Ex. No. 1 AMPLITUDE MODULATION

Aim:

To construct an Amplitude modulator using SL100 and study it’s output waveform.

Apparatus Required:

Transistor SL100, RPS(0-30V), Inductor, Capacitor, Resistor, Function Generator, CRO, Bread Board,

Connecting wires.

Circuit Diagram:

Design:

Given: Vcc = 12V,VTh=1.5V, Fc = 70KHz, Fm = 7 KHz,C=0.01µF, R2 = 10KΩ

Fc = 1/2π . So, L= 0.516 mH.

VTh =

. So, R1= 70 KΩ.

Theory:

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier

signal, with a modulating signal which typically contains information to be transmitted. The base band signal is

referred to as the modulating signal and the output of the modulation process is called as the modulation signal. In

Amplitude modulation, the amplitude of the carrier signal is varied in accordance to the modulating signal. The

envelope of the modulating wave has the same shape as the base band signal provided the following two

requirements are satisfied.

1. The carrier frequency fc must be much greater then the highest frequency components fm of the message signal m

(t) i.e. fc >> fm

2. The modulation index must be less than unity. if the modulation index is greater than unity,the carrier wave

becomes over modulated.

In radio communication, a continuous wave radio-frequency signal (a sinusoidal carrier wave) has its

amplitude modulated by an audio waveform before transmission. The audio waveform modifies the amplitude of the

carrier wave and determines the envelope of the waveform. In thefrequency domain, amplitude modulation produces

a signal with power concentrated at the carrier frequency and two adjacent sidebands. Each sideband is equal

in bandwidth to that of the modulating signal, and is a mirror image of the other. Amplitude modulation resulting in

two sidebands and a carrier is called "double-sideband amplitude modulation" (DSB-AM).

Amplitude modulation is inefficient in power usage; at least two-thirds of the power is concentrated in the

carrier signal. The carrier signal contains none of the original information being transmitted (voice, video, data,

etc.). However, it does contain information about the frequency, phase and amplitude needed to demodulate the

received signal most simply and effectively. In some communications systems, lower total cost can be achieved by

eliminating some of the carrier, thereby lowering electrical power usage even though this requires greater receiver

complexity and cost. If some carrier is retained (reduced-carrier transmission, or DSB-RC) receivers can be

designed to recover the frequency, phase, and amplitude information from this "pilot" carrier and use it in the

demodulation process. If the carrier is eliminated (Double-sideband suppressed-carrier transmission or DSB-SC) the

receiver must provide a substitute carrier, with inevitable loss of fidelity. Completely suppressing both the carrier

and one of the sidebands produces single-sideband modulation, widely used in amateur radio and other

communications applications. SSB occupies less than half the spectrum of AM so it also has greatly improved

bandwidth efficiency. In AM broadcasting, where there are many receivers for each transmitter, the full carrier is

provided to allow reception with inexpensive receivers. The broadcaster absorbs the extra power cost to greatly

increase potential audience.

Procedure:

The connections are made as per the circuit diagram.

The carrier signal is fed to the base and the modulating signal is fed to the emitter of the transistor.

The waveform of the carrier signal is obtained from CRO.

Tabulation:

S.No Parameter Amplitude(V) Time-period(ms)

1. Message signal

2. Carrier Signal

3. Modulated signal-Vmax

4. Modulated signal –Vmin

Model Graph:

Modulating wave

Vm

Carrier wave

Vc

Modulated wave

Vmax

+Vmin

-Vmin

Vmax

t(msec)

t(msec)

t(msec)

Result: The AM modulator was constructed using SL100 & the detection of the signal was obtained.

Ex. No.2 DIODE DETECTION

Aim:

To construct a Diode Detector and study it’s output waveform.

Apparatus Required:

Diode OA279, RF signal generator, Capacitor, Resistor, CRO, Bread Board, Connecting wires.

Circuit Diagram:

Theory:

The process of detection provides a means of recovering the modulating Signal from modulating signal.

