Patent ID: 6084431
Filing Date: 2000-07-04
Classification: H03K

Abstract:
A semiconductor integrated circuit comprising:a power-supply voltage terminal;an output terminal to which an external voltage higher than the power supply voltage can be applied; anda first MOS transistor which has a source, a drain, a gate, and a back gate, one end of a current path between the source and the drain being connected to said output terminal;a control circuit which is supplied with said power-supply voltage and supplies a control voltage to said gate of said first MOS transistor;wherein when an external voltage higher than said power-supply voltage is applied to said output terminal, said control circuit supplies to said gate of said first MOS transistor said control voltage having a value varying in an analogue relationship with said external voltage within a range of values lower than said power-supply voltage and turns on said first MOS transistor, so that a potential difference between said one end of said current path and said gate of said first MOS transistor is higher than an absolute value of a threshold voltage of said first MOS transistor, thereby permitting said external voltage at said one end of said current path between the source and the drain of said first MOS transistor to be transmitted to the other end of said current path,wherein said control circuit further includes:a control voltage output terminal outputting said control voltage;a first reference potential terminal having a lower potential than said power-supply voltage;a second MOS transistor of a conductivity type opposite to that of said first MOS transistor, having a source, a drain, a gate, a back gate, with a current path between the source and the drain being connected between said power-supply voltage terminal and said control voltage output terminal, and the gate being connected to the output terminal, to which an external voltage higher than the power supply voltage can be applied; anda pull-down element having a current path connected between said output terminal and said first reference potential terminal.