The term class "AB" power amplifier is sometimes used to refer to a single ended PA (e.g CS stage) whose conduction angle falls between 180 to 360 degrees i.e in which the output transistor turns off for less than half of a period. From another perspective, a class AB PA is less linear than class A stage and more linear than class B stage. This is usually accomplished by reducing the input voltage swing and hence backing off from the 1-dB compression point.

The amplifier classes are always defined as follows:-

Class A:- The amplifiers single output transistor conducts for the full 360° of the cycle of the input waveform.

Class B:- The amplifiers two output transistors only conduct for one-half, that is, 180° of the input waveform.

Class AB:- The amplifiers two output transistors conduct somewhere between 180° and 360° of the input waveform.