Small-signal responses realizable from d.c.-biased devices

It is suggested that there are realizability criteria pertaining to active as well as to passive systems. In particular, the small-signal stability properties of an active electrical network cannot be realized in practice unless the network conforms to certain limitations. Criteria are derived for small-signal immittances and afterwards extended to immittance matrices. The notion of general realizability is interpreted in terms of the physical nature of an active device. The non-linearity inherent in all active devices is assumed to `function¿ by means of a `diversion energy¿. This restricts the validity of some methods of non-linear analysis.