Semiconductor integrated circuit

1. A semiconductor integrated circuit operating on multiple supply potentials including a first supply potential and a second supply potential that is higher than the first supply potential, comprising:

a potential-lowering circuit operating on the second supply potential and including an N-channel MOS transistor whose gate and drain receive the second supply potential and that outputs a third supply potential from a source thereof, the third supply potential being lower than the second supply potential;

a judging circuit operating on the third supply potential outputted from the potential-lowering circuit and judging whether the first supply potential is high-level or low-level;

a buffer circuit outputting a control signal showing whether the first supply potential is fed based on judgment outputted from the judging circuit,

the judging circuit including:

a first inverter that receives and inverts the first supply potential; and

multiple P-channel MOS transistors whose source-drain paths are series-connected between the second supply potential and an output node of the first inverter, and

the judging circuit includes a second inverter that inverts a signal outputted from the first inverter, a signal outputted from the second inverter is fed to a gate of a first P-channel MOS transistor out of the multiple P-channel MOS transistors, and a gate of another P-channel MOS transistor out of the multiple P-channel MOS transistors is connected to the first supply potential.

2. The semiconductor integrated circuit according to claim 1 , the potential-lowering circuit includes multiple N-channel MOS transistors whose drain-source paths are series-connected and whose gates are applied with the second supply potential.

3. The semiconductor integrated circuit according to claim 1 , the potential-lowering circuit is constituted by series-connecting multiple N-channel MOS transistors that are saturation-connected.

4. The semiconductor integrated circuit according to claim 1 , the judging circuit includes a second inverter that inverts a signal outputted from the first inverter, a signal outputted from the second inverter is fed to a gate of a first P-channel MOS transistor out of the multiple P-channel MOS transistors, and a gate of another P-channel MOS transistor out of the multiple P-channel MOS transistors is connected to a ground potential.

5. A semiconductor integrated circuit operating on multiple supply potentials including a first supply potential and a second supply potential that is higher than the first supply potential, comprising:

a potential-lowering circuit operating on the second supply potential and including an N-channel MOS transistor whose gate and drain receive the second supply potential and that outputs a third supply potential from a source thereof; the third supply potential being lower than the second supply potential;

a judging circuit operating on the third supply potential outputted from the potential-lowering circuit and judging whether the first supply potential is high-level or low-level;

a buffer circuit outputting a control signal showing whether the first supply potential is fed based on judgment outputted from the judging circuit,

the judging circuit including:

a first inverter that receives and inverts the first supply potential; and

multiple P-channel MOS transistors whose source-drain paths are series-connected between the second supply potential and an output node of the first inverter,

the judging circuit includes a second inverter that inverts a signal outputted from the first inverter, a signal outputted from the second inverter is fed to a gate of a first P-channel MOS transistor out of the multiple P-channel MOS transistors, and a gate of another P-channel MOS transistor out of the multiple P-channel MOS transistors is connected to a ground potential,

the first inverter includes multiple P-channel MOS transistors whose drain-source paths are series-connected and whose gates are applied with the first supply potential, and

the second inverter includes multiple P-channel MOS transistors whose source-drain paths are series-connected and whose gates are applied with signals outputted from the first inverter.

6. The semiconductor integrated circuit according to claim 1 ,

the buffer circuit includes multiple inverters and outputs a differential signal showing whether the first supply potential is fed based on judgment outputted from the judging circuit.

7. A semiconductor integrated circuit operating on multiple supply potentials including a first supply potential and a second supply potential that is higher than the first supply potential, comprising:

a potential-lowering circuit operating on the second supply potential and including an N-channel MOS transistor whose gate and drain receive the second supply potential and that outputs a third supply potential from a source thereof, the third supply potential being lower than the second supply potential;

a judging circuit operating on the third supply potential outputted from the potential-lowering circuit and judging whether the first supply potential is high-level or low-level;

a buffer circuit outputting a control signal showing whether the first supply potential is fed based on judgment outputted from the judging circuit;

an internal circuit that operates on the first supply potential;

a first level-shifter and a second level-shifter that shift a potential of a signal outputted from the internal circuit;

an output driver including a P-channel MOS transistor and an N-channel MOS transistor that are series-connected to generate an output signal based on a signal outputted from the first level-shifter and the second level-shifter, respectively, when the second supply potential is fed; and

a switching circuit that fixes a gate potential of the P-channel MOS transistor at a high level and a gate potential of the N-channel MOS transistor at a low level based on the control signal outputted from the buffer circuit,

the judging circuit including:

a first inverter that receives and inverts the first supply potential; and

multiple P-channel MOS transistors whose source-drain paths are series-connected between the second supply potential and an output node of the first inverter.