R,B.V.R.R. Women,s College

(Autonomous)

A College with potential for Excellence

Accredited by NAAC with Grade ,A,

Narayanaguda, Hyderabad_500 029.

DEPARTMENT OF' ELECTRONICS CERTIFICATE

certified that this is a Bonofide record work done

in this loboratory during the year 20 _ 20 Name:

H.T. No.:.

Batch: Date: Subject: Electronics Paper IV: Analog Communication

Lecturer Incharge External Examiner INDEX

Particulars of the Experiments performed

S.No. Name of Experiment Page Date of Date of Remarks Experiment Submission

t: 1. MONOSTABLE MULTIVIBRATOR USING OP.AMP

AIM: To study Monostable multivibrators using op-amp and determine its pulse width.

APPARATUS:

1. Monostable multivibrators using op-amp trainer.

2. CRO

3. Connecting wires

THDORYi {'

Multivibrators are used extensively in pulse systems. There are three types:

1. Astable multivibrators (free running)

2. Monostable multivibrators (one shot) 3. Bistablemultivibrators(flip-flop)

MONOSTABLE MULTIVIBRATOR:

The connection of a in parallel with the timing in an astable multivibrator circuit may be used to prevent the phase inverting input terminal of the from going positive, this gives monostable multivibrator circuit.

It is known that monostable multivibrator has only one stable state. It can made to change its other state by the application of triggering pulse, but it then returns to its stable state after a time interval determined by circuit values.

In the stable state of this circuit the amplifier output is at positive saturation, terminal b is clamped to earth by diode Dr and terminal a is positive with respect to earth by an amount FVo" + where p has been defined previously. Rs is assumed to be greater at the terminal a is brought down to earth by the application a sufficiently large negative pulse the circuit regeneratively to its quasi-stable state when the potential at a reaches Vn. Waveforms are illustrated as in figure. The expression for timing period can be I

easily written down similar to previous circuit analysis. State in which the amplifier output is in negative saturation. Terminal a is then negative with respect to earth by an amount FVo" - and the potential at terminal b falls exponentially as capacitor C discharges through R and diode Dr is reverse biased. The circuit switches back to its stable state when the potential at terminal b reaches the value FV""' . The input trigger pulse, voltage waveform and the waveforms at terminals are shown in flrgure. The capacitor charging through R starts from zero voltage and continues up to FVo" - . The final value of voltage, if charging is continued, will be V""- . Therefore the charging period is given by

a T= RC In (Vos-- O) / (Vr"-- BVo" -) I/ CIRCUILDIAGRAM:

+Ue*x+{S,U -\*s$=*"lSV

PROCEDURE: 1. Connect the circuit as shown in circuit diagram. 2. Connect the given in the space provided. 3. Observe the waveforms for Monostable Multivibrator and find the pulse width using the formula

#:fllt il ffitr WAVEFORMS:

l, 1

OBSERVATIONS:

RESULT: The action of Monostable multivibrators using op-amp is studied and its pulse width is calculated. AIM: To study the Astable multivibrator using 555 timer. APPARATUS:

1. Astable multivibrator using 555 trainer. 2. CRO

3. BNC probes

4.TConnecting wires. a,

THEORY:

A multivibrator produces non-sinusoidal voltages that are very rich in harmonics. It produces pulsating output waveform of square, rectangurar, ramp voltage as required in different applications. There are three types of multivibrators. They are

1. The Astable Multivibrator or Free running multi. 2. The Monostable Multivibrator or one-shot Multi.

3. The Bistable Multivibrator or TWo shot Multi or Flip-Flop.

An Astable multivibrator, also known as free running multivibrator nothing is but an oscillator that generates a continuous train of rectangular pulses' These waves are required to control the timing circuits. These multivi- brator circuits can be designed using an op-Amp. The astable multivibrator has two quasi stable states, but it will not have a permanent state. Automatically it changes from one state to another state after certain period. Here 555 Timer is used as Astable multivibrator. The 555 timer has range wide of useful applications. A sample of these applications includes monostable and Astable multivibrators, waveforms generators, Analog frequency meters, Burglar alarms, voltage regulators etc., this can produce 5

