Charging Circuit for a Substrate Generator Pump Capacitor
Original Publication Date: 1985-May-01
Included in the Prior Art Database: 2005-Feb-18
A typical charging circuit for a substrate generator pump capacitor (Fig. 1) requires a diode 3 to prevent charge from being driven into ground during the pumping operation. When PA is high, capacitor C1 is charged through transistor 1 and diode 3. However, this means that at most, the capacitance voltage VC1 = 5V - Vt3, resulting in less charge available for pumping the substrate. A circuit is provided to eliminate the threshold voltage loss in a grounded source diode within a substrate generator pump, resulting in a smaller capacitance needed for the pump and less process sensitivity in the substrate voltage. The circuit in Fig. 2 eliminates the Vt loss when the capacitor is charged. In this circuit when PA is high, PC is low.