Quality Semiconductor Inc.

Steve W Liu

Chit Ah Mak

Hung T Nguyen

An overvoltage tolerant CMOS tristate output buffer capable of withstanding tristate overvoltages without reverse currents or latch-up, the output buffer having a stabilized protection circuit for driving the N-well and gate of the P-channel driver transistor to the output pad voltage when the output pad voltage becomes excessive. The stabilized protection circuit includes a hysteresis circuit for controlling switch transistors which bias the N-well. The presence of the hysteresis circuit causes the protection circuit to have an input hysteresis characteristic, thus preventing excessive switching of the N-well biasing transistors when the output pad voltage varies near the output buffer power supply voltage during tristate.

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Homebush, Australia

Steve W Liu