METHOD AND DEVICE FOR MODULATING AN ACTIVE LOAD WITH DAMPING OF AUTO OSCILLATION

• US 20130288599A1
• Filed: 09/21/2011
• Published: 10/31/2013
• Est. Priority Date: 09/21/2010
• Status: Active Grant

• Current Assignee: Verimatrix Incorporated (Verimatrix SA)
• Original Assignee: Inside Secure SA
• Inventors: Charrat, Bruno, Bernard, Frdric, Cordier, Nicolas, Pernisek, Florian
• Granted Patent: US 9,331,748 B2
• Time in Patent Office: Days
• US Class Current: 455/41.1
• 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: H04B 1/3816 Mechanical arrangements for accommodating identification devices, e.g. cards or chips; with connectors for programming identification devices
• CPC Class Codes: H04B 5/72 for local intradevice communication
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically

Abstract

A method for sending data by inductive coupling includes: extracting an antenna signal from an antenna circuit, extracting from the antenna signal a first periodic signal, producing a second periodic signal by way of a synchronous oscillator, placing the oscillator in a free oscillation mode and applying to the antenna circuit the second periodic signal, modifying the impedance of the antenna circuit, restoring the amplitude of the antenna signal, then resynchronizing the oscillator on the first periodic signal.

Claims

1. A method for sending data by inductive coupling, comprising:

applying an alternating external magnetic field to an inductive antenna circuit tuned to a carrier frequency of the external magnetic field,

extracting an antenna signal from the antenna circuit,

extracting from the antenna signal a first periodic signal,

producing a second periodic signal by way of a synchronous oscillator, having a synchronous oscillation mode set in phase with the first periodic signal (CKe) and a free oscillation mode,

placing the oscillator in the free oscillation mode, and

applying to the antenna circuit a burst of the second periodic signal, characterized in that it wherein the method further comprises, after applying to the antenna circuit a burst of the second periodic signal;

an attenuation step of modifying the impedance of the antenna circuit to attenuate the amplitude of the antenna signal,

a restoration step of ceasing to modify the impedance of the antenna circuit, to restore the amplitude of the antenna signal, and

a resynchronization step of placing the oscillator in the synchronous oscillation mode before applying a new burst of the second periodic signal to the antenna circuit.

2. The method according to claim 1, further comprising:

supplying a data-carrying modulation signal,

applying a burst of the second periodic signal to the antenna circuit when the modulation signal has a first logic value,

inhibiting the application of the first periodic signal to a synchronization input of the oscillator during the attenuation, restoration and synchronization periods.

3. The method according to claim 2, further comprising inhibiting the application of the first periodic signal to the synchronization input of the oscillator by way of a masking signal.

4. The method according to claim 1, further comprising phase shifting the second periodic signal relative to the antenna signal.

8. The device according to claim 1, wherein the means for modifying the impedance of the antenna circuit comprises a switch the closing of which modifies the impedance of the antenna circuit.

5. A device for sending/receiving data by inductive coupling comprising:

an inductive antenna circuit in which an antenna signal appears in the presence of an alternating external magnetic field,

means for extracting a first periodic signal from the antenna signal,

a synchronous oscillator having a synchronization input receiving the first periodic signal, supplying a second periodic signal, the oscillator having a synchronous oscillation mode set in phase with the first periodic signal and a free oscillation mode,

an active load modulation circuit configured to apply bursts of the second periodic signal to the antenna circuit and to generate an active load modulation magnetic field,

means for modifying the impedance of the antenna circuit and configured to;

place the oscillator in the free oscillation mode,

apply to the antenna circuit a burst of the second periodic signal,

modify the impedance of the antenna circuit to attenuate the amplitude of the antenna signal,

cease modifying the impedance of the antenna circuit, to restore the amplitude of the antenna signal, and

place the oscillator in the synchronous oscillation mode (Psyn) before applying a new burst of the second periodic signal (CKs) to the antenna circuit.

6. The device according to claim 5, configured to:

supply a data-carrying modulation signal,

apply a burst of the second periodic signal to the antenna circuit when the modulation signal has a first logic value,

inhibit the application of the first periodic signal to a synchronization input of the oscillator during the attenuation, restoration and synchronization periods.

7. The device according to claim 6, configured to inhibit the application of the first periodic signal to the synchronization input of the oscillator by way of a masking signal.

9. The device according to claim 5, wherein the means for modifying the impedance of the antenna circuit comprises a timer to determine a duration during which the impedance of the antenna circuit is modified.

10. The device according to claim 5, wherein the synchronous oscillator is of the astable oscillator type having a specific self-oscillation frequency determined by components of the oscillator.

11. The device according to claim 5, wherein the synchronous oscillator is of the digital type and is configured, in the synchronous oscillation mode, to copy at output the period of the periodic signal applied to the synchronization input, and, in the free oscillation mode, to reconstitute at output the frequency received at the synchronization input during the synchronous oscillation mode.

12. The device according to claim 6, wherein the synchronous oscillator comprises a phase locked loop comprising:

a phase comparator supplying a phase signal,

an active low-pass filter receiving the phase signal and supplying a control voltage,

a voltage-controlled oscillator receiving the control voltage and supplying the second periodic signal, and

means for inhibiting the phase comparator when switching into the free oscillation mode and for maintaining the value of the control voltage at the input of the voltage-controlled oscillator.

13. The device according to claim 5, comprising means for phase shifting the second periodic signal relative to the antenna signal.

14. A device comprising:

a device for sending and receiving data according to claim 5, and

at least one host processor supplying the device with data to be sent.

15. The device according to claim 14, mounted in or on to a portable medium.

16. A smart card, comprising at least one processor and a device for sending and receiving data according to claim 5.