FR3066868A1 - DETECTION OF AN NFC DEVICE - Google Patents

Abstract

The invention relates to a method for detecting, by a first NFC device (DEV1), a second NFC device, in which a resonant circuit of the first NFC device periodically generates an electromagnetic field by modifying the tuning frequency of said resonant circuit.

Description

DETECTION OF AN NFC DEVICE

Field

This description relates generally to electronic circuits and, more particularly, electromagnetic transponders or electronic tags (TAG). This description applies more particularly to electronic devices incorporating a near field communication circuit (NFC - Near Field Communication) and to the detection of the presence of such a device in the field of another device. State of the prior art

Communication systems with electromagnetic transponders are more and more frequent, in particular, since the development of near field communication technologies (NFC - Near Field Communication).

These systems use a radio frequency electromagnetic field by a device (terminal or reader) to communicate with another device (card).

In recent systems, the same NFC device can operate in card mode or in reader mode (for example in the case of near field communication between two mobile phones). It is then common for devices to be powered by batteries and their functions and circuits to be put on standby so as not to consume energy between periods of use. The devices must then be "awakened" when they are within range of each other. summary

One embodiment aims to reduce all or part of the drawbacks of known techniques for detecting the presence of an electronic device integrating a near-field communication circuit by another electronic device emitting an electromagnetic field.

One embodiment aims to propose a solution avoiding detection errors.

Thus, an embodiment provides a method of detection, by a first NFC device, of a second NFC device, in which a resonant circuit of the first NFC device periodically generates an electromagnetic field by modifying the tuning frequency of said resonant circuit.

According to one embodiment, a modification of the tuning frequency is carried out from one period to another.

According to one embodiment, a modification of the tuning frequency is carried out within each period.

According to one embodiment, the modification of the tuning frequency is carried out by varying a capacitance of the resonant circuit.

According to one embodiment, when it detects the second device, the first device initiates near field communication with it.

According to one embodiment, the first device is in a standby mode between two periods.

One embodiment provides a near field communication device, suitable for implementing the method described.

Brief description of the drawings

These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the appended figures, among which: FIG. 1 is a very schematic representation and in the form of blocks of an example of a near field communication system of the type to which, for example, the embodiments which will be described apply; Figure 2 is a block diagram partially illustrating an embodiment of circuits of a near field communication device; FIG. 3 represents, very schematically and in the form of blocks, steps of an embodiment of a method for activating NFC devices; and FIG. 4 represents, very schematically and in the form of blocks, steps of another embodiment of a method for activating NFC devices.

detailed description

The same elements have been designated by the same references in the different figures.

For the sake of clarity, only the steps and elements useful for understanding the embodiments which will be described have been shown and will be detailed. In particular, the generation of the radiofrequency signals and their interpretation have not been detailed, the embodiments described being compatible with the usual techniques for generating and interpreting these signals.

Unless otherwise specified, when reference is made to two elements connected to each other, this means directly connected without any intermediate element other than conductors, and when reference is made to two elements connected to each other, it means that these two elements can be directly connected (connected) or linked through one or more other elements.

In the following description, when reference is made to the terms "approximately", "approximately" and "on the order of", this means to the nearest 10%, preferably to the nearest 5%.

FIG. 1 is a very schematic representation in the form of blocks of an example of a near field communication system of the type to which the embodiments which will be described apply, by way of example.

We assume the case of two similar electronic devices, for example two mobile phones, but all that will be described more generally applies to any system in which a transponder picks up an electromagnetic field radiated by a reader, terminal or terminal. For simplicity, reference will be made to NFC devices to design electronic devices integrating near-field communication circuits.

Two NFC devices 1 (DEV1) and 2 (DEV2) are capable of communicating by electromagnetic coupling in the near field. Depending on the application, for communication, one of the devices operates in so-called reader mode while the other operates in so-called card mode, or the two devices communicate in peer-to-peer (P2P) mode. Each device comprises various electronic circuits for generating a radiofrequency signal emitted using an antenna. The radiofrequency field generated by one of the devices is picked up by the other device which is within range and which also has an antenna.

In the applications more particularly targeted by the present description, when an NFC device is not in communication, it is switched to standby mode in order to reduce the energy consumed. This is particularly the case for battery powered devices.

