I have a negative rail -10V generated from a switched cap charge pump (CP) and want to regulate it.
The rail varies +/-1V over the full load and have to stabilise to a specific voltage -7V.
Power efficiency isn't a concern for the application.
Linear regulator seems to be the most used method with an error amplifier and a pass device which
is an NPN or NMOS mostly.
I used an opamp designed by someone else for a different application and connect it to a big W/L
NPN/NMOS but sweeping the VIN shows no regulation.
The LTspice simulation is shown and the Cadence schematic is identical to it (with PDK devices):
I have seen positive LDO papers and they custom make the OTA/OPAMP for the
desired pass transistor gate capacitance etc. Would it be better to start making my own
OTA and do compensation specific to my pass device or should I keep on trying with
the pre-made and compensated OPAMP from a previous designer