Demodulation is the reverse process of modulation. The detector circuit is employed to separate the carrier wave and

eliminate the side bands. Since the envelope of an AM wave has the same shape as the message, independent of the

carrier frequency and phase, demodulation can be accomplished by extracting envelope. An envelope detector is an

electronic circuit that takes a high-frequency signal as input and provides an output which is the envelope of the

original signal. The capacitor in the circuit stores up charge on the rising edge, and releases it slowly through the

resistor when the signal falls.The simplest form of envelope detector is the diode detector which is shown above. A

diode detector is simply a diode between the input and output of a circuit, connected to a resistor and capacitor in

parallel from the output of the circuit to the ground. If the resistor and capacitor are correctly chosen, the output of

this circuit should approximate a voltage-shifted version of the original (baseband) signal. A simple filter can then

be applied to filter out the DC component.

Procedure:

The circuit is connected as per the circuit diagram.

The output from the RF signal generator is fed as the input to the diode detector circuit.

This output of the detector is fed t the CRO.

The CRO is fed to dual mode to see the modulated and the message signal simultaneously

Tabulation:

S.No Parameter Amplitude(V) Time-period(ms)

1. Modulated signal-Vmax

2. Modulated signal –Vmin

3. Demodulated signal

Model Graph: Modulated wave

Vmax

+Vmin

-Vmin

Vmax

De-modulated wave

Vm

Result: The Diode detector was constructed and the demodulated signal is obtained.

t(msec)

t(msec)

Ex. No. 3 FREQUENCY MODULATION

Aim:

To study the circuit of frequency modulation.

Apparatus required:

IC 2206, Capacitors, Resistors, Capacitors, Audio oscillators, DSO, Bread board, Connecting wires.

Circuit Diagram:

Theory:

The modulation systems, namely angle modulation in which the angle of the carrier wave is varied

according to the Base band signals. In this method of modulation, the amplitude of the carrier wave is maintained

constant. There are two common forms of angle modulation, namely phase modulation and frequency modulation.

FM is widely used for broadcasting music and speech, two-way radio systems, magnetic tape-recording systems and

some video-transmission systems. In radio systems, frequency modulation with sufficient bandwidth provides an

advantage in cancelling naturally-occurring noise.

Frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous

frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its

frequency remains constant Frequency Modulation is the process in which the frequency of the carrier signal is

varied by the modulating signal while the amplitude remains constant. The big advantage of frequency modulation is

its noise reduction ability, because most of noise is appeared as additional amplitude and in FM the amplitude of

signal is hold fixed. The modulation index is a measure of radian phase shift of the modulated FM signal compared

to the phase of the un-modulated carrier alone. In most communications systems using FM, maximum limits are put

on both the frequency deviation and modulating frequency.

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech. Normal

(analog) TV sound is also broadcast using FM. Narrowband FM is used for voice communications in commercial

and amateur radio settings. In broadcast services, where audio fidelity is important, wideband FM is generally used.

Procedure:

The connections are given as per the circuit diagram.

The FM wave is obtained by feeding the modulating signal to the integrator circuit that is designed.

The output of the integrator is given to the input of the phase modulation kit whose output is the FM signal

and the output is observed in the oscilloscope.

The graph is plotted from the output reading .

Tabulation:

INPUT

OUTPUT

AMPLITUDE(V) Vin Vc Vo(+Vc to -Vc)

TIME(s)

Model graph:

Result:

The circuit of the frequency modulation is studied and the graph is plotted.

Ex.No.4 PRE-EMPHASIS AND DE-EMPHASIS

Aim:

To design pre-emphasis and de-emphasis circuit to reduce the noise component in the communication

channel and to study its frequency response.

Apparatus Required:

Transistor BC547, Audio amplifier, CRO, Capacitors, Resistors, Inductor, Regulated Power Supply, Bread Board.

Circuit Diagram:

Pre-emphasis:

De-emphasis:

Theory:

In processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within

a frequency band) the magnitude of some (usually higher) frequencies with respect to the magnitude of other

(usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of

such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system. The

mirror operation is called de-emphasis, and the system as a whole is called emphasis. Pre-emphasis is achieved with

a pre-emphasis network which is essentially a calibrated filter. The frequency response is decided by special time

constants. The cut off frequency can be calculated from that value. Pre-emphasis is commonly used

in telecommunications, digital audio recording, record cutting, in FM broadcasting transmissions, and in displaying

the spectrograms of speech signals.

