Circuit for Pumping Current Out of a Negative Substrate
Original Publication Date: 1988-Jun-01
Included in the Prior Art Database: 2005-Feb-15
A field-effect transistor (FET) circuit for pumping current out of a negative substrate is disclosed which increases the efficiency of the substrate generator by eliminating a threshold voltage loss in the substrate discharge path. Fig. 1 shows FET 1, hereafter identified as T1, connected as a diode and used in a substrate generator circuit to provide a path for the discharging substrate, Vsub. Current is conducted through T1. However, because of the diode connection of T1 (gate tied to drain), not all of the charge on pump capacitor Cp is available for discharging the substrate, i.e., VT x Cp is not usable. Normally, a larger value of Cp is required to provide the needed charge because the gate of T1 cannot be tied directly to a high voltage - this would cause T1 to be on all the time and render the pump inoperative.