Active ESD shunt with transistor feedback to reduce latchup susceptibility or false triggering

We present an anomalous latchup failure phenomenon related to the large Nwell resistor associated with the generic RC-triggered, MOSFET-based active clamp circuit for on-chip ESD protection between VCC and VSS buses. A novel active clamp circuit with PMOS feedback technique has been proposed to reduce the IC's susceptibility to latchup during negative current injection at neighboring I/O pads or false triggering of the RC trigger circuit due to noise on the VCC power line. The effectiveness of this new active clamp circuit is confirmed by our experiment and simulation results. Optimisation of the size of the PMOS feedback transistor is also discussed in this paper.