Substrate bias modulation to improve mosfet circuit performance

摘要

A load device characteristic is improved for a static inverter by reducing the load device threshold voltage as the output voltage increases from its initial value. The circuit structure to accomplish this is an isolated substrate within which the FET load device is located, that substrate being connected to an inverter circuit for raising the voltage of the substrate as the source potential increases for the preferred depletion mode load device. The particular circuit is a two-stage inverter, the first stage being a modulating signal source, the output of the first stage inverter being connected to the isolated substrate of the FET load for a second inverter, so that the FET load device for the second stage inverter has its substrate modulated so that the magnitude of the substrate potential changes at a faster rate than does the source potential. This tracking of the potential of the substrate with respect to the potential of the source of the device decreases the threshold voltage as the output voltage of the second stage increases.