READER-WRITER FOR NON-CONTACT IC CARD, AND OUTPUT POWER CONTROL METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To prevent a non-contact IC card from being damaged by excessive power supply. SOLUTION: The output voltage V of an amplifier 2 increases when the coupling coefficient with a non-contact IC card antenna becomes large. Then, the relation of the voltage V (proportional to the output voltage Vs of a power control circuit 13) and the coupling coefficient is obtained and made into a table beforehand and an IC 12 obtains the coupling coefficient from the voltage V detected in a voltage detection circuit 11. Also, since the reception power P of the non-contact IC card is decided when the voltage V and the coupling coefficient are supplied, the IC 12 determines the voltage Vs from the relation of the voltage Vs for making the P be almost absolute minimum and the coupling coefficient and performs control so as to turn the output voltage of the power control circuit 13 to the value.