Wednesday, October 5, 2011

COMMON COLLECTOR AMPLIFIER Electronic devices and circuits lab manual

COMMON COLLECTOR AMPLIFIER

AIM:     1. To measure the voltage gain of a   CC amplifier
2. To draw the frequency response of the CC amplifier

APPRATUS:
Transistor BC 107
Regulated Power Supply (0-30V)
Function Generator
CRO
Resistors 33KΩ, 3.3KΩ, 330Ω, 1.5KΩ, 1KΩ, 2.2KΩ & 4.7KΩ

Capacitors     10µF                -2Nos
100µF
Connecting wires

THEORY:
In common-collector amplifier the input is given at the  base and the output is taken at the emitter. In this amplifier, there is no phase inversion between input and output. The input impedance of the CC amplifier is very high and output impedance is low. The voltage gain is less than unity. Here the collector is at ac ground and the capacitors used must have a negligible reactance at the frequency of operation.
This amplifier is used for impedance matching and as a buffer amplifier. This circuit is also known as emitter follower.

CIRCUIT DIAGRAM:

PROCEDURE:
1.    Connections are made as per the circuit diagram.
2.    For calculating the voltage gain the input voltage of 20mV peak-to-peak and 1 KHz frequency is applied and output voltage is taken for various load resistors.
The voltage gain calculated by using the expression,               Av=V0/Vi
4.    For plotting the frequency response the input voltage is kept constant a
20mV peak-to- peak and the frequency is varied from 100Hzto 1MHz.
5.    Note down the values of output voltage for each frequency.
All the readings are tabulated the voltage gain in dB is calculated by using the expression, Av=20log 10(V0/Vi)
6.    A graph is drawn by taking frequency on X-axis and gain in dB on y-axis on
Semi-log graph sheet.
The Bandwidth of the amplifier is calculated from the graph using the
Expression,
Bandwidth BW=f2-f1
Where f1 is lower cut-off frequency of CE amplifier
f2 is upper cut-off frequency of CE amplifier
10. The gain Bandwidth product of the amplifier is calculated using the
Expression,
Gain -Bandwidth product=3-dB midband gain X Bandwidth

OBSERVATIONS:

 LOAD RESISTANCE(KΩ) OUTPUT VOLTAGE( V0) GAIN               Av=V0/Vi GAIN IN dB                                Av=20log 10(V0/Vi)

FREQUENCY RESPONSE:
Vi=20mV
 FREQUENCY(Hz) OUTPUT VOLTAGE( V0) GAIN IN dB                                Av=20log 10(V0/Vi)

WAVEFORM:

PRECAUTIONS:

1. The input voltage must be kept constant while taking frequency response.
2. Proper biasing voltages should be applied.

RESULT:
The voltage gain and frequency response of the CC amplifier are obtained. Also gain Bandwidth product is calculated.

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