| 摘要 |
A contactless card and a contactless card system are provided to prevent internal damage of the contactless smart card by preventing overvoltage from occurring in a short distance between the contactless smart card and reader, as output voltage of a voltage generation circuit is linearly controlled by installing a variable capacitor, a shunt transistor, and a controller to the contactless smart card. A resonant capacitor(211) is connected between both ends of an antenna. The capacitors(213) are connected in parallel between both ends of the antenna through corresponding switches. The shunt transistor(214) forms a bypass current path by being connected between both ends of the antenna. A rectifier(215) generates DC voltage by being connected between both ends of the antenna. The control circuit(27) monitors the DC voltage, and controls gate voltage of the shunt transistor and a turn-on/off state of the switches according to a monitoring result. The control circuit includes a voltage detector(271) determining whether the DC voltage is the overvoltage, and a selector(273) adjusting the gate voltage of the shunt transistor depending on the result of the voltage detector and outputting selection signals for turning on/off the switches.
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