Inductive evaluation of the coupling factor of an electromagnetic transponder

• US 8,395,485 B2
• Filed: 06/15/2010
• Issued: 03/12/2013
• Est. Priority Date: 06/19/2009
• Status: Active Grant

• Current Assignee: Stmicroelectronics Rousset SAS (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Rousset SAS (STMicroelectronics NV)
• Inventors: Wuidart, Luc
• Primary Examiner(s): Lee, Benjamin C
• Assistant Examiner(s): CARLSON, ADAM C
• Application Number:
  US12/815,681
• Publication Number:
  US 20100321164A1
• Time in Patent Office: 1,001 Days
• Field of Search: 340 101- 104, 340/572, 340/636.17, 340/636.2, 340/655, 340/662, 340/664, 455/41.1, 455/125
• US Class Current: 340/10.4
• CPC Class Codes: G06K 7/10158 methods and means used by the interrogation device for reliably powering the wireless record carriers using an electromagnetic interrogation field

Abstract

A method for evaluating the current coupling factor between an electromagnetic transponder and a terminal, wherein a ratio between data representative of a voltage across an oscillating circuit of the transponder and obtained for two pairs of inductive and capacitive values of this oscillating circuit is compared with one or several thresholds, the two pairs of values preserving a tuning of the oscillating circuit to a same frequency.

Claims

1. A method for evaluating a current coupling factor between an electromagnetic transponder and a terminal, comprising:

obtaining data representative of a voltage across an oscillating circuit of the transponder for two pairs of inductive and capacitive values of the oscillating circuit, the two pairs of values preserving a tuning of the oscillating circuit to a same frequency;

comparing a ratio with one or several thresholds, wherein the ratio is between the data representative of the voltage across the oscillating circuit for the two pairs of inductive and capacitive values;

generating an evaluation of the current coupling factor between the transponder and the terminal based on a result of the comparing; and

operating the transponder in accordance with the evaluation.

2. The method of claim 1, wherein obtaining data representative of the voltage across the oscillating circuit comprises:

measuring and storing first data relative to the level of a D.C. voltage provided by a rectifier connected across the oscillating circuit for a first pair of inductive and capacitive values of the oscillating circuit; and

measuring and storing second data relative to the level of said D.C. voltage for a second pair of inductive and capacitive values of the oscillating circuit.

3. The method of claim 1, further comprising determining, based on the evaluation, a position of the current coupling factor with respect to an optimum coupling position with a first of the two pairs of values.

4. The method of claim 1, wherein a threshold of said one or several thresholds is a function of the inductive values of the respective pairs of values.

5. The method of claim 1, wherein the current coupling factor is evaluated against an optimum coupling position with a first of the two pairs of values.

6. A method for protecting an electromagnetic transponder against a possible overheating using the method of claim 1 by controlling operation of the transponder based on the evaluation, and further comprising detuning the oscillating circuit if the ratio between the current coupling factor and an optimum coupling ranges between two thresholds.

7. An electromagnetic transponder comprising:

an oscillating circuit, upstream of a rectifying circuit capable of providing a D.C. voltage when the transponder is in a magnetic field of a terminal; and

at least one switchable inductive element and at least one switchable capacitive element capable of being functionally connected in parallel with the oscillating circuit;

a processing unit programmed to;

obtain data representative of a voltage across the oscillating circuit for two pairs of inductive and capacitive values of the oscillating circuit, the two pairs of values preserving a tuning of the oscillating circuit to a same frequency; and

compare a ratio with one or several thresholds, wherein the ratio is between the data representative of the voltage across the oscillating circuit for the two pairs of inductive and capacitive values;

generate an evaluation of a current coupling factor between the transponder and the terminal based on a result of the comparing; and

operate the transponder in accordance with the evaluation.

8. The transponder of claim 7, wherein said switchable inductive and capacitive elements are connected to output terminals of the rectifying circuit.

9. The transponder of claim 7, wherein:

first switchable inductive and capacitive elements are connected between a first terminal of the oscillating circuit and the ground;

second switchable inductive and capacitive elements are connected between a second terminal of the oscillating circuit and the ground.

10. The transponder of claim 7, wherein the at least one switchable inductive element is formed by at least one active circuit.

11. A method comprising:

obtaining first data corresponding to a voltage across an oscillating circuit of an electromagnetic transponder tuned to a frequency, a capacitance and an inductance of the oscillating circuit being set to a first capacitance value and a first inductance value, respectively;

obtaining second data corresponding to the voltage across the oscillating circuit tuned to the frequency, the capacitance and the inductance of the oscillating circuit being set to a second capacitance value and a second inductance value, respectively;

evaluating a current coupling factor between the transponder and a terminal in accordance with one or more comparisons between a quantity and one or more respective thresholds, the quantity being derived from the second data and the first data; and

operating the electromagnetic transponder in accordance with a result of the evaluating.

12. The method of claim 11, wherein:

the first data comprises a level of a D.C. voltage provided by rectifying the voltage across the oscillating circuit having the first capacitance and inductance values; and

the second data comprises a level of a D.C. voltage provided by rectifying the voltage across the oscillating circuit having the second capacitance and inductance values.

13. The method of claim 11, wherein evaluating the current coupling factor comprises:

performing the one or more comparisons between the quantity and the one or more respective thresholds; and

identifying a position of the current coupling factor with respect to an optimum coupling position in accordance with the one or more comparisons.

14. The method of claim 11, wherein the one or more thresholds are functions of the first inductance and the second inductance.

15. The method of claim 11, further comprising:

in a case where a ratio between the current coupling factor and the optimum coupling ranges between a first threshold and a second threshold, detuning the oscillating circuit.

