Simple 2nd-order amplifier model for differential and common-mode gain

In this contribution, a simple 2nd-order model of an operational amplifier is presented. This model, which is based on the inclusion of both the first and second most dominant poles in expressions for the gain associated with the inverting and noninverting inputs to the amplifier, permits more detailed considerations of the effects of differential and common-mode gain characteristics on op. amp. circuits than is possible by using the single-dominant-pole model.