RAGHU INSTITUTE OF TECHNOLOGY
Dakamarri (v), Bheemunipatnam (M)
Visakhapatnam Dist, Andhra Pradesh, PIN-531162
(Approved by AICTE, New Delhi, and Affiliated to Jawaharlal Nehru Technological University: Kakinada (AP)
2014-15
II B.Tech
ECE II-SEM
LABORATORY MANUAL
For
ANALOG COMMUNICATIONS LAB
STUDENT MANUAL
Prepared by
Mr.R.Santosh
Assistant Professor
DEPARTMENT OF
ELECTRONICS AND COMMUNICATION ENGINEERING
RAGHU INSTIUTE OF TECHNOLOGY
(Affiliated to JNTU-KAKINADA)
Visakhapatnam-531162
CERTIFICATE
Name of the Laboratory
:
ANALOG COMMUNICATIONS
Name of the Faculty
:
R.Santosh
Department
:
ECE
Program
:
B.Tech
Year
:
II
Semester
:
II SEM
Regulation
:
R13
IQAC Members:
Name(s):
Signature(s):
HOD
CONTENTS
SNO
DESCRIPTION
PAGE NO
1
LAB OBJECTIVE
i
2
UNIVERSITY SYLLABUS
ii
3
LIST OF EXPERIMENTS
iii
4
CYCLE WISE LST OF EXPERIMNETS
iv
EXPERIMENTS USING HARDWARE
5
AMPLITUDE MODULATION & DEMODULATION
1
6
DSB-SC MODULATION AND DEMODULATION
7
7
FREQUENCY MODULATION AND DEMODULATION
13
8
PRE-EMPHASIS & DE-EMPHASIS
18
9
SAMPLING THEOREM VERIFICATION
23
10
PULSE AMPLITUDE MODULATION & DEMODULATION
28
11
PULSE WIDTH MODULATION AND DEMODULATION
33
12
PULSE POSITION MODULATION & DEMODULATION
38
13
PHASE LOCKED LOOP
42
14
DIODE DETECTOR CHARACTERISTICS
47
EXPERIMENTS USING SOFTWARE-MATLAB SIMULINK
15
AMPLITUDE MODULATION-SIMULINK
52
16
DSB-SC MODULATION-SIMULINK
54
17
FREQUENCY MODULATION-SIMULINK
56
18
SAMPLING-SIMULINK
58
19
ENVELOPE DETECTOR-SIMULINK
60
20
APPENDIX
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LAB OBJECTIVES
1. To generate amplitude modulated wave and determine the percentage modulation and to
demodulate the modulated wave using envelope detector.
2. To generate AM-Double Side Band Suppressed Carrier (DSB-SC) signal.
3. To generate frequency modulated signal and determine the modulation index and
bandwidth for various values of amplitude and frequency of modulating signal and to
demodulate a Frequency Modulated signal using FM detector.
4. To observe the effects of pre-emphasis on given input signal and to observe the effects of
De-emphasis on given input signal.
5. To verify the sampling theorem.
6. To generate the Pulse Amplitude modulated and demodulated signals.
7. To generate the pulse width modulated and demodulated signals.
8. To generate pulse position modulation and demodulation signals and to study the effect
of
amplitude of the modulating signal on output.
9. To measure the free-running frequency and capture frequency of the phase locked using
PLL with the help of IC565.
10. To demodulate amplitude modulated signal using diode detector.
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R-13/ 2014
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY
KAKINADA
II Year B.Tech ECE II-Sem
T P C
0 3 2
ANALOG COMMUNICATIONS LAB
LIST OF EXPERIMENTS:
1. Amplitude Modulation - Mod. & Demod.
2. AM - DSB SC - Mod. & Demod.
3. Spectrum Analysis of Modulated signal using Spectrum Analyzer
4. Diode Detector
5. Pre-emphasis & De-emphasis
6. Frequency Modulation - Mod. & Demod.
7. AGC Circuits
8. Sampling Theorem
9. Pulse Amplitude Modulation - Mod. & Demod.
10. PWM, PPM - Mod. & Demod.
11. PLL
EQUIPMENTS & SOFTWARE REQUIRED:
Software:
 Computer Systems with latest specifications
 Connected in LAN (Optional)
 Operating system (Windows XP)
 Simulations software (Simulink & MATLAB)
Equipment:
1. RPS
2. CRO
3. Function Generators 4. Components
5. Multi meters
6. Spectrum Analyzer
0 – 30 V
0 – 20 M Hz.
0 – 1 M Hz
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LIST OF EXPERIMENTS
1. Amplitude Modulation & Demodulation
2. DSB-SC Modulation and Demodulation
3. Frequency Modulation and Demodulation
4. PRE-Emphasis & DE-Emphasis
5. Sampling Theorem Verification
6. Pulse Amplitude Modulation & Demodulation
7. Pulse Width Modulation and Demodulation
8. Pulse Position Modulation & Demodulation
9. Phase Locked Loop
10. Diode Detector Characteristics
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CYCLE-WISE LIST OF EXPERIMENTS
I – CYCLE
1. Amplitude Modulation & Demodulation
2. DSB-SC Modulation and Demodulation
3. Frequency Modulation and Demodulation
4. PRE-Emphasis & DE-Emphasis
5. Sampling Theorem Verification
6. Pulse Amplitude Modulation & Demodulation
7. Pulse Width Modulation and Demodulation
II – CYCLE
8. Pulse Position Modulation
9. Phase Locked Loop
10. Diode detector characteristics
11. Amplitude Modulation using Simulink
12. DSB-SC Modulation using Simulink
13. Frequency Modulation using Simulink
14. Sampling using Simulink
15. Envelope Detector using Simulink
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EXPERIMENT: 1
AMPLITUDE MODULATION AND DEMODULATION
AIM:
1. To generate amplitude modulated wave and determine the modulation index.
2. To demodulate the modulated wave using simple diode detector.
EQUIPMENT REQUIRED:
1. Amplitude Modulation and demodulation trainer kit
2. Digital storage oscilloscope
3. Patch chords and probes
THEORY:
Amplitude Modulation is defined as a process in which the amplitude of the carrier wave
c (t) is varied linearly with the instantaneous amplitude of the message signal m(t). The standard
form of amplitude modulated (AM) wave is defined by
Where Ka is a constant called the amplitude sensitivity of the modulator.