29. The method of claim 13, wherein the quantity is a ratio between the second data and the first data.

16. An electromagnetic transponder comprising:

an oscillator configured to provide a signal in response to a magnetic field of a terminal;

a rectifier configured to rectify a voltage of the signal provided by the oscillator; and

a switchable inductive element and a switchable capacitive element connected in parallel,

wherein

an inductance and a capacitance of the oscillator are adjustable among a plurality of pairs of inductive and capacitive values which correspond to a tuning of the oscillating circuit to a same frequency; and

a processing unit programmed to;

obtain first data corresponding to a voltage across the oscillator, the oscillator being tuned to a frequency, the capacitance and the inductance of the oscillator being set to a first capacitance value and a first inductance value, respectively;

obtain second data corresponding to the voltage across the oscillator, the oscillator being tuned to the frequency, the capacitance and the inductance of the oscillator being set to a second capacitance value and a second inductance value, respectively;

evaluate a current coupling factor between the transponder and the terminal in accordance with one or more comparisons between a ratio and one or more respective thresholds, the ratio being between the second data and the first data; and

operate the electromagnetic transponder in accordance with a result of the evaluating.

17. The transponder of claim 16, wherein the oscillator comprises an inductive element and a capacitive element connected in parallel with the switchable inductive element and the switchable capacitive element.

18. The transponder of claim 16, wherein:

the oscillator comprises an inductive element and a capacitive element connected in parallel and connected to input terminals of the rectifier; and

the switchable inductive element and the switchable capacitive element are connected to output terminals of the rectifier.

19. The transponder of claim 16, wherein:

the oscillator comprises an inductive element and a capacitive element connected in parallel and connected to input terminals of the rectifier;

the switchable inductive element and the switchable capacitive element are connected in parallel between a first terminal of the oscillator and a ground; and

the transponder further comprises a second switchable inductive element and a second switchable capacitive element connected in parallel between a second terminal of the oscillator and the ground.

20. The transponder of claim 16, wherein the switchable inductive element is formed by at least one active circuit.

21. An electromagnetic transponder comprising:

an oscillator configured to provide a signal in response to a magnetic field of a terminal;

means for adjusting an inductance and a capacitance of the oscillator among a plurality of pairs of inductive and capacitive values, wherein each of the plurality of pairs of inductive and capacitive values corresponds to a tuning of the oscillating circuit to a same frequency, wherein the means for adjusting an inductance and a capacitance of the oscillator comprises a switchable inductive element and a switchable capacitive element connected in parallel; and

a rectifier configured to rectify a voltage of the signal provided by the oscillator, and

a processor programmed to;

obtain first data corresponding to a voltage across the oscillator, the oscillator being tuned to the first frequency, the capacitance and the inductance of the oscillator being set to a first capacitance value and a first inductance value, respectively;

obtain second data corresponding to the voltage across the oscillator, the oscillator being tuned to the first frequency, the capacitance and the inductance of the oscillator being set to a second capacitance value and a second inductance value, respectively;

evaluate a current coupling factor between the transponder and the terminal in accordance with one or more comparisons between a ratio and one or more respective thresholds, the ratio being between the second data and the first data; and

operate the electromagnetic transponder in accordance with a result of the evaluating.

22. The transponder of claim 21, wherein the oscillator comprises an inductive element and a capacitive element connected in parallel and connected to input terminals of the rectifier.

23. An electronic system for wireless communication, comprising:

a terminal comprising a first oscillator capable of generating a magnetic field; and

an electromagnetic transponder comprising;

a second oscillator configured to provide a signal in response to the magnetic field,

a switchable inductive element and a switchable capacitive element connected in parallel, wherein an inductance and a capacitance of the second oscillator are adjustable among a plurality of pairs of inductive and capacitive values which correspond to a tuning of the second oscillating circuit to a same frequency,

a rectifier configured to rectify a voltage of the signal provided by the second oscillator, and

a processing unit programmed to;

obtain first data corresponding to a voltage across the second oscillator, the second oscillator being tuned to a frequency, the capacitance and the inductance of the second oscillator being set to a first capacitance value and a first inductance value, respectively;

obtain second data corresponding to the voltage across the second oscillator, the second oscillator being tuned to the frequency, the capacitance and the inductance of the second oscillator being set to a second capacitance value and a second inductance value, respectively; and

evaluate a current coupling factor between the transponder and the terminal in accordance with one or more comparisons between a ratio and one or more respective thresholds, the ratio being between the second data and the first data; and

operate the electromagnetic transponder in accordance with a result of the evaluating.

24. The system of claim 23, wherein the second oscillator comprises an inductive element and a capacitive element connected in parallel with the switchable inductive element and the switchable capacitive element.

25. The system of claim 23, wherein:

the second oscillator comprises an inductive element and a capacitive element connected in parallel and connected to input terminals of the rectifier; and

the switchable inductive element and the switchable capacitive element connected to output terminals of the rectifier.

26. The system of claim 23, wherein:

the second oscillator comprises an inductive element and a capacitive element connected in parallel and connected to input terminals of the rectifier;

the switchable inductive element and the switchable capacitive element are connected in parallel between a first terminal of the second oscillator and a ground; and

the transponder further comprises a second switchable inductive element and a second switchable capacitive element connected in parallel between a second terminal of the second oscillator and the ground.

27. The system of claim 23, wherein the terminal includes a regulating circuit and an antenna, and the regulating circuit is configured to regulate a phase of a signal of the antenna such that a phase relationship between the antenna signal and a reference signal is constant.

28. The system of claim 27, wherein the regulating circuit is further configured to regulate the phase of the antenna signal such that, in static operation, an imaginary part of an apparent impedance of the first oscillator is zero.