Class C Amplifiers

Solid State Devices and Solid State Power Supplies and Amplifiers
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___________________________________________________________________________ Transistors

CLASS AB AMPLIFIERS - biased so that collector current is zero (cutoff) for a

portion of one alternation of the input signal. Therefore, collector current will

flow for more than 180 degrees but less than 360 degrees of the input signal.

The class AB amplifier is commonly used as a push-pull amplifier to overcome

a side effect of class B operations.

CLASS B AMPLIFIERS - biased so that collector current is cut off during one-

half of the input signal. So, for a class B operation, collector current will flow

for approximately 180 degrees (halt) of the input signal. The class B operated

amplifier is used as an audio amplifier and sometimes as the driver- and

power-amplifier stage of transmitters.

CLASS C AMPLIFIERS - biased so that collector current flows for less than one-

half cycle of the input signal. The class C operated amplifier is used as a RF

amplifier in transmitters.

FIDELITY AND EFFICIENCY - two terms used in conjunction with amplifiers.

Fidelity is the faithful reproduction of a signal while efficiency is the ratio of

output signal power compared to the total input power. The class A amplifier

has the highest degree of fidelity, but the class C amplifier has the highest

efficiency.

23 June 2005

TC 9-62

2-41

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