Switching characteristics of m.o.s. and junction-gate field-effect transistors

The nonlinear differential equations describing the large-signal switching behaviour of field-effect transistors (f.e.t.s) are derived. They are shown to be analogous to those of an RC transmission line having uniform linear resistance but nonlinear capacitance per unit length. Solutions of these equations, based on an effective linear-capacitance approximation, are obtained and applied to the cases of metal-oxide-semiconductor transistors (m.o.s.t.s) and junction-gate field-effect transistors. It is experimentally established that there is little difference between the response characteristics of an exact nonlinear RC distributed line, and these of a corresponding effective linear RC distributed line. Under switching conditions, the rise time associated with the short-circuit current response is shown to be smaller than the rise time associated with the open-circuit voltage response. The latter is found to be approximately equal to the small-signal channel transit time in both the m.o.s.t. and junction-gate f.e.t.