Resistance of Feedback Amplifiers: A Novel Representation

We propose a representation and a related methodology for evaluating the exact input and output resistances of feedback amplifiers. Our approach is based on the generalization of the Rosenstark theorem. Indeed, it requires the computation of two resistances (direct and asymptotic) each one evaluated in one of the two ideal and extreme conditions of the return ratio (zero or infinity). Due to these characteristics, the representation allows one to understand what happens to a feedback amplifier resistance in the case of absence of feedback or in the ideal case of infinite feedback.