Quote: the problem is that for low input Voltage=1V when i use source follower with nmos input opamp can drive large load, but can't drive low load and can't shutt off when it's needed.
When i use source follower with pmos input i can't drive large load.
i know this topology is not suitable for low voltage and i want to check other possibilities
Ah, if that is the case, you can use an OTA type output, with lots of gain. You do this in a Class-AB type structure with a PMOS and NMOS outputs being controlled. With lots of gain it give the capability for either the PMOS or NMOS output to be driven triode.
That will get your control for the PMOS power transistor to go from ground to power (or pretty bloody close)
in concept (sorry dont have a picture)
2 NMOS differential pairs
2 current mirror structures above the differential pairs
opposite polarity on the high gain output of each differential pair
one output drives the PMOS output of the OTA
other output drives a PMOS current source, that mirrors into a NMOS (diode connected) which drives the NMOS output of the OTA.
There are other ways of doing this as well, with one differential pair, and you may need additional gain before getting to the NMOS/PMOS outputs.
The key thing is the A/B output stage.
Jerry