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

• US 7,049,936 B2
• Filed: 05/11/2001
• Issued: 05/23/2006
• Est. Priority Date: 05/12/2000
• Status: Active Grant

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Wuidart, Luc
• Primary Examiner(s): ZIMMERMAN, BRIAN A
• Application Number:
  US09/853,891
• Publication Number:
  US 20020011922A1
• Time in Patent Office: 1,838 Days
• Field of Search: 340/10.3, 340/10.32, 340/5.92, 340/10.1, 340/572.7, 235/385
• US Class Current: 340/10.4
• 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 method for controlling an electromagnetic field generation terminal using a signal for exciting an oscillating circuit, provided with circuitry for regulating the signal phase in the oscillating circuit, including comparing current values of variables linked to the current in the oscillating circuit and to the voltage thereacross with predetermined values, to detect the presence of a transponder in the electromagnetic field.

Claims

1. A method for controlling an electromagnetic field generation terminal using a signal for exciting an oscillating circuit, provided with means for regulating a signal phase in the oscillating circuit, including comparing present values of variables linked to the current in the oscillating circuit and to the voltage across the oscillating circuit with predetermined values, to detect the presence of a transponder in the electromagnetic field,

wherein said presence detection is implemented when a demodulator included in the terminal detects no signal transmitted by a transponder.

2. The method of claim 1, wherein said predetermined values are measured and stored during an off-load operation of the electromagnetic field generation terminal, while no transponder is present in its field.

3. The method of claim 1, including, in case of the detected presence of a transponder:

deactivating a phase regulation; and

forcing an imaginary part of an impedance of an oscillating circuit of the electromagnetic field generation terminal to a predetermined value.

4. The method of claim 3, wherein forcing said imaginary part is performed by forcing a value of a variable capacitive element of the oscillating circuit.

5. The method of claim 3, applied to a terminal provided with an amplitude demodulator, wherein the predetermined value of forcing of said imaginary part corresponds to an off-load operation of the terminal.

6. The method of claim 3, applied to a terminal provided with a phase demodulator, wherein the predetermined value of forcing of said imaginary part is a function of the position of this imaginary part with respect to a limiting value corresponding to an off-load operation of the terminal.

7. The method of claim 1, including, in case of the detected presence of a transponder and in case of no data detection by an active demodulator among an amplitude demodulator and a phase demodulator included by the terminal, of selecting the other demodulator to detect the data.

8. An apparatus for controlling an electromagnetic field generated by an oscillating circuit, the apparatus comprising:

a demodulator to detect whether a signal is transmitted by a transponder in the electromagnetic field, and

a circuit to determine, in response to the demodulator detecting that a signal is not transmitted by a transponder in the electromagnetic field, whether a transponder is present in the electromagnetic field by comparing present values of variables linked to a current in the oscillating circuit and to a voltage across the oscillating circuit with predetermined values.

9. The apparatus of claim 8, wherein the circuit comprises means for comparing the present values of the variables with the predetermined values.

10. A method of controlling an electromagnetic field generated by an oscillating circuit, the method comprising:

(A) detecting whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter;

(B) if the comparison indicates that a transponder is present in the electromagnetic field, modifying an electrical property of the oscillating circuit in response to the detection; and

(C) determining that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the act (A) is performed in response to the act (C).

11. The method of claim 10, wherein (A) comprises detecting that a transponder is in the electromagnetic field by determining that the present value and the predetermined value are different.

12. The method of claim 10, wherein (C) comprises performing a first type of modulation that is either phase modulation or amplitude modulation, the method further comprising:

(D) in response to (A) and (C), switching from the first type of modulation to a second type of modulation, wherein the second type of modulation is either phase modulation or amplitude modulation and is a different type than the first type.

13. The method of claim 10, wherein (A) comprises detecting a demodulation gap in a detection of data transmitted from a transponder within the electromagnetic field.

14. The method of claim 10, wherein the one or more electrical properties include an electrical current in the oscillating circuit and a voltage across the oscillating circuit.

15. The method of claim 14, wherein the parameter is a ratio of the voltage to the current.

16. The method of claim 10, wherein the oscillating circuit comprises a variable capacitive element, and wherein (B) comprises adjusting a value of the variable capacitive element.

