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Fig. 3-17 Elementary amplifier made up of common-emitter amplifiers.

This is actually the maximum possible gain for the combination since in practice some of the collector current will flow into the collector load resistances and the biasing resistances. However, the preceding equation gives the order of magnitude of the over-all gain and is therefore quite useful. The common-emitter amplifier is probably the configuration most often used since it gives a large gain without the use of transformers.

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Fig. 3-18 Equivalent circuit for a common-collector (CC) stage.

The equivalent circuit for a common-collector stage including Rl may be drawn as shown in Fig. 3-18. The input resistance of the stage is

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