very brief insight to a complex technology. A more in-depth account of soldering ICs can be found in our “IC Package Databook” (order code 9398 652 90011). Soldering by dipping or by wave The maximum permissible temperature of the solder is 260 °C; solder at this temperature must not be in contact with the joint for more than 5 seconds. The total contact time of successive solder waves must not exceed 5 seconds. DEFINITIONS Data sheet status Objective specification
This data sheet contains target or goal specifications for product development.
Preliminary specification
This data sheet contains preliminary data; supplementary data may be published later.
Product specification
This data sheet contains final product specifications.
Limiting values Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or at any other conditions above those given in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended periods may affect device reliability. Application information Where application information is given, it is advisory and does not form part of the specification. LIFE SUPPORT APPLICATIONS These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Philips customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such improper use or sale.
May 1992
10
59
APPENDIX B Datasheet LM386
LM386 Low Voltage Audio Power Amplifier General Description
Features
The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value up to 200. The inputs are ground referenced while the output is automatically biased to one half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 volt supply, making the LM386 ideal for battery operation.
n n n n n n n n n
Battery operation Minimum external parts Wide supply voltage range: 4V–12V or 5V–18V Low quiescent current drain: 4 mA Voltage gains from 20 to 200 Ground referenced input Self-centering output quiescent voltage Low distortion Available in 8 pin MSOP package
Applications n n n n n n n n
AM-FM radio amplifiers Portable tape player amplifiers Intercoms TV sound systems Line drivers Ultrasonic drivers Small servo drivers Power converters
Equivalent Schematic and Connection Diagrams Small Outline, Molded Mini Small Outline, and Dual-In-Line Packages
DS006976-2
DS006976-1
© 1997 National Semiconductor Corporation
DS006976
Top View Order Number LM386M-1, LM386MM-1, LM386N-1, LM386N-3 or LM386N-4 See NS Package Number M08A, MUA08A or N08E
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LM386 Low Voltage Audio Power Amplifier
September 1997
Absolute Maximum Ratings
(Note 2)
Dual-In-Line Package Soldering (10 sec) +260˚C Small Outline Package (SOIC and MSOP) Vapor Phase (60 sec) +215˚C Infrared (15 sec) +220˚C See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of soldering surface mount devices. Thermal Resistance 37˚C/W θJC (DIP) 107˚C/W θJA (DIP) 35˚C/W θJC (SO Package) 172˚C/W θJA (SO Package) 210˚C/W θJA (MSOP) 56˚C/W θJC (MSOP)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (LM386N-1, -3, LM386M-1) Supply Voltage (LM386N-4) Package Dissipation (Note 3) (LM386N) (LM386M) (LM386MM-1) Input Voltage Storage Temperature Operating Temperature Junction Temperature Soldering Information
15V 22V 1.25W 0.73W 0.595W ± 0.4V −65˚C to +150˚C 0˚C to +70˚C +150˚C
Electrical Characteristics(Notes 1, 2) TA = 25˚C Parameter
Conditions
Min
Typ
Max
Units
Operating Supply Voltage (VS) LM386N-1, -3, LM386M-1, LM386MM-1
4
12
V
LM386N-4
5
18
V
8
mA
Quiescent Current (IQ)
VS = 6V, VIN = 0
4
Output Power (POUT)
LM386N-4
VS = 6V, RL = 8Ω, THD = 10% VS = 9V, RL = 8Ω, THD = 10% VS = 16V, RL = 32Ω, THD = 10%
Voltage Gain (AV)
VS = 6V, f = 1 kHz
26
10 µF from Pin 1 to 8 VS = 6V, Pins 1 and 8 Open VS = 6V, RL = 8Ω, POUT = 125 mW f = 1 kHz, Pins 1 and 8 Open
46
dB
300
kHz
0.2
%
50
dB
50
kΩ
250
nA
LM386N-1, LM386M-1, LM386MM-1 LM386N-3
Bandwidth (BW) Total Harmonic Distortion (THD) Power Supply Rejection Ratio (PSRR)
VS = 6V, f = 1 kHz, CBYPASS = 10 µF
250
325
mW
500
700
mW
700
1000
mW dB
Pins 1 and 8 Open, Referred to Output Input Resistance (RIN) Input Bias Current (IBIAS)
VS = 6V, Pins 2 and 3 Open
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: For operation in ambient temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and 1) a thermal resistance of 80˚C/W junction to ambient for the dual-in-line package and 2) a thermal resistance of 170˚C/W for the small outline package.
