Fig. 3-16 Approximate currents in a common-emitter (CE) amplifier.

Since Rin is usually much less than rc{ 1 — a), the above approximations are fulfilled in a cascade of common-emitter stages, except possibly for the last stage, where Rl may be fairly large. Such a cascade is shown in Fig. 3-17, where any resistors associated with the collector or base are assumed large compared with Rin. The power gain of the circuit in Fig. 3-17 is




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