m<1------------ Under Modulation
m=1------------ 100% Modulation
m>1------------ Over Modulation
The demodulation circuit is used to recover the message signal from the incoming AM
wave at the receiver. An envelope detector is a simple and yet highly effective device that is well
suited for the demodulation of AM wave, for which the percentage modulation is less than
100%. Ideally, an envelope detector produces an output signal that follows the envelop of the
input signal wave form.
The Modulation Index is defined as, m= (Vmax- Vmin) /(Vmax+ Vmin)
Where Vmax and Vmin are the maximum and minimum amplitudes of the modulated wave.
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BLOCK DIAGRAMS:
MODULATING
SIGNAL
GENERATOR
AM
MODULATOR
CRO
CARRIER
SIGNAL
GENERATOR
Figure (a): Modulator
MODULATED
INPUT
AM
DEMODULATOR
CRO
Figure (b): Demodulator
CIRCUIT DIAGRAMS:
Figure (a): Modulator Circuit
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Figure (b): Demodulator Circuit (Simple diode detector)
MODEL WAVEFORMS:
PROCEDURE:
1. Switch ON the trainer and measure the output voltages of the regulated power supply i.e
+12v and -8v.
2. Observe the output of the RF generator using CRO. Output should be a sine wave of
100KHZ frequency.
3. Observe the output of the AF generator using CRO. Output should be a sine wave of
5KHZ frequency.
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4. Short the both RF and AF inputs of the AM Modulator and connect to the output of the
RF generator.
5. Connect CRO CH1 input to input of the AM Modulator and CH2 input to the output of
the AM Modulator.
6. Measure the output frequency of the AM Modulator (output shape may be little bit
distorted in), it should be double to the input signal frequency. Until you get double in
frequency adjust the null adjust controller.
7. Now remove the short between RF and AF input of the AM Modulator, and connect AF
input to the AF generator output (keep AF signal amplitude at zero).
8. Connect CH1 of the CRO to AF signal and CH2 to output of the AM Modulator.
9. Observe the AM Modulator output by slowly increasing the amplitude of the AF signal.
10. Connect the AM signal input of the simple diode detector to the input of the AM
Modulator and RF input to the output of the RF generator.
11. Connect CH1 input of the CRO to the AF signal and CH2 to the output of the simple
diode detector.
OBSERVATIONS:
Message Signal:
Amplitude VP-P =
Frequency =
Time period =
Carrier signal:
Amplitude VP-P=
Frequency =
Time period =
Modulated signal:
(i) m<1 Vmax=
(ii) m=1 Vmax=
(iii) m>1 Vmax=
Vmin=
Vmin=
Vmin=
Demodulated signal:
Amplitude VP-P =
Frequency =
Time period=
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PRECAUTIONS:
1. Do not make any interconnections on the board when power is switched ON.
2. If any external AF generator is being used see that the amplitude does not exceed 3V (PP). Take readings without any parallax error.
RESULT:
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Viva Questions
1Q.
What is amplitude modulation?
2Q.
What is modulation?
3Q.
What happens in over modulation?
4Q.
What is demodulation?
5Q.
Explain the need of modulation and demodulation?
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EXPERIMENT: 2
BALANCED MODULATION AND DEMODULATION (DSB-SC)
AIM:
1. To study the process of Balanced Modulation and the corresponding waveforms.
2. To study the demodulation of Balanced modulated signal.
EQUIPMENT REQUIRED:
1. Balanced modulator trainer kit
2. Digital storage oscilloscope
3. Patch chords and probes
THEORY:
Balanced modulator is used for generation of double side band suppress carrier signal.
The output of balanced modulator is equal to the product of applied input signals .In order to
generate this it uses non linear characteristics of semi conductor devices. Since the carrier does
not convey any information, transmitting the carrier along with side band is only wasting of
transmission power; therefore carrier is suppressed before transmission. By doing suppression
67% of transmission power can be saved. The method of transmission of modulated wave
without carrier is DSBSC signal.
Balanced modulator is also used in generation of SSB signals. The modulated signal
undergoes a phase reversal whenever the base band signal crosses zero. Unlike AM, The
envelope of DSBSC is different from base band signal .The ring modulator is another circuit for
generation the DSBSC signal.
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BLOCK DIAGRAMS:
MODULATING
SIGNAL
GENERATOR
PRODUCT
MODULATOR
CRO
CARRIER
SIGNAL
GENERATOR
(a) Modulator
MODULATED
INPUT
DSB-SC
DEMODULATOR
CRO
(b) Demodulator
CIRCUIT DIAGRAMS:
(a) DSB-SC Modulator
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(b) DSB-SC Demodulator
MODEL WAVEFORMS:
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PROCEDURE:
1. Switch on the power supply through mains card.
2. As the circuitry is already wired, you just have to trace the circuit according to the circuit
diagram.
3. Connect 5KHZ sinusoidal signal to both the carrier and modulation inputs.
4. Observe the output on CRO and adjust the null potentiometer until the output is 10KHZ
sinusoidal wave. Note that this is very sensitive adjustment because you are making the
biasing at both inputs exactly the same to get the multiplying effect of the device.
5. Apply 100KHZ, 01V-peak sinusoidal wave to the carrier input and a 5KHZ sinusoidal
wave with 0.1V peak to the modulation input.
