Patent ID: 8364077

Claim:
A semiconductor device comprising: an antenna circuit receiving signals from a plurality of interrogators, the antenna circuit being configured to transmit a signal; an amplifier circuit for amplifying the signal to transmit, the amplifier circuit being configured to change amplification degree; a signal sorting portion for sorting the signals from the plurality of interrogators; and a signal detecting portion for detecting intensity of the signals sorted by the signal sorting portion, the signal detecting portion including a rectifier circuit, an A/D conversion circuit and a central processing unit, wherein the central processing unit is configured to calculate a distance between the semiconductor device and each of the plurality of interrogators, based on intensity of a signal output from the rectifier circuit for input to the central processing unit through the A/D conversion circuit, and wherein the antenna circuit is configured to transmit, to the nearest interrogator to the semiconductor device among the plurality of interrogators, a signal including information on the intensity of the signals from the plurality of interrogators.