Electronics Lab Manual by Er. Swapnil V. Kaware

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MKCT’s Manav School of Engineering & Technology, Vyala (Akola).
*Guidelines For Writing Lab Manual*
Designed & Developed By,
Er. Swapnil V. Kaware,
B.E. (Electronics),
M.E. (Electronics & Telecommunication),
Email Id:- svkaware@yahoo.co.in
Website:- www.slideshare.net/svkaware
Blank Page (Use Pencil) Ruled (Line) Page (Use Pen)
Practical No. Practical No.
Aim Aim
Apparatus Required Apparatus Required
Circuit Diagram Theory
Characteristics/ Waveform Procedure
Result Observation Table
Calculation
Precaution
Result

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*Instructions To The Students*
Draw circuit diagram of your practical in the given space as per circuit available in your
laboratory.
Write readings in the observation table.
Draw waveforms in the given space.
Simulate circuit using circuit simulator if hardware is not available in the lab.
Every student must construct at least one circuit as per his choice or as given by the faculty.
Do not handle any equipment before reading the instructions /Instruction manuals.
Read carefully the power ratings of the equipment before it is switched ON, whether ratings
230 V/50 Hz or 115V/60 Hz.
For Indian equipment, the power ratings are normally 230V/50Hz. If you have equipment
with 115/60 Hz ratings, do not insert power plug, as our normal supply is 230V/50Hz,
which will damage the equipment.
Observe type of sockets of equipment power to avoid mechanical damage.
Do not forcefully place connectors to avoid the damage.
Strictly observe the instructions given by the Teacher/ Lab Instructor.
Read all instructions carefully and proceed according to that.
Ask the faculty if you are unsure of any concept.
Give the connection as per the diagrams.
After verification by the faculty, tabulate the readings.
Write up full and suitable conclusions for each experiment and draw the graph.
After completing the experiment complete the observation and get signature from the staff.

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Before coming to next lab make sure that you complete the record and get sign from the
faculty.
Practical No:- 01.
Aim:- Study of Half Wave Rectifier with & without filter.
Apparatus Required: Power supply, rectifier kit, CRO, Digital multimeters, Transformer
(6V-0-6V), Diode 1N4007, Capacitor 100μf/470μf, Decade Resistance Box, CRO and CRO
probes, Connecting wires, etc.
Theory:-
Rectifier:- The process of converting an alternating current into direct current is known as
rectification. The unidirectional conduction property of semiconductor diodes (junction
diodes) is used for rectification. Rectifiers are of two types: (a) Half wave rectifier and
(b) Full wave rectifier. In a half-wave rectifier circuit, during the positive half cycle
of the input, the diode is forward biased and conducts. Current flows through the
load and a voltage is developed across it.
During the negative half-cycle, it is reverse bias and does not conduct.
Therefore, in the negative half cycle of the supply, no current flows in the load resistor as no
voltage appears across it. Thus the dc voltage across the load is sinusoidal for the first half
cycle only and a pure a.c. input signal is converted into a unidirectional pulsating output
signal.
Filters:- The output of a rectifier gives a pulsating d.c. signal. because of presence
of some a.c. components whose frequency is equal to that of the a.c. supply frequency.
Very often when rectifying an alternating voltage we wish to produce a "steady" direct
voltage free from any voltage variations or ripple. Filter circuits are used to smoothen the
output.
Various filter circuits are available such as shunt capacitor, series inductor, choke
input LC filter and -filter etc. Here we will use a simple shunt capacitor filter circuit. Since a
capacitor is open to d.c. and offers low impedance path to a.c. current, putting a capacitor
across the output will make the d.c. component to pass through the load resulting in small
ripple voltage.
Circuit Diagram:-

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Fig:- Half Wave Rectifier without filter.
Fig:- Half Wave Rectifier with filter.
WAVEFORMS:-