17. The method of claim 10, wherein the predetermined value of the parameter was measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

18. The method of claim 10, further comprising:

(C) deactivating a phase regulation of the oscillating circuit,

wherein (B) comprises forcing an imaginary part of an impedance of the oscillating circuit to a predetermined value.

19. The method of claim 18, wherein the oscillating circuit includes a variable capacitive element,

wherein forcing the imaginary part of the impedance comprises forcing a value of the variable capacitive element.

20. The method of claim 18, further comprising:

(D) performing amplitude demodulation to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein (B) includes forcing the imaginary part of the impedance of the oscillating circuit to a predetermined value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

21. The method of claim 18, further comprising:

(D) performing phase modulation to determine that a data signal has not been generated by a transponder within the electromagnetic field, wherein the predetermined value to which the imaginary part of the impedance is forced is a function of the position of the imaginary part with respect to a limiting value corresponding to a value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

22. An apparatus for controlling an electromagnetic field generated by an oscillating circuit, the apparatus comprising:

a first circuit to detect whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

a second circuit to modify an electrical property of the oscillating circuit in response to the comparison indicating that a transponder is present in the electromagnetic fields,

wherein the comparison indicating that a transponder is present in the electromagnetic field is indicative of detecting a demodulation gap in a detection of data transmitted from the transponder within the electromagnetic field.

23. The apparatus of claim 22, wherein the first circuit comprises means for detecting whether a transponder is present in the electromagnetic field by comparing the present value of the parameter corresponding to the one or more electrical properties of the oscillating circuit to the predetermined value of the parameter.

24. The apparatus of claim 22, wherein the second circuit comprises means for modifying an electrical property of the oscillating circuit in response to the comparison indicating that a transponder is present in the electromagnetic field.

25. The apparatus of claim 22, wherein the first circuit is operative to detect that a transponder is in the electromagnetic field by determining that the present value and the predetermined value are different.

26. The apparatus of claim 22, further comprising:

a first demodulator to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the first circuit is operative to detect whether a transponder is present in the electromagnetic field in response to the determination that a data signal has not been generated by a transponder within the electromagnetic field.

27. The apparatus of claim 26, wherein the first demodulator is operative to perform a first type of modulation that is either amplitude modulation or phase modulation, the apparatus further comprising:

a second demodulator operative to perform a second type of demodulation that is either phase demodulation or amplitude demodulation and is a different type than the first type; and

a selection circuit to select the output of the second demodulator in response to the determination by the first demodulator that a data signal has not been generated by a transponder within the electromagnetic field and the detection that a transponder is present in the electromagnetic field by the first circuit.

28. The apparatus of claim 22, wherein the one or more electrical properties include an electrical current in the oscillating circuit and a voltage across the oscillating circuit.

29. The apparatus of claim 28, wherein the parameter is a ratio of the voltage to the current.

30. The apparatus of claim 22, wherein the oscillating circuit comprises a variable capacitive element, and wherein the second circuit is operative to adjust a value of the variable capacitive element.

31. The apparatus of claim 22, wherein the predetermined value of the parameter was measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

32. The apparatus of claim 22, further comprising:

a phase regulation circuit to regulate the phase of the oscillating circuit,

wherein the second circuit is operative to deactivate the phase regulation performed by the phase regulation circuit, and to force an imaginary part of an impedance of the oscillating circuit to a predetermined value.

33. The apparatus of claim 32, wherein the oscillating circuit includes a variable capacitive element, and wherein the second circuit is operative to force the imaginary part of the impedance by forcing a value of the variable capacitive element.

34. The apparatus of claim 32, further comprising:

an amplitude modulator, to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the second circuit is operative to force the imaginary part of the impedance to a predetermined value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

35. The apparatus of claim 32, further comprising:

a phase demodulator to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the predetermined value to which the imaginary part of the impedance is forced is a function of a position of the imaginary part with respect to a limiting value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

36. A method of controlling an electromagnetic field generated by an oscillating circuit, the method comprising:

(A) detecting whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

(B) if the comparison indicates that a transponder is present in the electromagnetic field, modifying an electrical property of the oscillating circuit in response to the detection,

wherein the comparison indicating that a transponder is present in the electromagnetic field is indicative of detecting a demodulation gap in a detection of data transmitted from the transponder within the electromagnetic field.

