RESISTIVE EVALUATION OF THE COUPLING FACTOR OF AN ELECTROMAGNETIC TRANSPONDER

• US 20100323629A1
• Filed: 06/15/2010
• Published: 12/23/2010
• Est. Priority Date: 06/19/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Inventors: Wuidart, Luc
• Granted Patent: US 8,693,956 B2
• Time in Patent Office: Days
• US Class Current: 455/67.11
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• CPC Class Codes: G06K 19/0702 the arrangement including a battery
• CPC Class Codes: G06K 19/0715 the arrangement including means to regulate power transfer to the integrated circuit
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier

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 values of the resistive load, is compared with one or several thresholds.

Claims

1. 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 values of the resistive load, is compared with one or several thresholds.

2. The method of claim 1, wherein:

first data, relative to the level of a D.C. voltage provided by a rectifier across the oscillating circuit, are measured and stored for a first value of the resistive load; and

second data, relative to the level of said D.C. voltage, are measured and stored for a second value of the resistive load.

3. The method of claim 1, wherein the evaluation provides a position of the current coupling factor with respect to an optimum coupling position with one of the two values of the resistive load.

4. The method of claim 1, wherein said thresholds are a function of said values.

5. The method of claim 1, wherein a variation of the resistive load between the first and second values is obtained by modifying a power consumption of processing circuits comprised by the transponder.

6. The method of claim 1, wherein a variation of the resistive load between the first and second values is obtained by switching a resistive retromodulation element comprised by the transponder.

7. A method for protecting an electromagnetic transponder against a possible overheating based on an evaluation of the coupling according to claim 1, wherein a detuning of the oscillating circuit is caused if the ratio between the current coupling and the optimum coupling ranges between two thresholds.

8. An electromagnetic transponder comprising:

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

at least one processing unit programmed to implement the method of claim 1.

9. The transponder of claim 8, further comprising at least one switchable resistive element capable of being functionally connected in parallel on the oscillating circuit.

10. The transponder of claim 9, wherein said switchable resistive element is connected to the output terminals of the rectifying circuit.