Detection of the distance between an electromagnetic transponder and a terminal

  • US 6,473,028 B1
  • Filed: 04/05/2000
  • Issued: 10/29/2002
  • Est. Priority Date: 04/07/1999
  • Status: Expired due to Term
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First Claim
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1. A method of determining a distance separating an electromagnetic transponder from a terminal generating a magnetic field via a first oscillating circuit, the transponder including a second oscillating circuit, upstream of a rectifier adapted to provide a D.C. voltage having a level, the method comprising the steps of:

  • storing a first information relative to the level of the D.C. voltage when the second oscillating circuit is tuned on a determined frequency;

    storing a second information relative to the level of the D.C. voltage after having caused a frequency detuning of the second oscillating circuit; and

    comparing the first and second information.

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