When a device (for example device 1) emits an electromagnetic field to initiate communication with another NFC device (for example device 2), this field is picked up by this device 2 as soon as it is within range. This field is detected by the circuits of the device 2 which, if they are in standby, are reactivated. This results in a variation of the charge constituted by the circuits of the device 2 on the resonant circuit for generating the field of the device 1. In practice, the corresponding variation in phase or amplitude of the field emitted is detected by the device 1 which then initiates an NFC communication protocol with the device 2. On the device 1 side, it is detected in practice if the amplitude of the voltage across the resonant circuit drops below a threshold or a phase shift greater than a threshold.

Once the device 1 has detected the presence of the device 2 in its field, it initiates a communication establishment procedure, implementing requests by the device 1 and responses by the device 2.

A difficulty resides in the fact that the variation of the amplitude of the field or of its phase on the device 1 side depends on the coupling operated with the device 2. However, the coupling factor depends on several parameters among which the distance between the two devices and the size of the antenna of the device 2. In certain situations, although the device 2 has been awakened, the coupling is too weak for the amplitude or phase variation to be detected on the device 1 side, even when communication could be established.

Another situation in which the coupling is too weak to be detected is the case of a disagreement between the two devices. Typically, the tuning frequency of NFC devices is 13.56 MHz. However, if the device 2 is detuned, the variation which it introduces on the field at 13.56 MHz generated by the device 1 is too small to be detected.

Figure 2 is a block diagram partially illustrating an embodiment of circuits of a near field communication device.

In a simplified manner, the device (1 or 2, FIG. 1) comprises at least one resonant circuit 3, series or parallel. In the case of a parallel resonant circuit as shown, the circuit 3 includes an inductance L forming an antenna in parallel with a capacitive element C. The terminals of the association in parallel define input and output terminals 31 and 33 of the resonant circuit 3. In the example shown, the same resonant circuit 3 is used for transmission and reception. In this case, the terminals 31 and 33 are connected to input terminals 41 and 43 of a radio frequency reception chain and to output terminals 51 and 53 of a radio frequency transmission chain. According to another embodiment, the device comprises two transmitting and receiving antennas respectively. Each transmission chain (transmission or reception) generally comprises various circuits (impedance adapters, switches, couplers, etc.) not shown between the resonant circuit 3 and circuits for processing the radiofrequency signals, generally symbolized by a block 6. Side reception, the reception chain further comprises at least one field detection circuit (FD) 45. On the transmission side, the transmission chain comprises at least one amplifier 55 (PA).

If necessary, the device draws its power or recharges a battery 7 (BAT) from the electromagnetic field which it picks up. In this case, the device further comprises a rectifying bridge 8, the input terminals of which are connected to the terminals 31 and 33 and the output terminals of which are connected to the circuit 6 and to the battery 7. The battery 7 is furthermore connected to circuit 6 to supply it, in particular if the device can operate in reader mode.

According to the embodiments described, provision is made to vary the tuning of the oscillating circuit 3 of the transmitting device in order to detect the presence of a receiving device, even if the latter is not tuned to the same frequency as the circuit. oscillating of the transmitting device.

In the embodiments more particularly targeted by the present description, the transmitter device is on standby and exits from this standby mode periodically to emit a field for a short duration before this period. According to one embodiment, a cyclic variance is caused from one field emission to the next. According to another embodiment, the agreement is modified within each field emission period by the emitting device.

The variation of the tuning is preferably a discrete variation, that is to say that the transmitting device switches all or nothing of the components modifying the tuning of the oscillating circuit.

According to the embodiment represented in FIG. 2, the modification of the tuning (of the resonance frequency) of the oscillating circuit of the transmitting device is carried out, under control of the circuit 6 (link 62) by acting on the capacitance C of this circuit oscillating 3, for example, by switching one or more capacitive elements in series or in parallel, defining the capacity C of the oscillating circuit 3. An advantage of such an embodiment is that it takes advantage of the presence of a switchable capacity in the oscillating circuit of existing NFC devices. Indeed, in certain devices, the tuning frequency is adjusted during the communication in order to optimize the range.

However, unlike the systems in which one intervenes, to optimize the range of a communication, on the tuning of the oscillating circuit or circuits, the embodiments described provide for intervening on the tuning before any attempt at establishment of a communication, to reliably activate a receiving device.

In the applications of low consumption NFC devices placed in standby mode, these devices periodically activate (for example every 250 milliseconds, every second, etc.) their NFC circuits to emit a field for a duration (for example a few microseconds ) short compared to the period between two activations, in order to detect if another device is in range.

FIG. 3 represents, very schematically and in the form of blocks, steps of an embodiment of a method for detecting the presence of an NFC device.

