Two-level demodulation method and device
First Claim
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1. Method for demodulating information emitted by amplitude modulation with two levels by a reader to a transponder, the method comprising:
- using a voltage regulation loop to generate a slaving voltage that is a function of a signal received by the transponder, the voltage regulation being a regulation on a voltage at terminals of a load impedance;
determining a sign signal representing the variations of the slaving voltage, the sign signal taking a first or a second value depending on whether the slaving voltage is increasing or decreasing;
checking, for each symbol, the hold time of the sign signal; and
determining modulation level based on said checking.
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Abstract
The invention relates to a method for demodulating information emitted by amplitude modulation with two levels by a reader (2) to a transponder (4), comprising a step to determine if this symbol is identical to or is different from the previous symbol, after each symbol.
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Citations
15 Claims
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1. Method for demodulating information emitted by amplitude modulation with two levels by a reader to a transponder, the method comprising:
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using a voltage regulation loop to generate a slaving voltage that is a function of a signal received by the transponder, the voltage regulation being a regulation on a voltage at terminals of a load impedance; determining a sign signal representing the variations of the slaving voltage, the sign signal taking a first or a second value depending on whether the slaving voltage is increasing or decreasing; checking, for each symbol, the hold time of the sign signal; and determining modulation level based on said checking. - View Dependent Claims (2, 3, 4, 5, 6)
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7. Device for demodulating information emitted by amplitude modulation with two levels by a reader to a transponder, comprising:
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a voltage regulation loop configured to generate a transponder slaving voltage as function of a signal received by the transponder, the voltage regulation being a regulation on a voltage at terminals of a load impedance; and means to detect, for each symbol, a change of modulation level by checking the hold time of the sign signal translating the variations of the transponder slaving voltage, the sign signal taking a first or a second value depending on whether the slaving voltage is increasing or decreasing. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. Method for demodulating information emitted by amplitude modulation with two levels by a reader to a transponder, in which, for each received symbol, the following steps are implemented:
determining if a sign signal representing the variations of a slaving voltage of the transponder has changed several times during the duration of the received symbol; if not, and if the sign signal representing the variations of the slaving voltage of the transponder is equal to a first value, then the value of the received symbol is equal to 1; if not, and if the sign signal representing the variations of the slaving voltage of the transponder is equal to a second value, then the value of the received symbol is equal to 0; if yes, and if the hold time of the sign signal representing the variations of the slaving voltage of the transponder is lower than a threshold value, then the value of the received symbol is equal to the value of a previous symbol; if yes, and if the hold time of the sign signal is greater than the threshold value and if the sign signal is equal to the second value, then the value of the received symbol is equal to 0; if yes, and if the hold time of the sign signal is greater than the threshold value and if the sign signal is equal to the first value, then the value of the received symbol is equal to 1.
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15. Device for demodulating information emitted by amplitude modulation with two levels by a reader to a transponder, comprising:
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means for memorizing a sign bit of a received symbol; means for indicating changes to the sign bit of the received symbol; an “
identical sign”
string length counter;a comparator indicating if the value of the counter is greater or not than a threshold value; two means com_0 and com_1 whose values are determined such that; com_0=1 if the value of the counter is greater than the threshold value and if the value of the sign bit is equal to 0; com_1=1 if the value of the counter is greater than the threshold value and if the value of the sign bit is equal to 1; means for determining the value of the received symbol according to the values of com_0 and com_1 such that; if com_0=1, the value of the received symbol is equal to 0; if com_1=1, the value of the received symbol is equal to 1; if com_0=com_1=0, the value of the received symbol is equal to the value of a previous symbol; wherein the means for determining the value of the decoded bit operates at the symbol frequency and all other means of the device operate at an over-sampling frequency.
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Specification