Patent ID: 7012794

Claim:
An analog transfer gate connected to an external line also connected to a digital circuit, comprising: a NMOS transfer transistor connected between said external line and an analog circuit; a PMOS transfer transistor connected between said external line and said analog circuit; at least one protection transistor connected to one of said NMOS and PMOS transfer transistors; a voltage sensing circuit connected to said external line and configured to sense a voltage higher than a supply voltage of said analog circuit and produce a sense output signal; and a protection enabling circuit, having an input coupled to said voltage sensing circuit and outputs connected to said PMOS and NMOS transfer transistors and said protection transistor, said protection enabling circuit being responsive to said sense output signal to turn off said PMOS and NMOS transfer transistors and activate said protection transistor, wherein said voltage sensing circuit comprises: first and second interconnected PMOS sensing transistors coupled to said external line and said supply voltage, respectively, said first transistor turning on when a voltage on said external line exceeds said supply voltage by more than a predetermined amount; a transistor circuit connected between said first PMOS sensing transistor and ground; and a feedback circuit connected between said transistor circuit and said first and second PMOS sensing transistors for accelerating the turn-on time of said first transistor.