Single Stage RC Coupled Amplifier | Lab Experiment for Engineering | Diploma Students Electronic Circuits Lab | Part 1
AIM
To set up a single stage RC coupled CE amplifier with potential divider bias and
(i) Observe the phase difference between input and output waveforms
(ii) Measure mid band gain
(iii) Plot its frequency response and determine the bandwidth
EQUIPMENTS / COMPONENTS
Sl. no. Name and Specification Quantity
1. Resistors 470 Ω 1 no.
1 KΩ 1 no.
1.8 KΩ 1 no.
10 KΩ 1 no.
47 KΩ 1 no.
2. Capacitor 10 μF 2 nos.
22 μF 1 no.
3. Transistor BC 107
1 no.
4. Function generator 0 to 1 MHz 1 no.
5. Oscilloscope 0 to 20 MHz 1 no.
6. Power supply 12 V dc 1 no.
7. Multimeter 1 no.
8. Breadboard 1 no.
9. Connecting wires
PRINCIPLE
RC coupled CE amplifier is widely used in audio frequency applications as voltage
amplifiers. In a CE amplifier base current controls the collector current. A small change in
IB results in relatively large change in IC. The transistor is biased in active region using
potential divider bias. That is emitter - base junction is forward biased and collector - base
junction is reverse biased.
The output signal is 180o out of phase with input signal. RC coupled amplifier
provides uniform gain at mid frequencies. Gain decreases at low frequencies and high
frequencies. The output voltage and hence the voltage gain is decided by RL.
Voltage gain, Av= β*(Zin/zout)
But Zin = R1║ R2║Rin and is approximately equal to Rin (typically 1 KΩ), where Rin is
the input dynamic resistance of transistor. Similarly Zout = RC║ RL║ RO, where RO is the
output dynamic resistance of transistor. Voltage gain Av= β*(Rac/zin) . Since Rin is constant, voltage gain decreases with decrease in RL.
PROCEDURE
1) Test the components
2) Assemble the circuit in a bread board
3) Give VCC and measure the dc bias conditions
4) Give 1KHz, 50 mV (pp) sinusoidal signal as input, observe and plot the waveforms at
collector and at the output point
5) Then measure the output voltage without RL, with RL = 10 KΩ and with RL = 1 KΩ
6) Calculate the voltage gain in each case
7) To get the frequency response vary the input frequency from 0 - 1 MHz in suitable steps and
measure the output voltage in each step
8) Enter these values in tabular column and plot the frequency response in a graph sheet
9) Determine the midband gain and bandwidth from the frequency response plot
OBSERVATIONS
1. DC conditions
VCC =
VBE =
VCE =
2. Input and output waveforms
3. Calculation of gain at midband
(i) Without RL
Vin = 50 mV (pp)
F = 10 KHz
Gain = Vo/Vi=
(ii) Without RL = 10 KΩ
Vin = 50 mV (pp)
F = 10 KHz
Gain = Vo/Vi =
(iii) Without RL = 1 KΩ
Vin = 50 mV (pp)
F = 10 KHz
4. Frequency response
Frequency (f) in Hz Log f VO in Volt Gain = Vo/Vi Gain in dB 20 log (Gain)
5. Frequency response plot
Take log f on x-axis, gain in dB on y-axis
From frequency response plot
fL =
fH =
Bandwidth = fH - fL
Midband gain =
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