## Wednesday, October 5, 2011

### TRANSISTOR CE AMPLIFIER

TRANSISTOR CE AMPLIFIER

AIM:     1. To Measure the voltage gain of a CE amplifier
2. To draw the frequency response curve of the CE amplifier

APPARATUS:
Transistor BC-107
Regulated power Supply (0-30V, 1A)
Function Generator
CRO
Resistors    [33KΩ, 3.3KΩ, 330Ω, 1.5KΩ
1KΩ, 2.2KΩ, 4.7KΩ]
Capacitors- 10µF                 -2No
100µF
Connecting Wires

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. The collector current is controlled by the base current rather than emitter current. 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 +VE 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 –VE. Thus when input cycle varies through a -VE 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.
CIRCUIT DIAGRAM:

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.    Tabulate the readings in the tabular form.
5.    The voltage gain can be calculated by using the expression                               Av= (V0/Vi)
6.    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
7.    Note down the value of output voltage for each frequency.
8.    All the readings are tabulated and voltage gain in dB is calculated by  Using The expression Av=20 log10 (V0/Vi)
9.    A graph is drawn by taking frequency on x-axis and gain in dB on y-axis
On   Semi-log graph.
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
The bandwidth product of the amplifier is calculated using the
Expression
Gain Bandwidth product=3-dBmidband gain X Bandwidth

OBSERVATIONS:

Input voltage Vi=20mV

 LOAD RESISTANCE(KΩ) OUTPUT VOLTAGE (V0) GAIN    AV=(V0/Vi) GAIN IN dBAv=20log10 (V0/Vi)

FREQUENCY RESPONSE:        Vi=20mv
 FREQUENCY(Hz) OUTPUT VOLTAGE (V0) GAIN IN dBAv=20 log10 (V0/Vi)

MODELWAVE FORMS:

INPUT WAVE FORM:

OUTPUT WAVE FORM

FREQUENCY RESPONSE

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