04-01-2013, 04:39 PM
TWO STAGE RCCOUPLED AMPLIFIERS
[attachment=46537]
Theory :
The output from a single stage amplifier is usually insufficient to drive an o/p device. To
achieve more gain, the o/p of one stage is given as the input to the other stage which forms
multistage amplifier. If the two stages are coupled by R and C, then the amplifier is called
RC coupled amplifier. The performance of an amplifier can be determined from the
following terms.
Gain:-
The gain is defined as ratio of output to input. The gain of multistage
amplifier is equal to the product of gains of individual stages i.e G=G1.G2.G3.
EC-I Lab Manual EC-261
BAPATLA ENGINEERING COLLEGE (Autonomous):: BAPATLA
At low frequencies (<50HZ) the reactance of coupling capacitor cc is high
and hence very small part of signal will pass from one stage to next stage. This
increases the loading effect of next stage and reduces the voltage gain.
At high frequencies, capacitance reduces. Due to this base emitter junction is
low which increases the base current. This reduces the amplification factor.
At mid frequencies, the voltage gain of the amplifier is constant. In this
range, as frequency increases, reactance of CC reduces which tends to increase the
gain. At the same time, lower reactance means higher reactance of first stage and
hence lower gain, these two factors cancel each other resulting in a uniform gain at
mid frequency.
PROCEDURE
01. Connect the circuit as per the circuit diagram
02. Give 1 KHz signal, 25 mV (p-p) as Vs from signal generator
03. Observe the output on CRO for proper working of the amplifier
04. After ensuring the amplifier function, vary signal
frequency from 50 Hz to 600 Hz in proper steps for 15 to
20 readings. Keeping Vs = 25 mV (p-p) at every frequency,
note down the resetting output voltage and tabulate in a
table.
[attachment=46537]
Theory :
The output from a single stage amplifier is usually insufficient to drive an o/p device. To
achieve more gain, the o/p of one stage is given as the input to the other stage which forms
multistage amplifier. If the two stages are coupled by R and C, then the amplifier is called
RC coupled amplifier. The performance of an amplifier can be determined from the
following terms.
Gain:-
The gain is defined as ratio of output to input. The gain of multistage
amplifier is equal to the product of gains of individual stages i.e G=G1.G2.G3.
EC-I Lab Manual EC-261
BAPATLA ENGINEERING COLLEGE (Autonomous):: BAPATLA
At low frequencies (<50HZ) the reactance of coupling capacitor cc is high
and hence very small part of signal will pass from one stage to next stage. This
increases the loading effect of next stage and reduces the voltage gain.
At high frequencies, capacitance reduces. Due to this base emitter junction is
low which increases the base current. This reduces the amplification factor.
At mid frequencies, the voltage gain of the amplifier is constant. In this
range, as frequency increases, reactance of CC reduces which tends to increase the
gain. At the same time, lower reactance means higher reactance of first stage and
hence lower gain, these two factors cancel each other resulting in a uniform gain at
mid frequency.
PROCEDURE
01. Connect the circuit as per the circuit diagram
02. Give 1 KHz signal, 25 mV (p-p) as Vs from signal generator
03. Observe the output on CRO for proper working of the amplifier
04. After ensuring the amplifier function, vary signal
frequency from 50 Hz to 600 Hz in proper steps for 15 to
20 readings. Keeping Vs = 25 mV (p-p) at every frequency,
note down the resetting output voltage and tabulate in a
table.