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Procedure:-
1. Connections are made as per the circuit diagram.
2. Connect the primary side of the transformer to ac mains and the secondary side to the
rectifier input.
3.By the multimeter, measure the ac input voltage of the rectifier and, ac and dc voltage
at the output of the rectifier.
4. Find the theoretical of dc voltage by using the formula, Vdc=Vm/П. Where, Vm=2Vrms,
(Vrms=output ac voltage.)
5. The Ripple factor is calculated by using the formula, r = ac output voltage/dc output
voltage.
Observation Table:-

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Calculation:- (Leave 1 Page Blank)
Precautions:-
1. The primary and secondary side of the transformer should be carefully identified
2. The polarities of all the diodes should be carefully identified.
3. While determining the % regulation, first Full load should be applied and then it
should be decremented in steps.
Result:- The ripple factors & percentage regulation for Half wave Rectifier with and without
has been calculated.

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Practical No:- 02.
Aim:- Study of Full Wave Rectifier with & without filter.
Apparatus Required:- Power supply, rectifier kit, CRO, Digital multimeters, Transformer
(6V-0-6V), Diode 1N4007, Capacitor 100μf/470μf, Decade Resistance Box, CRO and CRO
probes Connecting wires.
Theory:- The circuit which allows us to do this is called a Full-wave Rectifier. Here,
unidirectional current flows in the output for both the cycles of input signal and rectifies it.
The rectification can be done either by a center tap full wave rectifier rectifier (using four
diodes). The circuit of a center-tapped full wave rectifier uses two diodes D1&D2. During
positive half cycle of secondary voltage (input voltage), the diode D1 is forward biased and
D2is reverse biased.
The diode D1 conducts and current flows through load resistor RL. During
negative half cycle, diode D2 becomes forward biased and D1 reverse biased. Now, D2
conducts and current flows through the load resistor RL in the same direction. There is a
continuous current flow through the load resistor RL, during both the half cycles and will get
unidirectional current as show in the model graph. The difference between full wave and
half wave rectification is that a full wave rectifier allows unidirectional (one way) current to
the load during the entire 360 degrees of the input signal and half-wave rectifier allows this
only during one half cycle (180 degree).
Circuit Diagram:-

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Waveform:-

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Procedure: 1. Connections are made as per the circuit diagram.
2. Connect the ac mains to the primary side of the transformer and the secondary side to
the rectifier.
3. Measure the ac voltage at the input side of the rectifier.
4. Measure both ac and dc voltages at the output side the rectifier.
5. Find the theoretical value of the dc voltage by using the formula Vdc=2Vm/π
6. Connect the filter capacitor across the load resistor and measure the values of Vac and
Vdc at the output.
7. The theoretical values of Ripple factors with and without capacitor are calculated.
8. From the values of Vac and Vdc practical values of Ripple factors are calculated. The
practical values are compared with theoretical values.
Observation Table:-
Calculation:- (Leave 1 Page Blank)
Precautions:
1. The primary and secondary side of the transformer should be carefully identified.
2. The polarities of all the diodes should be carefully identified.
Result: The ripple factors for Full wave Rectifier with and without load and the load
regulation has been calculated.

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Practical No:- 03.
Aim:- Study of Zener Diode As A Voltage Regulator
Apparatus Required:- Zener diode, Regulated Power Supply (0-30v), Voltmeter (0-20v),
Ammeter (0-20mA), Resistor (1K ohm), Bread Board, Connecting wires, etc.
Theory:- A zener diode is heavily doped p-n junction diode, specially made to operate
in the break down region. A p-n junction diode normally does not conduct when reverse
biased. But if the reverse bias is increased, at a particular voltage it starts conducting
heavily. This voltage is called Break down Voltage. High current through the diode can

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permanently damage the device
To avoid high current, we connect a resistor in series with zener diode.
Once the diode starts conducting it maintains almost constant voltage across the
terminals whatever may be the current through it, i.e., it has very low dynamic
resistance. It is used in voltage regulators.
a) Line Regulation
In this type of regulation, series resistance and load resistance are fixed, only input voltage is
changing. Output voltage remains the same as long as the input voltage is maintained above
a minimum value.
Percentage of line regulation can be calculated by,
where V0 is the output voltage and VIN is the input voltage and ΔV0 is the change in output
voltage for a particular change in input voltage ΔVIN.
b) Load Regulation
In this type of regulation, input voltage is fixed and the load resistance is varying. Output volt
remains same, as long as the load resistance is maintained above a minimum value.
Percentage of load regulation,
where is the null load resistor voltage (ie. remove the load resistance and measure the
voltage across the Zener Diode) and is the full load resistor voltage
Circuit Diagram:-

