The advantages of Miller compensation for OTA

what is the need for negative miller compensation for an Operational Transconductance Amplifier(OTA) ???

what is its advantage over conventional method of connecting a capacitor from the output of the OTA to ground???

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.

Re: Compensation of OTA

I second sutapanakis analysis..
Though OTA's always have a high impedance output node , be it a single stage or a 2-stage design. Adding to the above analysis, the presence of a larger "load capacitance" in fact helps in improving the phase margin in a conventional OTA. But if the design of the OTA is done for a particular load cap in mind, then the currents flowing in the output branches are fixed which in turn fixes the miller capacitance value. Hope that makes sense.