In high speed digital transmission, pre-emphasis is used to improve signal quality at the output of a data

transmission. In transmitting signals at high data rates, the transmission medium may introduce distortions, so pre-

emphasis is used to distort the transmitted signal to correct for this distortion. When done properly this produces a

received signal which more closely resembles the original or desired signal, allowing the use of higher frequencies

or producing fewer bit errors. Pre-emphasis is employed in frequency modulation or phase modulation transmitters

to equalize the modulating signal drive power in terms of deviation ratio. The receiver demodulation process

includes a reciprocal network, called a de-emphasis network, to restore the original signal power distribution.

In telecommunication, de-emphasis is the complement of pre-emphasis, in the anti noise system called

emphasis. Emphasis is a system process designed to decrease, (within a band of frequencies), the magnitude of some

(usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve

the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation differences or

saturation of recording media in subsequent parts of the system. Special time constants dictate the frequency

response curve, from which one can calculate the cut off frequency. Pre-emphasis is commonly used in audio digital

recording, record cutting and FM radio transmission.

In serial data transmission, de-emphasis has a different meaning, which is to reduce the level of all bits

except the first one after a transition. That causes the high frequency content due to the transition to be emphasized

compared to the low frequency content which is de-emphasized. This is a form of transmitter equalization; it

compensates for losses over the channel which are larger at higher frequencies. Well known serial data standards

such as PCI Express, SATA and SAS require transmitted signals to use de-emphasis.

Procedure:

Connections are made as shown in the circuit diagram.

First connect the audio oscillator directly to the CRO and note down the input voltage.

Now the signal generator and the CRO are connected to the circuit.

In this circuit, BC147 is enabled using a 18v supply which is set using a regulated power supply.

Now the output is taken by varying the frequency.

The gain is calculated using the formula 20 log (Vo/Vin )

Tabulation for Pre-emphasis:

Frequency (Hz) Output Voltage(Vo) Gain= 20 log (Vo/Vin ) dB

Tabulation for De-emphasis:

Frequency (Hz) Output Voltage(Vo) Gain= 20 log (Vo/Vin ) dB

Model Graph:

Result:

Thus the design of Pre-emphasis and De-emphasis are obtained and its frequency response is plotted on the

graph.

Ex. No.5 PULSE AMPLITUDE MODULATION

Aim:

To construct the pulse amplitude modulation circuit and to plot its output waveform.

Apparatus Required:

Audio Oscillators, CRO, BY-127 diode, BFW11 JFET, BC177 BJT, Resistors, Power Supply, Bread Board.

Circuit Diagram:

Theory:

Pulse-amplitude modulation, acronym PAM, 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

amplitudes of a train of carrier pulses are 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 modulated 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.

Pulse-amplitude modulation has also been developed for the control of light-emitting diodes (LEDs),

especially for lighting applications. LED drivers based on the PAM technique offer improved energy efficiency over

systems based upon other common driver modulation techniques such as pulse-width modulation (PWM) as the

forward current passing through an LED is relative to the intensity of the light output and the LED efficiency

increases as the forward current is reduced. Pulse-amplitude modulation LED drivers are able to synchronize pulses

across multiple LED channels to enable perfect colour matching. Due to the inherent nature of PAM in conjunction

with the rapid switching speed of LEDs it is possible to use LED lighting as a means of wireless data transmission at

high speed.

Procedure:

Make the circuit connections as shown in the figure.

Switch ON the power supply.

Set the signal generator, which generates a sinusoidal signal (modulating signal fm) at a low frequency.

The frequency of this message signal is kept at least 10 times lesser than the carrier signal.

Set the signal generator, which generates square pulses at least 10 times greater than the message signal.

This will act as the carrier signal.

This carrier signal modulates the message signal and the ratio of carrier frequency to the message signal

frequency will determine the number of pulses that will appear on the CRO. Thus we will get the Pulse

Amplitude Modulated waveform in the CRO.

Different graphs are plotted for time vs amplitude.

The above steps can be repeated for different values of fm and fc.

Tabulation:

Waveform Amplitude Time Period Frequency

Message Signal

Carrier Signal

Modulated(output) signal

Number of Pulses: fc/ fm

Model Graph:

Modulating Signal:

Carrier Signal:

Output Signal:

Result:

Thus the pulse amplitude modulation circuit was constructed and its output waveform is plotted.

Ex. No. 6 IF AMPLIFIER

Aim:

To construct an IF amplifier circuit and to find out the peak frequency response.

Apparatus Required:

IF amplifier kit, Function Generator 1 MHz, Dual Trace Oscilloscope, 20 MHz.