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Waveform/Characteristics:-
Procedure:-
A) Static characteristics:
2. The Regulated power supply voltage is increased in steps.
3. The Forward current (lf), and the forward voltage (Vf.) are observed and then
noted in the tabular form.
4. A graph is plotted between Forward current (lf) on X-axis and the forward voltage
(Vf) on Y-axis.
B) Regulation characteristics:
1. Connections are made as per the circuit diagram
2. The load is placed in full load condition and the zener voltage (Vz), Zener current
(lz), load current (IL) are measured.
3. The above step is repeated by decreasing the value of the load in steps.
4. All the readings are tabulated.
5. The percentage regulation is calculated using the below formula
6. The voltage regulation of any device is usually expressed as percentage regulation.
Observation Table:-

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Calculation:-
The percentage regulation is given by the formula
% Regulation = (VNL-VFL) /VFLX100
VNL=Voltage across the diode, when no load is connected.
VFL=Voltage across the diode, when load is connected.
Precaution:- 1. The terminals of the zener diode should be properly identified.
2. While determined the load regulation, load should not be immediately shorted.
3. Should be ensured that the applied voltages & currents do not exceed the ratings of
the diode.
Result:- The percentage regulation of the Zener Diode is _________________________________
Practical No:- 04.
Aim:- Draw Frequency Response & Bandwidth of CE Amplifier.
Apparatus: Transistor BC107, Regulated power Supply (0-30V), Function Generator, CRO,
Resistors [33KΩ, 3.3KΩ, 330Ω,1.5KΩ,1KΩ, 2.2KΩ, 4.7KΩ], Capacitors 10μF, 100μF, Bread
Board, Connecting Wires, etc.
Theory:-
The CE amplifier provides high gain &wide frequency response. The emitter lead is common
to both input & output circuits and is grounded. The emitter-base circuit is forward biased.

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The collector current is controlled by the base current rather than emitter current. When a
transistor is biased in active region it acts like an amplifier. The input signal is applied to
base terminal of the transistor and amplifier output is taken across collector terminal. A very
small change in base current produces a much larger change in collector current.
When positive half-cycle is fed to the input circuit, it opposes the forward
bias of the circuit which causes the collector current to decrease; it decreases the voltage
more negative. Thus when input cycle varies through a negative half-cycle, increases the
forward bias of the circuit, which causes the collector current to increases thus the output
signal is common emitter amplifier is in out of phase with the input signal. An amplified
output signal is obtained when this fluctuating collector current flows through a collector
resistor, Rc. The capacitor across the collector resistor Rc will act as a bypass capacitor. This
will improve high frequency response of amplifier.
Circuit Diagram:-
Waveform:-

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Fig:- bandwidth (f2-f1)
Observation table:-

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Procedure:-
1. Connect the circuit as shown in circuit diagram
2. Apply the input of 20mV peak-to-peak and 1 KHz frequency using Function Generator
3. Measure the Output Voltage Vo (p-p) for various load resistors.
4. The voltage gain can be calculated by using the expression , Av= (V0/Vi)
5. For plotting the frequency response the input voltage is kept Constant at 20mV peak-to-
peak and the frequency is varied from 100Hz to 1MHz Using function generator
6. Note down the value of output voltage for each frequency.
7. All the readings are tabulated and voltage gain in dB is calculated by Using The expression
Av=20 log10 (V0/Vi)
8. A graph is drawn by taking frequency on x-axis and gain in dB on y-axis On Semi-log
graph.
9.The band width of the amplifier is calculated from the graph Using the expression,
Bandwidth, BW=f2-f1
Where f1 lower cut-off frequency of CE amplifier, and
Where f2 upper cut-off frequency of CE amplifier
Result:- The 3-dB Bandwidth of the CE Amplifier is ____________________________.
Practical No: 05.
Aim:- Study of CE amplifier with & without feedback.
Apparatus Required:- DC power supply +12V, Function Generator, Oscilloscope, 5. 2 mm
patch cords, etc.
Theory:- Single amplifier circuits, such as a common base, common emitter and common
collector amplifiers are seldom found alone, as a single stage amplifier, in any system.
Generally, at least two or more than two stages are connected in cascade combination. If the
output of one amplifier is connected (coupled) to the input of another amplifier the stages
are said to be connected in "cascade". The advantage of cascaded amplifiers is to develop an
output voltage larger than either stage alone can develop. In fact, the overall gain of the
cascaded amplifiers (called system gain) is the product of each individual stage gain.
Because of this the gain of a single stage is not as important as the system
gain. Designers usually set individual stage gains relatively low to reduce signal distortion.

