Synchronous-phase contactless demodulation method, and associated demodulator and reader

• US 20050280510A1
• Filed: 05/26/2005
• Published: 12/22/2005
• Est. Priority Date: 06/16/2004
• Status: Active Grant

• Current Assignee: Thales DIS France SA (Thales SA)
• Original Assignee: Gemplus (Thales SA)
• Inventors: Capomaggio, Gregory, Guinet, Alain, Caruana, Jean-Paul
• Granted Patent: US 8,154,388 B2
• Time in Patent Office: Days
• US Class Current: 340/10.4
• CPC Class Codes: H04B 5/45 Transponders
• CPC Class Codes: H04B 5/77 for interrogation

Abstract

A method of demodulating signals of an electromagnetic field induced by a contactless transponder includes a step in which the signals from the transponder are detected at given times or frequency. The times or frequency of the detection are synchronised in phase with the electromagnetic field. An associated demodulator and reader are also disclosed.

Claims

1. A method of demodulating signals from an electromagnetic field induced by a contactless transponder comprising a step of detecting signals from the transponder at given times or frequency, wherein the times or frequency of the detection are synchronised in phase with the electromagnetic field.

2. A demodulation method according to claim 1, wherein in order to synchronise, the flux caused by the electromagnetic field is picked up in an additional coil and the phase of the flux is used as a synchronisation element.

3. A demodulation method according to claim 1, wherein, in order to synchronise, the phase of the current generating the electromagnetic field is picked up and is used as a synchronisation element.

4. A demodulation method according to claim 2, wherein the signals of the transponder are detected at a sampling frequency equal to and in phase with the frequency of the electromagnetic field.

5. A demodulation method according to claim 2, wherein a synchronisation clock is generated from the phase taken from the electromagnetic field or its generating current and this clock is used to time the signal detection time.

6. A contactless transponder reader comprising a main antenna for transmitting/receiving an electromagnetic field, an electromagnetic signal demodulator comprising means of sampling the electromagnetic signal at a sampling frequency, and synchronisation means able to time and synchronise in phase the said sampling frequency of the demodulator with the phase of the electromagnetic field.

7. A contactless transponder reader according to claim 6, wherein the synchronisation means comprise an additional antenna able to pick up part of the magnetic field used by the transponder, and a sampling control circuit able to generate a signal controlling the synchronous sampling of the electromagnetic field.

8. A contactless transponder reader according to claim 6, wherein the synchronisation means comprise an antenna sensitive to the electrical field.

9. A contactless transponder reader according to claim 6, wherein the synchronisation means comprise current diversion means able to take off part of the current flowing in the conductor forming the reading antenna and to extract therefrom phase information for synchronising the sampling.

10. A transponder reader according to claim 7, wherein said additional antenna is detuned with respect to the main antenna.

11. A transponder reader according to claim 6, wherein the demodulator is a synchronous detection demodulator.

12. A transponder reader according to claim 6, wherein the synchronous detection is digital.

13. A demodulator for signals induced by a contactless transponder in an electromagnetic field, said demodulator comprising a detector for signals occurring at given times, means of slaving the detection to the phase of the electromagnetic field, wherein the slaving means continuously provide synchronisation with the phase.