| 摘要 |
<p>PROBLEM TO BE SOLVED: To stabilize voltage induced by a card and to enlarge a communication distance range for the change of a distance between a reader/writer and the card by switching the sensitivity of an antenna in accordance with the level of a reception signal. SOLUTION: Since power supply largely fluctuates by the distance between the reader/writer W20 and the card 10, the quality factor Q of an antenna resonance circuit 4 is changed in accordance with voltage after rectification on a card 10-side for absorbing the fluctuation so as to stabilize voltage induced by the card 10. A comparator 7 and a reference power source unit 7a constitute a reception level detection means and a variable resistance element 8 constitutes a quality factor adjusting means. When the comparator 7 detects that voltage after rectification exceeds a prescribed value, the variable resistance element 8 is adjusted so that the quality factor Q of the antenna resonance circuit 4 becomes low in accordance with exceeding quantity. Thus, received voltage is adjusted by the dropping of Q.</p> |
