CONTACTLESS ELECTRONIC BOARD INCLUDING A VOLTAGE RECTIFIER CIRCUIT

Abstract

The invention relates to a contactless electronic card comprising: a body (101); a radio frequency antenna (102) integrated into the body (101) and configured to generate an alternating electrical signal; and at least one active device (106) integrated into the body (101) and configured to operate on direct current. The electronic card includes a center-tapped rectifier circuit comprising the radio frequency antenna (102), the active device (106), and an electronic circuit (107) configured to convert the alternating electrical signal generated by said radio frequency antenna (102) into a direct electrical signal to power at least one active device (106). Figure 3

Description

Title of the invention: CONTACTLESS ELECTRONIC CARD COMPRISING A VOLTAGE RECTIFIER CIRCUIT FIELD OF THE INVENTION

[0001] The invention relates to the field of electronic documents, in particular contactless electronic cards, i.e. cards configured to communicate without contact with a terminal, for example by high-frequency communication, typically via RFID (for "radio frequency identification" in English) or near-field technology known as "NFC" (for "near-field communication" in English) which operates on a frequency of 13.56 MHz. Such cards may however be provided with a chip for traditional contact communication, thus forming for example a so-called "dual" card. PRIOR ART

[0002] A contactless electronic card generally includes a memory and / or a microprocessor. It is used in a growing number of applications, for example for controlling access to a building, for a means of public transport, a show ticket, or other, or for making a payment. Such a card mainly uses a radio frequency (RF) communication technology called "near field" or "NFC", defined in particular through the NFCIP-1 (ISO / IEC 18092), ISO / IEC 14443 or ISO 10373-6 standards.

[0003] For certain applications, it is advantageous to be able to integrate additional functionalities into such an electronic card, for example a user detection function and / or a lighting function. These functionalities require the integration into the card of suitable components, for example a biometric sensor and / or a lighting source, such as a light-emitting diode (LED) and a corresponding controller.

[0004] At least some of these components require a DC power supply to operate.

[0005] However, the electrical energy in the electronic card is supplied by the radiofrequency antenna which, when magnetically coupled with an NFC reader, generates an alternating electrical signal (designated “AC” for “alternative current” in English).

[0006] The electronic card then comprises a voltage rectifier circuit in association with the radiofrequency antenna and configured to convert the alternating electrical signal generated by the radiofrequency antenna into a direct electrical signal and thus power the components described previously.

[0007] For example, document FR2206206 describes such an electronic card in which the rectifier circuit comprises a “double alternation” or “full-wave” bridge.

[0008] However, the use of a full-wave bridge has the disadvantage of forcing the electrical signal generated by the radiofrequency antenna to pass successively through two diodes in series, which causes a relatively significant voltage drop, of the order of twice the direct voltage of the diodes. When the radiofrequency antenna is small, for example class 2 or lower according to the ISO / IEC 104443-1 standard, the rectified electrical signal may no longer be sufficient to power the aforementioned components.

[0009] To limit this voltage drop due to the presence of a full-wave bridge, it is known to use Schottky diodes rather than ordinary diodes, due to their lower forward voltage, typically between 0.2 V and 0.4 V.

[0010] However, a Schottky diode has the disadvantage of undergoing a drift of its forward current with temperature, which can lead to a loss of 50% of the forward current as soon as the temperature exceeds approximately 40°C.

[0011] The object of the present invention is to solve at least in part the aforementioned drawbacks, further leading to other advantages. Statement of the invention

[0012] According to a first aspect, the invention relates to a contactless electronic card comprising:

[0013] - a body,

[0014] - a radiofrequency antenna integrated into the body configured to generate a alternating electrical signal,

[0015] - at least one active device integrated into the body and configured to operate in direct current,

[0016] the electronic card being characterized in that it comprises a centrally tapped rectifier circuit comprising the radiofrequency antenna, the active device and an electronic circuit configured to convert the alternating electrical signal generated by said radiofrequency antenna into a continuous electrical signal for supplying the at least one active device.

[0017] A contactless electronic card here designates a card configured to communicate contactlessly with an external terminal, for example by communication via a high-frequency link, typically 13.56 MHz.

[0018] An active device herein means an electronic component operating in direct current, typically, but not necessarily, a semiconductor component, for example example an LED or OLED diode or a sensor, for example a biometric sensor such as a fingerprint sensor.

[0019] A center-tapped rectifier circuit, also known as a "center-tapped rectifier," herein refers to a type of voltage rectifier circuit comprising a portion of a center-tapped transformer.

