Consumer Electronics

INTERSTAGE COUPLING

The ac output signal from a common-emitter stage can be coupled to the input of the next stage either by means of a transformer or by a resistance-capacitance combination. Maximum power gain will be obtained with a transformer having a suitable primary-to-secondary step-down ratio to match the output resistance of the first stage to the input resistance of the second stage. The turns step-down ratio will be typically between five and ten-to-one. Transformers, however, are relatively expensive components and are also susceptible to magnetic pick-up. Accordingly they are rarely used in low level transistor amplifiers.

With resistance-capacitance coupling the input resistance of the second stage effectively becomes the load resistance ...