LAB MAUNAL FOR MULTI-SIM

For Analog Communication (ECP-

Paritosh Chhabra
GEC-1731579
 LIST OF EXPERIMENTS

1. To study the AM waveform generated from AM source in MULTI-SIM and measure the

modulation index by

(a) Sine wave Method (b) Trapezoidal Method

2. To study the frequency spectrum and determine the bandwidth of AM wave on MULTI-SIM.

3. To generate DSB-SC AM and DSB-F AM using Multiplier on MULTI-SIM and observe the

waveforms on C.R.O.

4. To study the FM wave generated from FM source in MULTI-SIM and measure the

modulation index by approximate method.

5. To study the amplitude spectrum and determine the bandwidth of FM wave on MULTI-SIM.

6. To generate FM signal using Voltage Control Oscillator on MULTI-SIM and observe the

waveform on C.R.O.

7. To generate PWM signal using 555 timer IC on MULTI-SIM and observe the waveform on

C.R.O.

8. To study the spectrum of pulses using spectrum analyser on MULTI-SIM.

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 INTRODUCTION TO MULTI-SIM
Multi-sim is an electronic schematic capture and simulation program, which is part of a

suite of circuit design programs, along with NI Ultiboard. Multi-sim is one of the few

circuit design programs to employ the original Berkeley SPICE based software

simulation. A company named Electronics Workbench, which is now a division of

National Instruments, originally created Multi-Sim. Multi-Sim includes microcontroller

simulation (formerly known as Multi-MCU), as well as integrated import and export

features to the Printed Circuit Board layout software in the suite, NI Ultiboard.

Multi-Sim is widely used in academia and industry for circuit education, electronic

schematic design and SPICE simulation. Multi-Sim was originally known as Electronics

Workbench and was created by a company called Interactive Image Technologies. At the

time, it was mainly used as an educational tool to teach electronics technician and

electronics engineering programs in colleges and universities. National Instruments has

maintained this educational legacy, with a specific version of Multi-Sim with features

developed for teaching electronics. In 1999, Multi-Sim was integrated with Ultiboard

after the original company merged with Ultimate Technology, a PCB layout software

company. In 2005, National Instruments Electronics Workbench Group acquired

Interactive Image Technologies and Multi-Sim was rebranded as NI Multi-Sim. The

National lnstruments Electronics Workbench Group is responsible for innovating the

electronic circuit design software NI Multi-Sim and NI Ultiboard, which was previously a

Canada-based company that first produced Multi-sim, and integrated Ultiboard with it.

The logo design for the group incorporates the initials of the groups' former company

name, "Electronics Workbench", in the form of printed circuit board tracks.

FEATURES:-

 Powerful tools to learn circuit theory.

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INITUITIVE AND EFFICIENT CAPTURE:-
Multisim combines an intuitive simulation environment with advanced capture features

to enhance development, reduce repetitive tasks, and become an asset to any circuit

designer. The true benefits of these features are easily realized in Multisim, because

they are implemented within an easy-to-use environment with intuitive interfaces. In

the majority of EDA tools tasks such as component selection, placement, and wiring are

time-intensive and laborious. Multi-Sim has been developed to break away from this

arduous mold.

Every schematic begins with the selection and placement of components, and as a

result, an engineer’s initial task is to search their capture tool’s database for specific

components. Many traditional EDA tools are lumbered with disorganized databases that

are difficult to navigate. In these tools, component selection is a hurdle in the design

process. In Multisim, all 17,000 components in the master database are logically

organized into easy-to navigate groups. These groupings reflect the type of device and

functionality, so that components such as diodes are in one group, while op-amps

populate a separate analog group. This logical organization mirrors the way most

manufacturers present their own parts libraries, providing an intuitive interface that an

engineer has encountered many times before.

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With components selected from the database, the engineer is faced with the second

fundamental task in capture: wiring together individual components.

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 EXPERIMENT - 1

AIM- TO study the spectrum of pulses using spectrum analyser on MULTISIM.

