Patent ID: 6176433
Filing Date: 2001-01-23
Classification: G06K

Abstract:
A reader/writer comprising:a power supply portion which generates a voltage as a power transmission signal to be supplied to an IC card;an encoder circuit which encodes an input communication data and outputs an encoded communication signal to be transmitted to the IC card;an amplitude-modulator which superimposes a signal being amplitude-modulated by the encoded communication signal outputted from said encoder circuit on the signal generated from said power supply portion and outputs an amplitude-modulated signal;a feeding circuit which feeds the amplitude-modulated signal outputted from the amplitude-modulator as a current signal;an antenna which generates an electromagnetic wave to perform transmission of both operating power and communication to the IC card; andwherein said antenna comprises a main coil which generates an electromagnetic field used for transmission of both said operating power and said communication by feeding the current signal from the feeding circuit and a plurality of auxiliary coils which are disposed with substantially symmetry with respect to said main coil and which generate magnetic fields opposite in phase to a magnetic field generated by said main coil by feeding the current signal from the feeding circuit to thereby restrain an intensity of the electromagnetic field at a distance.