accurate and highly stable time delays or oscillations. Like general purpose op- amp the 555 timer is reriable, easy to use and economicar. The figure shows the 555 timer connected for astable (free-running) operation' when Q is low, the is cut-off and the capacitor is charging through a total resistance of Ra + Re. Because of this, the charging time constant is (Ra+Re)c. As the capacitor charges, the threshold voltage increases. Eventually, the threshold voltage exceeds +2y"./3i then the upper comparator has a high output, and this sets the flip-flop. with e high, the transistor saturates and grounds pin T. Now the capacitor discharges through- Rs. Therefore, the discharging time constant is ReC. When the capacitor voltage drops s_lightly,below +v""/3, the rower comparator has a high output and this a. resets the flip-flop.

sQ

HQ

The figure illustrates the waveforms. The timing capacitor has an exponentially rising and falling voltage. The output is a rectangular wave. since the charging time constant is larger than the discharging time constant, the output is not symmetrical; the high output states last longer than the low_output state. 6

A mathematical solution to the charging and dischargrng equations gives the following formulas:

The output frequency is f =

and the Duty cycle is D= xLOOo/o - If Re is much smaller than Re, the duty cycle approaches 50 percent. An astable 555 timer is often called a free-running multivibrator because it produces a continuous train of rectangular pulses. { a, CIRCUIT DIAGRAM:

Sntput Ground vcc

Trigger Discharge

0utput Thresholtl

Reset Controt Uottrge

WAVEFORMS:

1., .l '* l'"

CAFICTTOft cl{Af&Es + Tt+ao{rGH (Br + I Rel r" 2I3Vsc 'o'* I

c *p,"ctto r c* t ;r,J;-lilr* 7

PROCEDURE: 1. on Astable Multivibrator using -s55 trainer. 2' Connect the circuit as per the circuit diagram by using external and capacitors. 3. connect the channel 1 of cRo to the output terminal of 555 timer. 4. observe the output waveform on channel 1 of cRo. 5' Observe the waveform across capacitorI ------on chann eI2 of CRO aL (C) terminals. vr\v at the capacitor

6. Calculate the output frequencSr from the output waveforms. t' 7. compare piacticar and theoretical varues Frequencies. OBSERVATIONS:

RESULT: The action of Astable multivibrators using 555 timer is studied and its frequency is calculated demonstrate AlMiTo the op-amp as an integrator.

APPARATUS: 1.) op-amp (t}74t)

2) Decade resistance boxes-2 3) Signalgenerator 4) Mu,ltimeter

5) patch cords 6) cno

THEOBY: A circuit that performs the mathematical integration of the input signar is cared lntegrator as and is connected as shown in figure which is an op-amp integrator circuit. rt is the modification and input resistor in the inverting op-amp circuit. since the output is across a capacitor it is obtained as follows .since the change stored by the capacitor is given by e = CVo

Vo= Q"/C

Differentiating on both sides we get

dvo/Ot = -Vc(de/dt)

dvo/dt = -(L/cli (t = de/dt)

t= Vi/R

,t'value Substituting get we dVo/dt = -1lRC (Vi)

lntegrating both sides we get

I dvo/dt = -VRC I Vi dt

Vo= -URC J Vi dt

Vs c 6Jt V; dt is proportionarto lil llliJlili:::::Jji:[:'ff::ve the time integrar orthe input signar

The product Rc is referrelJ to as integrator a time constant and since it invotves op-amp' the circuit is known irre output vortage as active exhibits a triangurar The waye form. critical frequency of integrator is F, = l/ZnRF, CIRCUIT DIAGRAM

1) Connect the intesratnr eira,,i+ peak to n..u ,,riiiI:1[Tl;ffij::*nction ,.nu,..::lto produce a square r wave aneously output -' or Iv Vo & Vi is viewed.