APPARATUS REQUIRED -PC AND MULTISIM Software.

THEORY -A pulse wave or pulse train is a kind of non-sinusoidal waveform that is similar

to a square wave, but does not have the symmetrical shape associated with a perfect

square wave. It is a term common to synthesizer programming, and is a typical

waveform available on many synthesizers. The exact shape of the wave is determined

by the duty cycle of the oscillator. In many synthesizers, the duty cycle can be

modulated (sometimes called pulse-width modulation) for a more dynamic timbre. The

pulse wave is also known as the rectangular wave, the periodic version of the

rectangular function.

PULSE TRAIN

The shape of pulse is determined by its duty cycle D, which is the relation between

pulse duration (t) and period (T).

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PROCEDURE

1. Run the MULTISIM Simulator “MULTISIM14.EXE “ and open the new ‘ms.14’file.

2. Save the file as ‘AM.ms.14’.

3. Collect different component from MULTISIM menu bar into Multisim page.

4. Connect them according to the circuit diagram as-

Place the two-pulse voltage source of the period of 1ms and of duty cycle, 20 %

and 50 %. Connect spectrum analyser to each source and apply the signal of

both the sources at both the channels of CRO.

5. Now run the simulation after saving changes.

6. Double click on the CRO for viewing the output waveforms.

7. Double click on the spectrum analyser for viewing the output spectrum of

PULSES.

Adjust the various controls of the oscilloscope for getting proper waveform.

WAVEFORM ON CRO

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PRECAUTION

1. At least one ground should be there in circuit.

2. Make the circuit carefully just adding by clicking on the list of instruments.

RESULT

Pulse wave is generated from Pulse source by simulation on Multi-Sim and is observed

on CRO and the spectrum on the spectrum analyser.

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 Experiment - 2

AIM:-To measure the modulation index of AM signals using the Multi-Sim software by

(a)Sine wave Method (b) Trapezoidal Method

APPARATUS REQUIRED - Multisim simulation software, PC

THEORY: - Modulation is the process by which some characteristics of carrier are varied

in accordance with the modulating signal. The frequency of sinusoidal carrier is much

higher than the modulating Signal. In Amplitude Modulation, the instantaneous

amplitude of sinusoidal high frequency carrier is varied in proportion to the

instantaneous amplitude of the modulating signal. The information in the AM signal is

contained in the amplitude variations of the carrier of the envelope .The frequency and

the phase of carrier remain constant. The envelope, or boundary, of the amplitude-

modulated signal embeds the information-bearing signal. A nonlinear device is used to

combine the carrier and the modulating signal to generate an amplitude-modulated

signal.

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10
MODULATION INDEX:-

It is defined as the ratio of maximum amplitude of the modulating signal to the

maximum Amplitude of the carrier signal. It is also called depth of modulation. Its

multiplication with 100 gives percentage modulation.

m = Vm/Vc

The two methods for measuring the modulation index are:

(a) Sine wave method- In sine method, we measure Amplitude corresponding to

maximum peak of AM is taken as V max (P).While Amplitude corresponding to Min

peak of AM is taken as V min (Q). Then by using Vmax (P) and Vmin (Q), we will

calculate the value of Vm and Vc as

Amplitude Modulated Carrier Wave

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12
 (b) Trapezoidal Method- in Trapezoidal method, firstly we will apply the modulating

signal on one channel of C.R.O. and modulated signal at the other channel of the

C.R.O. and C.R.O. would operate in X-Y mode. By doing this, a trapezoid is

formed on the C.R.O. screen. The larger length (arm) of the trapezoid

corresponds to 'A’ & smaller one corresponds to ‘B’.

Modulation Index is given by M= (A-B)/(A+B)

PROCEDURE:-

1. Run the MULTISIM Simulator “MULTISIM10.1.EXE" and open the new ‘.ms14’ file.

2. Save the file, as ‘AM .ms14’.

3. Collect different component from Multisim menu bar into Multisim page.

4. Connect them according to the circuit diagram as shown in fig:

(a) SINE WAVE METHOD: Connect AM source to CRO, as shown in Fig above.

