| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a semiconductor integrated circuit for surely receiving power from a reader/writer so as to extend the communication distance even when a plurality of responders such as wireless tags are superposed on each other. <P>SOLUTION: A rectifier circuit converts an AC current produced by an external mounted antenna coil and a tuning capacitor into a DC voltage. A tuning control circuit outputs a control signal in response to the DC voltage detected by a voltage detection circuit. The capacitance of the tuning capacitor is changed when receiving the control signal. For example, when the DC voltage does not reach a prescribed voltage because inductance is increased by allowing a plurality of antenna coils to approach to each other, the tuning control circuit controls the tuning capacitor to decrease its capacitance. Thus, the resonance frequency is increased up to an optimum value to increase the DC voltage at which the semiconductor integrated circuit can be operable. Accordingly, even when the antenna coils are overlapped, communication with the reader/writer or the like can be ensured. Further, the communication distance of the reader/writer or the like can be extended. <P>COPYRIGHT: (C)2004,JPO |
