Simplified model of an amplifier with two poles and a pole-zero doublet

A simple representation of an open-loop two-pole amplifier with a pole-zero doublet is proposed. It is based on the consideration that a pole-zero doublet does not greatly modify the behaviour of the closed-loop two-pole amplifier. Indeed, assuming an underdamped behaviour we have found that the pole-zero doublet only affects the phase margin and, hence, it can accurately be accounted by properly modifying the second pole of the original two-pole amplifier.