Electromagnetic transponder read terminal operating in very close coupling
First Claim
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1. A terminal for generating an electromagnetic field adapted to cooperate with at least one transponder when the transponder enters in the electromagnetic field of the terminal, the terminal including:
- an oscillating circuit adapted to receiving a high frequency A.C. excitation voltage; and
means for detuning the oscillating circuit to a detuned mode with respect to a determined transmission frequency when the at least one transponder is very close to the terminal;
wherein the terminal provides power to the at least one transponder via the electromagnetic field when the terminal is in the detuned mode.
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Abstract
A terminal for generating an electromagnetic field adapted to cooperating with at least one transponder when the latter enters its field, the terminal including an oscillating circuit adapted to receiving a high frequency A.C. excitation voltage, and circuitry for detuning this oscillating circuit with respect to a determined transmission frequency when a transponder is very close to the terminal.
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Citations
14 Claims
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1. A terminal for generating an electromagnetic field adapted to cooperate with at least one transponder when the transponder enters in the electromagnetic field of the terminal, the terminal including:
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an oscillating circuit adapted to receiving a high frequency A.C. excitation voltage; and
means for detuning the oscillating circuit to a detuned mode with respect to a determined transmission frequency when the at least one transponder is very close to the terminal;
wherein the terminal provides power to the at least one transponder via the electromagnetic field when the terminal is in the detuned mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A terminal that generates an electromagnetic field, the terminal being adapted to communicate with a transponder when the transponder enters the electromagnetic field, the terminal comprising:
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an oscillating circuit including a resistive element and a variable capacitive element;
a controller, coupled to the oscillating circuit, that switches the oscillating circuit between a tuned mode and a detuned mode; and
a first comparator that provides a comparison bit, a value of the comparison bit indicating a distance between the terminal and the remote transponder relative to a critical coupling point;
wherein the controller switches the oscillating circuit between the tuned mode and the detuned mode in response to the value of the comparison bit. - View Dependent Claims (10)
a measuring device that measures a current in the oscillating circuit to provide a measured current; and
a second comparator that compares a phase of the measured current with a reference value and generates a control signal;
wherein the controller adjusts the variable capacitive element to detune the oscillating circuit based at least in part on the control signal.
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11. A wireless data transmission system comprising:
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at least one transponder that does not have an independent power source; and
a terminal that generates an electromagnetic field, the terminal including;
an oscillating circuit having resistive element and a variable capacitive element and adapted to receive an AC excitation voltage; and
a controller that switches the oscillating circuit between a tuned mode and a detuned mode based on a distance between the transponder and the terminal;
wherein the transponder receives operating power from the terminal via the electromagnetic field when the terminal is in the detuned mode. - View Dependent Claims (12, 13, 14)
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Specification