lhlbluesky
Banned
i have designed a two stage fully differential opamp with hybrid ahuja compensation (that is, two compensation capacitor used in the two cascode nodes of each branch), the first stage is folded cascode, the second is common source, and the CMFB is continuous common mode feedback which have two input pairs, one pair connected to vcm, the other pair connected to outp and outn (the two output of opamp).
my question is, how to simulate the common mode loop characteristic, such as AC response (GBW and PM)? the differential characteristic is good for my circuit, and
the transcient response is ok also, but when i disconnect the common mode feedback loop, and add a stimilus in the cut point to simulate the AC response, i observe that, the output has a PM of -90 degree(the start phase is 180 degree, and the 0dB gain relating to a -90 degree phase, so PM is -90 degree also), while the transcient response is ok, why? what is the reason? how to understand this?
pls help me, i'm very confused here, thanks all.
my question is, how to simulate the common mode loop characteristic, such as AC response (GBW and PM)? the differential characteristic is good for my circuit, and
the transcient response is ok also, but when i disconnect the common mode feedback loop, and add a stimilus in the cut point to simulate the AC response, i observe that, the output has a PM of -90 degree(the start phase is 180 degree, and the 0dB gain relating to a -90 degree phase, so PM is -90 degree also), while the transcient response is ok, why? what is the reason? how to understand this?
pls help me, i'm very confused here, thanks all.
