Introduction

Feedback is one of the most powerful ideas in amplifier design, and this chapter builds the foundation for understanding how it reshapes an amplifier's behaviour. In a basic amplifier the four important characteristics — voltage gain, input impedance, output impedance and bandwidth — are essentially fixed once the circuit is built, and the designer has very little control over them. Crude methods such as adding a resistive network or a series resistance can nudge these values, but they waste useful signal. Feedback offers a far cleaner route: by sampling a part of the output and returning it to the input, we can reshape all of these characteristics in a controlled way.

In this chapter you will learn what feedback means, how positive and negative feedback differ, the four ways a negative-feedback signal can be connected to an amplifier, and a detailed analysis of the voltage-series negative-feedback amplifier — how it changes gain, gain stability, input impedance, output impedance and bandwidth. This is a core, frequently examined topic in Karnataka 2nd PUC Electronics, and a firm grasp of the recurring factor $(1+A\beta)$ will carry you through most II PUC board exam questions on feedback amplifiers.