METHOD FOR DISTINGUISHING BETWEEN ACTIVE AND PASSIVE CONTACTLESS DEVICES, AND CORRESPONDING READER

Abstract

An embodiment method comprises transmitting a reader carrier signal from a contactless reader to a contactless device, receiving by the reader, a device modulated carrier signal from the device, the device modulated carrier signal having a carrier frequency, preferably turning off by the reader, the transmission of the reader carrier signal during reception of the device modulated carrier signal, and after having turned off the transmission of the reader carrier signal, determining by the reader the presence or the absence at the reader's antenna of a modulated carrier signal having at the reader's antenna the carrier frequency with a tolerance, without relying on the data content of the modulated carrier signal.

Claims

1. A method comprising: transmitting a reader carrier signal from a contactless reader to a contactless device: receiving by the reader, a device modulated carrier signal from the device, the device modulated carrier signal having a carrier frequency: turning off by the reader, the transmission of the reader carrier signal or reducing by the reader, a level of the reader carrier signal, during reception of the device modulated carrier signal: and after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal, determining by the reader a presence or an absence at an antenna of the reader of a modulated carrier signal having at the antenna of the reader the carrier frequency with a tolerance, without relying on a data content of the modulated carrier signal.

2. The method according to claim 1, further comprising determining whether the device is an active load modulation device based on the presence of the modulated carrier signal.

3. The method according to claim 1, further comprising determining whether the device is a passive load modulation device based on the absence of the modulated carrier signal.

4. The method according to claim 1, wherein the determining comprises determining by the reader an indication related to a level of the signal present at the antenna of the reader.

5. A method comprising: transmitting a reader carrier signal from a contactless reader to a contactless device; receiving by the reader, a device modulated carrier signal from the device, the device modulated carrier signal having a carrier frequency; turning off by the reader, the transmission of the reader carrier signal or reducing by the reader, a level of the reader carrier signal, during reception of the device modulated carrier signal; and after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal, determining by the reader an indication related to a level of a signal at an antenna of the reader.

6. The method according to claim 5, further comprising determining whether the device is an active load modulation device based on whether the level indication is greater than a first threshold.

7. The method according to claim 5, further comprising determining whether the device is a passive load modulation NFC device based on whether the level indication is lower than a second threshold.

8. The method according to claim 5, wherein determining the indication related to the level of the signal comprises performing a down transposition into a baseband, of the signal present at the antenna of the reader after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal, and determining a strength indication of the baseband signal.

9. The method according to claim 5, wherein determining the indication related to the level of the signal comprises detecting by a field detector of the reader, a presence or an absence of an electromagnetic field at the antenna of the reader, after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal.

10. The method according to claim 5, wherein determining the indication related to the level of the signal comprises performing an amplitude measurement of the signal present at the antenna of the reader after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal.

11. A contactless reader comprising: a transmitter configured to transmit a reader carrier signal to a contactless device; a receiver configured to receive a device modulated carrier signal from the device, the device modulated carrier signal having a carrier frequency; a controller configured to control the transmitter to turn off the transmission of the reader carrier signal or to reduce a level of the reader carrier signal during reception of the device modulated carrier signal; and a detection unit configured to determine, after the transmission of the reader carrier signal has been turned off or after the reduction of the level of the reader carrier signal, a presence or an absence at an antenna of the reader of a modulated carrier signal having at the antenna of the reader the carrier frequency with a tolerance, without relying on a data content of the modulated carrier signal.

12. The reader according to claim 11, wherein the detection unit is further configured to determine whether the device is an active load modulation device based on the presence of the modulated carrier signal.

13. The reader according to claim 11, wherein the detection unit is further configured to determine whether the device is a passive load modulation device based on the absence of the modulated carrier signal.

14. The reader according to claim 11, wherein the detection unit is configured to determine an indication related to a level of a signal present at the antenna of the reader.

15. A contactless reader comprising: a transmitter configured to transmit a reader carrier signal to a contactless device; a receiver configured to receive a device modulated carrier signal from the device, the device modulated carrier signal; a controller configured to control the transmitter to turn off the transmission of the reader carrier signal or to reduce a level of the reader carrier signal during reception of the device modulated carrier signal; and a detection unit configured to determine, after the transmission of the reader carrier signal has been turned off or after the reduction of the level of the reader carrier signal, an indication related to a level of a signal at an antenna of the reader.

16. The reader according to claim 15, wherein the detection unit is further configured to determine whether the device is an active load modulation device based on whether the level indication is greater than a first threshold.

17. The reader according to claim 15, wherein the detection unit is further configured to determine whether the device is a passive load modulation device based on whether the level indication is lower than a second threshold.

18. The reader according to claim 15, wherein the detection unit comprises a transposition unit configured to perform a down transposition into a baseband, of the signal present at the antenna of the reader after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal, and a processing unit configured to determine a strength indication of the baseband signal.

19. The reader according to claim 15, wherein the detection unit comprises a field detector configured to detect a presence or an absence of an electromagnetic field at the antenna of the reader, after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal.