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One of the very important requirements to cascade one stage of amplifier to another is the
impedance matching. When the output impedance of previous stage matches with the input
impedance of its next stage, maximum power is transferred. One of the coupling methods to
couple the two stages is RC-Coupling. RC-Coupling has the advantages of wide frequency
response and relatively small cost and size. RC coupled amplifier is simple & low cost circuit
.In these circuit voltage divider biasing is used for drive the transistors BC547. Here in the
circuit coupling capacitor is using before an input. Since the impedance of the capacitor is
inversely proportional to frequency, the capacitor effectively blocks DC voltage and
transmits AC voltage. When the frequency is high enough, the capacitive reactance is much
smaller than the résistance. So capacitor used for this purpose is called a coupling capacitor.
Bandwidth of an RC-Coupled Amplifier :
Bandwidth is a term used to describe the band of frequencies at which a particular amplifier
amplifies the given input effectively.
The bandwidth of RC-Coupled Amplifier is given by,
Bandwidth (B) = fH – fL
Here gain is directly proportional to the feedback resistance. With using feedback
gain is decrease. The feedback factor is,
β = RE1/ (RE1+RF) …..……(1)
Feedback Factor range is 0.01 to 1
and Gain with feedback is
AVF = AV / (1+ β AV) ………..(2)
Circuit diagram:-

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Procedure :-
1. Connect +12V variable DC power supply at their indicated position.
2. Switch ‘On’ the power supply.
3. Connect 2Vp-p, 20Hz Sine wave signal at the input (between points Vin and ground) of board
and observe the same on oscilloscope CH1.
4. Observe the output waveform between points Vout and ground on Oscilloscope CH 2.
5. Increase the input frequency from lowest value and observe the output waveform amplitude
on Oscilloscope.
6. Calculate gain in dB and plot a semi log graph between AV (dB) and Frequency. Measure
frequency range for which the output wave amplitude is 3dB down the maximum amplitude
on graph (this will give two values of frequency fL and fH, the lower 3dB frequency and
higher 3dB frequency respectively) as shown in figure.
7. Calculate Bandwidth of RC-Coupled Amplifier without feedback.
8. Keep the potentiometer RF at 60K and calculate feedback factor β.
9. Connect the patch chord between ‘a’ and ‘b’.
10. Follow procedure from step 3 to 7. This will give a plot between AVF (dB) and Frequency.
11. Calculate Bandwidth of RC-Coupled Amplifier with feedback.
12. Compare the frequency response and Bandwidth of RC-Coupled Amplifier with &
without feedback.
Observation Table:-

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Calculation:-
Without feedback,
fL (lower 3dB frequency) = ……………………
fH (higher 3dB frequency) = ……………………
Bandwidth (fH – fL) = ……………………
With feedback,
Feedback factor =…………………….
fL (lower 3dB frequency) = ……………………
fH (higher 3dB frequency) = ……………………
Bandwidth (fH – fL) = …………………….
Precautions:-
2. The polarities of all the diodes should be carefully identified
Result:- The CE amplifier with & without feedback have been studied.
Practical No: 06.
Aim:- Study of Colpitts Oscillator.
Apparatus required:- Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.

