class AB biasing

Thread Starter

jsnx

Joined Mar 17, 2022
21
Hello I was looking at circuit to bias a class B amplifier in order to avoid crossover distortion and I found the circuit shown below. Can someone please explain to me how does it work?All biasing circuits that I've found in theory use diodes and resistors and I have not seen a circuit like this one
1654029018514.png
 

dl324

Joined Mar 30, 2015
14,683
All biasing circuits that I've found in theory use diodes and resistors and I have not seen a circuit like this one
Diodes can only be used for bipolar transistors and are used to keep the output transistors always on slightly.

The biasing method you showed is only realistic if all of the MOSFETs are in the same integrated circuit so you have better device matching. The current sources on M4 and M7 bias the sources of M5 and M8, respectively, away from the supply rails to avoid clipping. This works best if the threshold voltages of M3 and M4 and M6 and M7 are closely matched and are at the same temperature. You can't achieve that level of matching with discrete devices.

EDIT: Also note that they drew the arrows on the MOSFETs backwards and they drew a solid line at the gate when they should have used a dashed line to indicate enhancement mode.
 
Last edited:

MrSalts

Joined Apr 2, 2020
1,832
Hello I was looking at circuit to bias a class B amplifier in order to avoid crossover distortion and I found the circuit shown below. Can someone please explain to me how does it work?All biasing circuits that I've found in theory use diodes and resistors and I have not seen a circuit like this one
View attachment 268481
Your circuit is conceptual - the details are missing. Point us to where you found this miss or post the commentary that explains the design assumptions and strategy.
 
Top