5. Save the changes and run the simulation.

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 6. Observe the waveform on oscilloscope by double clicking on the icon of

oscilloscope.

7. Take Readings of Vmax & Vmin.

(b) TRAPEZOIDAL METHOD: Connect AM source to channel A of CRO & connect

Function generator of similar frequency, as that of modulating signal to channel

B of CRO, shown in diagram above.

8. Now run the simulation after saving changes.

9. Adjust CRO settings & view Wave shapes in AB mode.

10. In case of Trapezoidal method note down, values of ‘2Vmax’ & ‘2Vmin’.

OBSERVATIONS AND CALCULATION:-

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A. SINE WAVE METHOD

Vmax = 7.305 V Vmin = 2.277 V

m= (Vmax - Vmin)/ (Vmax + Vmin) = 5.028/10.056 = 0.5

B. TRAPEZOIDAL METHOD

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 Vmax = 14.015 V

Vmin = 6.146 V

m= (Vmax -Vmin)/ (Vmax +Vmin)

= 0.39

PRECAUTIONS:-

1. At least one ground should be there in the circuit.

2. Make the circuit carefully just adding by clicking on the list of instruments.

3. CRO setting must be done carefully so that Wave shapes can be observed properly.

RESULT:-

AM wave is generated from AM source by Simulation on Multisim & is observed on CRO.

The value of modulation index is also calculated. Modulation index as from

source=Calculated by Sine method=Calculated by Trapezoidal Method=0.75

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 Experiment - 3

AIM: To observe the frequency spectrum and measure the bandwidth of AM signal on

Multi-Sim software.

APPARATUS REQUIRED - Multisim Simulation software, PC

THEORY:

The Expression for the amplitude modulated signal can given by the formula shown

below:

VAM = Vcsinωct + mVcsinωct sinωmt

= Vcsinωct + mVc/2 sin(ωc-ωm)t + mVc/2 sin(ωc + ωm)t

It is clear from the above expression that a sinusoidal modulated wave consists of a

carrier wave of amplitude Vc and a pair of sidebands.

The mathematical expression for this complex wave shows that it is the sum of three

sinusoids of different frequencies.

One of these sinusoids has the same frequency and amplitude as the unmodulated

carrier. The second sinusoid is at a frequency equal to the sum of the carrier frequency

and the modulation frequency; this component is the upper sideband. The third

sinusoid is at a frequency equal to the carrier frequency minus the modulation

frequency; this component is the lower sideband. The two-sideband components have

equal amplitudes, which are proportional to the amplitude of the modulating signal.

Figure shows the carrier and sideband components of the amplitude modulated wave

of Figure as they appear in the frequency domain (amplitude versus frequency).

AM FREQUENCY SPECTRUM:

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BANDWIDTH OF AN AM WAVE:-

An ideal carrier wave contains a single frequency and occupies very little of the

frequency spectrum. When the carrier is amplitude modulated, sideband frequencies

are generated both above and below the carrier frequency. This causes the signal to use

up a greater portion of the frequency spectrum. The amount of space in the frequency

spectrum required by the signal is called the BANDWIDTH of the signal.

It is given by 2fm (where fm is the frequency of the modulating signal).

CIRCUIT DIAGRAM:-

PROCEDURE:-

1. Run the Multi-Sim Simulator "Multi-sim14.EXE" and open the new ‘.ms10’ file.

2. Collect different component from Multi-Sim menu bar into MULTISIM page.

3. Connect according to the circuit diagram as:

Take an AM source and connect its output to the Spectrum Analyser.

4. Save the changes and run the simulation.

5. Observe the waveform on the spectrum analyser by double clicking on its icon.

6. By proper setting of the parameters of the Analyser, Adjust the waveforms such

that the readings can be taken easily.

