Analysis and compensation of two-pole amplifiers with a pole-zero doublet

A simple representation of a two-pole amplifier with a pole-zero doublet is proposed which can be used in the compensation of transconductance amplifiers. The model is based on the consideration that a pole-zero doublet does not greatly modify the behavior of the closed-loop amplifier. Indeed, assuming an underdamped behavior we have found that the pole-zero doublet only affects the phase margin and, hence, it can accurately be accounted for by properly modifying the second pole of the original two-pole amplifier. Simulations on a two-stage transconductance amplifier show that such a model closely agrees with the time response of the real amplifier.