:H o d t r i a n g u, ilIJ:lT :jllffi' a r wa ve ro r m M ff ffi :H T-ff ;T;n* e a s u re t h e 3) verify the following relationship between Ri< F and input frequency f for good integrator. F > F,l/RrCr

4) Now set the funct. Adiust wave or 1v peak trre rrequen;;rlJil[::T;'e to peak and 5oHz rrequency. te output is negative going cosine wave, 5) Measure the frequency and ampritude of the input and output waveforms. ,orr ro**,

OBSERVATIONS

RESUTT: The action of op-amp as integrator is studied. Al{vl;-To demonstrate the op-amp as differentiator.

APPARATUS:

1) op-Amp (tcr4L)

2) Pecade resistance boxes-2 I, 3) Signal generator 4)Multimeter

5) Patch cords 6) cRo

TqEoRY: ln the integrator circuit if the position of R and c are interchanged (Ro=x, Ri=c) then it acts as a differentiator' The circuit that perform mathematical differentiator of the input signal is known as differentiator, the output voltage Vo is given by

Vo=_iRIi=cdv,/dtJ

Vo= -RC dvildt

Vo o dv;/dt ___-__1

RC = T = time constant of the differentiator from equation 1 we see that the output voltage is proportional to the time derivative of the input. Hence it is known as differentiator Circuit. CIRCU!T DIAGRAM

{l --l I F'"trd

PROCEDURE:

1} connect the differentiator circuit . Adjust the signal generator to produce a 5v peak sine wave at 100H2.

2) observe input v1 and output voltage vo simultaneously on the osciiloscope. Measure the peak value of Vo, record it phase and angle of Vo with respect to V;.

3) Repeat step2 while increasing the frequency of the input signal. Find the maximum frequency at which the circuit performs differentiator. compare it with the calculated value of Fa

WAVEFORMS: OBSERVAT!ONS

RESULT: The action of the op-amp as a differentiator is studied. s.OP-AMP AS A WINDOW CAMPARATOR

!!ETo demonstrate the op-amp as a window comparator

APPARATUS:

1)Op-Amp trainer kit

2) Connecting wires i l, 3)CRO wires

WIN,DOW COMPARATOR: A Comparator is a non-linear signal processor. lt is an open loop mode application of op-amp operated in saturation mode, comparator compares a signal voltage at one input with a reference voltage at the other input. Hence the op-amp is operated in the open loop mode and hence is *-Vrr1 it is basically classified as inverting comparator and non-ihverting comparator. ln a non-inverting comparator Vin is given to the positive terminals and V."r to the negative terminal. When Vin ( Vlsl the output is -Vs1 and when V;n > Vr6 the output is * Vsat. In an inverting comparator, input is given to the inverting terminal and reference is given to the non-inverting terminal.

Window comparator is obtained by connecting an inverting type comparator and a non-inverting type comparator as shown in figure,

CIRCUIT DIAGRAM:

il], ila. 1f{*14 1.4

PROCEDURE:

1) Switch on trainer.

2) By using op-amp's (324/74L) and external resistor, capacitors, , construct the circuit As shown in figure.

3) verify all the linear, non-tinear applications and characteristics of op_amp.

WAVEFORMS: OBSERVATIONS:

RESUIT: The action of op-amp as a window comparator is studied. AIM: To study amplifier modulation and demodulation

APPARATUS:

1) Amplitude modulation and demodulation trainer

2) Function generator {20 to 20M Hz) or equivalent

3) Oscillosr,f,pe (300MHz)

4) BNC probes

5) Connecting wires

THEORY: Amplitude modulation (AM) is defined as a process in which the amplitude of the carrier wave is varied about a mean value, linearly with the base band signal m(t).

