As we know, we can get a formula for dominant pole using zero-value time constant method.But, It is very hard to get a formula for the first non-dominant pole.The first non-dominant pole is very important for feedback amplifier stability andfrequency performance.
What I mean is that if we get a formula for the first non-dominant pole, then we can know what factors influence the first non-dominant pole and how to improve it.
As we know, for stability, GBP must be smaller than the first non-dominat pole by a factor 4 or 3.
Normally, the GBP of the forward amplifier is the bandwidth of the feedback ampifier, so if we improve the GBP of the forward amplifier, we get wider bandwidth of the feedback amplifier.But, there is a promblem that when the GBP is bigger than the first non-dominant pole, the feedback amplifier become unstable.