Validation of the presence of an electromagnetic transponder in the field of a phase demodulation reader

• US 20060111043A1
• Filed: 10/27/2005
• Published: 05/25/2006
• Est. Priority Date: 05/12/2000
• Status: Active Grant

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Wuidart, Luc
• Granted Patent: US 7,263,330 B2
• Time in Patent Office: Days
• US Class Current: 455/41.100
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

A terminal for generating an electromagnetic field adapted to communicating with at least one transponder, and a method for controlling such a terminal including: an oscillating circuit adapted to being excited by a remote supply signal of the transponder; a phase demodulator for detecting possible data transmitted by the transponder; circuitry for regulating the signal phase in the terminal'"'"'s oscillating circuit on a reference value; circuitry for measuring variables linked to the current in the oscillating circuit and to the voltage thereacross; and circuitry for comparing current values of these variables with predetermined values, to determine the presence of a transponder.

Claims

11. A system for determining whether at least one transponder is present in an electromagnetic field generated by an oscillating circuit, comprising:

a first circuit to measure at least one present value of at least one electrical property of the oscillating circuit; and

a second circuit to compare the at least one present value with at least one previously measured value of the at least one electrical property that was measured when no transponder was present in the electromagnetic field.

12. The system of claim 11, wherein the first circuit includes a means for measuring the at least one present value.

13. The system of claim 11, wherein the second circuit includes means for comparing the at least one present value with the at least one previously measured value.

14. The system of claim 11, wherein the second circuit comprises a microprocessor.

15. The system of claim 11, wherein the second circuit is operative to determine at least one transponder is present in the electromagnetic field if the at least one present value and the at least on previously measured value are not equal.

16. The system of claim 11, wherein a first of the at least one electrical property corresponds to a current in the oscillating circuit.

20. The system of claim 11, further comprising:

a first circuit to force a value of an electrical property of the oscillating circuit to a particular value in response to the comparison performed by the second circuit.

21. The system of claim 20, wherein the oscillating circuit includes a variable capacitive element, and wherein the third circuit is operative to control a value of the variable capacitive element.

22. The system of claim 20, wherein the second circuit is operative to calculate a present imaginary part of an impedance of the oscillating circuit, to compare a present absolute value of this imaginary part with a predetermined limiting value, to select, if the present absolute value is greater than the limiting value, a forcing value that forces an imaginary part of the impedance of the oscillating circuit to a same absolute value as, but opposite sign of, the present imaginary part, and to choose, if the present absolute value is smaller than or equal to the limiting value, a different forcing value according to whether the present imaginary part is positive or negative.

23. The system of claim 11, wherein the third circuit is operative to prevent a regulation of a signal phase of the oscillating circuit if the second circuit determines that the at least one present value in the at least one previously measured value are not equal.

18. The system of claim 17, wherein a second of the at least one electrical property corresponds to a current in the oscillating circuit.

1. A method of determining whether at least one transponder is present in an electromagnetic field generated by an oscillating circuit, comprising:

measuring at least one present value of at least one electrical property of the oscillating circuit; and

comparing the at least one present value with at least one previously measured value of the at least one electrical property that was measured when no transponder was present in the electromagnetic field.

2. The method of claim 1, further comprising:

determining at least one transponder is present in the electromagnetic field if the at least one present value and the at least one previously measured value are not equal.

3. The method of claim 1, wherein a first of the at least one electrical property corresponds to a current in the oscillating circuit.

4. The method of claim 1, wherein a first of the at least one electrical property corresponds to a voltage across the oscillating circuit.

5. The method of claim 4, wherein a second of the at least one electrical property corresponds to a current in the oscillating circuit.

6. The method of claim 5, wherein the measuring includes measuring a present value of the first electrical property and measuring a present value of the second electrical property, and

wherein the comparing includes comparing a value of a ratio of the present values of the first electrical property and the second electrical property to a ratio of a previously measured value of the first electrical property and a previously measured value of the second electrical property.

7. The method of claim 1, further comprising:

in response to the comparing, forcing a value of an electrical property of the oscillating circuit to a particular value.

8. The method of claim 7, wherein the oscillating circuit includes a variable capacitive element, and

wherein the forcing includes controlling a value of the variable capacitive element.

9. The method of claim 7, further comprising:

calculating a present imaginary part of an impedance of the oscillating circuit;

comparing a present absolute value of this imaginary part with a predetermined limiting value;

if the present absolute value is greater than the limiting value, choosing a forcing value that forces an imaginary part of the impedance of the oscillating circuit to a same absolute value as, but opposite sign of, the present imaginary part; and

if the present absolute value is smaller than or equal to the limiting value, choosing a different forcing value according to whether the present imaginary part is positive or negative.

10. The method of claim 1, further comprising:

if the comparing determines that the at least one present value and the at least one previously measured value are not equal, preventing regulation of a signal phase of the oscillating circuit.

19. The system of claim 11, wherein a first of the at least one electrical property corresponds to a voltage across the oscillating circuit.

19-1. The method of claim 18, wherein the first circuit is operative to measure a present value of the first electrical property and to measure a present value of the second electrical property, and

wherein the second circuit is operative to compare a value of a ratio of the present values of the first electrical property and the second electrical property to a ratio of a previously measured value of the first electrical property and a previously measured value of the second electrical property.