6. Adjust carrier null potentiometer to obtain a DSBSC wave as output varies the amplitude
frequency of the message signals at different levels.
7. Observe the variation inside in side bands and suppression of carrier.
8. Record the exact frequency levels of side bands suppressed carrier from CRO.
OBSERVATIONS:
Message Signal:
Amplitude VP-P =
Frequency =
Time period =
Modulated signal:
Frequency =
Time period =
Vmax=
Vmin=
Carrier signal:
Amplitude VP-P =
Frequency =
Time period =
Demodulated signal:
Amplitude VP-P =
Frequency =
Time period =
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PRECAUTIONS:
1. Do not make any interconnections on the board when power is switched ON.
2. If any external AF generator is being used see that the amplitude does not exceed 3V (pp).
3. Take readings without any parallax error.
RESULT:
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Viva Questions
Q1.
What is a DSB-SC modulation?
Q2.
How can we obtain a DSB-SC signal?
Q3.
What is the band width of a DSB-SC signal?
Q4.
What are demodulation methods for DSB-SC signal?
Q5.
What is the advantage of DSB-SC over AM system?
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EXPERIMENT: 3
FREQUENCY MODULATION AND DEMODULATION
AIM:
1. To generate frequency modulated signal and determine the modulation index and
bandwidth.
2. To demodulate a Frequency Modulated signal using FM detector.
EQUIPMENT REQUIRED:
1. Experimental board of frequency modulation and demodulation.
2. Digital storage oscilloscope.
3. Patch cords and probes.
THEORY:
The process, in which the frequency of the carrier is varied in accordance with the
instantaneous amplitude of the modulating signal, is called Frequency Modulation.
The FM signal is expressed as: S (t) =Ac cos (2
+
(2
))
Where Ac is amplitude the carrier signal, fc is the carrier frequency and β is the modulation index
of the FM wave.
β=Δf/fm, where Δf is frequency deviation and fm is frequency of modulating signal.
The Bandwidth expression for FM is given by: BW= 2(β+1) fm
BLOCK DIAGRAM:
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CIRCUIT DIAGRAM:
Figure (a): FM-Modulator Circuit
Figure (b): FM-Demodulator Circuit
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MODEL WAVEFORMS:
PROCEDURE:
1. Switch ON the power to the board.
2. Measure the amplitude and time period of the modulating signal.
3. Measure the amplitude and time period of the carrier signal.
4. Now, apply the modulating signal into the input of modulating circuit.
5. Observe the modulated signal and determine fc(max) and fc(min) and calculate
modulation index.
6. Apply the modulated signal to the detector circuit and observe the demodulated signal.
7. Plot the graphs of modulating, carrier, modulated and demodulated signals
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OBSERVATIONS:
Message Signal:
Amplitude VP-P =
Frequency =
Time period =
Carrier signal:
Amplitude VP-P =
Frequency =
Modulated signal:
Amplitude VP-P =
Time period:
Tmax=
Tmin=
Demodulated signal:
Amplitude VP-P =
Frequency =
Time period =
Time period =
PRECAUTIONS:
1. Do not make any interconnections on the board with power ON.
2. If external AF generator is used, see that amplitude doesn’t exceed 3VP-P.
RESULT:
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Viva Questions
1Q.
What is Frequency modulation (FM)?
2Q.
What are the different types of analog modulation?
3Q.
Why frequency modulation is better than amplitude modulation?
4Q.
What is frequency deviation?
5Q.
Define modulation index for FM?
6Q.
What is transmission BW for FM?
7Q.
What are disadvantages of FM?
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EXPERIMENT: 4
PRE -EMPHASIS AND DE-EMPHASIS
AIM:
To calculate the gain of pre-emphasis and de-emphasis circuit and plot the corresponding
frequency response curve.
EQUIPMENT REQUIRED:
1. Pre-emphasis and De-emphasis trainer kit.
2. Digital storage oscilloscope.
3. Probes and Patch cards.
THEORY:
Signals with higher modulation frequencies have lower SNR, In order to compensate this,
the high frequency signals are emphasized or boosted in amplitude at the transmitter section of a
communication system prior to the modulation process. That is, the pre emphasis network allows
the high frequency modulating signal to modulate the carrier at higher level, this causes more
frequency deviation.
De emphasis is the inverse process of pre-emphasis, used to attenuate the high frequency
signal that is boosted at the transmitter section. The de-emphasis network at the receiver section
restores the original amplitude Vs frequency characteristics of the information signal, after the
demodulation process. The pre-emphasis and de-emphasis produces a more uniform SNR
throughout the modulating signal frequency spectrum.
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CIRCUIT DIAGRAMS:
Figure (a): Pre-Emphasis Circuit
Figure (b): De-Emphasis Circuit
MODEL WAVEFORMS:
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PROCEDURE:
PRE- EMPHASIS:
1. Connect the circuit as shown in the figure.
2. Apply a sine wave of 1V with a frequency of 1 KHz to the input terminals of preemphasis.
3. Vary the frequency of function generator and note down the corresponding output
voltage.
4. Plot the graphs of frequency response of pre-emphasis circuit.
DE- EMPHASIS:
1. Connect the circuit as shown in the figure.
2. Apply a sine wave of 1V with a frequency of 1 KHz to the input terminals of deemphasis circuit.
3. Vary the frequency of function generator and note down the corresponding output
voltage.
4. Plot the graphs of frequency response of de-emphasis circuit.
OBSERVATIONS:
PRE-EMPHASIS
Vin=
S. No
Frequency (Hz)
Vo (V)
Gain in db
20log(Vo /Vi )
1
2
3
4
5
6
7
8
9
10
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DE-EMPHASIS
Vin=
S. No
Frequency
(KHz)
Vo (mV)
Gain in db
20log(Vo /Vi )
1
2
3
4
5
6
7
8
9
10
PRECAUTIONS:
1. Do not make any interconnections on the board with power switched ‘ON’.
2. Take readings without parallax error.
RESULT:
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Viva Questions
1Q.
