Re: Compensation of OTA
These are different things. One stage OTA, or rather an amplifying stage with one high impedance node, that is meant to work in a feedback configuration is compensated by a cap to ac ground. If you have a 2 stage amplifier you also have two poles which in uncompensated state are kind of close to each other. You can still compensate by a cap to ground and thus move one of the poles to very low frequencies such that the ac response roll off is -20 dB/dec until it crosses 0db, but this would require a very large capacitor which is not practical and the loop-gain BW will be very low. Much more practical solution is to use Miller type of compensation which apart from moving one of the poles to low frequencies has the additional advantage of moving the non-dominant pole to higher frequencies - the so called pole splitting and thus requiring less capacitance and less power compared to the case when only the dominant pole was moved to lower frequencies.