Class AB amplifier

Thread Starter


Joined Dec 18, 2006
Hi there,

I a bit confused how to examine the currents/voltages in a Class AB amplifier. In the circuit attached, why would there be less cross over distortion compared to the Class B amplifier? From the reading I've done, I think there's something to do with drawing current from the load when both transistors are off, but I don't really understand what this means..

Thanks for any help.



Joined Apr 26, 2005
In class B operation, the transistors are at cut-off during quiesence. In Class AB operation the transistors are typically at 0.9 of cutoff allowing some current flow in both halves of the push-pull configuration.

With class-B, the input signal must overcome the B-E junction potential before there is current flowing through the load. That is the source of the "cross-over distortion". To reduce the distortion, you overcome that B-E junction potential so that the appropriate transistor is conducting for the complete half-cycle ... and we call that Class AB bias.