Quote ERIKL:
......this all is well-known stuff, and I think the open-loop simulation is quite ok for a first check in order to find the original poles and zeroes, open-loop gain, bandwidth a.s.o. The real application, however, is always running in closed-loop, and this changes all the a.m. properties quite a lot. If you really want to know the actual properties of your application circuit, you better run your analysis on the circuit as it is configured, i.e. in its closed-loop configuration.
Hi ERIK,
just a few comments. An LDO is a circuit to be designed according to control theory laws.
During open loop analysis you do NOT find "original poles and zeros" for closed-loop operation.
The only purpose of the open-loop analysis is to see the loop gain and its phase in order to verify stability properties after closing the loop. Doing an ac analysis only for the closed loop not always gives the right information about stability properties.