20. The reader according to claim 15, wherein the detection unit comprises a measurement unit configured to perform an amplitude measurement of the signal present at the antenna of the reader after having turned off the transmission of the reader carrier signal or after having reduced the level of the reader carrier signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0107] Other advantages and features of the invention will appear in the detailed description below and in the appended drawings which are not limitative, in which:

[0108] FIG. 1 illustrates a contactless system;

[0109] FIG. 2 illustrates modulation differences between passive and active devices;

[0110] FIGS. 3-8 illustrate disparate active load modulation behaviors on the antenna signal upon field suppression;

[0111] FIG. 9 illustrates a method for detecting a passive or active load modulation device;

[0112] FIG. 10 illustrates example signal shapes for detection of an active device;

[0113] FIG. 11 illustrates a detection unit;

[0114] FIG. 12 illustrates a detection unit;

[0115] FIG. 13 illustrates a detection unit; and

[0116] FIG. 14 illustrates an active device charging method.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0117] FIG. 1 illustrates diagrammatically a contactless system, for example an NFC or RFID, system, including a contactless reader, for example an NFC or RFID reader RD configure to exchange data with a contactless device DV, for example an NFC or RFID device, according to a contactless protocol.

[0118] The reader RD comprises transmitter MTR configured to transmit a reader carrier signal RCS, through an impedance matching circuit MC and an antenna ANTI, to the contactless device DV.

[0119] The reader carrier signal RCS has for example a carrier frequency equal to 13.56 MHz.

[0120] The reader comprises also receiver RCM connected to the impedance matching circuit MC and the antenna ANTI and configured to receive a device modulated carrier signal DMCS from the device DV, the device modulated carrier signal DMCS having the carrier frequency (here 13.56 MHz) and a modulation frequency equal for example to 848 kHz.

[0121] The device DV comprises a component CMPD configured to generate the device modulated carrier signal DMCS for it to be transmitted through the device antenna ANT2.

[0122] If the device is a passive one, the component retro-modulates the reader carrier signal RCS coming from the reader to transmit information and does not integrate, for the transmission of information, a transmitter themselves, or an emitter, capable for example of generating its own magnetic field during the broadcast.

[0123] Such a “passive” device may also be designated by the expression “passive load modulation device.”

[0124] If the device is an active one, both the reader RD and the active device DV generate an electromagnetic field. In such a case the active device is provided with a power source, for example a battery.

[0125] Each of the reader and active device transmits the data using a modulation scheme of the corresponding generated electromagnetic field. Here again, the modulation results in a load modification and this is then referred to as active load modulation (ALM) communication.

[0126] Such an «active» device may also be designated by the expression “active load modulation device.”

[0127] The reader RD comprises also controller CTRL configured to control the transmitter MTR to turn off the transmission of the reader carrier signal RCS during reception of the device modulated carrier signal DMCS.

[0128] Many applications of NFC technology utilize an NFC reader to interrogate and receive data from an NFC device. The NFC reader typically outputs an interrogation signal. If an NFC device is within range of the interrogation signal, then the NFC device responds by providing an identification signal identifying the NFC device. After the NFC device has identified itself, the NFC reader and the NFC device can further exchange information.

[0129] Thus in a particular embodiment, the controller CTRL may control the transmitter for turning off during a frame of the received identification signal.

[0130] The reader comprises also detection unit MDT configured to determine, after the transmission of the reader carrier signal has been turned off, an indication related to a level of signal at the reader's antenna.

[0131] This searched signal has, at the reader's antenna, the carrier frequency (here 13.56 MHz) with a possible tolerance. This detection will permit to distinguish between a passive device DV or an active device DV.

[0132] As a matter of fact, as illustrated in FIG. 2, upon triggering the detection/sensing phase, corresponding to the logic state transition of a trigger signal TRGS generated by the controller, there is no modulation in the signal SGN present at the antenna ANT1 of the reader after suppression of the reader carrier signal RCS if the device DV is a passive one, for example a passive card (left part of FIG. 2) while there is a certain modulation (for example at a frequency equal to 848 kHz) in the signal SGN present at the antenna ANT1 of the reader after suppression of the reader carrier signal RCS if the device DV is an active one, for example an ALM enabled smartphone in the card emulation mode (right part of FIG. 2).

[0133] In other words there is no modulated carrier signal at the antenna ANT1 if the device DV is a passive one while there is a modulated carrier signal at the antenna ANT1, during a certain duration, if the device is an active one.

[0134] The presence or the absence of such modulated carrier signal permits to distinguish between a passive and active device without relying on the data content of the modulated carrier signal.

[0135] As a matter of fact, unlike passive cards, ALM devices are self-powered and the field suppression does not cause the device to shut down.

[0136] Each ALM implementation behaves different upon reader's field suppression during ongoing transmission.

[0137] Although behavior upon RF carrier synchronization loss is not defined, most ALM implementations continue to produce some sort of modulation after RF carrier suppression which can be used to determine the presence of ALM.

[0138] FIGS. 3 to 8 illustrate disparate ALM behaviors on the signal SGN upon field suppression (Signal TRGS at high state).

[0139] We refer now more particularly to FIG. 9 which illustrates an embodiment of a method according to the invention.

