Multistage amplifier

The most common reason for using multiple stages is to increase the gain of the amplifier in applications where the input signal is very small, for instance in radio receivers.

It is used in UHF television and radio receivers because its low input resistance is easier to match to antennas than common emitter.

[2] The final stage can be a common collector configuration to act as a buffer amplifier.

The load can thus draw high current without affecting the amplifier performance.

Audio power amplifiers will typically have a push-pull output as the final stage.

A Darlington pair of transistors is another way of obtaining a high current gain.

DC amplifiers are also subject to drift requiring careful adjustment and high stability components.

The capacitance (C) of the capacitor and the input and output resistances of the stages form an RC circuit.

The capacitor value must be made large enough that this filter passes the lowest frequency of interest.

The inductance of the transformer windings serves as the inductor of an LC tuned circuit.