ABSTRACT
This chapter shows that the return difference can be evaluated by measuring driving-point impedances at a convenient port in the feedback amplifier. The measurement of the return difference provides an elegant solution to the stability problem. The zeros of the network determinant are called the natural frequencies. Their locations in the complex frequency plane are extremely important in that they determine the stability of the network. A network is said to be stable if all of its natural frequencies are restricted to the open left-half side of the complex-frequency plane. However, for a physical network there remains the difficulty of getting an accurate formulation of the network determinant itself, because every equivalent network is, to a greater or lesser extent, an idealization of the physical reality. As frequency is increased, parasitic effects of the physical elements must be taken into account.
