Patent ID: 8138893

Claim:
A semiconductor integrated circuit device used in an IC tag converting a radio wave received from a reader/writer to power and returning information to the reader/writer comprising: a rectification circuit receiving the radio wave outputted from the reader/writer, rectifying power caused by electromagnetic induction of the radio wave and generating a primary voltage; a voltage stabilization circuit stabilizing the primary voltage generated by the rectification circuit and generating an internal power source voltage; a command demodulation circuit demodulating a command added to the radio wave outputted from the reader/writer to a digital signal; a command decode unit decoding the command of the digital signal demodulated by the command demodulation circuit; and a communication distance limitation control circuit limiting a communication distance with the reader/writer, the communication distance limitation control circuit comprising: a communication distance setting unit storing communication distance limitation setting data for setting the limitation of the communication distance with the reader/writer; and a power intensity monitor unit monitoring power of the primary voltage generated by the rectification circuit and making a judgment as to whether or not the power of the primary voltage is greater than or equal to a predetermined field intensity, wherein the communication distance limitation control circuit performs control so that: (1) the command decode unit receives an input of the digital signal outputted from the command demodulation circuit by making a connection between the command demodulation circuit and the command decode unit conductive when the communication distance limitation setting data is not set in the communication distance setting unit, (2) the command decode unit receives the input of the digital signal outputted from the command demodulation circuit by making the connection between the command demodulation circuit and the command decode unit conductive when the communication distance limitation setting data is set in the communication distance setting unit and the power intensity monitor unit makes judgment that the power of the primary voltage is greater than or equal to the predetermined field intensity, and (3) the command decode unit receives no input of the digital signal outputted from the command demodulation circuit by making the connection between the command demodulation circuit and the command decode unit nonconductive when the communication distance limitation setting data is set in the communication distance setting unit and the power intensity monitor unit makes iudgment that the power of the primary voltage is less than the predetermined field intensity.