Circuit Diagram:

Theory:

In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a

carrier frequency is shifted as an intermediate step in transmission or reception. The intermediate frequency is

created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a

signal at the difference or beat frequency. Intermediate frequencies are used in super heterodyne radio receivers, in

which an incoming signal is shifted to an IF for amplification before final detection is done.

Conversion to an intermediate frequency is useful for several reasons. When several stages of filters are used, they

can all be set to a fixed frequency, which makes them easier to build and to tune. Lower frequency transistors

generally have higher gains so fewer stages are required. It's easier to make sharply selective filters at lower fixed

frequencies.

The main reason for using an intermediate frequency is to improve frequency selectivity. In communication circuits,

a very common task is to separate out or extract signals or components of a signal that are close together in

frequency. This is called filtering. Some examples are, picking up a radio station among several that are close in

frequency, or extracting the chrominance subcarrier from a TV signal. With all known filtering techniques the filter's

bandwidth increases proportionately with the frequency. So a narrower bandwidth and more selectivity can be

achieved by converting the signal to a lower IF and performing the filtering at that frequency.

Perhaps the most commonly used intermediate frequencies for broadcast receivers are around 455 kHz for AM

receivers and 10.7 MHz for FM receivers. In special purpose receivers other frequencies can be used. A dual-

conversion receiver may have two intermediate frequencies, one higher one to improve image rejection and a

+Vcc

second, lower one, for desired selectivity. A first intermediate frequency may even be higher than the input signal,

so that all undesired responses can be easily filtered out by a fixed-tuned RF stage.

Modern satellite television receivers use several intermediate frequencies. The 500 television channels of a typical

system are transmitted from the satellite to subscribers in the Ku microwave band, in two sub bands of 10.7 - 11.7

and 11.7 - 12.75 GHz. The downlink signal is received by a satellite dish. In the box at the focus of the dish, called a

low-noise block down converter (LNB), each block of frequencies is converted to the IF range of 950 - 2150 MHz

by two fixed frequency local oscillators at 9.75 and 10.6 GHz. One of the two blocks is selected by a control signal

from the set top box inside, which switches on one of the local oscillators. This IF is carried into the building to the

television receiver on a coaxial cable. At the cable company's set top box, the signal is converted to a lower IF of

480 MHz for filtering, by a variable frequency oscillator. This is sent through a 30 MHz band pass filter, which

selects the signal from one of the transponders on the satellite, which carries several channels. Further processing

selects the channel desired, demodulates it and sends the signal to the television.

Procedure:

Connect the unit to AC mains 230V, 50 Hz supply.

Switch ON the mains switch. The neon lamp will glow indicating that the unit is ready for

experimentation.

Connect the function generator with sine signal as input across terminals marked ‘INPUT’.

Set the amplitude to a predefined level of 40 mVp-p(peak to peak) and this amplitude is to be maintained in

the same level for all values of input frequencies.

Observe the output amplitude in an Oscilloscope across the terminals marked ‘OUTPUT’.

Vary the frequencies and note down the corresponding output voltages.

Tabulate the readings.

Tabulation:

Sine signal – Input amplitude (Vi) = 40 mVp-p

Frequency Output Voltage Gain=Vo/Vi Gain in dB =

20 log Vo/Vi

Model Graph:

Result:

The output of IF amplifier is verified by using IF amplifier trainer kit.

Ex. No. 7 ATTENUATORS

Aim: To design the π–type, T-type and Lattice type network and to find the attenuation of the network.

Apparatus Required:

Resistors, RPS, Function generator, CRO, Multimeter.

Circuit Diagram:

∏ – Type Attenuator:

T-Type Attenuator:

R1

Signal

Generator Rs

Vs

R2 R2 R0 V0

R1 R1

R2 R0

RPS

V0

Lattice Type:

Design:

π – Type:

T- Type:

Lattice Type:

R1

Signal

Generator Rs

Vs

R1

R2 R2 R0 V0

Theory:

An attenuator is an electronic device that reduces the power of a signal without appreciably distorting its

waveform. An attenuator is effectively the opposite of an amplifier, though the two work by different methods.

While an amplifier provides gain, an attenuator provides loss, or gain less than 1. Attenuators are usually passive

devices made from simple voltage divider networks. Switching between different resistances forms adjustable

stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely

matched low VSWR resistance networks are used.

