vivkr
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Hi,
I assume that you are referring to the Ahuja compensation (Ahuja, B., JSSC, Dec. 1983) when you say "cascode compensation", and the lead compensation involves using a MOS transisor in triode to realize a series compensation with an R and Cc (by Tsividis I believe).
From my experience, I can list the following pros and cons:
1. Ahuja compensation:
+ Breaks the feedforward path completely, gives excellent phase margin + Owing to above fact, compensation relatively independent of process etc. + Easier to design + Good PSRR at high frequencies - 1 extra stage (level shifter) - Systematic offset introduced, since the tail of the level shifter is tied to the output of first stage - Slew rate of opamp affected by current flowing in the intermediate stage as well
2. Lead compensation (assuming a good MOS implementation as described in Johns & Martin):
+ Good phase margin, but less than what one would get from the former approach. + Fairly good control over process variation etc. when the gate bias of the compensating device generated properly to ratio with input Gm + No extra stage (less current consumed) + No systematic offset + Slew rate should not be affected - PSRR worse, and similar to that of a standard Miller compensated stage without R - 1 extra pole (Other scheme also introduces an extra pole, but typically at a much higher frequency) - Slightly harder to design (Ahuja compensation can be made to work first time even by a novice)
Both schemes will add extra noise, and a good comparison on this point eludes me.
I prefer the lead compensation scheme in most cases, although I feel that the first approach is much more elegant and simple.
Regards Vivek
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