[0020] Indeed, a center-tapped transformer typically comprises a component to be supplied with direct current, two diodes, namely a first diode and a second diode, a primary winding and a secondary winding.

[0021] Each diode has an anode and a cathode.

[0022] The component to be supplied with direct current typically has a first terminal and a second terminal.

[0023] The first terminal of the component to be supplied with direct current is connected both to the cathode of the first diode and to the cathode of the second diode.

[0024] Each winding has a first end and a second end.

[0025] The first end of the secondary winding is electrically connected to the anode of the first diode and the second end of the secondary winding is electrically connected to the anode of the second diode.

[0026] The secondary winding further comprises an intermediate connection point, located between its first end and its second end, which is connected to the second terminal of the component to be supplied with direct current.

[0027] In the electronic card according to the invention, the radiofrequency antenna constitutes the secondary winding of the center-tapped transformer, and the active device constitutes the component to be supplied with direct current from the center-tapped transformer.

[0028] In contrast, the primary winding is arranged in an external terminal, such as an NFC reader.

[0029] The part of the center-tapped transformer constituting the center-tapped rectifier circuit therefore corresponds to the center-tapped transformer without primary winding.

[0030] The invention is in fact based on the observation that the radiofrequency antenna of a contactless electronic card behaves in a similar manner to the secondary winding of a transformer when it is magnetically coupled with an external terminal (thus acting as a primary winding), in particular an NFC reader. In other words, the radiofrequency antenna is configured to generate an alternating electrical signal in the circuit when it is magnetically coupled with an external terminal, such as an NFC reader.

[0031] Thanks to the center-tapped rectifier circuit, the electrical signal generated by the radiofrequency antenna passes through a single diode (instead of two for a full-wave bridge) to reach the active device.

[0032] Limiting the number of diodes makes it possible to reduce a voltage drop linked to a diode crossing.

[0033] Reducing the number of diodes also helps to limit the corresponding costs.

[0034] At the same time, the manufacture of the circuit is facilitated due to the reduced number of connections to be established.

[0035] In such an electronic card, the at least one active device is connected to the radiofrequency antenna via a diode on either side.

[0036] Optional features of embodiments of the invention are defined below.

[0037] The radio frequency antenna may comprise a first end and a second end. The electronic circuit may comprise a first diode and a second diode, each diode comprising an anode and a cathode, the first end of the radio frequency antenna being electrically connected to the anode of the first diode and the second end of the radio frequency antenna being electrically connected to the anode of the second diode.

[0038] The active device may comprise a first terminal and a second terminal, the first terminal of the active device being electrically connected to both the cathode of the first diode and the cathode of the second diode.

[0039] The radiofrequency antenna may further comprise an intermediate connection point, located between its first end and its second end, the intermediate connection point being electrically connected to the second terminal of the active device.

[0040] The radiofrequency antenna thus comprises a first winding between the intermediate connection point and its first end, and a second winding between the intermediate connection point and its second end.

[0041] The intermediate connection point may be located at the center of the radiofrequency antenna, i.e. equidistant from the first end and the second end of the radiofrequency antenna, such that the first winding of the radiofrequency antenna has a resonant frequency equal to a resonant frequency of the second winding.

[0042] The resonant frequency of the first winding and / or the second winding may be equal to 13.56 MHz. This promotes satisfactory coupling with an NFC reader.

[0043] The electronic circuit may comprise a smoothing capacitor. Such a capacitor is configured to smooth the continuous electrical signal converted by the electronic circuit. The smoothing capacitor is for example connected in parallel with the at least one active device.

[0044] The electronic circuit may comprise a first tuning capacitor configured to vary the resonant frequency of the first winding of the radio frequency antenna and / or a second tuning capacitor configured to vary the resonant frequency of the second winding of the radio frequency antenna.

[0045] For example, the first tuning capacitor is connected in parallel with the first winding of the radiofrequency antenna and / or the second tuning capacitor is connected in parallel with the second winding of the radiofrequency antenna.

[0046] The electronic card may include an electronic module. An electronic module here designates a printed circuit or PCB (for “printed circuit board” in English).

[0047] The electronic module comprises, for example, a support on which the diodes and / or the active device and / or the smoothing capacitor and / or the first tuning capacitor and / or the second tuning capacitor are mounted.

[0048] The diodes and / or the active device and / or the smoothing capacitor and / or the first tuning capacitor and / or the second tuning capacitor may be surface mounted, i.e. directly soldered to the surface of the support. Surface mounted components or "CMS" (or "SMD" for "surface mounted device" in English) have many advantages: miniaturization, simpler printed circuits, improved component density, reduced costs, etc.