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 7. There are three frequency components; now measure the frequency of the

component present at the leftmost side i.e. lower side band by placing the

pointer of the analyser on it.

8. Similarly measured the frequency of the upper sideband by placing cursor on

rightmost side frequency component.

WAVEFORMS:-

CALCULATIONS AND OBSERVATIONS:-

fmax = 55.215 kHz

fmin = 45.132 kHz

Bandwidth = fmax-fmin = 55.215 – 45.132 = 10.083 kHz

This is the theoretical Bandwidth and practically we have seen that the sidebands are

not only single freq. components they are the frequency bands and the band ends at

some other frequency from central frequency.

This also shows that Frequency spectrum of am signal is continued.

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PRECAUTIONS:-

1. At least one ground should be provided in the circuit.

2. Make the circuit carefully just adding by clicking on the list of instruments.

RESULT:-

The frequency spectrum of AM wave is perfectly studied and results shows that Freq.

spectrum of am signal is continues in a particular time range. In addition, the bandwidth

for the AM signal is Bandwidth: 10.083 kHz.

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 Experiment - 4

AIM: To generate DSB-SC AM using multiplier on Multisim and observe the waveform

on the CRO.

APPARATUS REQUIRED - Multi-Sim simulation software, PC

THEORY:

The simplest modulation method to implement is DSB, in which the translated

spectrum of the message signal is transmitted without further modification. The

modulated waveform Xc(t) is.

Xc(t) =Acx(t) cos(2πfct) where spectrum is Xc(f)=Ac{ X (f+fc) + X (f-fc) }

The message signal is usually referred to as the baseband signal and the spectral range

that occupies is called the baseband frequency range. In communication systems, the

baseband Signal is limited in frequency to a bandwidth of f x Hz, and the carrier

frequencies much higher than fx.

The spectral components of the baseband signal that occupy the positive side of the

frequency axis appear in the range f c to fc+fx in the spectrum of the DSB signal, this

portion of the spectrum is called the upper sideband. Similarly, the spectral

components of the baseband signal that occupy the negative side of the frequency axis

are translated to the lower sideband of the spectrum of the DSB signal in the frequency

range fc-fx to fc. Hence the (one-sided) spectrum consists of two sidebands that occupy

the frequency range fc-fx to fc+fx and therefore the bandwidth required for transmission

is

BT= 2f

For DSB-SC:-

Double-sideband suppressed-carrier transmission (DSB-SC) is transmission in which

frequencies produced by amplitude modulation AM are symmetrically spaced above

and below the carrier frequency and the carrier level is reduced to the lowest practical

level ideally being completely suppressed.

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In the DSB-SC modulation unlike. in AM the wave carrier is not transmitted thus much of

the power is distributed between the Sidebands which implies an increase of the cover

in DSB-SC, compared to AM for the same power used. DSB-SC transmission is a special

case of DSB-SC. It is used for radio data transmission.

GENERATION

DSB-SC is generated by a mixer. This consists of a message Signal multiplied by a carrier

signal. The mathematical representation of this process is shown below, where the

product to sum trigonometric identity is used.

CIRCUIT DIAGRAM

PROCEDURE:

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1. Run the MULTISIM Simulator "MULTISIM14.EXE" and Open the new ‘.ms14’ file_

2. Collect different component from MULTISIM menu bar into MULTISIM page.

3. Connect according to the Circuit diagram as:

Take an AM source and connect its output to the CRO.

4. Save the changes and run the simulation.

5. Observe the waveform on the CRO by double clicking on its icon.

6. By proper setting of the parameters of the CRO, Adjust the waveforms such that

the readings can be taken easily.

WAVEFORM

PRECAUTIONS:-

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1. At least one ground should be there in the circuit.

2. Make the circuit carefully just adding by clicking on the list of' instruments.

3. CRO setting must be done carefully so that Wave shapes can be observed

properly.

RESULT:

Hence, we have observed the waveform of DSB-SC AM generation on CRO by using

Multi-Sim.

