Indefinite-admittance matrix formulation of feedback amplifier theory

It is shown that the return-difference and the null return-difference functions of a feedback amplifier can be elegantly and compactly formulated in terms of the first- and the second-order cofactors of the elements of its indefinite-admittance matrix. The relationship between the generalized cofactors of the elements of the cutset-admittance matrix and the second-order cofactors is indicated. Based on these results, topological formulas for these functions are presented. The significance of the new formulation is that it avoids the necessity of interpreting the loop gain in terms of the actual signal transmission around the closed loops in a flow graph, which in many cases is very misleading.