Patent ID: 8038070

Claim:
A noncontact data carrier which performs radio communication with a reader/writer, using electromagnetic wave or electromagnetically-induced binding via an antenna, comprising: a power supply unit for obtaining a power source from a reception signal received by the antenna; a demodulation unit for demodulating the reception signal; a decoding unit for decoding the demodulated signal; a signal processing unit for performing data processing based on the contents of the decoded signal, and generation of a signal to be transmitted to the reader/writer; a coding unit for coding the signal to be transmitted to the reader/writer, which signal is generated in the signal processing unit; a modulation unit for changing the signal coded by the coding unit to a modulated signal; a battery for performing supply of electric power to a part of the noncontact data carrier or to the whole circuit; and a power supply control unit for controlling start or stop of the supply of electric power from the battery to a part of the noncontact data carrier or to the whole circuit, on the basis of the signal state of the reception signal, wherein said power supply control unit comprises: a frequency judgment unit for performing a first judgment as to whether the frequency of the reception signal is included in a predetermined frequency range or not, and a time judgment unit for performing a second judgment as to whether the state where the frequency of the reception signal is included in the predetermined frequency range is continued for a predetermined period of time or not, after the first judgment is made by the frequency judgment unit, and said power supply control unit starts supply of electric power from the battery to the noncontact data carrier when the second judgment is made by the time judgment unit after the first judgment has been made by the frequency judgment unit.