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Theory:- The Colpitt oscillator is one of the simplest and best known oscillators and is used
extensively in circuits, which work at radio frequencies. Fig.1 shows the basic Colpitt
oscillator circuit configuration. The transistor is in voltage divider bias which sets up Q-point
of the circuit.In the circuit note that Vout is actually the ac voltage across C2. This voltage is
fed back to the base and sustains oscillations developed across the tank circuit, provided
there is enough voltage gain at the oscillation frequency. The resonant frequency of the
Colpitt oscillator can be calculated from the tank circuit used. We can calculate the approx.
resonant frequency as,
Here, the capacitance used is the equivalent capacitance the circulating
current passes through. In Colpitt oscillator the circulating current
passes through the series combination of C1 and C2. therefore
equivalent capacitance is,
Circuit Diagram:-
Procedure:-
1. Connect +12V dc power supplies at their indicated position from external source.
2. Connect a patch cord between points a and b and another patch chord between points d
and g1.
3. Switch ON the power supply.
4. Connect oscilloscope between points f and g2.
5. Record the value of output frequency on oscilloscope.

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6. Calculate the resonant frequency using equation 1.
7. Compare measured frequency with the theoretically calculated value.
8. Switch off the supply.
9. Remove the patch chord connected between points a and b and connect it between points
a and c.
10. Remove the patch chord connected between points d and g1 and connect it between
points e and g2.
11. Follow the procedure from point 4 to 8.
12. Connect +5V supply instead of +12V supply and follow the procedure from point 2 to
point 11.
Observation:-
When patch chord connected across C1 and C2
Practically calculated Output frequency(on CRO): …………………….
Theoretically calculated values
Cequ : ……………………………………... ( use eq.2 )
Resonant frequency (fr) : ………………….. ( use eq.1 )
Output voltage amplitude : …………………… Vp-p
When patch chord connected across C3 and C4
Practically calculated Output frequency(on CRO): …………………….
Cequ : ……………………………………... ( use eq.2 )
Resonant frequency (fr) : ………………….. ( use eq.1 )
Output voltage amplitude : …………………… Vp-p.
Precautions:-
2. The polarities of all the components should be carefully identified.
Result:- The Colpitts Oscillator have been studied.
Practical No: 07.
Aim:- Study of Hartley Oscillator.
Apparatus Required : Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.

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Theory:- The Hartley oscillator is one of the simplest and best known oscillators and
is used extensively in circuits, which work at radio frequencies. The transistor is in
voltage divider bias which sets up Q-point of the circuit. The output voltage is fed back to the
base and sustains oscillations developed across the tank circuit, provided there is enough
voltage gain at the oscillation frequency. The resonant frequency of the Hartley oscillator can
be calculated from the tank circuit used. We can calculate the approx. resonant frequency as,
Here, the Inductor used is the equivalent
Inductance. In Hartley oscillator the circulating current passes through the series
combination of L1 and L2. Therefore equivalent Inductance is,
LT = L1 + L2 + 2 M ……….…………… (2)
Where, M is the mutual inductance between two inductors.
M = K √ L1 L2 ………………………… (3) Where, K is the coefficient of coupling, lies between 0 to
1. The coefficient of coupling gives the extent to which two inductors are couple. Starting
condition for oscillations is AB > l, Where, B is approx. equal to L2/L1.
The feedback should be enough to start oscillations under all conditions as
different transistor, temperature, voltage, etc. but it should not be much that you lose more
output than necessary. The resonant frequency can be changed by either changing the value
of inductor or changing the value of capacitor but the combination of the three components
should satisfy the above given two conditions for oscillation.
Circuit Diagram:-
Procedure :-
1. Connect +12V dc power supplies at their indicated position.
2. Connect a patch cord between points a and b and another patch cord between point d and
ground.
4. Connect oscilloscope between Vout and ground.
5. Record the value of output frequency on oscilloscope.
6. Calculate the resonant frequency using equation 1.

