Importance

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Abstract

A non-contact IC card communication in which power consumption of a driver of a reader/writer is reduced and the size of a power supply circuit for operating the driver is made small. The driver has a low output impedance. A current detecting circuit including a detecting coil magnetically coupled with a transceiver coil of the reader/writer through a magnetic coiling element and a resistor detects a current which flows through the transceiver coil. A voltage drop to be detected is small and is approximately constant for a variation of the transceiver coil current. When data is read from an IC card, a load of the driver is changed. The driver drives the transceiver coil in a constant voltage fashion even if a current flowing through the transceiver coil changes due to the change in load. Input voltages of a rectifying/smoothing circuit and a regulator in the IC card become approximately constant. As a result, the amplitude of a high frequency output voltage of the driver can be made small. Also, a high frequency signal current sent from a reader/writer is subjected to double modulation including amplitude modulation by card data and modulation by second information, such as information indicative of the abnormality of an IC card, in synchronism with a timing at which data transmission between the reader/writer and the card is made, and the second information is extracted by the reader/writer.

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First Claim