vivkr
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[quote author=loose-electron link=1307475244/0#14
AC coupled signal, Gate drive of source follower is on OTA output, with a current source off of it to keep it biased properly (goes triode when its down, but still works). Source feeds a cap (drive the bottom plate side) and the other side of the cap goes to your feedback point. Done. [/quote]
Jerry,
Would you mind posting a schematic? Still cannot see how you get rail-rail output with the arrangement you are describing.
By the way, the Ahuja compensation scheme was published in JSSC about 30 years ago (Dec. 1983), around the time when MOS circuits started to phase out BJTs in common telecomm ICs, i.e. when MOS started to go mainstream, and the problem of the RHP zero started to get more attention as BJT amps didn't suffer much from this.
There were countless variations published around this time and earlier which all attempted to get rid of the nasty RHP zero. The scheme using a MOS biased in triode region as a resistor to push out the zero is a little older and was published by Tsividis if I recall correctly. The approach using a source follower which you describe was also published around this time although I cannot recall by whom (The output swing limitation was a problem there as most people want to use two-stage opamps precisely to get high swing).
The difference between using an active stage (source foll./Ahuja) and a passive R is of course one of topology. You are burning a bit more current but you have an active stage. In principle, you can be about gm*ro times better in mitigating the problem loosely speaking.
Vivek
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