type of CLASS for Power Amplifier

hi everybody,

can somebody tell me why this circuit is identified as a AB Class power amplifier?
can somebody tell me the characteristics of a AB class PA? what is the differents between AB class and the other classes. i really need to know this. pls help me out.thank you.The circuit is in this link below.


https://www.edaboard.com/viewtopic.php?p=577799#577799

So there's the 3 basic class A,B,C. The difference in the operational point.
The Class D is the switching mode. (There's AD, BD)
Class E,F,Inverse F are used in RF application mainly.
And there's the class S, if you are interested in look some audio amplifier design book.

The Class A:
the operational current

where

is the maximum collector peak current (if the power transistor is BJT)

maximum efficiency: 50 % (when full swing)

The Class B:
If we don"t control the transistor the operational point current is 0.
The Problem is the crossmodulation (nonlinear distortion
maximum efficiency: 78% (when full swing)

The Class AB:
The operational point current between the class A and the class B operation point current. (we can depress the distortion)
maximum effieciency>75 % (when full swing)

Class G, H: they use 4 supply voltage( +/- Vcc1, +/-Vcc2, when the swing is small the transistors use the smaller positive/negative supply voltage.