Reader/writer having coil arrangements to restrain electromagnetic field intensity at a distance

  • US 6,176,433 B1
  • Filed: 05/15/1998
  • Issued: 01/23/2001
  • Est. Priority Date: 05/15/1997
  • Status: Expired due to Fees
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First Claim
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1. 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; and

    wherein 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.

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