Semiconductor integrated circuit device and IC card equipped with the same having transistor switch for disconnecting contact power during contactless mode

A semiconductor integrated circuit device comprising:

• a pair of antenna terminals connected to an antenna;
• a power supply circuit for rectifying and smoothing an alternating current signal supplied to the antenna terminals from the antenna to obtain a direct current voltage;
• first and second power supply terminals supplied with electric power from an external apparatus;
• a power supply switch circuit connected between the first power supply terminal and an output terminal of the power supply circuit;
• and
• an internal circuit which operates using a voltage generated by the power supply circuit received by the output terminal of the power supply circuit,
• wherein the power supply switch circuit includes:
• first and second MOS transistors serially connected between the first power supply terminal and the output terminal of the power supply circuit;
• a first pull-up circuit connected to a gate terminal of the first MOS transistor;
• a second pull-up circuit connected to a gate terminal of the second MOS transistor;
• and
• a pull-down circuit connected to the gate terminals of the first and second MOS transistors,
• wherein, when the alternating current signal is obtained from the antenna, the first pull-up circuit short-circuits the gate terminal of the first MOS transistor to the first power supply terminal and the second pull-up circuit short-circuits the gate terminal of the second MOS transistor to the output terminal of the power supply circuit;
• and
• wherein, when no alternating current signal is obtained from the antenna, the first and second pull-up circuits stop operating and potentials at the gate terminals of the first and second MOS transistors become one of a plurality of setup potentials that are set so as to track in a direction from a potential at the first power supply terminal to a potential at the second power supply terminal, and
• wherein, when no alternating current signal is obtained from the antenna, the pull-down circuit sets potentials at the gate terminals of the first and second MOS transistors to one of said setup potentials.