EP3035439B1 - Antenna for electronic device - Google Patents

Description

Field

The present description relates generally to electronic devices and, more particularly, to devices using a radiofrequency communication or energy transfer antenna.

Disclosure of prior art

More and more electronic devices are so-called "communicating" devices. For the most part, communication takes place by radio frequency, either passively (electronic label equipped only with passive components) or active (label or electronic device equipped with one or more active circuits).

In particular, devices of the mobile phone type are more and more often equipped with a near field communication function (NFC - Near Field Communication) allowing electronic circuits of the telephone to communicate wirelessly and without contact with similar devices. , electronic labels, suitable readers, etc. The telephone is then generally equipped with a communication interface between an antenna and its circuits. This interface is generally called a radiofrequency head or a contactless (communication) head (CLF - Contact Less Front end). One or more antennas are then connected to this RF head for radio frequency communications.

In such devices, and more generally in any electronic device equipped with an RF communication and / or energy transfer antenna, the integration of the antenna (or antennas) in the device conditions the performance of these. ci, therefore communication and / or energy transfer.

The document US 2008/0150693 describes a multiple loop antenna for RFID reader, RFID reader and RFID system.

The document US 2011/0068385 describes a semiconductor device. The document US2011 / 287715A1 describes an antenna formed of a plane winding, said antenna being placed opposite an opening formed in a conductive plane.

summary

One embodiment aims to overcome all or part of the drawbacks of electronic devices equipped with radiofrequency communication and / or energy transfer antenna (s).

One embodiment aims to propose a new solution for integrating an antenna into an electronic device.

One embodiment is aimed at a solution which is particularly suitable for an antenna intended to be connected to a radiofrequency communication head of an electronic device.

One embodiment is aimed at a solution which is particularly suitable for the integration of an antenna in a metallic environment.

Thus, one embodiment provides a device according to claim 1.

Brief description of the drawings

• la figure 1 représente, de façon schématique et sous forme de blocs, un exemple d'architecture de dispositif électronique du type auquel s'appliquent les modes de réalisation qui vont être décrits ;
• les figures 2A, 2B et 2C illustrent un exemple de disposition usuelle d'une antenne au niveau d'un plan métallique d'un dispositif électronique ;
• la figure 3 est une représentation schématique d'un mode de réalisation d'une antenne ;
• la figure 4 représente, de façon schématique et partielle, un mode de réalisation d'un dispositif électronique intégrant une antenne du type de celle de la figure 3 ;
• les figures 5A et 5B sont des représentations schématiques de deux modes de réalisation d'une antenne ;
• la figure 6 représente une variante d'un mode de réalisation d'un réseau d'adaptation entre une antenne et une tête radiofréquence ; et
• la figure 7 est une vue, à rapprocher de celle de la figure 2A, d'un capot métallique d'un dispositif électronique.

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 accompanying figures, among which:

• the figure 1 represents, schematically and in the form of blocks, an example of an electronic device architecture of the type to which the embodiments which will be described apply;
• the figures 2A, 2B and 2C illustrate an example of the usual arrangement of an antenna at the level of a metal plane of an electronic device;
• the figure 3 is a schematic representation of an embodiment of an antenna;
• the figure 4 schematically and partially shows an embodiment of an electronic device incorporating an antenna of the type of that of the figure 3 ;
• the figures 5A and 5B are schematic representations of two embodiments of an antenna;
• the figure 6 represents a variant of an embodiment of a matching network between an antenna and a radiofrequency head; and
• the figure 7 is a view, to be compared to that of the figure 2A , a metal cover of an electronic device.

detailed description

The same elements have been designated by the same references in the various figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties. For the sake of clarity, only the elements useful for understanding the embodiments described have been shown and will be detailed. In particular, the generation and use of communications sent or received by the antenna described have not been detailed, the embodiments described being compatible with the usual applications. In addition, the rest of the electronic device incorporating an antenna has not been further detailed, the embodiments described being, here again, compatible with the rest of the components of the electronic devices incorporating one or more radiofrequency communication antennas. or energy transfer. In the following description, when reference is made to the terms “approximately”, “approximately” or “of the order of”, this means within 10%, preferably within 5%.

In the present description, reference is made more particularly to an example of application to an electronic device of the mobile telephone type equipped with near-field communication functions. However, all that will be described applies more generally to any other electronic device incorporating a radiofrequency communication or energy transfer antenna to be placed in a metallic environment.

The figure 1 represents, schematically and in the form of blocks, an example of the architecture of an electronic device of the type to which the embodiments which will be described apply.

