BJT—MOSFET transconductance comparisons

Through normalization it becomes possible to construct curves of considerable generality for comparing the transconductance properties of BJT\´s and MOSFET\´s. Three comparisons are given. The first presents transconductance as a function of output current; the second, transconductance divided by output current as a function of input voltage; and the third, transconductance as a function of input voltage. The BJT advantage increases rapidly with output current and (or) input voltage. The curves approach each other under extremely low-level conditions, but appreciable deviations from the simple theory upon which the present analysis is based also occur in the low-level regime--especially deviations connected with subthreshold conduction in the MOSFET, as well as "excess" conduction near but above threshold. For these reasons, the moderate-level portions of the simple-theory comparisons are the most meaningful. Recently developed subthreshold analysis is also used in the second comparison.