37. A method of controlling an electromagnetic field generated by an oscillating circuit, the method comprising:

(A) detecting whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

(B) if the comparison indicates that a transponder is present in the electromagnetic field, modifying an electrical property of the oscillating circuit in response to the detection,

wherein the one or more electrical properties include an electrical current in the oscillating circuit and a voltage across the oscillating circuit, and

wherein the parameter is a ratio of the voltage to the current.

38. A method of controlling an electromagnetic field generated by an oscillating circuit, the method comprising:

(A) detecting whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter;

(B) if the comparison indicates that a transponder is present in the electromagnetic field, modifying an electrical property of the oscillating circuit in response to the detection; and

(C) deactivating a phase regulation of the oscillating circuit,

wherein the act (B) comprises forcing an imaginary part of an impedance of the oscillating circuit to a predetermined value.

39. The method of claim 38, wherein the oscillating circuit includes a variable capacitive element,

wherein forcing the imaginary part of the impedance comprises forcing a value of the variable capacitive element.

40. The method of claim 38, further comprising:

(D) performing amplitude demodulation to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein (B) includes forcing the imaginary part of the impedance of the oscillating circuit to a predetermined value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

41. The method of claim 38, further comprising:

(D) performing phase modulation to determine that a data signal has not been generated by a transponder within the electromagnetic field, wherein the predetermined value to which the imaginary part of the impedance is forced is a function of the position of the imaginary part with respect to a limiting value corresponding to a value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

42. An apparatus for controlling an electromagnetic field generated by an oscillating circuit, the apparatus comprising:

a first demodulator to determine that a data signal has not been generated by a transponder within the electromagnetic field;

a first circuit to detect, in response to the determination that a data signal has not been generated by a transponder within the electromagnetic field, whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

a second circuit to modify an electrical property of the oscillating circuit in response to the comparison indicating that a transponder is present in the electromagnetic field.

43. The apparatus of claim 42, wherein the first demodulator is operative to perform a first type of modulation that is either amplitude modulation or phase modulation, the apparatus further comprising:

a second demodulator operative to perform a second type of demodulation that is either phase demodulation or amplitude demodulation and is a different type than the first type; and

a selection circuit to select the output of the second demodulator in response to the determination by the first demodulator that a data signal has not been generated by a transponder within the electromagnetic field and the detection that a transponder is present in the electromagnetic field by the first circuit.

44. An apparatus for controlling an electromagnetic field generated by an oscillating circuit, the apparatus comprising:

a first circuit to detect whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

a second circuit to modify an electrical property of the oscillating circuit in response to the comparison indicating that a transponder is present in the electromagnetic field,

wherein the one or more electrical properties include an electrical current in the oscillating circuit and a voltage across the oscillating circuit, and

wherein the parameter is a ratio of the voltage to the current.

45. An apparatus for controlling an electromagnetic field generated by an oscillating circuit, the apparatus comprising:

a phase regulation circuit to regulate the phase of the oscillating circuit;

a first circuit to detect whether a transponder is present in the electromagnetic field by comparing a present value of a parameter corresponding to one or more electrical properties of the oscillating circuit to a predetermined value of the parameter; and

a second circuit to modify an electrical property of the oscillating circuit in response to the comparison indicating that a transponder is present in the electromagnetic field,

wherein the second circuit is operative to deactivate the phase regulation performed by the phase regulation circuit, and to force an imaginary part of an impedance of the oscillating circuit to a predetermined value.

46. The apparatus of claim 45, wherein the oscillating circuit includes a variable capacitive element, and wherein the second circuit is operative to force the imaginary part of the impedance by forcing a value of the variable capacitive element.

47. The apparatus of claim 45, further comprising:

an amplitude modulator, to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the second circuit is operative to force the imaginary part of the impedance to a predetermined value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.

48. The apparatus of claim 45, further comprising:

a phase demodulator to determine that a data signal has not been generated by a transponder within the electromagnetic field,

wherein the predetermined value to which the imaginary part of the impedance is forced is a function of a position of the imaginary part with respect to a limiting value measured and stored during an off-load operation of the oscillating circuit, while no transponder was present in the electromagnetic field.