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2
Application Hints INPUT BIASING
GAIN CONTROL To make the LM386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open the 1.35 kΩ resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35 kΩ resistor, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitively coupling a resistor (or FET) from pin 1 to ground. Additional external components can be placed in parallel with the internal feedback resistors to tailor the gain and frequency response for individual applications. For example, we can compensate poor speaker bass response by frequency shaping the feedback path. This is done with a series RC from pin 1 to 5 (paralleling the internal 15 kΩ resistor). For 6 dB effective bass boost: R ≅ 15 kΩ, the lowest value for good stable operation is R = 10 kΩ if pin 8 is open. If pins 1 and 8 are bypassed then R as low as 2 kΩ can be used. This restriction is because the amplifier is only compensated for closed-loop gains greater than 9.
The schematic shows that both inputs are biased to ground with a 50 kΩ resistor. The base current of the input transistors is about 250 nA, so the inputs are at about 12.5 mV when left open. If the dc source resistance driving the LM386 is higher than 250 kΩ it will contribute very little additional offset (about 2.5 mV at the input, 50 mV at the output). If the dc source resistance is less than 10 kΩ, then shorting the unused input to ground will keep the offset low (about 2.5 mV at the input, 50 mV at the output). For dc source resistances between these values we can eliminate excess offset by putting a resistor from the unused input to ground, equal in value to the dc source resistance. Of course all offset problems are eliminated if the input is capacitively coupled. When using the LM386 with higher gains (bypassing the 1.35 kΩ resistor between pins 1 and 8) it is necessary to bypass the unused input, preventing degradation of gain and possible instabilities. This is done with a 0.1 µF capacitor or a short to ground depending on the dc source resistance on the driven input.
3
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Typical Performance Characteristics Quiescent Supply Current vs Supply Voltage
Power Supply Rejection Ratio (Referred to the Output) vs Frequency
DS006976-5
Peak-to-Peak Output Voltage Swing vs Supply Voltage
DS006976-13 DS006976-12
Voltage Gain vs Frequency
Distortion vs Frequency
DS006976-15
DS006976-14
Device Dissipation vs Output Power — 4Ω Load
Device Dissipation vs Output Power — 8Ω Load
DS006976-17
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Distortion vs Output Power
DS006976-18
4
DS006976-16
Device Dissipation vs Output Power — 16Ω Load
DS006976-19
Typical Applications Amplifier with Gain = 20 Minimum Parts
Amplifier with Gain = 200
DS006976-4 DS006976-3
Amplifier with Gain = 50
Low Distortion Power Wienbridge Oscillator
DS006976-6
DS006976-7
Amplifier with Bass Boost
Square Wave Oscillator
DS006976-8
DS006976-9
5
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Typical Applications
(Continued) Frequency Response with Bass Boost
DS006976-10
AM Radio Power Amplifier
DS006976-11
Note 4: Twist Supply lead and supply ground very tightly. Note 5: Twist speaker lead and ground very tightly. Note 6: Ferrite bead in Ferroxcube K5-001-001/3B with 3 turns of wire. Note 7: R1C1 band limits input signals. Note 8: All components must be spaced very closely to IC.
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6
Physical Dimensions
inches (millimeters) unless otherwise noted
SO Package (M) Order Number LM386M-1 NS Package Number M08A
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8
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
8-Lead (0.118” Wide) Molded Mini Small Outline Package Order Number LM386MM-1 NS Package Number MUA08A
9
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LM386 Low Voltage Audio Power Amplifier
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Dual-In-Line Package (N) Order Number LM386N-1, LM386N-3 or LM386N-4 NS Package Number N08E
LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component in any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email:
[email protected]
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[email protected] Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Français Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80
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