[0049] The first diode may be identical to the second diode.

[0050] At least one of the diodes may be a Schottky diode. Such a diode has a lower forward voltage than a conventional diode, which further limits the voltage drop.

[0051] The electronic card may comprise an RFID module and an RFID antenna electrically connected to said RFID module, integrated into the body. The electronic card may thus also provide a conventional function, such as contactless payment.

[0052] The active device may comprise at least one light-emitting diode and / or a biometric sensor, for example a fingerprint sensor. BRIEF DESCRIPTION OF THE FIGURES

[0053] Other features and advantages of the invention will become apparent in the description below, illustrated by the attached figures which illustrate exemplary embodiments which are not in any limiting nature.

[0054] [Fig. 1] illustrates a center-tapped full-wave voltage rectifier circuit.

[0055] [Fig.2] schematically represents, in the form of oscillograms, an electrical signal passing through different parts or meshes of the voltage rectifier circuit of [Fig.l].

[0056] [Fig.3] schematically illustrates a contactless electronic card according to a first embodiment of the invention.

[0057] [Fig.4] schematically illustrates a contactless electronic card according to a second embodiment of the invention. DETAILED DESCRIPTION

[0058] [Fig. 1] illustrates a center-tapped full-wave rectifier circuit 1. In known manner, such a rectifier circuit comprises a center-tapped transformer 2, 3, two diodes, namely a first diode DI and a second diode D2, and a component to be supplied with direct current 7.

[0059] The rectifier circuit 1 also comprises two input terminals, namely a first input terminal P2 and a second input terminal P3, and two output terminals, namely a first output terminal PI and a second output terminal P4.

[0060] The transformer comprises a primary winding 2 and a secondary winding 3. Each winding 2, 3 comprises a set of turns. The primary winding 2 is connected to a power source. The power source is configured to circulate an alternating electrical signal in the primary winding. According to the invention, the primary winding 2 is formed by an antenna of an external terminal, such as an NFC reader.

[0061] The secondary winding 3 comprises a first end 4, a second end 5 and an intermediate connection point 6, also called a central tap.

[0062] Each of the diodes D1, D2 of the center-tapped rectifier circuit 1 comprises an anode and a cathode.

[0063] The first input terminal P2 is electrically connected to the first end 4 of the secondary winding 3 and to the anode of the first diode DL

[0064] The second input terminal P3 is electrically connected to the second end 5 of the secondary winding 3 and to the anode of the second diode D2.

[0065] Thus, the input terminals P2, P3 receive an alternating electrical signal from the first end 4 and the second end 5 of the secondary winding 3 respectively. This signal is generated by the magnetic coupling of the primary winding 2 and the secondary winding 3 of the transformer.

[0066] The component to be powered 7 comprises a first terminal and a second terminal.

[0067] The first output terminal PI is electrically connected to the connection point intermediate 6 and to a first terminal of the component to be supplied with direct current 7.

[0068] Thus, the first end 4 of the secondary winding 3 is electrically connected to the anode of the first diode D1 while the second end 5 of the secondary winding 3 is electrically connected to the anode of the second diode D2.

[0069] The second output terminal P4 is electrically connected to the cathode of the first diode D1, to the cathode of the second diode D2 and to the second terminal of the component to be powered 7.

[0070] Thus, the first terminal of the component to be powered 7 is electrically connected to the intermediate connection point 6 of the secondary winding 3 while its second terminal is electrically connected to the cathode of each of the first diode D1 and the second diode D2.

[0071] The centrally tapped rectifier circuit 1 thus comprises a first mesh (top mesh in [Fig.l]) in which the alternating electrical signal successively passes through the first input terminal P2, the first diode D1, the second output terminal P4 and the component to be supplied 7.

[0072] The centrally tapped rectifier circuit 1 also comprises a second mesh (bottom mesh in [Fig.l]) in which the alternating electrical signal successively passes through the second input terminal P3, the second diode D2, the second output terminal P4 and the component to be powered 7.

[0073] When the alternating electrical signal is positive with respect to the intermediate connection point 6 (top mesh in [Fig.l]), the first diode D1 is directly polarized and conducts current, while the second diode D2 is inversely polarized and does not conduct current.

[0074] Conversely, when the alternating electrical signal is negative with respect to the intermediate connection point 6 (bottom mesh in [Fig.l]), the second diode D2 is directly polarized and the first diode D1 is inversely polarized.

