Editing Network analysis (electrical circuits) (section)

===Time-varying components===
In linear analysis, the components of the network are assumed to be unchanging, but in some circuits this does not apply, such as sweep oscillators, [[voltage controlled amplifier]]s, and variable [[Electronic filter|equalisers]].  In many circumstances the change in component value is periodic. A non-linear component excited with a periodic signal, for instance, can be represented as a periodically varying ''linear'' component. [[Sidney Darlington]] disclosed a method of analysing such periodic time varying circuits. He developed canonical circuit forms which are analogous to the canonical forms of [[Ronald M. Foster]] and [[Wilhelm Cauer]] used for analysing linear circuits.<ref>{{Ref patent |country=US |number=3265973 |status=patent |title=Synthesis of two-port networks having periodically time-varying elements |gdate=1966-08-09 |fdate=1962-05-16 |inventor=Sidney Darlington, Irwin W. Sandberg }}</ref>