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Detecting a presence of near field communications (NFC) devices

  • US 9,026,048 B2
  • Filed: 12/14/2011
  • Issued: 05/05/2015
  • Est. Priority Date: 12/05/2011
  • Status: Active Grant
First Claim
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1. A first near field communication (NFC) device, comprising:

  • a modulator configured to modulate a detection signal onto a carrier wave to provide a modulated detection sequence, the detection signal having a first power level for a first duration to provide a first interval, a second power level for a second duration to provide a second interval, and a third power level for a third duration to provide a third interval, the second power level being greater than the first power level;

    a demodulator configured to demodulate the modulated detection sequence to provide a recovered detection sequence; and

    a controller configured to;

    determine a first signal metric of the recovered detection sequence corresponding to the first interval and a second signal metric of the recovered detection sequence corresponding to the second interval,estimate a signal metric estimate of the recovered detection sequence based upon a relationship between the first and the second signal metrics,determine a third signal metric of the recovered detection sequence corresponding to the third interval, anddetermine, based upon a difference between the third signal metric and the signal metric estimate, whether the third signal metric is non-linearly related to the first and the second signal metrics indicating that a second NFC device is present within a magnetic field of the first NFC device.

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