time delay for Folded cascode Opamp

[sdvc]

How to calculate the time delay from the input to the output of the folded cascode opamp. Is it enough to calculate the slew rate SR=Ibias/Cl? How does time delay change with frequency?

 

[frankrose]

Normally OPAmps have gain bandwidth, settling time and slew-rate parameters, time delay or propagation delay is a parameter of a comparator.

 

[sdvc]

Yes, but you can use folded cascode opamp as preamplifier in comparator.

 

[frankrose]

You mentioned OPAmp, not an OTA before an inverter or comparator. If you say OPAmp I think most of us will assume negative feedback, which isn't possible with a comparator.
Comparator delay simulation/measurement is not equal with slew-rate. If you know that only large differential signals will appear you can suppose the slew-rate determines the worst delay. Otherwise you have to know the minimum input overdrive voltage and the delay will be much larger with that.

 

[vivekroy]

There are two delays:
Small signal delay (when you have very small input variations at the input) which is typically given by your dominant pole. Not entirely true, but I always use that as a first approximation. I approximate my transfer function as a single pole system whose pole is given by the dominant pole and then you can calculate out the time delay. Your time delay will depend upon the frequency of your SMALL SIGNAL as at different frequencies you have different phase shifts which will translate to different delays at different frequencies.
Large signal delay (when you have a large input signal variations at the input) --> This is where your slewing effects come into picture.