[0075] [Fig.2] illustrates three oscillograms a, b, c, representing the electrical signal passing through the rectifier circuit 1 as a function of time. Thus, [Fig.2] shows, in a, the electrical signal passing through the first mesh of the rectifier circuit 1, in b, the electrical signal passing through the second mesh of the rectifier circuit 1 and in c, the combination of the electrical signal passing through the first mesh and the second mesh. The signal represented in c corresponds to the electrical signal between the output terminals PI, P4 of the rectifier circuit 1. The center-tapped rectifier circuit 1 is thus configured to convert the alternating electrical signal generated by the secondary winding 3 at the input terminals P2, P3 into a continuous electrical signal between the output terminals PI, P4.

[0076] Optionally, the circuit includes a smoothing capacitor C. The smoothing capacitor C is here connected in parallel with the component to be supplied with direct current 7 so as to smooth the direct electrical signal. The electrical signal shown in [Fig.2] comes from a rectifier circuit without a smoothing capacitor.

[0077] [Fig. 3] schematically illustrates a contactless electronic card 100 according to a first embodiment of the invention.

[0078] The electronic card 100 has, for example, the ID-1 dimensions of a credit card as defined in the ISO / IEC 7810 standard, namely 85.60 x 53.98 x 0.76 mm. Of course, other formats can be envisaged.

[0079] The electronic card 100 comprises a body 101 or support or even substrate.

[0080] The electronic card 100 also includes a radiofrequency antenna 102, for example wired example, integrated into the body 101.

[0081] The radiofrequency antenna 102 comprises a first end 103, a second end 104 and an intermediate connection point 105 located between the first end 103 and the second end 104.

[0082] The radiofrequency antenna 102 comprises a first winding 102a between the intermediate connection point 105 and its first end 103, and a second winding 102b between the intermediate connection point 105 and its second end 104.

[0083] The intermediate connection point 105 is here located at the center of the radiofrequency antenna 102 so that the first winding 102a of the radiofrequency antenna 102 has a resonant frequency equal to the resonant frequency of the second winding 102b.

[0084] The radio frequency antenna 102 is configured so that, when magnetically coupled with an external terminal, an alternating electrical signal is generated at its first end 103 and at its second end 104.

[0085] The electronic card 100 further comprises an active device 106, represented by a resistor in [Fig.3] operating in direct current.

[0086] The active device 106 here comprises two terminals, namely a first terminal and a second terminal.

[0087] The active device 106 is for example a component of the LED, OLED type or a sensor, for example a biometric sensor.

[0088] The electronic card 100 comprises an electronic circuit 107 configured to convert the alternating electrical signal generated by the radiofrequency antenna 102 into a continuous electrical signal for powering the active device 106.

[0089] The electronic card 100 thus performs an electronic NFC energy recovery function.

[0090] The electronic circuit 107 comprises a first diode DI and a second diode D2.

[0091] Optionally, the electronic circuit 107 comprises a smoothing capacitor C.

[0092] The radio frequency antenna 102, the diodes D1, D2 of the electronic circuit 107 and the active device 106 are electrically connected in accordance with the diagram of the center-tapped rectifier circuit of [Fig.l].

[0093] In other words, the electronic card 100 comprises a centrally tapped rectifier circuit comprising the radiofrequency antenna 102, the active device 106 and the electronic circuit 107.

[0094] Thus, when the electronic card 100 is brought close to an external terminal, the magnetic coupling (induction) of their antennas makes it possible to induce an alternating electrical signal, generally of frequency 13.56 MHz, at the ends of the radiofrequency antenna 102.

[0095] The center-tapped rectifier circuit operates as described in [Fig.l] to convert the alternating electrical signal generated at the ends of the radio frequency antenna 102 into a direct electrical signal for powering the active device 106.

[0096] Techniques for forming radiofrequency antennas in electronic cards are particularly effective for this type of circuit, which requires increased precision, particularly when it comes to creating two windings of identical lengths.

[0097] The smoothing capacitor C is mounted according to the diagram in [Fig.l]. For a rectified NFC signal, a capacitance greater than 100 pF, or even 150 pF, can be adapted.

[0098] In the embodiment shown, the electronic card 100 comprises an electronic module 110. The electronic module 110 comprises, for example, a support 111 on which the diodes D1, D2 and the active device 106 are mounted.