Fixed attenuators in circuits are used to lower voltage, dissipate power, and to improve impedance

matching. In measuring signals, attenuator pads or adaptors are used to lower the amplitude of the signal a known

amount to enable measurements, or to protect the measuring device from signal levels that might damage it.

Attenuators are also used to 'match' impedances by lowering apparent SWR.

Key specifications for attenuators are:

Attenuation expressed in decibels of relative power. A 3dB pad reduces power to one half, 6dB to one

fourth, 10dB to one tenth, 20 dB to one hundredth, 30dB to one thousandth and so on. For voltage you

double the dBs so for example 6dB is half in voltage.

Frequency bandwidth, for example DC-18 GHz

Power dissipation depends on mass and surface area of resistance material as well as possible additional

cooling fins.

SWR is the standing wave ratio for input and output ports

Accuracy

Repeatability

Procedure:

Resistor values are calculated based on design of circuit.

Connections are made as shown in the circuit diagram.

Input is given using RPS & output is taken using mutli meter.

Varying input voltage from 0V to 20V output readings are noted.

Graph is plotted between input and output voltage.

Tabulation:

π-type:

S.

No

I/P Voltage

(Vi)

O/P Voltage

(Vo)

N = Vi / Vo

T-type:

S.

No

I/P Voltage

(Vi)

O/P Voltage

(Vo)

N = Vi / Vo

Lattice type:

S.

No

I/P Voltage

(Vi)

O/P Voltage

(Vo)

N = Vi / Vo

Model Graph:

Result: The π–type, T-type and Lattice type attenuators are constructed and the attenuation has been found.

I/P (Vi )

O/P

(V

o)

T-TYPE

I/P (Vi )

O/P

(V

o)

∏-TYPE

I/P (Vi )

O/P

(V

o)

LATTICE TYPE

Ex. No.8 EQUALIZER

Aim: To design a shunt capacitance and shunt inductance equalizer with an attenuation of 20dB.

Equipments required: Audio oscillator, Cathode ray oscilloscope, Inductance box, Capacitor 0.0029µf, resistors 600Ω, Bread

boards, connecting wires.

Circuit diagram:

Shunt capacitance equalizer

Shunt inductance equalizer

Theory:

Equalizers are electrical networks designated to counteract the attenuation or distortion occurring in any

part of the network that counter acts attenuation are called as attenuation equalizers. They are used in carrier

telephone systems and also in the design of the feedback of the control systems. They are used as log networks and

as lead networks to improve the stability response and performance of the system. When equalizer has capacitor

connected in parallel, it is called capacitor shunt and when inductor in parallel, it is called shunt inductance

equalizer.

Procedure: Connections are made as per the circuit diagram.

The input voltage is fixed at a constant value.

The frequency of the input wave is arranged with constant interval and the corresponding output voltage

are observed and measured.

A graph is drawn from the tabulated readings.

The cutoff frequency is obtained from the graph.

Tabulation:

Input Voltage (Vin):

Sl.No Frequency

(Hertz)

Output Voltage

(V0)

Gain=20log(Vin/Vo)

Model Graph:

Result: Thus the shunt capacitance and shunt inductance are designed and the output is studied.

Ex. No. 9 PULSE WIDTH MODULATION

Aim: To construct a Pulse width modulator.

Apparatus required: IC471, Resistor, Capacitor, Signal generator, Cathode Ray Oscilloscope, Breadboard, Connecting wires.

Circuit Diagram:

Theory:

Pulse modulation may be used to transmit information, such as continuous speech or data. It is a

system in which continuous waveforms are sampled at regular intervals. Information regarding the signal is

transmitted only at the sampling times, together with any synchronizing pulses that may be required. At the

receiving end, the original waveforms may be reconstituted from the information regarding the samples, if these are

taken frequently enough. Despite the fact that information about the signal is not supplied continuously, as in AM

and FM, the resulting receiver output can have negligible distortion. Pulse modulation may be subdivided broadly

into two categories, analog and digital. In the former case, the indication of sample amplitude is the nearest variable,

while in the latter case, a code, which indicates the sample amplitude to the nearest predetermined level, is sent.

