Method for managing the operation of an object that is able to contactlessly communicate with a reader

Abstract

A device for managing operation of an object capable of contactless communication with a reader magnetically coupled to the object includes a modulator configured to modulate an impedance of a load connected across terminals of an antenna of the object during a transmission phase during which information is transmitted from the object to the reader. The device further includes a monitor configured to carry out a monitoring phase, prior to the transmission phase. The monitoring phase includes a test modulation of the impedance of the load, a monitoring of a level of amplitude modulation of a modulated test signal present at the antenna of the object and resulting from the test modulation, and a capacitive modification of the impedance of the load if this level is lower than a threshold.

Claims

1. A device for managing operation of an object capable of contactless communication with a reader magnetically coupled to the object, the device comprising: a modulator configured to modulate an impedance of a load connected across terminals of an antenna of the object during a transmission phase during which information is transmitted from the object to the reader; and a monitor configured to carry out a monitoring phase, prior to the transmission phase, the monitoring phase comprising a test modulation of the impedance of the load, a monitoring of a level of amplitude modulation of a modulated test signal present at the antenna of the object and resulting from the test modulation, and a capacitive modification of the impedance of the load comprising shifting a phase of sidebands of the modulated test signal if the level is lower than a threshold.

2. The device according to claim 1, wherein the threshold corresponds to a sensitivity threshold of an amplitude demodulator of the reader.

3. The device according to claim 1, wherein the monitor comprises: a processor configured to determine an envelope of the modulated test signal and an amplitude between peaks and troughs of the envelope; and a comparator with a first input coupled to receive the amplitude and a second input coupled to receive the threshold.

4. The device according to claim 3, wherein the monitor comprises a capacitor connected to the terminals of the antenna via an auxiliary switch controlled by an output signal of the comparator.

5. The device according to claim 4, wherein the capacitor is configured to modify the impedance of the load by shifting the phase of the sidebands of the modulated test signal by about 90 degrees when the level of amplitude modulation is lower than the threshold.

6. The device according to claim 1, wherein the monitor comprises a tester configured to carry out the test modulation, the tester comprising a generator of the test modulation signal designed to successively modify the impedance in such a manner that it alternately takes two different values.

7. The device according to claim 6, wherein the load comprises a first resistor connected across the terminals of the antenna, and the tester comprises a second resistor connected across the terminals of the antenna via a switch controlled by the test modulation signal, the test modulation signal successively and alternately taking a low level and a high level so as to successively and alternately electrically connect, or otherwise, the second resistor to the terminals of the antenna.

8. An object capable of contactless communication with a reader magnetically coupled to the object, the object comprising: an antenna comprising first and second terminals; a modulator coupled between the first and second terminals of the antenna, the modulator configured to modulate an impedance of a load connected across the first and second terminals during a transmission phase during which information is contactlessly transmitted from the object to the reader; a processor configured to determine an envelope of a test signal and an amplitude between peaks and troughs of the envelope; a comparator with a first input coupled to receive the amplitude and a second input coupled to receive a threshold; and a capacitor connected to the first and second terminals of the antenna via an auxiliary switch controlled by an output signal of the comparator, the capacitor configured to modify the impedance of the load by shifting a phase of sidebands of the test signal.

9. The object according to claim 8, wherein the load comprises a first resistor connected across the first and second terminals of the antenna, the object further comprising a second resistor connected across the first and second terminals of the antenna via a second switch.

10. The object according to claim 8, further comprising a generator of a test modulation signal that is designed to successively modify the impedance in such a manner that it alternately takes two different values.

11. The object according to claim 10, wherein the load comprises a first resistor connected across the first and second terminals of the antenna, the object further comprising a second resistor connected across the first and second terminals of the antenna via a second switch controlled by the test modulation signal, the test modulation signal successively and alternately taking a low level and a high level so as to successively and alternately electrically connect, or otherwise, the second resistor to the first and second terminals of the antenna.

12. The object according to claim 8, wherein the capacitor is configured to modify the impedance of the load by shifting the phase of the sidebands of the test signal by about 90 degrees when the amplitude is lower than the threshold.

13. The object according to claim 8, wherein the threshold corresponds to a sensitivity threshold of an amplitude demodulator of the reader.

14. An object capable of contactless communication with a reader magnetically coupled to the object, the object comprising: an antenna comprising first and second terminals; a modulator coupled between the first and second terminals of the antenna, the modulator configured to modulate an impedance of a load connected across the first and second terminals during a transmission phase during which information is contactlessly transmitted from the object to the reader; a processor configured to determine an envelope of a modulated test signal comprising sidebands offset in frequency from a carrier frequency, and determine an amplitude difference between peaks of the envelope and troughs of the envelope; a comparator configured to compare the amplitude difference received at a first input of the comparator with a threshold received at a second input of the comparator, and send an output signal to an auxiliary switch; and a capacitor connected to the first and second terminals of the antenna via the auxiliary switch controlled by the output signal of the comparator, wherein the capacitor is configured to modify the impedance of the load by shifting a phase of the sidebands of the modulated test signal by about 90 degrees when the amplitude difference is lower than the threshold.

