Simple expressions for the effect of substrate doping on the gain of m.o.s.t.s

Approximate expressions have been derived for the gain falloff of an m.o.s.t. with substrate doping. The expressions compare the mutual conductance on an extrinsic substrate with that on an intrinsic substrate for criteria of equal power dissipation, channel current or gate voltage. For the first two criteria, the approximation gives agreement to within 15% over all practical substrate doping levels when substrate biasing is small. The third, however, can only be used for low and moderate doping levels. It is shown that, with moderate substrate doping, thc gain falloff is small if a criterion of constant power or channel current is used.