In pulse width modulation of pulse amplitude modulation is also often called PDM (pulse duration

modulation) and less often, PLM (pulse length modulation). In this system, we have fixed amplitude and starting

time of each pulse, but the width of each pulse is made proportional to the amplitude of the signal at that instant.

Procedure:

The connections are made as per the circuit diagram.

The carrier signal is fed to the base and modulating signal to the emitter of the transistor through an audio

transformer.

The modulating signal, carrier signal and the modulated signal are obtained using a CRO/DSO and plotted.

The modulation index is determined.

Tabulation:

Scheme Nature of Signal Amplitude Time period Frequency

PWM Input signal

Modulated signal Ton

Toff

Demodulated signal

Model Graph: Message Signal

Carrier Signal

Modulated Signal

Result: Thus a PWM modulator is constructed using IC741.

Amplitude(v)

time(ms)

Amplitude(v)

time(ms)

Amplitude(v)

time(ms)

Ex. No.10 a) SAMPLING THEOREM

Aim:

To study the signal sampling and its reconstruction techniques.

Apparatus Required:

1. Analog Sampling and reconstruction unit, 2. Function Generator 3. Patch cards 4. CRO- (0-20MHz)

5. AC Adapter 6. CRO Probes

Block Diagram:

Sampling Logic:

Analog Signal Sampling and Reconstruction Logic:

Sampling signal (2,4,8,16,32 KHz)

Sampled Output

Signal Input

CD 4016

Analog Switch

Theory:

A band limited signal of finite energy, which has no frequency components higher than the ‘W’ Hz, is

completely described by specifying the values of the signal at instant of time separated by the ½ W seconds.

Through the use of sampling process, an analog signal is converted into a corresponding sequence of samples that

are usually spaced uniformly in time and the sampling rate is so chosen such that the sequence of samples uniquely

defines the original analog signal. The finite energy signal g(t) is sampled instantaneously and a uniform rate, once

every Ts seconds, We obtain an finite sequence of samples spaced Ts seconds apart and denoted by g(nTs). The

sampling rate fs=1/Ts. We have three types of Modulated pulses

1. Natural Top sampling

2. Sample and Hold circuit

3. Flat Top sampling

Procedure:

Connect the 2 kHz 5V p-p signal generated on board to the ANALOG INPUT, by means of the patch

chords provided.

Connect the sampling frequency signal in the INTERNAL mode, by means of the shorting pin provided.

Observe the output of the sampling amplifier at the SAMPLE OUTPUT.

Connect SAMPLE OUTPUT to the INPUT of the second order and fourth order low pass filter.

Tabulation:

Parameters Amplitude Frequency Time Period (1/f)

Message Signal

Sampling Signal

Sampled Signal

Reconstructed Signal

(Natural)

Reconstructed Signal

(Flat top)

Sample and Hold Signal

Model Graph:

Result:

From the above, we infer that for signal reconstruction with no distortion, Nyquist criterion has to be satisfied

and hence we prove the sampling theorem. If Nyquist Criteria is not satisfied or if the signal is not band limited, then

the spectral overlap called aliasing occurs, causing higher frequency signal to show up at lower frequencies in the

recovered signal.

Ex. No. 10(b) MONOSTABLE MULTIVIBRATOR

Aim: To design and test the performance of a monostable multivibrator to generate clock pulse for a given

frequency.

Apparatus Required:

CRO, Power supply 0-30V, Bread board, Connecting wires Resistors, Capacitors, Transistors 2N2369

Circuit Diagram:

Design:

Given:

To find

To find

To find

To find

To find

To find

To find

=

Theory:

A monostable multivibrator has only one stable state, the other state being quasi-stable. Normally the

multivibrator is in the stable state, and when an external triggering pulse is applied, it switches from the stable to the

quasi-stable state. It remains in the quasi-stable state for a short duration, but automatically reverts i.e. switches back

to its original stable state, without any triggering pulse. A collector-coupled Monostable multivibrator of the two

transistors Q1 and Q2, Q1 is normally OFF and Q2 is Normally ON. Resistor R1 and R2 are connected to the

normally OFF transistor, and the capacitor C is connected to the normally ON transistor. It is seen from the circuit of

the monostable multivibrator that, under normal conditions, the supply voltage VCC provides enough base drive to

the transistor Q2 through resistor R, with the result that Q2 goes into saturation. With Q2 ON, Q1 goes OFF, as

already studied in the context of binary operation. With Q2 ON and Q1 OFF, the capacitor finds a charging path.

