| 摘要 |
A circuit and a method are disclosed to provide a tristate input/output buffer which is compatible with 5 volt input signals, applied to its input/output (I/O) node, while operating with a 3 volt power supply and is resistant to CMOS latchup. The 5 volt compatibility is achieved by inserting an additional p-channel transistor in series with the existing p-channel transistor and circuitry to control the additional p-channel transistor. The control circuit is comprised of 2 transistors. The CMOS latchup resistance is provided by a N-well bias generator that changes the N-well bias to be equal to the higher of the 2 voltages, VDD or the voltage present at the I/O pad. The N-well bias generator is comprised of 3 transistors.
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