Folded cascode toplology

Thread Starter


Joined Apr 19, 2012
Here is a folded cascode amplifier. There are two problems that I am confused. Hope anyone can
come up with an answer.
1. Why the small signal current gm1*Vin flows from NMOS to PMOS not in the opposite direction?
2. There seems to be a contradiciton here. The current flows through M2 is always a constant (I2).
However, there is a small signal current gm1*Vin that is varying flows through it.
How is it possible for the PMOS current constant?

Folded cascode topology.PNG