ACTIVE TWO–PORT NETWORKS

In Chap. 1 we introduced many fundamental concepts related to linear, time-invariant n-port networks. Some of the results, although very general, are difficult to apply. In Chap. 2 we discussed a useful description of the external behavior of a multiterminal network in terms of the indefinite-admittance matrix, and demonstrated how it can be employed effectively for the computation of network functions.

In practical applications, the most useful class of n-port or n-terminal networks is that of two-port or three-terminal networks. Many active devices of practical importance such as transistors are naturally subsumed in this class. In this chapter, we consider the specialization of the general passivity condition for n-port networks in terms of the more immediately useful two-port parameters. We introduce various types of power gains, sensitivity, and the notion of absolute stability as opposed to potential instability. Llewellyn's conditions for absolute stability and the optimum terminations for absolutely stable two-port networks at a single frequency will be derived.