Damping factor control for multistage amplifiers?

Hello,

I saw a quite interesting compensation technique for multistage amplifiers : damping factor control. It connected another amplifier stage with capacitor negative feedback at one pole of the original amplifier.

(There are several IEEE papers on it. For example, the slides on **broken link removed**)


I just really want to understand how does this technique work and where can it be used?

I don't have experience with that kind of amplifier and also see it for the first time and obviously there is some math behind it. But here is what I can say by just looking at the schematic on slide 5 of your attachment. Obviously Cm1 serves as a Miller capacitance to create the dominant pole. Cm2 with gm4 create another Miller capacitor applied at the intermediate node. This one controls the non-dominant pole. The thing is that in contrast to the nested millar compensation you avoid the RHP zeros. Cm2 doesn't connect to the output, so no zero from there in the main signal path. Cm1 does connect to the output and forms a feed-forward non-inverting path to output which would cause a RHP zero to appear but I guess by the help of gmf2 which is an inverting feed-forward you can compensate the current at output that would come from Cm1 and thus remove also that RHP. Probably other non-dominant poles/zeros appear in the circuit but they can be pushed to frequencies beyond the unity gain frequency of the loop gain.

It was mainly used for loop stability and phase compensation.