What is meant by pre-emphasis?
2Q.
What is meant by de-emphasis?
3Q.
The main purpose of pre-emphasis and de-emphasis networks in FM communication
systems is to?
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EXPERIMENT: 5
SAMPLING THEORM
AIM:
To verify the sampling theorem.
EQUIPMENT REQUIRED:
1. Sampling theorem trainer kit
2. Digital Storage Oscilloscope
3. Patch cords and connecting wires
THEORY:
Sampling Theorem Statement: A band limited signal of finite energy which has no
frequency components higher than fm HZ, is completely described by specifying the
values of the signal at instants of time separated by ½ fm seconds.
The sampling theorem states that, if the sampling rate in any pulse modulation
system exceeds twice the maximum signal frequency, the original signal can be
reconstructed in the receiver with minimum distortion.
fs > 2fm is called Nyquist Rate.
fs - sampling frequency
fm - modulation signal frequency.
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CIRCUIT DIAGRAMS:
Figure (a): Sampling Circuit
Figure (b): Reconstructing Circuit
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MODEL WAVEFORMS:
PROCEDURE:
1. Apply clock pulse to pulse input of the modulator.
2. Apply modulating signal to modulating signal input of modulator.
3. Observe sampled output at the output terminals of the modulator.
4. Apply sampled output to detector input and observe reconstructed signal at the output of
the filter.
5. Varying the frequency of pulse of pulse generator and observe the demodulated signal at
various frequencies.
6. Plot the graphs of modulating, pulse, sampled and demodulated signals.
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OBSERVATIONS:
Message Signal:
Sample and Hold Signal:
Amplitude VP-P=
Amplitude VP-P =
Frequency =
Frequency =
Time period =
Time period =
Clock pulse signal:
Flat-Top Signal:
Amplitude VP-P =
Amplitude VP-P =
Frequency =
Frequency =
Time period =
Time period =
Sampled Signal:
Demodulated signal:
Amplitude VP-P =
Amplitude VP-P =
Frequency =
Frequency =
Time period =
Time period =
PRECAUTIONS:
1. Make sure that trainer kit is switched OFF while making inter-connections.
2. Take readings without any parallax error.
RESULT:
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AC LAB
Viva Questions
1Q.
What is sampling?
2Q.
What is sampling theorem?
3Q.
What do you mean by Nyquist rate?
4Q.
What is under sampling?
5Q.
How can be aliasing be avoided?
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EXPERIMENT: 6
PULSE AMPLITUDE MODULATION AND DEMODULATION
AIM:
To generate the Pulse Amplitude modulated and demodulated signals.
EQUIPMENT REQUIRED:
1. Pulse Amplitude Modulated trainer kit
2. Digital Storage Oscilloscope
3. Patch cords and Probes
THEORY:
Pulse-amplitude modulation is a form of signal modulation where the message
information is encoded in the amplitude of a series of signal pulses. It is an analog pulse
modulation scheme in which the amplitude of train of carrier pulse is varied according to the
sample value of the message signal.
The signal is sampled at regular intervals and each sample is made proportional to the
magnitude of the signal at the instant of sampling. These sampled pulses may then be sent either
directly by a channel to the receiving end or may be made to modulate using a carrier wave
before transmission. For the generation of a PAM signal we use a flat top type PAM scheme
because during the transmission, the noise is interfered at top of the transmission pulse which can
be easily removed if the PAM pulse in flat top.
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BLOCK DIAGRAM:
CIRCUIT DIAGRAM:
Figure (a): Modulator Circuit
Figure (b): Demodulator Circuit
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MODEL WAVEFORMS:
PROCEDURE:
1. Connect the circuit as shown in figure and switch on the power supply of amplitude
modulation kit.
2. Adjust the frequency and amplitude of the modulating signal to 1KHz and 4V(p-p)
respectively.
3. Adjust the frequency of the sampling signal to 10 KHz.
4. Observe the Pulse Amplitude Modulated signal at output of modulator.
5. Connect the modulated signal to the input of demodulator and observe the demodulated
output signal.
6. Plot the graphs of modulating, sampling pulse train, modulated and demodulated signals.
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OBSERVATIONS:
Message Signal:
Amplitude VP-P=
Frequency =
Time period =
Clock pulse signal:
Amplitude VP-P =
Frequency =
Time period =
Modulated signal:
Amplitude A1 =
Amplitude A2 =
Amplitude A3 =
Amplitude A4 =
Amplitude A5 =
Frequency =
Time period =
Demodulated signal:
Amplitude VP-P =
Frequency =
Time period =
PRECAUTIONS:
1. Do not make the interconnections on the board when the power is ‘ON’.
2. If the external AF generator is given to modulated signal see that amplitude does not
exceed 3 V (p-p).
RESULT:
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AC LAB
Viva Questions
1Q.
Define PAM.
2Q.
Write down its drawbacks of PAM?
3Q.
What are the analog analogies of PAM, PPM & PWM?
4Q.
What are the advantage of PAM and PWM?
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AC LAB
EXPERIMENT: 7
PULSE WIDTH MODULATION AND DEMODULATION
AIM:
To generate the pulse width modulated and demodulated signals.
EQUIPMENT REQUIRED:
1. Pulse Width Modulation and Demodulation trainer kit.
2. Digital Storage Oscilloscope.
3. Patch cords.
4. Probes.
THEORY:
Pulse Time Modulation is also known as Pulse Width Modulation or Pulse Length
Modulation. In PWM, the samples of the message signal are used to vary the duration of the
individual pulses. Width may be varied by varying the time of occurrence of leading edge, the
trailing edge or both edges of the pulse in accordance with modulating wave. It is also called
pulse Duration Modulation.
