Detection of the distance between an electromagnetic transponder and a terminal
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United States of America Patent
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Oct 29, 2002
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N/A
app pub date -
Apr 5, 2000
filing date -
Apr 7, 1999
priority date (Note) -
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Abstract
A method and apparatus for determining the distance separating an electromagnetic transponder from a terminal generating a magnetic field by a first oscillating circuit, the transponder including a second oscillating circuit, upstream of a rectifying circuit adapted to providing a D.C. voltage. The method includes 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 two stored pieces of information.
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