For differential op-amp, you will have to use AC=0.5 for positive input and AC=-0.5 for the negative input. As you mentioned, you will need to probe VOUTP-VOUTN for phase and gain.
You are correct about the Phase margin and Gain calculation.
Please note than you will have to use a CMFB circuit to set the output common mode level of the differential op-amp. In case you are using a Switched Capacitor based CMFB, please replace it with an ideal circuit before you perform the AC analysis.
You are correct about the Phase margin and Gain calculation.
Please note than you will have to use a CMFB circuit to set the output common mode level of the differential op-amp. In case you are using a Switched Capacitor based CMFB, please replace it with an ideal circuit before you perform the AC analysis.
wow,you pre-answered my question before i ask it.
ya i am using a SC CMFB structure,
does it mean i should replace the CMFB op with an ideal one(infinite gain OP)?
or just bias the whole circuit in saturation and run AC analysis?
You will need to replace the Switched Capacitor section of the CMFB loop with an equivalent ideal circuit. The op-amp in the CMFB circuit is not a switched circuit and can be retained as such.
One implementation of ideal CMFB circuit is mentioned at
You will need to replace the Switched Capacitor section of the CMFB loop with an equivalent ideal circuit. The op-amp in the CMFB circuit is not a switched circuit and can be retained as such.
One implementation of ideal CMFB circuit is mentioned at
my favorite test circuit is using one AC source, then with two 0.5X VCVS
genernate two differential input signal, for DC biasing/CM, you can stack one
DC source there. The easy way to check the phase margin and gain margin
is to use stb simulation avaiable in spectre.
, for DC biasing/CM, you can stack one
DC source there. The easy way to check the phase margin and gain margin
is to use stb simulation avaiable in spectre.
since the two vcvs coming from the same AC source with +-0.5 gain,
they will be +0.5vin and -0.5vin, exactly what you want for the
differential input signals.