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 Experiment - 5

AIM: To study the FM wave generated from FM source in MULTISIM and measure the

modulation index by approximate method.

APPARATUS REQUIRED - PC AND MULTISIM Software.

THEORY:-

The purpose of this simulation is to demonstrate the characteristics and operation of a

simple Frequency modulator and detector.

In analog frequency modulation, such as FM radio broadcasting of an audio signal

representing voice or music, the instantaneous frequency deviation, the difference

between the frequency of the carrier and its centre frequency, is proportional to the

modulating signal. The modulation index and deviation ratio for FM are two of the

major ones used. These appear to be very similar to each other but they are subtly

different. In view of the slight differences between the definitions for PM modulation

index and FM deviation ratio, there is often confusion between the two terms.

APPROXIMATION METHOD FOR CALCULATING BANDWIDTH:-

Approximation method for calculating bandwidth of FM signal state that a good

approximation of the bandwidth of PM can be made by taking bandwidth as twice the

sum of the deviation and the highest Modulating frequency. However, it must me

remember that it is just an approximation.

B.W. = 2(deviation+ modulating frequency)

CIRCUIT DIAGRAM

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 PROCEDURE

1. Run the MULTISIM Simulator MULTISIM14.EXE and open the new ‘ms.14’file.

2. Save the file as ‘AM.ms14’.

3. Collect different component from MULTISIM menu bar into Multisim page.

4. Connect them according to the circuit diagram as:

Place the FM generation source .And connect spectrum analyser to source and apply

the signal of the sources at the channel of CRO.

5. Now run the simulation after saving changes.

6. Now, double click on the CRO for viewing the output waveforms.

7. Now, double click on the spectrum analyser for viewing the output spectrum of

FM generation.

8. Adjust the various controls of the oscillator for getting proper waveform.

WAVEFORM ON CRO

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OUTPUT OF SPECTRUM ANALYSER

PRECAUTION

1. At least one ground should be there in circuit.

2. Make the circuit carefully just adding by clicking on the list of instruments

RESULT

FM Signal is generated from FM source by simulation on Multisim and is observed

on CRO & the spectrum on the spectrum analyser. In addition, find the

approximated bandwidth = 1200 Hz.

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 Experiment - 6

AIM:-To study the frequency spectrum and determine the bandwidth of FM wave on

Multi-Sim

APPARATUS REQUIRED -Multisim Simulation software, PC.

THEORY-In frequency modulation frequency of the carrier is varied accordance with

the amplitude of the modulating signal.

As the equation of FM is a sine of sine function, thus its bandwidth can be calculated

by the use of Bessel functions. The Bessel functions are generally the coefficients J 0,

J1, J2, J3….

The equation for the frequency modulation using the Bessel functions is shown

below:

VC- {J0(M) cos ωct + J1(M)[cos(ωc + ωm)t - cos(ωc - ωm)t] + J2(M)[cos(ωc + 2ωm)t - cos(ωc -

2ωm)t] + J3(M)[cos(ωc + 3ωm)t - cos(ωc - 3ωm)t]

Thus above expression shows that fm has an infinite number of sidebands thus the

theoretical bandwidth of fm is infinite but due to the Bessel functions only the

significant side bands are considered.

Value of j coefficients from the table is given by:

Value of J coefficients

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DEVIATION:-

The amount by which carrier frequency changes from 1ts unmodulated value is known

as deviation (δ). The rate at which the frequency Variation takes place is called

modulating frequency.

MODULATON INDEX: -

Modulation index m = δ / fm.

Modulation Index decides the bandwidth of FM wave and hence significant sidebands.

Its value can be greater than one.

CIRCUIT DIAGRAM

PROCEDURE

1. First, run the MULTISIM Simulator "MULTISlM14.EXE” and open the new '.ms14'

file.

2. Collect different components from MULTISIM menu bar into MULTISIM page.

3. Connect according to the circuit diagram as:

Connect the FM source to CRO as shown in figure above.

