Feedback Amplifiers: Definition, Types, Applications

Introduction

• Definition : The amplifier in which a part of output is sampled and fed back to the input of the amplifier is called feedback amplifier. Therefore, at input we have two signals : Input signal, and part of the output which is fed back to the input.

• Types : Both these signals may be in phase or out of phase. When input signal and part of output signal are in phase, the feedback is called positive feedback. On the other hand, when they are in out of phase, the feedback is called negative feedback.

• Applications : Use of positive feedback results in oscillations and hence used in oscillators and negative feedback gives stability and hence used in amplifiers.

Comparison of Positive and Negative Feedback

Review Question

1. Define negative and positive feedback.

2. When a portion of the output signal is fed to input, as you are aware, feedback is generated. Distinguish between negative feedback and positive feedback and elaborate on their individual advantages. How different parameters of an amplifier (say) will be affected by these two types of feedback ?