This is, for example, a mobile phone equipped with near-field communication functions. The electronic circuits 1 (ICs) of the device are capable of exchanging signals (link 12) with a radiofrequency transmission-reception head 2 (CLF) constituting an interface between these circuits 1 and an antenna 3. A matching network 4 (MATCHING), constituting a frequency tuning and impedance matching circuit, is interposed between the radiofrequency inputs-outputs 21 of the head 2 and the antenna 3. The antenna generally consists of a winding driver plan.

The operation of such an architecture is known and will not be detailed, the embodiments described not modifying the operation in terms of generation and use of signals by the various elements.

It happens that the position of the antenna in the device is opposite a metal plate (typically an element of a housing of the device such as the shell of a mobile phone). We are then led to make an opening in this metallic element and to place the flat winding constituting the antenna in this opening.

The figures 2A, 2B and 2C illustrate an example of a usual arrangement at the level of a metal plane 5 ′ of an electronic device. The figure 2A schematically represents the metal plane 5 '. The figure 2B represents an example of a flat conductive winding constituting the antenna 3. The figure 2C represents the equivalent electrical diagram of the assembly.

In this example, it is desired to place the antenna 3 under the metal shell of the mobile telephone constituting the metal plane 5 '. The winding 3 is then placed, at least partially, inside an opening 52 'of the metallic plane to allow radiofrequency communication and to pass the field lines through the antenna. Advantage is taken of the presence of an opening generally present for other purposes, for example for an electronic camera, a microphone, a light sensor, etc. The two ends 32 and 34 of the winding 3 are connected to the matching network 4 ( figure 1 ). This connection is made by insulated wires and / or by conductive tracks deposited on an insulating layer (not shown) covering, at least partially, the internal face of the plate 5 ′.

The presence of the metallic plane disrupts communication and, in order to avoid the harmful consequences of eddy currents (eddy currents), we are forced to make a slot 54 'in the metal plane 5', so that the opening 52 ' opens, through the slot 54 ', into an edge of the metal plane 5'.

The need for a slot 54 'complicates the construction and is generally not desired. In addition, this weakens the cover or metal case.

The figure 3 is a schematic representation of an embodiment of an antenna. This figure represents an equivalent diagram to be compared to the figure 2C .

According to this embodiment, the antenna 3 is formed of a plane winding placed in an opening 52 of a metal plane 5. Unlike the figure 2C , the outline of the opening 52 is closed, that is to say that the opening 52 does not open into one of the edges of the plane 5. Another difference is that one of the ends, for example the outer end 34, of the winding forming the antenna 3 is connected to the metal plane 5 which is itself intended to be connected to the ground of the electronic device. In addition, the winding 3 is completely contained in the opening.

The inventor noticed that, surprisingly, by electrically connecting one end of the antenna to the ground plane which surrounds it, the disturbances due to eddy currents are considerably reduced and the performance of the antenna is improved. , including if the opening in which the antenna is placed has a closed contour.

The figure 4 schematically and partially shows an embodiment of an electronic device incorporating an antenna of the type of that of the figure 3 .

We find the electronic circuits 1 (ICs) of the device, capable of exchanging signals (link 12) with a radiofrequency transmission-reception head 2 (CLF) constituting an interface between these circuits 1 and an antenna 3. A network of adaptation 4 (MATCHING), constituting a frequency tuning and impedance adaptation circuit, is interposed between the radiofrequency inputs-outputs of head 2 and antenna 3. In the example of figure 4 , it is assumed that a head 2 has two reception terminals Rx and two transmission terminals Tx, of differential mode signals.

The terminals Rx and the terminals Tx of the head 2 are intended to be connected to the ends of the winding of the antenna, by means of the matching network 4. This matching network 4 comprises at least one capacitive element in series between each Rx or Tx terminal and the end of the winding to which this terminal is to be connected. For example, capacitors Cs are interposed between the terminals Tx and the ends 32 and 34 and capacitors Crx are interposed between the terminals Rx and the ends 32 and 34. In addition, a capacitive element Cp generally connects the ends 32 and 34 together. . The capacitors of the network 4, and in particular the capacitor Cp, participate in the frequency tuning of the oscillating circuit comprising the antenna 3, both in reader mode (generation of a field) by adapting the output impedance seen from the Tx terminals to the antenna impedance, and in card or reception mode adapting the impedance to present a resonant circuit having a resonant frequency close to the frequency of the carrier.

While one might think it would be detrimental to connect one end of winding 3 to ground because this would introduce a common mode component in the signals received or transmitted by head 2, the presence at the level of matching network 4 series capacitors, between each terminal of circuit 2 and the end 32 or 34 to which this terminal is connected, filters this common mode component which would otherwise be provided by ground.

The two ends 32 and 34 of the winding 3 are connected to the matching network 4 by insulated wires 42 and / or by conductive tracks deposited on an insulating layer (not shown) covering, at least partially, the internal face of the plate. 5.