[0140] In a step S90, the reader transmits the reader carrier signal RCS to the contactless device.

[0141] In a step S91, the reader receives the device modulated carrier signal DMCS, for example an identification signal, from the contactless device DV, the device modulated carrier signal DCMS having the carrier frequency, for example 13.56 MHz, and a modulation frequency, for example 848 kHz.

[0142] In step S92, the reader turns off the transmission of the reader carrier signal RCS during reception of the device modulated carrier signal DMCS.

[0143] In step S93, the reader determines, after having turned off the transmission of the reader carrier signal RCS, an indication LV related to a level of a signal SGN at the reader's antenna ANT1.

[0144] This searched signal SGN has the carrier frequency with a tolerance.

[0145] For example the tolerance maybe some percent, for example about 5 percent, of the carrier frequency.

[0146] Turning off the transmission of the reader carrier signal may advantageously occur during reception of a frame of the received device modulated carrier signal, for example during reception of an identification signal from the device.

[0147] The interruption of transmission of the reader carrier signal may last for an interruption duration, for example between few microseconds and several milliseconds.

[0148] This interruption duration maybe greater than or equal to the duration during which the level determination is performed.

[0149] According to an embodiment, the method further comprises in step S94 a comparison of the indication level LV to a threshold TH1.

[0150] In this embodiment, there is only one threshold.

[0151] If the indication level LV is greater than or equal to TH1, the device DV is detected as being an active load modulation device (S95).

[0152] If the indication level LV is smaller than TH1, the device DV is detected as being a passive load modulation device (S96).

[0153] FIG. 10 illustrates example of signal shapes in case of a detection of an active device.

[0154] More precisely, in this example, the reader has sent the reader carrier signal RCS and has modulated it for transmitting for example an interrogation signal to the device.

[0155] In step S100 the device starts to modulate its response (identification signal for example) and sends accordingly the device modulated carrier signal DCMS having the carrier frequency, for example 13.56 MHz and a modulation frequency equal for example to 848 kHz.

[0156] In step S101 the reader identifies an ongoing reception of the device modulated carrier signal DCMS and triggers the detection process of the type of device (trigger signal TRGS takes a high state).

[0157] This is the beginning of detection process S102.

[0158] In step S103, the reader suppresses the reader carrier signal RCS and will determine the level indication of the signal SGN present at the reader's antenna.

[0159] As in the present example, the device is an active device, the signal SGN has the carrier frequency (13.56 MHz) and comprises ALM pulses (at the modulation frequency, for example 848 kHz) even in absence of the reader carrier signal RCS.

[0160] The level indication will be accordingly greater than the first threshold TH1, representative of an active device.

[0161] Many possibilities exist for implementing the detection unit MDT, as illustrated diagrammatically in FIGS. 11 to 13.

[0162] As illustrated in FIG. 11, the detection unit comprises transposition unit MX configured to perform in the reception chain CHR a down transposition into a base band, of the signal SGN present at the antenna of the reader after having turned off the transmission of the reader carrier signal.

[0163] More precisely, the mixers MX use as transposition signals an oscillator signal having the carrier frequency (13.56 MHz) issued from a local oscillator LO and the same oscillator signal but 90° phase shifted.

[0164] The two transposed signals on paths I and Q are then converted in analog to digital converters ADC to obtain the components BSBSI and BSBSQ of the digital baseband signal.

[0165] The detection unit MDT comprises a processing unit configured to determine a strength indication (RSSI) of the baseband signal.

[0166] The RSSI is then compared to the threshold TH1 which can be equal for example to 5 mVpp.

[0167] As illustrated in FIG. 12, the detection unit MDT may comprise a field detector, for example an external field detector, configured to detect the presence or the absence of an electromagnetic field EMF at the antenna of the reader, after having turned off the transmission of the reader carrier signal.

[0168] For determining the presence or the absence of the electromagnetic field, the level of the electromagnetic field is compared to the threshold TH1 which can be equal for example to 25 mVpp.

[0169] As illustrated in FIG. 13, detection unit MDT may comprise measurement unit MMS configured to perform an amplitude measurement of the signal SGN present at the antenna of the reader after having turned off the transmission of the reader carrier signal.

[0170] The amplitude is compared to the threshold TH1 which can be equal for example to 25 mVpp.

[0171] As illustrated in FIG. 14, if in step S140, an active device is detected, the charging bay CHG of the reader can output a wireless charging signal to the active device (step S141), for example a charging signal according to the Qi standard.

[0172] Of course a charging application is not the sole application which can use the detection between passive and active contactless devices.

[0173] Access control or transportation systems could for example use ALM detection to dismiss cards emulated on easily accessible mobile phones.

[0174] Although in the above described embodiments, the ALM detection uses a turning off of the reader carrier signal, the advantages of other embodiments of the invention maybe also obtained with a reduction of the level of the reader carrier signal or the reader carrier field chosen for passive devices not to be able to operate/modulate, for example a reduction of 95% with respect to a nominal level.

[0175] When a level reduction is used, the values of the different thresholds mentioned above are adapted for taking into account the residual level of the reduced reader carrier signal (reader carrier field).