Chapter 4

Common-emitter and common-source amplifiers

Common-emitter amplifiers

Introduction

We have already seen (page 29) that the common-emitter amplifier has a considerable current gain β. In the following analysis we shall derive expressions for the input resistance, output resistance and voltage gain for this circuit in terms of the parameters of the equivalent T-network, the source resistance Rs and the output load Rl

The basic circuit for a common-emitter amplifier is given in Fig. 4.1(a), in which Rs is the resistance of the signal source and Rl is the collector load resistance. Bias sources are omitted from this diagram for the sake of simplicity. Fig. 4.1(b) gives the equivalent circuit in which the transistor is represented by the T-network ...

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