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8. Switch off the supply.
9. Remove the patch cord connected between points a and b and connect it between points a
and c.
10. Remove the patch cord connected between points d and ground and connect it between
point e and ground.
11. Follow the procedure from point 4 to 7.
Observation:-
When patch cord connected across a and b
Practically calculated Output frequency (on CRO): .......................................
LT: …………………………………… ( use eq.2 )
Resonant frequency (fr) : ………………. (use eq.l )
Output voltage amplitude: ……………... Vp-p
When patch cord connected across a and c
Practically calculated Output frequency (on CRO) : ………..........................
LT: …………………………………… ( use eq.2 )
Resonant frequency (fr) : ………………. (use eq.l )
Output voltage amplitude: ……………... Vp-p.
Precautions:-
Result:- The Hartley Oscillator have been studied.
Practical No:- 08.
To study Phase shift Oscillator
Apparatus Required:- Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.
Theory:-

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The basic RC Oscillator which is also known as a Phase-shift Oscillator, produces a sine
wave output signal using regenerative feedback obtained from the resistor-capacitor
combination. This regenerative feedback from the RC network is due to the ability of the
capacitor to store an electric charge, (similar to the LC tank circuit).
This resistor-capacitor feedback network can be connected as shown above
to produce a leading phase shift (phase advance network) or interchanged to produce a
lagging phase shift (phase retard network) the outcome is still the same as the sine wave
oscillations only occur at the frequency at which the overall phase-shift is 360o.
By varying one or more of the resistors or capacitors in the phase-shift
network, the frequency can be varied and generally this is done by keeping the resistors the
same and using a 3-ganged variable capacitor. this circuit uses the property of RC filters to
cause a phase shift, and by using multiple filters, a feedback circuit with exactly 180° phase
shift can be produced.
When used with a common emitter amplifier, which also has a phase shift of
180° between base and collector, the filters produce positive feedback to cause oscillation to
take place. The RC network commonly used is that of a high pass filter, (Fig. 3.1.1) which
produces a phase shift of between 0° and 90° depending on the frequency of the signal used,
although low pass filters can also be used.The frequency of oscillation of RC Phase Shift
Oscillator is given by
Circuit Diagram:-
Procedure :
1. Connect +12V, -12V dc power supplies at their indicated position from external source or
ST2612 Analog Lab.
2. Connect a 2mm patch cord between test point B & C, D & E, F & A
4. Measure frequency at any test points T1, T2, T3, T4 using CRO.
6. Measure phase difference between test points Tl & T2, T2 & T3, T3 & T4, and T4 & T1 with
the help of dual channel CRO.
7. Vary gain Pot of 470K to adjust gain of the amplifier in case of clipped waveform.

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Observation Table:-
1.Theoretical value of output frequency = ………………………………………..
2. Practical value of output frequency = ………………………………………..
3. Phase shift between test point T1 & T2 = ………………………………………..
Precautions:-
Result:- The phase shift oscillator have been studied.
Practical No:-09.
Aim:- Study of RC Coupled 2-Stage Amplifier.
Apparatus required : Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.
Theory:- To achieve higher gain, we can use multi-stage amplifier where output of one
amplifier is connected to input of next amplifier. Amplifiers are connected in cascade
arrangement so it is also called cascade amplifier. Output of first amplifier is connected to

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input of second amplifier by coupling device like coupling capacitor. Direct coupling or
transformer coupling is also used. This is most popular type of coupling as it provides
excellent audio fidelity.
A coupling capacitor is used to connect output of first stage to input of
second stage. Resistances R1, R2,Re form biasing and stabilization network. Emitter bypass
capacitor offers low reactance paths to signal coupling Capacitor transmits ac signal, blocks
DC. Cascade stages amplify signal and overall gain is increased total gain is less than product
of gains of individual stages. Thus for more gain coupling is done and overall gain of two
stages equals to A=A1*A2
A1=voltage gain of first stage
A2=voltage gain of second stage.
Capacitor coupling is used to couple AC signal from output of first amplifier to input of
second amplifier. Coupling capacitor does not pass DC signal so DC biasing of second stage is
not affected by first stage and vice-versa. In this practical, we will use capacitor coupling
which is also known as two stage RC coupled amplifier.
Circuit Diagram:-
Procedure:-
1. Connect function generator at the input of the amplifier circuit.
2. Set input voltage V1=1 mV and frequency 100 Hz.
3. Connect CRO at the output of the first amplifier circuit at point V2.
4. Observe amplified signal and measure output voltage at V2
5. Find out gain of first amplifier A1=V2/V1.
6. Observe amplified signal at the output of second amplifier and measure output voltage at V3
7. Find out gain of second amplifier A2=V3/V2.
8. Find overall gain of amplifier A = V3/V1= A1A2
9. Increase frequency from the function generator and repeat above steps.
10. Note down readings of output voltage in the observation table for frequency range from 100
Hz to 10 MHz.