The figures 5A and 5B are schematic representations of two embodiments of an antenna 3.

The figure 5A illustrates the embodiment of an antenna 3 in the form of a circular planar winding surrounded by a conductive section 5, also circular. In the example of figure 5A , the outer end of winding 3 is connected to section 5.

The figure 5B illustrates the case of a flat conductive winding 3 of square shape, placed in an opening 52, itself of square shape, made in a metal plane 5. In the example of figure 5B , the internal end of the winding 3 is connected to the section 5.

The figure 6 represents a variant of an embodiment of a matching network 4 ′ between an antenna 3 and a radiofrequency head. This is, for example, a case where the transmission and reception modes are each associated with a separate antenna.

In this example, it is assumed that the antenna is used only to receive data and to return data by load modulation (card emulation mode). The network 4 'then comprises a capacitor Crx between each terminal Rx and the end 32 or 34 of the antenna to which the terminal is to be connected and a capacitor Cp connecting the two ends 32 and 34 of the antenna.

The figure 7 is a view, to be compared to that of the figure 2A , a metal cover of an electronic device.

As emerges from this figure 7 , the opening 52 (here circular), for example for an electronic camera, a microphone, a light sensor, etc., in which the antenna 3 is placed (not shown in figure 7 ) has a closed contour and does not open into one of the edges of the cover 5.

As a particular example of embodiment, the winding 3 has an external diameter or is part of a diameter between about 5 and about 20 mm and the center of the winding has a diameter or is part of a diameter included between 2 and 5 mm.

One advantage of the embodiments described is that it is now possible to associate an antenna with a device equipped with a metal wall.

Another advantage is that it is not necessary to interrupt the electrical continuity of such a metallic environment around the antenna, the latter now being able to be surrounded by a ground plane.

The performance of an antenna thus produced is considerably improved.

Thus, the inventor was able to carry out the following comparative measurements. An antenna of 6 mm in diameter inscribed in a square opening of 10 mm on the side has a back-modulation level 3 cm from the antenna of a test reader that is 3 to 4 times higher than the level obtained for the same antenna of which l The outer end of the winding is not connected to the ground plane.

According to another example of application, an antenna produced with a connection from one end to a ground plane is formed on the rear face (generally metallic) of a flat liquid crystal screen and connected to the ground thereof.

Various embodiments have been described. Various variations and modifications will be apparent to those skilled in the art. In particular, the shape of the metallic plane surrounding the antenna and to which it is connected depends on the applications and on the shape of the electronic device in which the antenna is integrated. Likewise, the shape of the opening made in the metal plane depends on the applications and different variants are possible provided that this opening is closed, that is to say that it does not open into one of the edges of the plane. In addition, it is possible to provide other constitutions of matching network 4, provided to respect an isolation of the common mode between the terminals of the transmission and / or reception circuit 2 and the ends 32 and 34 of the winding forming the Antenna 3. In addition, the embodiments described are particularly suited to circuits carrying out active back-modulation, that is to say not content with modulating the load of the antenna but participating in supplying it with energy. Finally, the practical implementation of the embodiments which have been described is within the abilities of those skilled in the art based on the functional indications given above.

Claims (9)

1. An electronic device comprising:

   a metallic plane (5) comprising an opening (52); and

   a radiofrequency communication or energy transfer antenna made of a planar conductive winding (3),

   wherein the planar winding (3) is placed within said opening (52), one of the two ends (32, 34) of the planar winding being directly connected to the metal plane (5) which continuously surrounds the planar winding,

   the opening of the metal plane being adapted to receive a camera, a microphone, or a light sensor.
2. The device of claim 1, wherein the metal plane (5) is intended to be grounded.
3. The device of claim 1 or 2, wherein the end connected to the plane (5) is the external end (34) of the winding.
4. The device of any of claims 1 to 3, wherein the winding (3) is inscribed within an external diameter in the range from approximately 5 to approximately 20 mm.
5. The device of any of claims 1 to 4, wherein the center of the winding (3) is inscribed within a diameter in the range from 2 to 5 mm.
6. A radio frequency circuit comprising:

   a device of any of claims 1 to 5;

   a contactless front end (2); and

   a matching network (4) provided, between each end of the winding (32, 34) and a terminal of the circuit, with a first capacitive element (Cs, Crx).
7. The circuit of claim 6, wherein the matching network (4) further comprises a second capacitive element (Cp) coupling the two ends (32, 34) of the winding (3).
8. An electronic device integrating the device of any of claims 1 to 5 and/or the radio frequency circuit of claim 6 or 7.
9. The device of claim 7 or 8, wherein the metal plane (5) is a cell phone shell.

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