NMOS triggered NMOS ESD protection circuit using low voltage NMOS transistors

摘要

An integrated circuit is provided with electrostatic discharge (ESD) protection circuitry (120) which uses low voltage transistors (N1, N2) to provide protection to a signal pad that handles high voltage signals during normal operation of the integrated circuit. The external signal is operable at a second supply voltage that is higher than the Vdd supply voltage. The internal circuitry of the integrated circuit is comprised of MOS transistors that have gate oxide of a first thickness that has a Vox-max suitable for the Vdd supply voltage but not for the second supply voltage. The ESD protection transistors use the same gate oxide thickness as the MOS transistors used in the internal circuitry. A substrate region in the semiconductor substrate is enclosed by a highly doped region (250) so that the back-gates of the ESD protection transistors can be voltage pumped by pump circuitry (202) in order to trigger bipolar conduction of the ESD protection transistors at a lower voltage. Control circuitry (204) is connected to the signal bond pad and to gates of the ESD protection transistors and to gates of the pump transistors to provide a voltage pulse to each gate in response to an ESD zap applied to the signal bond pad. The control circuitry provides a bias potential to the gates of the ESD protection transistors and pump transistors such that the maximum operating voltage of the gate oxide of each device is not exceeded during normal operation of the integrated circuit, thereby avoiding electrical over-stress (EOS) of the low voltage devices in the ESD protection circuitry.