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

• US 20020011922A1
• Filed: 05/11/2001
• Published: 01/31/2002
• 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 7,049,936 B2
• Time in Patent Office: Days
• 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 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.

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

4. The method of claim 3, 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.

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

6. The method of claim 4, 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.

7. The method of claim 4, 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.

8. The method of claim 3, 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.

9. A terminal of generation of an electromagnetic field adapted to cooperating with at least one transponder when said transponder enters this field, including means for implementing the method of claim 1