Chapter 5

Common-collector and common-drain amplifiers (emitter and source followers)

Common-collector amplifiers


The fundamental circuit of a common-collector amplifier is given in Fig. 5.1(a) in which Rs represents the resistance of the signal source and Rl represents the load resistance. For simplicity, bias sources are omitted from this diagram. In Fig. 5.1(b) the transistor is represented by an equivalent network of resistances re, rb and rc together with a voltage generator of e.m.f. αrcie where ie is the alternating current in the emitter circuit. If the base current ib and emitter current ie are both shown acting in clockwise directions as in Fig. 5.1(b), then the current in the common-collector resistance rc is the difference ...

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