Patent attributes
A trigger circuit is provided for a pull-down device by connecting a diode between the I/O pad and the body of the pull-down device. In one embodiment, the pull-down device is formed as a plurality of discrete transistors in a single well. The drain of each transistor is connected through a ballast resistor to the I/O pad; and the source of each transistor is connected through a ballast resistor to ground. The trigger circuit is a diode formed in a different well from that of the transistors. The cathode of the diode is connected to the I/O pad and the anode is connected to the transistor well through a center tap located between the transistors. Preferably, the transistors are NMOS transistors formed in a P-well. Advantageously, the diode is an N+/PLDD diode. Alternatively, the diode is an N+/P diode where the P region is formed by an ESD implant. In other embodiments the diode is formed in the same well as the transistors. In these embodiments, either an N+/PLDD diode or an implanted diode is formed in place of one of the transistors.
