FR3066870A1 - ACTIVATION OF AN NFC DEVICE - Google Patents

Abstract

The invention relates to a method for activating, by a first NFC device, a second NFC device, in which, in response to an activation of the second device by a first electromagnetic field (F1) generated by the first device, the second device device generates a second electromagnetic field (F2).

Description

ACTIVATION 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, one embodiment provides a method of activating, by a first NFC device, a second NFC device, in which, in response to activation of the second device by a first electromagnetic field generated by the first device, the second device generates a second field.

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

According to one embodiment, the method comprises the following successive steps: the first device is activated; the first device emits said first radiofrequency electromagnetic field; the second device is activated by the first field; the second device generates the second field; the first device detects the second field; and the first device initiates a near field communication process.

According to one embodiment, the activation of the first device is periodic.

According to one embodiment, the activation corresponds to an exit from a standby mode.

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

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; and FIG. 3 represents, very schematically and in the form of blocks, steps of an 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 (NFC DEV1) and 2 (NFC 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 begins an NFC communication protocol with the device 2. On the device 1 side, it is detected in practice if the amplitude of the voltage at the terminals of the resonant circuit drops below a threshold or if the voltage has 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.

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, 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 have a field emitted by the receiving device as soon as it is awakened by the presence of a field emitted by the transmitting device. Thus, this field will be detected by the transmitting device, even in the event of weak coupling. Unlike a communication in which the receiving device modulates the electromagnetic field by modifying the charge it represents on the field of the transmitter, we are here in the presence of a second field emission. This enables the two devices to be reliably activated. In fact, if the coupling is too weak for the field emitted by the receiver to be detected by the transmitting device, this means that the communication will not be able to operate. However, as soon as this field can be received, it is considered that a communication can be initialized.

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 activating NFC devices.

Initially, the two (or more than two) devices DEV1 and DEV2 are on standby (SM).

It is assumed that one of the devices (for example the first 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 device DEV1 then emits a field F1 intended to be picked up by the other device or devices in range.

Assuming that the second DEV2 device is in range and that the field is sufficient to activate its field detector (block 21, FD), the DEV2 device is awakened (block 22, WU). It then starts to send a field F2 (block 23, FE).

As the DEV1 device is in range, it picks up this field which activates its field detector (block 13, FD).

The device DEV1 can also, during its detection phase, detect the field emitted by the device DEV2. The field emitted by the DEV2 device is then picked up by the DEV1 device as a phase or amplitude variation. Thanks to the emission of a field (by the DEV2 device), this variation is significant, even in the event of weak coupling.

Finally, the device DEV1 initializes a communication (block 14, INIT COM) in the usual way.

An advantage is that, even if the coupling is too weak to trigger the usual detector of the device DEV1 by detection of a variation in amplitude or phase of the field which it emits, the devices can initiate communication.

The method described above can be executed in place of or in addition to the usual method according to which the activation of the circuits of the receiving device DEV2 modifies the load which it represents on the field of the transmitter DEV1.

An advantage of the embodiments described is that they do not modify the communication protocols between the devices. We simply insert an activation phase 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 activation process. 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 (6)

1. Method for activating, by a first NFC device (1), a second NFC device (2), in which, in response to activation of the second device by a first electromagnetic field (F1) generated by the first device , the second device (2) generates a second electromagnetic field (F2). 2. Method according to claim 1, wherein when it detects the second field (F2), the first device (1) initiates near field communication with the second device (2). 3. Method according to claim 1 or 2, comprising the following successive steps: the first device (1) is activated; the first device emits said first electromagnetic field (F1); the second device (2) is activated by the first field; the second device generates the second field (F2); the first device detects the second field; and the first device initiates a near field communication process. 4. The method of claim 3, wherein the activation of the first device (1) is periodic. 5. Method according to any one of claims 1 to 4, in which the activation corresponds to an exit from a standby mode. 6. Near-field communication device (1, 2), suitable for implementing the method according to any one of claims 1 to 5.