Theory of four-terminal double-diffused field-effect transistors

Measurements on 4-terminal double-diffused field-effect transistors show considerable dissimilarity in the control characteristics of each gate, which can only be explained on the basis of a nonuniform channel doping. By using a linear approximation to the actual form of the channel doping, a theory of these devices in the pinchoff region is developed and compared with experimental observations. For the devices used, the agreement is extremely good in that it accurately predicts the ratios of the two transconductances and their variation with voltage. It is observed that the transconductance of the more heavily doped gate (gate 1) exhibits a nearly linear variation with voltage applied to the other gate and that the linearity is maintained over a wide range of gate 1 voltages. Such a property could be usefully exploited in automatic gain control systems.