Finnegan, Henderson, Farabow, Garrett & Dunner
Semiconductor input/output circuits operating at different power supply voltages
 In an integrated circuit device using a plurality of different power supply voltages, the application of an input voltage exceeding the power supply voltages to an input/output circuit is prevented. When a p-type substrate is used, a plurality n-wells are formed to surround an integrated circuit region on a central portion of the substrate. When an n-type substrate is used, a plurality of p-wells are formed in the same manner. A predetermined power supply voltage is applied to each well to select transistors of the input/output buffer in accordance with the voltage level of an external voltage. 
Kabushiki Kaisha Toshiba
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Toshiaki Izumi Yukinori Yasunori
Mori Sakai Uchino Tanaka