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Title
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Date Of
Experiment
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Lab Number
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Instructor
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Name
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Roll No
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Mechanical Electronics Lab
Build and implement a common emitter
amplifier using transistor.
06
__________Muhammad Qaseem_________
_________210501036__________
Page 1
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Objectives:


Learn to set the Q-point on DC load Line to mid for amplification.
Build a common emitter amplifier using transistor.
Equipment:
1. Transistor (2N3904) NPN.
2. Resistors.
3. Capacitor.
Theory:
An amplifier is an electronic device or circuit which is used to increase the
magnitude of the signal applied to its input. Amplifier is the generic term used to describe
a circuit which produces and increased version of its input signal.
There are different types of transistor amplifiers operated by using an AC signal input.
Which are interchanged between the positive value and negative value; hence this is the
one way of presenting the common emitter amplifier circuit to function between two peak
values. This process is known as the biasing amplifier and it is an important amplifier
design to establish the exact operating point of a transistor amplifier which is ready to
receive the signals hence it can reduce any distortion to the output signal.
Common Emitter Amplifier:
The common emitter amplifier is a three basic single stage bipolar junction
transistor and is used as a voltage amplifier. The input of this amplifier is taken from the
base terminal, the output is collected from the collector terminal and the emitter terminal
is common for both the terminals.
Mechanical Electronics Lab
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Here we can see that R1 and R2 are used as voltage divider bias circuit to set the q
point to center for the amplification process. RL is the load resistance and capacitor C1 is
known as coupling capacitor which act as a filter between input voltage and DC bias
Voltage, so that no DC voltages are added up in input signal. While the C2 capacitor is
known as bypass capacitor which is used to give easy path to the emitter current to
complete its path. It is used to achieve the high voltage gain. Generally, the value of the
bypass capacitor, C2 is chosen to provide a reactance of at most, 1/10th the value of RE
at the lowest operating signal frequency. A decoupling capacitor is also used at the output
terminal to separate DC component of voltages to add up in the actual AC output.
The Voltage Gain of the common emitter amplifier is equal to the ratio of the
change in the input voltage to the change in the amplifiers output voltage. Then ΔVL is
Vout and ΔVB is Vin. But voltage gain is also equal to the ratio of the signal resistance in
the Collector to the signal resistance in the Emitter and is given as:
Transistor Biasing:
As voltage divider bias circuit is used in common emitter amplifier so these formulas are
used to properly set the Q point to center for amplification.
Mechanical Electronics Lab
Page 3
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Task 1:
1. Implement the common emitter amplifier circuit.
2. Don’t connect the input signal at base terminal.
3. Draw the DC load line and find the Q – operating point (Vce-q and Ie-q) through
DC analysis.
4. Set and make sure that q-point is set at center.
5. Measure the Vce-q and Ie-q value using multimeter to verify.
Task 2:
1.
2.
3.
4.
5.
Now apply input signal of 20mVp-p of 1KHz at the input.
Using the oscilloscope, observe the input and output voltages using both channels.
Find the voltage gain through multimeter as well as from the oscilloscope.
Find the current gain through multimeter as well.
Increase the value of input voltages from (0.2mVp-p to 1Vp-p) with fixed
frequency of 1KHz and observe the output voltage behavior through oscilloscope.
6. Find voltage gain for different amplitude values of input signal in tabular form.
7. Now fix the Input voltage at 20mVp-p and increase the frequency from (50 Hz to
1MHz) of input signal and observe the output voltage behavior through
oscilloscope.
8. Find voltage gain at different frequency values of input signal in tabular form.
9. Now again set input at 20mVp-p and 1KHz frequency.
10. Now remove the by-pass capacitor and observe the both gain value.
TASK 1
Mechanical Electronics Lab
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Qpoint is at
V= 7.47 I=0.62
transistor used 2n2222
TASK 2
Mechanical Electronics Lab
Page 5