BLOCK DIAGRAM:
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CIRCUIT DIAGRAM:
Figure (a): Modulator Circuit
Figure (b): Demodulator Circuit
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MODEL WAVEFORMS:
PROCEDURE:
1. Switch on supply to the trainer kit.
2. Connect the analog signal output to analog signal input of Pulse Width Modulation
circuit.
3. Adjust the frequency to 1 KHz and amplitude to 3 V(p-p) by potentiometer P2.
4. Connect the pulse generator output to pulse input of modulator. Adjust the frequency of
sampling signal to 10 KHz.
5. Observe the pulse width modulated output waves and plot graphs of modulating, pulse
train and the pulse width modulated waves.
6. Connect the PWM output to input of PWM demodulation circuit.
7. The output of filter is demodulated. Observe the demodulated signal in Digital Storage
Oscilloscope (DSO) and plot the graph.
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OBSERVATIONS:
Message Signal:
Amplitude VP-P=
Frequency =
Time period =
Modulated signal:
Amplitude VP-P=
Time period:
TON1= TOFF1 = TON2 =
TOFF2 = TON3 = TOFF3 = TON4 = TOFF4 =
TON5 =
Clock pulse signal:
Amplitude VP-P=
Frequency =
Time period =
Demodulated signal:
Amplitude VP-P=
Frequency =
Time period =
PRECAUTIONS:
1. Do not make the interconnections on the board when the power is ‘ON’.
2. If the external AF generator is given to modulated signal see that amplitude does not
exceed 3 VP-P.
RESULT:
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Viva Questions
1Q.
What is PWM or Pulse length modulation or pulse duration modulation?
2Q.
What are the disadvantages of PWM?
3Q.
Explain the principle of PWM?
4Q.
What is the advantage of PPM over PWM and PAM?
5Q.
Mention the applications of PWM.
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EXPERIMENT: 8
PULSE POSITION MODULATION AND DEMODULATION
AIM:
To generate pulse position modulation and demodulation signals and to study the effect
of amplitude of the modulating signal on output.
EQUIPMENT REQUIRED:
1. Pulse Position modulation trainer kit
2. Dual trace oscilloscope
3. Patch Cords and Probes
THEORY:
In Pulse Position Modulation, both the pulse amplitude and pulse duration are held
constant but the position of the pulse is varied in proportional to the sampled values of the
message signal. Pulse time modulation is a class of signaling techniques that encodes the sample
values of an analog signal on to the time axis of a digital signal and it is analogous to angle
modulation techniques. The two main types of PTM are PWM and PPM. In PPM the analog
sample value determines the position of a narrow pulse relative to the clocking time. In PPM rise
time of pulse decides the channel bandwidth. It has low noise interference.
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CIRCUIT DIAGRAM:
MODEL WAVEFORMS:
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PROCEDURE:
1. Switch on supply to the trainer kit.
2. Connect the analog signal output to analog signal input of Pulse Position Modulation
circuit. Adjust the frequency to 1 KHz and amplitude to above 3 V(p-p) by potentiometer
P2.
3. Connect the sampling pulse output to pulse input of the modulator.
4. Adjust the frequency of sampling signal to 5 KHz.
5. Observe PPM wave form at pin number 3 of IC 555
6. To modulate the signal apply output of PPM modulator to the input of demodulation
circuit.
7. The output of Low pass filter is replica of the AF signal.
8. Plot the graphs of modulating, sampling pulse, modulated and demodulated signals.
OBSERVATIONS:
Message Signal:
Modulated signal:
Amplitude VP-P=
Amplitude VP-P=
Frequency =
Time period =
Demodulated signal:
Amplitude VP-P=
Clock pulse signal:
Frequency =
Amplitude VP-P=
Time period =
Frequency =
Time period =
PRECAUTIONS:
1. Do not make the interconnections on the board when the power is ‘ON’.
2. Take the reading without parallax error.
RESULT:
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Viva Questions
1Q.
What is Pulse position modulation?
2Q.
What are the applications of pulse position modulation?
3Q.
What is the purpose of using differential pulse position modulation?
4Q.
What are the advantages of PPM?
5Q.
What are the applications of PPM?
6Q.
Explain the principle of PPM?
7Q.
What is the purpose of PPM?
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EXPERIMENT: 9
PHASE LOCKED LOOP
AIM:
To study PLL and obtain free-running frequency and capture frequency of the Phase
Locked using IC565.
EQUIPMENT REQUIRED:
1. Phased locked loop trainer kit.
2. Digital storage oscilloscope.
3. Probes and patch cards.
THEORY:
A phase-locked loop or phase lock loop (PLL) is a control system that generates an
output signal whose phase is related to the phase of an input signal. While there are several
differing types, it is easy to initially visualize as an electronic circuit consisting of a variable
frequency oscillator and a phase detector. The oscillator generates a periodic signal. The phase
detector compares the phase of that signal with the phase of the input periodic signal and adjusts
the oscillator to keep the phases matched. Bringing the output signal back toward the input signal
for comparison is called a feedback loop since the output is 'fed back' toward the input forming a
loop.
Keeping the input and output phase in lock step also implies keeping the input and output
frequencies the same. Consequently, in addition to synchronizing signals, a phase-locked loop
can track an input frequency, or it can generate a frequency that is a multiple of the input
frequency. These properties are used for computer clock synchronization, demodulation, and
frequency synthesis, respectively.
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BLOCK DIAGRAM:
CIRCUIT DIAGRAM:
PROCEDURE:
1. Connect the circuit as shown in the figure.
2. The square wave of amplitude 3v from square wave generator TP1 – TP2.
3. The Vco output TP5 to TP6.
4. Switch ON the power supply.
5. Observe the free running frequency at TP5 on the oscilloscope without giving the input.
6. Switch OFF the power supply.
7. Then calculate the free- running frequency Fout by using the formula
fout =1.2/4R1C1
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Where R1 and C1 are external resistors and capacitors.
