Quality Semiconductor Inc.

Hung T Nguyen

Leo Lee

Chit Ah Mak

Steve W Liu

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.

CMOS tristate output buffer with having overvoltage protection and

A mixed-mode, overvoltage tolerant input buffer for interfacing to a tristate bus line is disclosed, the input buffer having a bus hold feature for maintaining the state of the input buffer output and bus line when the bus line enters into the tristate mode, the input buffer being capable of suppressing leakage currents from the bus input through the bus hold circuit to the input buffer power supply during overvoltage conditions. The bus hold circuit has a feedback inverter coupled between the output and the bus input for providing a stabilizing feedback signal to the bus input, the inverter being powered by a source voltage which is selectively coupled to the input buffer power supply, the source voltage being isolated from the input buffer power supply during overvoltage conditions.

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San Jose, CA, United States of America

Hung T Nguyen