15. The object according to claim 14, wherein the threshold corresponds to a sensitivity threshold of an amplitude demodulator of the reader.

16. The object according to claim 14, further comprising: a signal generator configured to generate a test signal designed to successively modify the impedance in such a manner that it alternately takes two different values.

17. The object according to claim 16, further comprising: a resistor connected across the first and second terminals of the antenna via a second switch, wherein during a monitoring phase performed prior to the transmission phase, the second switch is controlled by the test signal, and during the transmission phase, the second switch is controlled by a modulation signal comprising data transmitted to the reader.

18. The object according to claim 16, further comprising: a tester comprising a resistor connected across the first and second terminals of the antenna via a second switch controlled by the test modulation signal, the test modulation signal alternately taking the two different values comprising a low level and a high level so as to alternately electrically connect the resistor to the first and second terminals of the antenna.

19. The object according to claim 14, wherein the load comprises a resistor connected across the first and second terminals of the antenna.

20. The object according to claim 14, wherein the object is a cellular mobile telephone emulated in card mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: Other advantages and features of the invention will become apparent upon examining the detailed description of non-limiting embodiments and the appended drawings in which:

(2) FIGS. 1 to 7 illustrate schematically some embodiments of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(3) In FIG. 1, the reference 1 denotes a reader, for example but not limited to, a cellular mobile telephone emulated in reader mode or else a conventional contactless smartcard or tag reader such as a badge, comprising an antenna 10 together with an amplitude demodulator 11 configured for carrying out an amplitude demodulation of a signal able to be amplitude modulated and received at the antenna 10, for example the voltage across the terminals of this antenna.

(4) The reference 2 denotes an object, for example a cellular mobile telephone emulated in card mode, and more generally, an electromagnetic transponder such as a tag or a badge.

(5) This object 2 here comprises an integrated circuit 20 also having an antenna 200 magnetically coupled to the reader 1 by a magnetic field irradiated by the reader 1.

(6) In FIG. 2, it can be seen that the integrated circuit comprises, with the coil 200, a capacitor 201 forming with this coil a parallel resonant circuit for modulating the magnetic field generated by an oscillating circuit of the reader. This resonant circuit 200-201 is connected to the two AC inputs of a diode rectifier bridge 203. As a variant, it would be possible to use as rectifier element a single-alternation rectifier element.

(7) When the transponder enters into the magnetic field of the reader, a high-frequency voltage is generated across the terminals of the resonant circuit 200-201. This voltage, rectified by the bridge rectifier 203, provides a power supply voltage for the electronic circuit 205 of the transponder, via a voltage regulator 204. The electronic circuit 205, more often than not incorporating the regulator 204, can contain at least a memory and a processor.

(8) In order to enable the transmission of data from the transponder to the reader 1, the circuit 205 sends a command to a stage 202 for feedback-modulation of the resonant circuit 200-201. This stage 202 comprises at least one electronic switch, controlled by a signal SM delivered by the circuit 205, and at least one resistor so as to modify the load connected across the terminals of the antenna 200 and allow the detection by the reader.

(9) The integrated circuit 20 also comprises a monitor 206 controllable by a control signal SCTRL delivered by the circuit 205. The monitor 206 is configured for carrying out, prior to a data transmission phase, a monitoring phase comprising a test modulation of the impedance of the load connected across the terminals of the antenna, and a monitoring of the level of amplitude modulation of a modulated test signal STM present at the antenna of the object and resulting from the test modulation and a capacitive modification of the impedance of the load if this level is lower than a threshold.

(10) For this purpose, as will be seen in more detail hereinafter, the monitor 206 generates a test modulation signal SMT.

(11) As illustrated in FIG. 3, the monitoring phase S30 is carried out just before the data transmission phase S31 comprising the load modulation. In practice, if there exist several successive transmission phases, a monitoring phase S30 will be carried out prior to each transmission phase S31.

(12) As illustrated in FIG. 4, the monitoring phase S30 comprises a test modulation S300 carried out on the load connected to the terminals of the antenna 200 using the test modulation signal SMT so as to obtain at the antenna 200 a modulated test signal STM, for example the voltage across the terminals of the coil 200.

(13) Subsequently (step S301), the level of amplitude modulation of the modulated test signal STM is determined.

(14) Then, in a step S302, this level is compared with a threshold VTH chosen as a function of the sensitivity threshold of the demodulator 11 of the reader.

(15) It is recalled here, as illustrated schematically in FIG. 5 which illustrates schematically the frequency spectrum of the signal (voltage) across the terminals of the antenna of the reader, that the useful signal containing the transmitted information is situated in the side lines BLB and BLS frequentially offset from the central line BP centered on the carrier frequency, for example 13.56 MHz.

(16) If the level of the modulated test signal is higher than the threshold VTH, then this means that there is a sufficient amplitude modulation on the antenna 200 of the object and, as a consequence, sufficient amplitude modulation on the signal received by the antenna 10 of the reader which will allow the demodulator 11 of the reader to be able to correctly demodulate the signal for detecting the information.

