Electronics · 2nd Puc Science

Ch 4Feedback in Amplifiers — 2nd PUC Electronics, concept-first.

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.

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Key concepts

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Gain with Negative Feedback

Negative feedback reduces the voltage gain from A to Af = A/(1+Aβ), the open-loop gain divided by the loop factor (1+Aβ).

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Chapter contents

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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.

4.1

Introduction to Feedback

The important characteristics of an amplifier are its voltage gain, input impedance, output impedance and bandwidth.

4.2

Types of feedback

Depending on whether the feedback signal increases or decreases the net input signal, there are two types of feedback in amplifiers: (1) positive feedback and (2) negative feedback.

4.3

Four types of negative feedback

In an amplifier both voltage and current can be fed back to the input, and the feedback signal can be connected either in series or in parallel with the input.

4.4

Voltage series negative feedback

In the voltage series negative feedback connection, a fraction of the output voltage is applied in series with the input signal through the feedback network.

Chapter Summary

- Feedback is the process of taking a part of an amplifier's output and feeding it back to the input; the returned sample modifies the net input to control the output.