An extension of the classical feedback theory

The classical feedback theory (CFb theory) is a useful tool for circuit analysis but has some limitations: it deals with one-input one-output circuits only; in order to simplify the calculations the signal fed forward by the feedback network is usually neglected but a thorough analysis of the resulting errors is not provided. Moreover, it supplies a degree of traditionalism in the feedback circuits´ analysis and design. This paper presents an extension of the CFb theory that provides a unitary approach to the analysis of feedback circuits, dealing with both voltage and current as input and output signals. The new analysis method is no more difficult to use than the classical one and it spotlights the elements that control the circuit parameters, such as the ideal closed loop gain and the bandwidth. The method was verified by comparision with a direct analysis, at Kirchhoff´s laws level, for circuits having a Π and a T feedback network. Thus its validity was demonstrated for any reciprocal two-port feedback network; also, an estimation of its errors when compared with the direct (i.e. accurate) analysis is provided