(17) If the level of amplitude modulation of the modulated test signal STM is lower than the threshold VTH, this then means that the phase amplitude of the signal present at the antenna 200 of the object is preponderant with respect to the amplitude modulation, which will result in a level of amplitude modulation of the signal present at the antenna 10 of the reader that is insufficient to allow demodulation of the signal and, as a consequence, detection of the information transmitted.

(18) In this case, a capacitive modification of the load impedance is carried out (step S303) in such a manner as to (ideally) apply a phase rotation of 90° to the frequency side lines BLB and BLS of the signal received by the antenna 10 of the object.

(19) In practice, as illustrated in FIG. 6, the determination of the amplitude level of the modulated test signal STM can comprise a determination S3010 of the envelope of the signal STM then a determination S3011 of the peaks and troughs of this envelope and, finally, a determination of the difference between the peaks and the troughs (step S3012). This difference is representative of the level of amplitude modulation of the modulated test signal STM.

(20) In practice, as illustrated schematically in FIG. 7, the monitor 206 comprises a processor comprising a block 2001 configured for determining the envelope of the modulated test signal STM, here the envelope of the voltage across the terminals of the resonant circuit 200-201, a block 2002 configured for determining the peaks of this envelope and a block 2003 configured for determining the troughs of this envelope.

(21) The processor also comprises, at the output of the blocks 2002 and 2003, a block 2004 configured for effecting the difference between the level of the peaks and the level of the troughs so as to determine the amplitude between the peaks and the troughs of this envelope. The blocks 2001, 2002, 2003 and 2004 are blocks known per se and of conventional structure.

(22) The output of the block 2004 is therefore representative of the level of amplitude modulation of the signal STM.

(23) The monitor 206 further comprises a comparator 2005 for comparing this level with the threshold VTH so as to deliver a comparison signal SCMP which can take a high logic state or a low logic state depending on the comparison.

(24) In this exemplary embodiment, the stage 202 for feedback-modulation further comprises a first resistor R1 connected to the terminals of the resonant circuit 200-201 and a second resistor R2 connected to the terminals of the resonant circuit via a switch SW2.

(25) In a transmission phase, this switch SW2 is controlled by the modulation signal SM delivered by the processor 205 so as to be able to transmit the data to the reader.

(26) On the other hand, in the monitoring phase, this switch SW2 is controlled by the test modulation signal SMT delivered by a generator 2007 and here comprising a succession of logic “0”s and “1”s so as to successively and alternately open and close the switch SW2.

(27) The stage 202 for feedback-modulation further comprises at least one capacitor CX connected to the terminals of the antenna 200 via a switch SWX controlled by the comparison signal SCMP.

(28) More precisely, if the comparison signal SCMP is equal to 0, the switch SWX is open and the capacitor CX is not electrically connected to the terminals of the antenna.

(29) If the signal SCMP is in the logic state “1”, the switch SWX is then closed electrically connecting the capacitor CX to the terminals of the antenna 200.

(30) If the level of amplitude modulation of the signal STM is higher than the threshold VTH, then the signal SCMP takes the logic state “0”, whereas if the level of amplitude modulation of the signal STM is lower than the threshold VTH, the signal SCMP takes the logic state “1”.

(31) The monitor 206 also comprises a monitoring block 2006 receiving the control signal SCTRL coming from the processor 205 and capable of activating, upon a command, all of the elements of the monitor 206 so as to effectively trigger the monitoring phase prior to the data transmission phase.

(32) The value of the threshold VTH and the value of the capacitor CX may be determined by simulation.

(33) More precisely, the value of the threshold VTH is linked to the transmission standard used.

(34) It is, for example, assumed that the transmission has to satisfy the EMVCo standard.

(35) According to this standard, on a probe of the reader called J2 and at a certain position of the object (card for example) with respect to the reader, the reader must receive a minimum level Vpp of signal resulting from the load modulation.

(36) Those skilled in the art will for example be able to refer, at their convenience, notably to page 32 of the book entitled EMV Contactless Specifications for Payment Systems, EMV Contactless Communication Protocol Specification, version 2.0.1, July 2009, which shows a figure illustrating the signal J2 of the reader with the definition of Vpp, and also to the table A3 (page 134) in this same book for finding the various values of Vpp for various positions (z, r) of the card.

(37) Furthermore, by simulation, those skilled in the art will be able to determine the value of the threshold VTH which guarantees that the signal received by the reader has a higher level than Vpp.

(38) With regard to the capacitance of the capacitor CX, this depends on the circuit layout of the object, and, by simulation, those skilled in the art will be able to determine the capacitance of CX needed to rotate the phase of the side bands by around 90°. The phase of these side bands may for example be determined by simulation by finding the Fourier transform of the signal J2.

(39) In other words, the value of VTH and the capacitance of CX may be evaluated by simulating the circuit of the object coupled to the reader, and the difficulties of detection of the object always occur when the object is too far from the reader. Accordingly, the value of VTH and the capacitance of CX will be determined at limiting positions of the object (for example for z greater than 2 and r equal to 2.5 in the aforementioned table A3). Various simulated values for VTH and CX are then obtained and it is then for example possible to choose the average of these values as values effectively implemented for VTH and CX.