The voltage across the capacitor is VCC with polarity. It is obvious that in the stable state of the multivibrator, Q2 is

ON and Q1 is OFF. If the negative triggering pulse is applied to the collector of Q1, it is transmitted to the base of

Q2 through the capacitor, and hence makes the base of Q2 negative. Immediately Q2 goes OFF and Q1 becomes

ON. However, this is only a quasi-stable state as is obvious form the following observation. With Q1 ON and Q2

OFF, the capacitor C finds a discharging path. As the capacitor discharges, it is seen that the potential at the base of

the transistor Q2 becomes less and less negative, and after a time, we have VB = Vγ, the cut-in-voltage of Q2. As

soon as VB crosses the level of Vγ, Q2 starts conducting and gets saturated. When Q2 becomes ON, Q1 becomes

OFF. Thus the original stable state of the multivibrator is restored.

The interval during which the quasi-stable state of the multivibrator persists i.e., Q2 remains OFF is

dependent upon the rate at which the capacitor C discharges. This duration of the quasi-stable state is termed as

delay time or pulse width or gate time. It is denoted as T. The wave forms of the voltage at base of the transistor Q2

and C (Collector of Q1).

Procedure:

Connect the circuit as shown in figure.

With the help of a triggering circuit and using the condition T (trig) > T(Quasi) a pulse waveform is

generated.

The output of the triggering circuit is connected to the base of the off transistor.

The Off transistor goes into ON state.

Observe the waveforms at VBE1, VBE2, VCE1 and VCE2.

Keep the DC- AC control of the Oscilloscope in DC mode.

Tabulation:

Transistor Terminal Amplitude(V) Time Period(ms)

Q1

Collector

Base

Emitter

Q2

Collector

Base

Emitter

Model Graph:

Result:

The monostable multivibrator is designed and studied.

Ex. No. 11 ASTABLE MULTIVIBRATOR

Aim:

To design and test the performance of an Astable Multivibrator to generate clock pulse for a given

frequency.

Apparatus Required:

Resistors, Capacitors, Transistors 2N2369, CRO, Power supply 0-30V, Bread board, Connecting wires

Circuit Diagram:

Design:

ICMAX = 5 mA; VCC = 12 V; VCE (SAT) = 0.2V

RC = (VCC - VCE (SAT)) / ICMAX

Let C = 0.1 mf and R= 10KW

T = 0.69 (R1C1+R2C2) = 0.69(2RC) (R1=R2; C1=C2)

=TON+TOFF

Theory:

An Astable multivibrator has two quasi-stable states, and it keeps on switching between these two states, by

itself, No external triggering signal is needed. The astable multivibrator cannot remain indefinitely in any of these

two states. The two amplifiers of an astable multivibrator are regenerative cross-coupled by capacitor.

The working of an astable multivibrator can be studied with respect to the given circuit. Let it be assumed

that the multivibrator is already in action and is oscillating i.e., switching between the two states. Let it be further

assumed that at the instant considered, Q2 is ON and Q1 is OFF. Since Q2 is ON, capacitor C2 charges through

resistor RC1. The voltage across C2 is VCC. Capacitor C1discharges through resistor R1, the voltage across C1

when it is about to start discharging is VCC (Capacitor C1 gets charged to VCC when Q1 is ON). As capacitor C1

discharges more and more, the potential of point A becomes more and more positive (or less and less negative), and

eventually VA becomes equal to Vg, the cut in voltage of Q1. For VA > Vg, transistor Q1 starts conducting. When

Q1 is ON Q2 becomes OFF. Similar operations repeat when Q1 becomes ON and Q2 becomes OFF. Thus with Q1

ON and Q2 OFF, capacitor C1 charges through resistor RC2 and capacitor C2 discharges through resistor R2. As

capacitor C2 discharges more and more , it is seen that the potential of point B becomes less and less negative (or

more and more positive), and eventually VB becomes equal to Vg, the cut in voltage of Q2. When VB > Vg,

transistor Q2 starts conducting. When Q2 becomes On, Q1 becomes OFF. It is thus seen that the circuit keeps on

switching continuously between the two quasi-stable states and once in operation, no external triggering is needed.

Square wave voltage are generated at the collector terminals of Q1 and Q2 i.e., at points C and D.

