I see.
That is what i am observing.
If I connect a current source at the output to start sinking current, the PMOS will start to deliver current to the output.
I understand the circuit as that the gate drive will then start to decrease for the NMOS and increase for the PMOS.
What I now see, is that when the node driving the NMOS gate falls below a certain level as it start to shut off, M16 and M18 falls out of saturation. This occurs for a common-mode input voltage of around 1.5V, as it seems to avoiding me having rail-to-rail output operation. I would like this to occur for common-mode inputs closer to the rail I think. Is there any tips you can give me in order to achieve this? Any dimensions I should be looking into to tweak?
-Thanks.