LOCK FREQUENCY:
1. Connect the circuit diagram as shown in figure. The square wave of amplitude 3v from
square wave generator TP1 to TP2.
2. Switch ON power supply.
3. Observe the output at TP5 by varying the frequency of square wave from 350Hz to
10KHz at some frequency of the output, the out frequency of Vco at TP5 is same as the
input frequency, note down the frequency ‘f1’ .
4. Continue varying the input frequency and at some frequency the output frequency differs
from that of the input frequency. Let the frequency be ‘f2’. This range of frequency over
which output frequency is equal to the input is the lock range and is given by
fl = (f2 –f1) Hz
5. Switch OFF the power supply.
6. Now calculate,
fl = ± 8fout/Vcc
CAPTURE FREQUENCY:
1. Connect the circuit as shown in the figure
2. The square wave of amplitude 3V from square wave generator TP1 to TP2.
3. The Vco output TP5 to TP6.
4. Switch ON the power supply.
5. Observe the output at TP5 by varying the output signal will be same as the input signal
notes this frequency as ‘fmin’.
6. Continue varying the frequency of input signal at some frequency, the output signal phase
changes and this frequency is ‘fmax’. The range of frequency over which PLL acquires
phase lock is given as,
fc = fmax – fmin
7. Switch OFF the power supply.
8. Calculate the capture frequency by the formula.
fc = ± (fL/2πRC)½
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CHARACTERISTICS OF PLL:
OBSERVATIONS:
Practical calculations:
Lock range=fl(max) – fl(min) =
Time period of i/p signal (T) =
Capture range= fc(max) – fc(min) =
Free running frequency (f0) =
fc(min)=
Theoretical calculations:
fc(max)=
f0 = 1.2/R1C1 =
fl(min)=
C1 =
fl(max)=
fl = ± 8fout/VCC =
for R1=
, (VCC =12 V)
fc = ± (fl/2πRC)1/2 =
PRECAUTIONS:
1. Do not make interconnections on the board with power switched ‘ON’.
2. A slow variation of frequency knob is required to calculate the capture frequency.
RESULT:
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Viva Questions
1Q.
What is the importance of VCO in PLL?
2Q.
What are the various blocks in PLL?
3Q.
List out the applications of PLL.
4Q.
What do you meant by Capture range and Lock range?
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EXPERIMENT: 10
DIODE DETECTOR CHARECTERISTICS
AIM:
To demodulate amplitude modulated signal using diode detector.
EQUIPMENT REQUIRED:
THEORY:
The process of extracting a baseband signal for modulated signal is called demodulation.
This demodulation here is performed by means of diode detector. This diode detector works with
the help of V-I characteristics. In the absence of capacitor the circuit behaves as half wave
rectifier. When the capacitor is present the diode conducts until capacitor is charged to peak
value. During negative cycle the diode is reversed biased and does not conduct i.e input carrier
voltage is disconnected from RC circuit. Therefore capacitor starts discharging through
resistance R with RC time constant. If the time constant RC is suitably chooses the voltage
across capacitor C will not fall during small period of negative half cycle. This means voltage
across C is same as the envelop of modulated carrier signal.
The envelop detector or linear diode detector is most popular in commercial circuits.
Since it is very simple and very less expensive. In the input portion of the circuit the tuned
transformer provides perfect tuning at desired carrier frequency. If the magnitude of the
modulated signal at the input of the detector is 1V or more then operation takes place in the
linear region of operation based on V-I characteristics of diode.
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CIRCUIT DIAGRAM:
MODEL WAVEFORMS:
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PROCEDURE:
1. Measure amplitude and frequency of carrier signal that is generated from RF generator.
2. Apply RF signal to RF input terminal of modulator circuit.
3. Measure amplitude and time period of AF signal at output terminal of AF generator.
4. Apply AF signal to AF input terminal of modulation circuit.
5. Measure the amplitude and frequency of modulated signal at output terminal of
modulation.
6. Connect the modulation signal to input terminals of diode detector circuit.
7. Measure amplitude and frequency of AF signal at the output terminal of modulation
circuit and observe that the AF signal is same as the AF generator and plot graphs
of
modulated and demodulated signals.
OBSERVATIONS:
Message Signal:
Modulated signal:
Amplitude VP-P =
Vmax=
Frequency =
Modulation index (m) =
Time period =
Frequency =
Carrier signal:
Time period =
Amplitude VP-P =
Demodulated signal:
Frequency =
Amplitude VP-P =
Time period =
Frequency =
Vmin=
Time period=
PRECAUTIONS:
1. Do not make interconnections on the board with power switch on.
2. If and external AF generator is given to modulated signal see that amplitude do not
exceed 3VP-P.
RESULT:
Using a diode detector an amplitude modulated signal is demodulated.
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Viva Questions
1Q.
What is the condition required to get envelope of Amplitude modulated signal?
2Q.
What is the disadvantage of square law demodulator compared with diode detector?
3Q.
What is the limitation of envelope detector?
4Q.
List out the various demodulators of AM?
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MATLAB-SIMULINK
EXPERIMENT PROCEDURE– SIMULINK:
1. Type simulink at the MATLAB COMMAND prompt.
* The Simulink Library Browser window is opened.
2. Create a new model window by clicking the Create a new model button
on the
Library Browser toolbar or click File >> New >> Model.
* A new empty workspace window is opened.
3. Double-click to expand the Simulink folder at the Library Browser window.
4. Double-click to expand the Sources sub-folder in the Simulink folder.
5. Drag and drop required modules into the new empty workspace window.
6. Set the parameters of the different blocks in your workspace as follows:
7.