An AM wave may thus be described in its most generalform, as a function of time as follows' s(t) A"[t=ka m(t]Jcos[2nF.t] = where ka - Amplitude sensitivity of the modulator

S(t)- Modulated signat

A. - Carrier amplitude

m(t)- Message signal

The amplitude of ka m{t) is always less than unity that is lka m(t) l< 1 for all t

FORMULAE: The absolute maximum value of ka m(t) multiplied by 100 is referred to as the

Percentage modulation (or)

Percentage modulation = (Vrn.* - V*in)/ (Vru, + Vmin)*100

CIRCUIT DESCRIPTION: ln amplitude modulation and demodulated trainer the IC z20G is used as a carrier generator. lt provides 100 kHz sine wave as carrier output at pin2. ln modulator section series modulation. The first transistor works as RF amplifier and second transistor as the modulator' The controls percentage the of modulation. ln this circuit it is not possible to obtain L}o% modulation. This is due to the RF amplifier junction capacitance which allows RF to feed through to the output when the transistor is normally shut off. By varying the potentiometer, percentage modulation is changed . At certain point, the AM waveform is over modulated. This causes several distortion of the output wave, diode detector is used in demodulator section, to get unmodulated output.

CIRCUIT DIAGRAM:

11; ii llt;jj i*ri:,-.i,.::...tirtl i::.ia.!:Jrit:::.:.'.il,:ai PROCEDURE:

1) Switch on the trainer and check the output of carrier generator on oscilloscope and fix the carrier frequency to 100kHz.

2) Connect around 3kHz to 10kHz with 2 volts AF signal to the AF input to the modulator circuit.

3) connect the carrier signal output at carrier input of modulator circuit.

4) Observe the modulator output signal at AM output terminal.

5) Vary the modulating frequency and amplitude , observe the effects on the modulated wave form.

6)The depth of modulation can be varied using the variable knob provided at AF input.

7) The Percentage of modulation and modulation index can be calculated using the following formulas. L9

Percentage modulation = {V*rr - V*in)/ (V,nr* * V*rn)*L00 Modulation index = (V*r* - Vmin)/ (Vra" + V*in)

8) Connect the output of the modulator to the input of the demodulator circuit and observe the output i.e., message signal.

WAVEFORMs: t_

OBSERVATIONS

EESULT: The amplitude modulation and demodulation is studied and the percentage of modulation index is calculated. T.DIODE DETECTOR

AIM: To study the demodulation of AM wave using diode detector.

APPARATUS:

1) Diode detector trainer

2)Oscilloscope

3) BNC probes

4) Connecting wires

THE0U The diode is by far the most common device used for AM demodulation or detection. The simple diode detector has the disadvantages that demodulated output voltage in addition to being proportional to the modulating voltage, also has dc component which represents the average envelope amplitude (i.e., carrier strength) and a small RF ripple. The unwanted components are removed in a practical detector.

ln this diode has been reversed so that the negative envelope is demodulated. This has no effect on detection, but it does ensure that a negative AGC voltage will be available. Here two resistors are used to ensure that there is a series dc path to ground for the diode but at the same time a low pass filter has been added in the form of R.-C, this has the function of removing any RF ripple that might still be present. Capacitor c2 is a coupling capacitor, whose Main function is to prevent the diode ac output from reaching the volume control R4. The Combination R3, -C3 pass of is lolv filter designed to remove AF components. proving a dc voltage whose amplitude is proportional to the carrier strength and which may be used for Automatic gain control. CIBCUIT DIAGRAM:

PROCEDURE;

1) switch on the trainer and check the output of carrier generator at AM output without giving external generator should observe on oscilloscope.

2) connect around 1 kHz with 2volts AF by varying frequency knob which is located on kit. Give Output of AF to input of AF.

3) observe the modulating output signal at AM output spring by making necessary changes in AF signal.

4) Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. 23

5) The depth of modulation can be varied using the variable knob (potentiometer) provided at AF input.

6) Connect the output of the modulator to the input of diode detector i.e. (AM input) circuit and observe the demodulated output.

7) Connect the output of the demodulator to the input of amplifier circuit and observe the amplitude output.

8) Now study the detector, output for applied input of over modulating and under modulation condition of the AM. WAVEFORMS: i OBSERVATIONS

RESULT: The dbmodulation of AM wave is studied by using diode detector.