Area-efficient clamp for power ring esd protection using a transmission gate

Abstract

Electrostatic discharge (ESD) protection is provided by a charge-latching power-to-ground clamp circuit. A filter capacitor and resistor generate a filter voltage that is buffered by three stages to drive the gate of a BigFET such as a large n-channel transistor. A transmission gate between the stages turns off when BigFET turns on, causing charge to be latched. The filter capacitor can then discharge while the BigFET remains on. A leaker resistor slowly discharges the gate of the large BigFET and turns the transmission gate back on when the BigFET turns off after shunting the ESD current. The length of time that the clamp shunts the ESD current is determined by the leaker resistor and gate capacitance of the BigFET, not by the filter capacitor, so a small filter capacitor may be used.