Patent ID: 8810375

Claim:
A semiconductor device comprising: an antenna circuit; a power supply circuit; and a signal control circuit, wherein the power supply circuit comprises: a rectifier circuit which rectifies signals from the antenna circuit; a battery which is charged by the rectified signals; a control circuit connected at one end to the rectifier circuit and the other end to the battery; a switching circuit connected between the control circuit at said one end and a power source circuit to selectively provide power to the power source circuit; and a low-frequency signal generation circuit connected to the control circuit at said one end and selectively controls the switching state of the switching circuit, wherein the low-frequency signal generation circuit comprises: a ring oscillator that outputs an oscillation signal at a frequency; a divider circuit configured to divide the oscillation signal and provide a plurality of outputs from 1 to n (n is an integer) as sequentially output signals from the divider circuit; and an AND circuit configured to generate an output signal whose duty ratio of the output signal is 1:n, from the sequentially output signals of the divider circuit; wherein the control circuit is configured to selectively supply power from the rectifier circuit and/or the battery to the power source circuit through the switching circuit, wherein power supplied by the control circuit is selected by the switching circuit to be supplied to the power source circuit when the output signal is a high signal, wherein the power supplied by the control circuit is selected by the switching circuit to be not supplied to the power source circuit when the output signal is a low signal, wherein the power source circuit comprises a circuit configured to generate a reference voltage, and wherein the power source circuit outputs the same potential as a potential of the reference voltage in a period depending on the duty ratio of the output signal when the power is supplied to the power source circuit by the switching circuit.