We consider the case of an NFC device (for example DEV1) which periodically transmits a field for a relatively short duration compared to the duration between two transmission periods P, in order to detect the presence of another NFC device in range . Between two transmission / detection periods, the device DEV1 is in a standby mode SM.

According to the embodiment described, the frequency of the generated field is different from one phase P to the next. To simplify, we consider the case of an alternation between two frequencies f1 and f2, but we could provide for a cyclic permutation of a greater number of frequencies, preferably less than ten. At each period P or P ', the device DEV1 is awakened or activated (block 11, WU) to establish a communication. This activation can take various usual forms, for example, an action of a user, a periodic triggering, the reception of a communication of another type (for example using the telephone network), etc.

The oscillating circuit 3 of the device DEV1 is then tuned to a frequency f1 or f2 (period P, block 12, TUN1 -period P ', block 12', TUN2) by alternating, from one transmission period to the next, the frequency of agreement.

The device DEV1 then emits a field (block 13, FE) at the chosen tuning frequency.

Assuming that a second device (DEV2, FIG. 1) is in range and that the field emitted by the device DEV1 is sufficient to activate its field detector (block 45, FD), the device DEV2 is awakened. The variation of the load formed by the circuits of the device 2 on the oscillating circuit 3 of the device DEV1 is then detected in the usual way. If the coupling is sufficient, this phase or amplitude variation is detected by the circuits (6, FIG. 2) of the device DEV1. Otherwise, the device DEV1 returns to standby until the next period P or P '.

However, unlike usual situations, changing the tuning frequency from one period P to the next increases the chances that the device DEV2 is in a coupling situation allowing detection.

FIG. 4 very schematically represents in the form of blocks steps of another embodiment of a method for detecting the presence of an NFC device.

Compared to the embodiment of FIG. 3, the variation of the tuning capacity of the oscillating circuit is carried out within each period P ". In the example of FIG. 4, where it is further assumed switching between three resonant frequencies, each wake-up or activation (block 11, WU) of the DEV1 device is followed by a succession of three field transmissions (blocks 13, FE), each preceded by an adjustment (block 12, TUN1 - block 12 ', TUN2 - block 12 ", TUN3).

As long as no device is detected (usually by variation of phase or amplitude detected by the circuits of the device DEV1), the device DEV1 goes back to standby until the next period P ". As soon as a receiving device is detected, the detection process stops (for example if the detection takes place on the frequency f2, step 12 "(and step 13 which follows) are not carried out, and the device DEV1 initializes communication in the usual way.

If necessary, the emission of the field is not interrupted between frequency changes.

The embodiments of Figures 3 and 4 can be combined.

An advantage of the embodiments described is that they do not require any modification of the receiving devices. Therefore, an NFC device equipped with the described functionality will more easily detect including existing NFC devices.

Another advantage of the described embodiments is that they do not modify the communication protocols between the devices. We simply insert a detection procedure before initiating a communication. Thus, the solutions described are compatible with the usual systems.

Another advantage is that the implementation of the described embodiments does not require any hardware modification of the devices. Indeed, we use the existing hardware functions in the devices. Thus, according to one embodiment, the implementation of the embodiments described in existing devices requires only a software update in order to integrate the steps of the device detection method. As a variant, the embodiments described can be implemented by a hardware solution, for example by a state machine (in wired logic). This generally allows faster execution and lower consumption.

Various embodiments have been described. Various modifications will appear to those skilled in the art. In particular, the choice of the duration of emission of the field can vary from one application to another. In addition, the practical implementation of the embodiments which have been described is within the reach of those skilled in the art using the functional indications given above.

Claims (7)

1. Method of detection, by a first NFC device (1), of a second NFC device (2), in which a resonant circuit (3) of the first NFC device periodically generates an electromagnetic field by modifying the tuning frequency of said resonant circuit. 2. Method according to claim 1, in which a modification of the tuning frequency is carried out from one period to another. 3. Method according to claim 1 or 2, in which a modification of the tuning frequency is carried out within each period. 4. Method according to any one of claims 1 to 3, in which the modification of the tuning frequency is carried out by varying a capacitance of the resonant circuit. 5. Method according to any one of claims 1 to 4, wherein when it detects the second device (2), the first device (1) initiates near field communication with it. 6. Method according to any one of claims 1 to 5, wherein the first device is in a standby mode between two periods. 7. Near-field communication device (1, 2), suitable for implementing the method according to any one of claims 1 to 6.