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Reader/writer for performing efficient transmission/reception with no-battery information storage medium

  • US 5,966,404 A
  • Filed: 09/15/1997
  • Issued: 10/12/1999
  • Est. Priority Date: 09/19/1996
  • Status: Expired due to Term
First Claim
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1. A reader/writer which transmits power and modulated data to a no-battery information storage medium having a communication function in a noncontact state, and receives modulated data from said no-battery information storage medium, comprising:

  • a driver for transmitting the power a nd the modulated data;

    a loop antenna connected to an output line of said driver to receive a transmission carrier current from said driver; and

    current detection means, arranged between said loop antenna and the output line of said driver, for extracting, as a reception signal, a change in transmission carrier current of said loop antenna caused by a signal of the modulated data received by said loop antenna while the transmission carrier current is supplied from said driver upon reception of the modulated data from said no-battery information storage medium wherein, when a binary-phase-modulated signal having undergone binary phase modulation with a sub-carrier having a frequency 1/n (n is an integer) a transmission carrier frequency used for transmission is received as the modulated data from said no-battery information storage medium, said reader/writer uses said current detection means to extract, as the modulated data received by said loop antenna, a signal current of the binary-phase-modulated signal having undergone binary phase modulation with the sub-carrier having the frequency 1/n the transmission carrier frequency used for transmission, and further comprisessignal processing means for changing the binary-phase-modulated signal extracted by said current detection means into a binary signal; and

    demodulation means for starting counting from an edge of a pulse for an ON period of the pulse of the binary signal from said signal processing means on the basis of the transmission carrier frequency to detect a timing of substantially a center of a width of the pulse, and starting dividing the transmission carrier frequency from a detection timing to generate a clock having the same frequency as that of the sub-carrier, and to use the clock as a demodulation clock for the binary-phase-modulated signal.

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