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11. Calculate voltage gain A1 and A2 for different frequencies and gain in dB. Plot frequency
response.
Observation Table:-
Calculation:- (Leave 1 page blank)
Precautions:-
Result:- The RC Coupled 2-Stage Amplifier have been studied.
Practical No:- 10.
Aim:- Study of Class A Power Amplifier.
Apparatus Required:- Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.
Theory:- The power amplifier is said to be Class A amplifier if the Q point and the input
signal are selected such that the output signal is obtained for a full input signal cycle.
For all values of input signal, the transistor remains in the active region and never enters
into cut-off or saturation region. When an a.c signal is applied, the collector voltage varies
sinusoidally hence the collector current also varies sinusoidally. The collector current flows
for 3600 (full cycle) of the input signal. i e the angle of the collector current flow is 3600 .
The most commonly used type of power amplifier configuration is the Class A Amplifier.
The Class A amplifier is the most common and simplest form of power amplifier that uses

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the switching transistor in the standard common emitter circuit configuration as seen
previously. The transistor is always biased “ON” so that it conducts during one complete
cycle of the input signal waveform producing minimum distortion and maximum amplitude
to the output.
This means then that the Class A Amplifier configuration is the ideal operating mode,
because there can be no crossover or switch-off distortion to the output waveform even
during the negative half of the cycle. Class A power amplifier output stages may use a single
power transistor or pairs of transistors connected together to share the high load current.
Circuit Diagram:-
Observation Table:-

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Procedure:-
1. Connect the circuit as per the circuit diagram.
2. Set Vi =50 mv, using the signal generator.
3. Keeping the input voltage constant, vary the frequency from 10 Hz to 1M Hz in regular
steps and note down the corresponding output voltage.
4. Plot the graph; Gain (dB) vs Frequency(Hz).
Calculation :- Maximum power transfer =Po,max=V 2/R Effeciency, η = Po,max/Pc.
Precautions:-
Result:- Thus the Class A power amplifier was constructed. The following parameters were
calculated:
(a). Maximum output power= ……………………... (b). Efficiency=…………………………
Practical No:- 11.
Aim:- Frequency response & bandwidth of JFET Amplifier.

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Apparatus Required:- : Analog board, DC power supplies +12V, Oscilloscope, 4.2mm Patch
cords, etc.
Theory:- he amplifier circuit consists of an N-channel JFET, but the device could also be an
equivalent N-channel depletion-mode MOSFET as the circuit diagram would be the same just
a change in the FET, connected in a common source configuration. The JFET gate
voltage Vg is biased through the potential divider network set up by resistors R1 and R2 and
is biased to operate within its saturation region which is equivalent to the active region of
the bipolar junction transistor.
Unlike a bipolar transistor circuit, the junction FET takes virtually no input
gate current allowing the gate to be treated as an open circuit. Then no input characteristics
curves are required. Since the N-Channel JFET is a depletion mode device and is normally
“ON”, a negative gate voltage with respect to the source is required to modulate or control
the drain current. This negative voltage can be provided by biasing from a separate power
supply voltage or by a self biasing arrangement as long as a steady current flows through the
JFET even when there is no input signal present and Vg maintains a reverse bias of the gate-
source pn junction.
Circuit Diagram:-
Procedure :
1. Connect +12V variable DC power supply at the indicated position from external source.
2. Switch ‘On’ the power supply.
3. Connect maximum 200 mVp-p, 50 Hz sine wave signal at the signal input of board and
observe the same on oscilloscope CH I.
4. Connect socket ‘a’ with socket ‘b’.

