Patent ID: 6181193
Filing Date: 2001-01-30
Classification: H03K

Abstract:
A driver circuit for driving a bidirectional pad, comprising:a diode connected from ground to said pad;one or more series connected diodes connected from said pad to a first voltage supply;a thick oxide PFET having a source connected to said first voltage supply, a drain connected to said pad, and an N-WELL;a first thick oxide NFET having a drain connected to said pad, a gate connected to said first voltage supply, and a source;a second thick oxide NFET having a drain connected to said source of said first NFET and a source connected to said ground;a bias circuit for biasing said N-WELL of said PFET to the higher of either the voltage at said pad or said first voltage supply, andan isolation circuit for turning off said PFET when said voltage at said pad rises above said first voltage supply.