Tofu,
Tofu wrote on Apr 15th, 2009, 2:07pm:- Apart from slewing, is the output impedance of the folded cascode the only factor that contributes to the delay (output cap is very small)?
I'd say it's bandwidth, not impedance. Also: (very) small diff. input signal = (very) small diff. current = slow, even for small load cap.
Quote:are there any other factors that can potentially make it slower?
A few Farad of cap should do it.... (Sorry, coudn't resist. [Added:] Usually, the more details you add to your question the better the answers.)
Quote:- I tried to calibrate the output impedance of the folded cascode (biased in common mode) by connecting its output to a vsource with ac mag=1 and check the low freq current. This calibrated low freq impedance (actually Rout) is several times lower than the one obtained via standard textbook calculation (based on Gds etc). Did I do something wrong here?
Did you check the DC operating point of your voltage source (idc should be 0)? Why not use a current source?
B.O.E.