31 | P a g e
5. Observe the output waveform from “output signal” on oscilloscope CHI or CHII and note
down output voltage (VOUT) peak to peak.
6. Vary the frequency of input signal from function generator with a margin of 100Hz
initially. After 1 KHz vary the frequency with a margin of 1 KHz.
7. After 10 KHz, vary the frequency of input signal with a margin of 10 KHz. After 100 KHz
vary the frequency with a margin of 100 KHz till output does not become equal to input.
8. Note down the output voltage corresponding the input frequency in the observation table
given below.
9. Calculate the voltage gain of amplifier at each frequency by the formula given Voltage gain
AV = VOUT (peak to peak) / VIN (peak to peak)
10. Find out the value of gain in db by formula, Gain (in db) =20 log (AV)
11. Plot the graph between gain (in db) and frequency (in Hz) on log paper and calculate the
bandwidth given by equation : Bandwidth = (fH – fL )
Where, fL = lower 3dB cutoff frequency & fH = higher 3dB cutoff frequency.
12. Observe the output waveform from “output signal” on oscilloscope CH I or CHII for the
different values of input voltages less than 200Vp-p.
Observation Table:-
Calculation:-
Precautions:- 1. The primary and secondary side of the transformer should be carefully
identified. 2. The polarities of all the components should be carefully identified.
Result:- fL (lower 3dB cutoff frequency) = …… fH (higher 3dB cutoff frequency) = ……
Bandwidth (fH – fL) = …………………
Practical No:- 12.
Aim:- Study of UJT as relaxation oscillator.
Apparatus Required:- Bread board trainer, UJT 2N 2646, Resistors-(4.7k, 47k,330k),
Capacitors-(0.1uf), CRO, Regulated power supply(0-30V), Connecting wires, etc.

32 | P a g e
Theory:- UJT relaxation oscillator is a type of RC ( resistor-capacitor) oscillator where the
active element is a UJT (uni-junction transistor). UJT is an excellent switch with switching
times in the order of nano seconds. It has a negative resistance region in the characteristics
and can be easily employed in relaxation oscillators. The UJT relaxation oscillator is called so
because the timing interval is set up by the charging of a capacitor and the timing interval is
ceased by the the rapid discharge of the same capacitor.
Before going into the details of UJT relaxation oscillator let’s have a look at
the uni junction transistor (UJT). From the name itself, the UJT or uni junction transistor is a
semiconductor device that has only one junction. The UJT has three terminals
designated B1, B2 and E. The base material for a UJT is a lightly doped N-Type Silicon bar
with ohmic contacts given at the lengthwise ends. These end terminals are called B1 and B2.
Since the silicon bar is lightly doped, the resistance between B1 and B2 is
very high (typically 5 to 10 KΩ). A heavily doped P-type region is constructed on one side of
the bar close to the B2 region. This heavily doped P region is called emitter and it is
designated as E. Resistance between E & B1 is higher than the resistance between E & B2
because E is constructed close to B2.
Circuit Diagram:-
Expected Waveform:-

33 | P a g e
•
Procedure:-
2. The Output Vo is noted, time period is also noted.
3. The theoretical time period should be calculated.
4. T=RTCT ln(1/1-n)
5. The Output at base 1 and base 2 should note.
6. Graph should be plotted and waveforms are drawn for V0, VB1,VB2.
Calculation:-T = RTCT ln(1/(1-n) )
n = (VP - VD)/VBB
Let η=0.56 ,RT=24.7Kohm ,CT=0.1microfarad Then T=…………………..
Precautions:
1. Connections should be tight.
2. UJT terminals are identified properly.
3. Readings can not be exceeding the limits.
Result:- The UJT as a relaxation oscillator have been studied.

Electronics Lab Manual by Er. Swapnil V. Kaware

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Electronics Lab Manual by Er. Swapnil V. Kaware