EVALUATION OF THE COUPLING FACTOR OF AN ELECTROMAGNETIC TRANSPONDER BY CAPACITIVE DETUNING

• US 20110300800A1
• Filed: 06/02/2011
• Published: 12/08/2011
• Est. Priority Date: 06/03/2010
• Status: Active Grant

• Current Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SAS (STMicroelectronics NV)
• Inventors: Wuidart, Luc
• Granted Patent: US 8,798,533 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• CPC Class Codes: G06K 19/0715 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

Abstract

A method for evaluating the current coupling factor between an electromagnetic transponder and a terminal, and a transponder implementing this method, wherein a ratio between data representative of a voltage across an oscillating circuit of the transponder and obtained for two capacitance values of the oscillating circuit 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 capacitance values of the oscillating circuit, 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 capacitance; and

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

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

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 capacitance between the first and second values is obtained by switching a capacitive element comprised by the transponder.

6. An electromagnetic transponder comprising:

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

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

7. The transponder of claim 6, further comprising at least one switchable capacitive element capable of being functionally connected in parallel to the oscillating circuit.