Procedure:

Connect the circuit as shown in the figure.

Observe the waveforms at VBE1, VBE2, VCE1 and VCE2 and find frequency.

Vary C from 0.01 to 0.001mF and measure the frequency at each step.

Keep the DC- AC control of the Oscilloscope in DC mode.

Tabulation:

Transistor Terminal Amplitude(V) Time Period(ms)

Q1

Collector

Base

Q2

Collector

Base

Model Graph:

Result:

Thus the astable multivibrator is designed and its performance is tested.

Ex. No. 12 CLIPPERS AND CLAMPERS

Aim:

a) To observe the clipping waveform to different clipping configurations.

b) To study the clamping circuits.

1. Positive clamping circuits

2. Negative clamping circuits

Apparatus required:

Audio oscillator, Diode, Resistor, Capacitor, RPS, CRO

Circuit diagram :

1.1Clipping-1 Positive Series

1.2 Clipping-2 Positive Series

1.3 Clipping1 Negative series

-

1.4 Clipping- 2Negative Series

1.5 Positive Parallel Clipper I

1.6 Positive Parallel Clipper II

1.7 Negative Parallel Clipper I

1.8 Negative Parallel Clipper II

1.9 Two Level Clippers

2.1 Positive Clamper

2.2Negative Clamper

Theory:

A clipper is a device designed to prevent the output of a circuit from exceeding a predetermined voltage

level without distorting the remaining part of the applied waveform.

A clipping circuit consists of linear elements like resistors and non-linear elements like junction diodes or

transistors, but it does not contain energy-storage elements like capacitors. Clipping circuits are used to select for

purposes of transmission, that part of a signal wave form which lies above or below a certain reference voltage level.

Clipping Circuits are also called as Slicers, amplitude selectors or limiters.

Clippers may be classified into two types based on the positioning of the diode.

Series Clippers, where the diode is in series with the load resistance, and

Shunt Clippers, where the diode in shunted across the load resistance.

Clipper & clamper operation:

A circuit which cutoff voltage above or below are both specified level is called clipper. A

clipper which removes a portion of positive half cycle of the input signal is called positive clipper. A clipper circuit

that removes the negative half cycle is called negative clipper. Itconsists of a diode D and a resistor R with output

taken across the resistor. During positive half cycle the input voltage, the terminal A is positive with respect to B.

This reverse biases the diode and it acts as an open switch. Therefore all the applied voltage drops across the diode

and none across the resistor. As a result of this, there is no output voltage during the positive half cycle of the input

voltage.

During the negative half cycle of the input voltage, the terminal B is positive with respect to

A. Therefore it forward biases the diode and it acts as a closed switch. Thus, there is no voltage drop across diode.

During negative half cycle of the input voltage. All the input voltage is drop across the resistor as shown in the

output waveform. During the positive half cycle of the voltage, the terminal A is positive with respect to the terminal

B. Therefore the diode is forward biased; as a result all the input voltage appears across the resistor. During negative

half cycle of the input voltage, the terminal B is positive with respect to the terminal A. Therefore the diode is

reverse biased and hence there is no voltage drop across the resistor during negative half cycle.

Procedure:

1. Connections are made as per the circuit diagram

2. Set the input signal(5 V, 1KHz) using signal generator

3. Observe the output waveform using CRO(D.C mode)

4. Sketch the waveform on a graph sheet.

Tabulation:

S. No. Type Amplitude(v) Width Time(s)

1. Clipping-1 Positive Series 2. Clipping-2 Positive Series 3. Clipping- 1 Negative series 4. Clipping- 2Negative Series 5. Positive Parallel Clipper I 6. Positive Parallel Clipper II 7. Negative Parallel Clipper I 8. Negative Parallel Clipper II 9. Two Level Clippers 10. Positive Clamper 11. Negative Clamper

Model Graph:

1.1 Clipping-1 Positive Series

1.2Clipping-2 Positive Series

1.3 Clipping- 1 Negative series

1.4 Clipping- 2Negative Series

1.5 Positive Parallel Clipper I

1.6 Positive Parallel Clipper II

1.7 Negative Parallel Clipper I

1.8 Negative Parallel Clipper II

1.9 Two Level Clippers

2.1Positive Clamper

2.2 Negative Clamper

Result:

The clipping and clamping waveforms are observed and verified for their output.