Patent ID: 8301915

Claim:
A semiconductor integrated circuit device comprising: an antenna terminal coupled to an antenna; a first power supply circuit for rectifying and smoothing an AC signal supplied from the antenna to the antenna terminal, thereby obtaining a DC voltage in a first power supply line; a power supply terminal and a ground terminal to which power is supplied from the outside; a second power supply circuit comprising a first MOS transistor disposed between the power supply terminal and the first power supply line and a voltage control circuit for controlling a voltage of a gate terminal of the first MOS transistor; a substrate potential control circuit for controlling substrate voltage of the first MOS transistor; and a second MOS transistor, wherein in the case of using the voltage generated by the first power supply circuit as a power supply, the first MOS transistor is interrupted, thereby isolating the power supply terminal and the first power supply line from each other, wherein in the case of using a power supply from an external terminal, the voltage control circuit controls the first MOS transistor to suppress voltages supplied from the power supply terminal and the ground terminal to a predetermined voltage and outputs the resultant voltage to the first power supply line, wherein the second MOS transistor which substrate voltage and gate voltage of the first MOS transistor conductive in the case of using the voltage generated by the first power supply circuit as a power supply, and which makes the substrate voltage and the gate voltage nonconductive in the case of using a power supply from an external terminal, and wherein the substrate potential control circuit outputs the voltage of the first power supply line as the substrate voltage in the state where the first MOS transistor is interrupted, and outputs the voltage of the first power supply terminal as the substrate voltage in a state where the first MOS transistor is not interrupted.