Block Model
Parameters to be set
Example:
Waveform type: Sine
Signal Generator
Amplitude: 0.8
Frequency: 100 Hz
8. Run (Simulation >> Start) the simulation and observe the output waveforms in both
time and frequency domains of the message, carrier, modulated and demodulated signals.
Compare these graphs with that obtained using Hardware.
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EXPERIMENT: 11
AMPLITUDE MODULATION
AIM:
To draw the circuit for Amplitude Modulation and to simulate the circuit using
MATLAB-Simulink.
SOFTWARE REQUIRED: MATLAB version 7.1-Simulink
SIMULINK DESIGN CIRCUIT:
DESIGN PARAMETERS:
Block Model
Parameters to be set
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SIMULATED WAVEFORMS:
RESULT:
The circuit for Amplitude Modulation is drawn and simulated using MATLAB-Simulink
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EXPERIMENT: 12
DSB-SC MODULATION
AIM:
To draw the circuit for DSB-SC Modulation and to simulate the circuit using MATLABSimulink.
SOFTWARE REQUIRED: MATLAB version 7.1-Simulink
SIMULINK DESIGN CIRCUIT:
DESIGN PARAMETERS:
Block Model
Parameters to be set
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SIMULATED WAVEFORMS:
RESULT:
The circuit for Amplitude Modulation is drawn and simulated using MATLAB-Simulink
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EXPERIMENT: 13
FREQUENCY MODULATION
AIM:
To draw the circuit for Frequency modulation and to simulate the circuit using
MATLAB-Simulink.
SOFTWARE REQUIRED: MATLAB version 7.1-Simulink
SIMULINK DESIGN CIRCUIT:
DESIGN PARAMETERS:
Block Model
Parameters to be set
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SIMULATED WAVEFORMS:
RESULT:
The circuit for Frequency Modulation is drawn and simulated using MATLAB-Simulink
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EXPERIMENT: 14
SAMPLING
AIM:
To draw the Sampling circuit and to simulate the circuit using MATLAB-Simulink.
SOFTWARE REQUIRED: MATLAB version 7.1-Simulink
SIMULINK DESIGN CIRCUIT:
DESIGN PARAMETERS:
Block Model
Parameters to be set
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SIMULATED WAVEFORMS:
RESULT:
Sampling circuit is drawn and simulated using MATLAB-Simulink.
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EXPERIMENT: 15
ENVELOPE DETECTOR
AIM:
To draw the circuit for Envelope Detector and to simulate the circuit using MATLABSimulink.
SOFTWARE REQUIRED: MATLAB version 7.1-Simulink
SIMULINK DESIGN CIRCUIT:
DESIGN PARAMETERS:
Block Model
Parameters to be set
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SIMULATED WAVEFORMS:
RESULT:
The circuit for Envelope Detector is drawn and simulated using MATLAB-Simulink
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APPENDIX
IC 555
Description:
The operation of SE/NE 555 timer directly depends on its internal function. The three
equal resistors R1, R2, R3 serve as internal voltage divider for the source voltage. Thus one-third
of the source voltage VCC appears across each resistor. Comparator is basically an Op amp which
changes state when one of its inputs exceeds the reference voltage. The reference voltage for the
lower comparator is +1/3 VCC. If a trigger pulse applied at the negative input of this comparator
drops below +1/3 VCC, it causes a change in state. The upper comparator is referenced at voltage
+2/3 VCC. The output of each comparator is fed to the input terminals of a flip flop.
The flip-flop used in the SE/NE 555 timer IC is a bistable multivibrator. This flip flop
changes states according to the voltage value of its input. Thus if the voltage at the threshold
terminal rises above +2/3 VCC, it causes upper comparator to cause flip-flop to change its states.
On the other hand, if the trigger voltage falls below +1/3 VCC, it causes lower comparator to
change its states. Thus the output of the flip flop is controlled by the voltages of the two
comparators. A change in state occurs when the threshold voltage rises above +2/3 VCC or when
the trigger voltage drops below +1/3 Vcc.
The output of the flip-flop is used to drive the discharge transistor and the output stage.
A high or positive flip-flop output turns on both the discharge transistor and the output stage.
The discharge transistor becomes conductive and behaves as a low resistance short circuit to
ground. The output stage behaves similarly. When the flip-flop output assumes the low or zero
states reverse action takes place i.e., the discharge transistor behaves as an open circuit or
positive VCC state. Thus the operational state of the discharge transistor and the output stage
depends on the voltage applied to the threshold and the trigger input terminals.
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Block Diagram of IC 555:
Pin Configuration:
Function of Various Pins of 555 IC:
Pin (1) of 555 is the ground terminal; all the voltages are measured with respect to this pin.
Pin (2) of 555 is the trigger terminal, if the voltage at this terminal is held greater than one-third
of VCC, the output remains low. A negative going pulse from VCC to less than VCC/3 triggers the
output to go high. The amplitude of the pulse should be able to make the comparator (inside the
IC) change its state. However the width of the negative going pulse must not be greater than the
width of the expected output pulse.
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Pin (3) is the output terminal of IC 555. There are 2 possible output states. In the low output
state, the output resistance appearing at pin (3) is very low (approximately 10 Ω). As a result the
output current will goes to zero , if the load is connected from Pin (3) to ground , sink a current I
Sink
(depending upon load) if the load is connected from Pin (3) to ground, and sinks zero current
if the load is connected between +VCC and Pin (3).
Pin (4) is the Reset terminal. When unused it is connected to +Vcc. Whenever the potential of
Pin (4) is drives below 0.4V, the output is immediately forced to low state. The reset terminal
enables the timer over-ride command signals at Pin (2) of the IC.