4. Save the changes and run the simulation.

5. Observe the waveform on oscilloscope by double clicking on the icon of

oscilloscope.

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 6. Observe the number of sidebands created and save the output.

OUTPUT OF SPECTRUM ANALYSER

OBSERVATION AND CALCULATION

fc = 60 kHz

fm = 5 kHz.

Deviation = fm δ = 15 x 5 = 75 kHz

Band Width = 2 (75 +5) = 2 * 80 = 160 kHz.

PRECAUTIONS:-

1. Connections should be made as per circuit diagram.

2. Proper values should be set.

3. Readings should be taken with great care.

RESULT:-

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Hence, we have studied the frequency spectrum of the FM wave on the spectrum

analyser and the bandwidth of the signal is 160 kHz.

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 Experiment - 7

AIM- To generate FM signal using Voltage Control Oscillator on MULTISIM and observe

the waveform on C.R.O.

APPARATUS REQUIRED - PC loaded with MULTISIM Simulator.

THEORY: In analog frequency modulation, such as FM radio broadcasting of an audio

signal representing voice or music, the instantaneous frequency deviation, the

difference between the frequency of the carrier and its center frequency, is

proportional to the modulating signal.

A voltage-controlled oscillator or VCO is an electronic oscillator whose frequency is

changing linearly with an input voltage. The applied input voltage determines the

instantaneous oscillation frequency. It is used to perform direct frequency modulation

on signals. VCO has a central frequency FC and input control voltage m(t) modulates the

instantaneous frequency around the central frequency. Consequently, modulating

signals applied to control input may cause frequency modulation (FM) or phase

modulation (PM). A VCO may also be part of a phase-locked loop.

CIRCUIT DIAGRAM

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PROCEDURE

1. Run the MULTISIM Simulator “MULTISIM14.1EXE “and open the new ‘ms.14’ file.

2. Collect different component from MULTISIM menu bar into Multisim page.

3. Connect them according to the circuit diagram as:

4. Take the VCO, apply sine wave signal to its input terminal by using function

generator and

5. Apply its output to the oscillator for observation purpose.

6. Now run the simulation after saving changes.

7. Now, double click on the CRO for viewing the output waveforms.

8. Double click on the spectrum analyser for viewing the output.

WAVEFORM ON CRO

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 OUTPUT OF SPECTRUM ANAYLSER

PRECAUTIONS

1. Make the circuit carefully by adding components and instruments.

2. CRO setting must be done carefully so that wave shapes can be obtained

properly.

RESULT

Hence, we have seen that a frequency modulated wave can be generated using

Voltage Control Oscillator.

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 Experiment - 8

AIM:-To set up the circuit of pulse width modulation using IC-555 on MULTISIM

software.

APPARATUS REQUIRED - MULTISIM, PC.

THEORY

PULSE WIDTH MODULATION

Pulse width modulation is also known as PDM (Pulse duration modulation). In this

system the carrier signal is a train of pulses and we have fixed amplitude and

starting time of each pulse is made proportional to the amplitude of the signal at

that instant.

GENERATION OF PWM:

Pulse width signal is generated by applying trigger pulses to control the starting time

of pulses from a mono-stable multi-vibrator and feeding in the signal to control the

duration of these pulses.

CIRCUIT DIAGRAM:-

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 PROCEDURE

1. Run the MULTISIM Simulator “MULTISIM14.EXE" and open the new ‘.ms14’ file.

2. Save the file as ‘AM.ms14’.

3. Collect different component from MULTISIM menu bar into MULTISIM page.

4. Connect them according to the circuit diagram as:

Select 555 from the component list and connect it to work as a mono-stable multi-

vibrator. Apply audio signal at its control voltage terminal.

5. Save the changes and run the simulation.

6. Now, double click on the CRO for viewing the output waveforms.

7. Adjust the various controls of the oscilloscope for getting proper waveform.

WAVEFORM

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RESULT

Hence, we have generated PWM signal by using 555 timer and have observed the

waveform on CRO.

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