blackuni thanks for your answer.I am aware of these methods you proposed me.But my question is more theoritical and intuitional and concerns an approach to my problem that does not require from somebody to make hand calculations or circuit analysis.Maybe i was not much clear to my first post...i don't care about the exact equation that gives me the poles and zeros of an analog cmos topology but i care about their position,that is at which node we expect to have a pole or zero or pole zero doublet.ofcourse i do not know if this approach is feasible,but in any case that's why i opened this question.thanks for any future helpful feedback.