Pin (5) is the Control Voltage terminal. This can be used to alter the reference levels at which the
time comparators change state. A resistor connected from Pin (5) to ground can do the job.
Normally 0.01μF capacitor is connected from Pin (5) to ground. This capacitor bypasses supply
noise and does not allow it affect the threshold voltages.
Pin (6) is the threshold terminal. In both astable as well as monostable modes, a capacitor is
connected from Pin (6) to ground. Pin (6) monitors the voltage across the capacitor when it
charges from the supply and forces the already high O/p to Low when the capacitor reaches +2/3
VCC.
Pin (7) is the discharge terminal. It presents an almost open circuit when the output is high and
allows the capacitor charge from the supply through an external resistor and presents an almost
short circuit when the output is low.
Pin (8) is the +VCC terminal. 555 can operate at any supply voltage from
+3 to +18V.
Features of 555 IC:
1. The load can be connected to o/p in two ways i.e. between pin 3 & ground 1 or between
pin 3 & VCC (supply)
2. 555 can be reset by applying negative pulse, otherwise reset can be connected to +Vcc to
avoid false triggering.
3. An external voltage effects threshold and trigger voltages.
4. Timing from micro seconds through hours.
5. Monostable and bistable operation
6. Adjustable duty cycle
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7. Output compatible with CMOS, DTL, TTL
8. High current output sink or source 200mA
9. High temperature stability
10. Trigger and reset inputs are logic compatible.
Specifications:
1. Operating temperature
:
SE 555-- -55oC to 125oC
NE 555-- 0o to 70oC
2. Supply voltage
:
+5V to +18V
3. Timing
:
μsec to Hours
4. Sink current
:
200mA
5. Temperature stability
:
50 PPM/oC change in temp or 0-005% /oC.
Applications:
1. Monostable and Astable Multivibrators
2. dc-ac converters
3. Digital logic probes
4. Waveform generators
5. Analog frequency meters
6. Tachometers
7. Temperature measurement and control
8. Infrared transmitters
9. Regulator & Taxi gas alarms etc.
IC 565
Description:
The Signetics SE/NE 560 series is monolithic phase locked loops. The SE/NE 560, 561,
562, 564, 565, & 567 differ mainly in operating frequency range, power supply requirements and
frequency and bandwidth adjustment ranges. The device is available as 14 Pin DIP package and
as 10-pin metal can package. Phase comparator or phase detector compare the frequency of
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input signal fs with frequency of VCO output fo and it generates a signal which is function of
difference between the phase of input signal and phase of feedback signal which is basically a
d.c voltage mixed with high frequency noise. LPF remove high frequency noise voltage. Output
is error voltage. If control voltage of VCO is 0, then frequency is center frequency (fo) and mode
is free running mode. Application of control voltage shifts the output frequency of VCO from f o
to f. On application of error voltage, difference between fs & f tends to decrease and VCO is said
to be locked. While in locked condition, the PLL tracks the changes of frequency of input signal.
Block Diagram of IC 565:
Pin Configuration:
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Specifications:
1. Operating frequency range
:
0.001 Hz to 500 KHz
2. Operating voltage range
:
±6 to ±12V
3. Inputs level required for tracking
:
10mV rms minimum to 3v (p-p) max.
4. Input impedance
:
10 KΩ typically
5. Output sink current
:
1mA typically
6. Drift in VCO center frequency
:
300 PPM/oC typically (fout) with temperature
7. Drif in VCO centre frequency with :
1.5%/V maximum supply voltage
8. Triangle wave amplitude
:
typically 2.4 VPP at ± 6V
9. Square wave amplitude
:
typically 5.4 VPP at ± 6V
10. Output source current
:
10mA typically
11. Bandwidth adjustment range
:
<±1 to >± 60%
Applications:
1. Frequency multiplier
2. Frequency shift keying (FSK) demodulator
3. FM detector
IC 566
Description:
The NE/SE 566 Function Generator is a voltage controlled oscillator of exceptional
linearity with buffered square wave and triangle wave outputs. The frequency of oscillation is
determined by an external resistor and capacitor and the voltage applied to the control terminal.
The oscillator can be programmed over a ten to one frequency range by proper selection of an
external resistance and modulated over a ten to one range by the control voltage with exceptional
linearity.
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Block Diagram of IC566:
Pin diagram:
Specifications:
1. Maximum operating Voltage ---
26V
2. Input voltage
---
3V (P-P)
3. Storage Temperature
---
-65oC to + 150oC
4. Operating temperature
---
0oC to +70oC for NE 566
---
300mv
-55oC to +125oC for
SE 566
5. Power dissipation
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Applications:
1. Tone generators.
2. Frequency shift keying
3. FM Modulators
4. Clock generators
5. Signal generators
6. Function generator
IC 1496
Description:
IC balanced mixers are widely used in receiver IC’s. The IC versions are usually
described as balanced modulators. Typical example of balanced IC modulator is MC1496. The
circuit consists of a standard differential amplifier (formed by Q5 _ Q6 combination) driving a
quad differential amplifier composed of transistor Q1 – Q4. The modulating signal is applied to
the standard differential amplifier (between terminals 1 and 4). The standard differential
amplifier acts as a voltage to current converter. It produces a current proportional to the
modulating signal. Q7 and Q8 are constant current sources for the differential amplifier Q5 – Q6.
The lower differential amplifier has its emitters connected to the package pins ( 2 & 3) so that an
external emitter resistance may be used. Also external load resistors are employed at the device
output (6 and 12 pins).The output collectors are cross-coupled so that full wave balanced
multiplication takes place. As a result, the output voltage is a constant times the product of the
two input signals.
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Schematic of IC1496:
Pin Configuration:
Applications of MC 1496:
1. Balanced modulator
2. AM Modulator
3. Product Modulator
4. AM Detector
5. Mixer
6. Frequency Doublers.
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