| 摘要 |
It is an object of the present invention to provide a semiconductor device which can be surely supplied electric power by electromagnetic waves in different frequency bands without preventing reduction in size and weight of a semiconductor device. A semiconductor device capable of wireless communication is provided with a frequency determining circuit which detects the frequency of the electromagnetic waves received by the antenna and a circuit which automatically adjusts impedance in accordance with information from the frequency determining circuit, and the semiconductor device communicates and obtains electric power by one antenna. For adjustment of impedance, a circuit which can change the inductance or the capacitance, or an antenna which can change the length is used.
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