When the collector current flows for less than half cycle of the input signal, the power amplifier is known as class C power amplifier. The efficiency of class C amplifier is high while linearity is poor. The conduction angle for class C is less than 180o. It is generally around 90o, which means the transistor remains idle for more than half of the input signal. So, the output current will be delivered for less time compared to the application of input signal.
The following figure shows the operating point and output of a class C amplifier.
This kind of biasing gives a much improved efficiency of around 80% to the amplifier, but introduces heavy distortion in the output signal. Using the class C amplifier, the pulses produced at its output can be converted to complete sine wave of a particular frequency by using LC circuits in its collector circuit.
