Chapter: Electronic Devices and Circuits : Feed Back Amplifiers and Oscillators
Gain of Negative Voltage Feedback Amplifier
Gain of Negative Voltage Feedback Amplifier
Consider the negative voltage feedback
amplifier shown in Fig. . The gain of the amplifier without feedback is Av.
Negative feedback is then applied by feeding a fraction mv of the output
voltage e0 back to amplifier input. Therefore, the actual input to the
amplifier is the signal voltage eg minus feedback voltage mv e0 i.e.,
Actual input to amplifier = eg − mv e0
The output e0 must be equal to the input
voltage eg − mv e0 multiplied by gain Av of
But e0/eg is the voltage gain of the amplifier
with feedback. Voltage gain with negative feedback is
It may be seen that the gain of the amplifier
without feedback is Av. However, when negative voltage feedback is applied, the
gain is reduced by a factor 1 + Av mv. It may be noted that negative voltage
feedback does not affect the current gain of the circuit.
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