[0099] The support 111 is for example made of polyimide (PI), FR4 or any other dielectric substrate. The dimensions of the support 111 here are those of conventional electronic card modules, namely 5.1 x 8.0 mm, in order to reuse existing industrial tools. Of course, other dimensions are possible within the scope of the invention.

[0100] The electronic module 110 comprises a metallization layer (produced using conventional techniques), typically made of copper, deposited on the support 111.

[0101] The metallization layer forms four metal terminals PI to P4 insulated from each other, namely a first input terminal P2, a second input terminal P3, a first output terminal PI and a second output terminal P4. In this example, each terminal extends in the form of substantially rectangular or square metal pads.

[0102] The first end 103 of the radio frequency antenna 102 is electrically connected to the first input terminal P2 and the second end 104 of the radio frequency antenna 102 is electrically connected to the second input terminal P3.

[0103] The first input terminal P2 is electrically connected to the anode of the first diode D1 and the second input terminal P3 is electrically connected to the anode of the second diode D2.

[0104] The intermediate connection point 105 is electrically connected to the first PI output terminal.

[0105] The first output terminal PI is electrically connected to the first terminal of the active device 106.

[0106] The second output terminal P4 is electrically connected to both the cathode of the first diode D1, the cathode of the second diode D2 and the second terminal of the active device 106.

[0107] The smoothing capacitor C is connected in parallel with the active device 106.

[0108] Thus, the center-tapped rectifier circuit rectifies the received alternating electrical signal at input terminals P2, P3 into a continuous electrical signal at output terminals PI, P4.

[0109] In the illustrated embodiment, the input terminals P2, P3 and the first output terminal PI are aligned and arranged along a large side of the electronic module 110.

[0110] In particular, the first output terminal PI is arranged between the input terminals P2, P3. This facilitates the connection with the radiofrequency antenna 102.

[0111] The second output terminal P4 is arranged along an opposite large side, facing the first output terminal PI in a direction perpendicular to the direction of alignment of the input terminals P2, P3 and the first output terminal PL

[0112] This arrangement advantageously makes it possible to improve the compactness of the electronic module 110. Other spatial configurations of the terminals on the electronic module are also possible.

[0113] The second output terminal P4 here has two respective arm-shaped extensions each extending towards a respective input terminal P2, P3.

[0114] Preferably, the diodes D1, D2 are connected via their cathode to the terminal parts of the extensions of the output terminal P4.

[0115] [Fig.4] schematically illustrates a contactless electronic card 100 according to a second embodiment of the invention.

[0116] In this electronic card 100, the electronic circuit 107 further comprises a first tuning capacitor A1 configured to vary the resonant frequency of the first winding 102a of the radiofrequency antenna 102 and a second tuning capacitor A2 configured to vary the resonant frequency of the second winding 102b of the radiofrequency antenna 102.

[0117] The first tuning capacitor A1 is here mounted in parallel with the first winding 102a of the radiofrequency antenna 102 and the second tuning capacitor A2 is mounted in parallel with the second winding 102b of the radiofrequency antenna 102.

[0118] The electronic card 100 according to the invention makes it possible, thanks to the centrally tapped rectifier circuit, to supply an active device with direct current from an alternating electrical signal generated by the radiofrequency antenna, with a relative efficiency tively satisfactory. In particular, it is possible to limit voltage drops with a lower number of diodes compared to a full-wave bridge rectifier circuit.

[0119] Although the present invention has been described above with reference to a specific embodiment, the present invention is not limited to this specific embodiment, and modifications, which are within the scope of the present invention, will be apparent to a person skilled in the art.

[0120] Numerous other modifications and variations will become apparent to those skilled in the art upon reference to the above illustrative embodiment, which is given by way of example only and does not limit the scope of the invention, which is determined solely by the appended claims.

Claims

Claims

1. Contactless electronic card, comprising - a body (101), - a radiofrequency antenna (102) integrated in the body (101) and configured to generate an alternating electrical signal, - at least one active device (106) integrated in the body (101) and configured to operate in direct current, the electronic card being characterized in that it comprises a centrally tapped rectifier circuit comprising the radiofrequency antenna (102), the active device (106) and an electronic circuit (107) configured to convert the alternating electrical signal generated by said radiofrequency antenna (102) into a direct electrical signal for supplying the at least one active device (106).

2. Electronic card according to claim 1, characterized in that the radiofrequency antenna (102) comprises a first end (103) and a second end (104), in that the electronic circuit (107) comprises a first diode (D1) and a second diode (D2), each diode (D1, D2) comprising an anode and a cathode, the first end (103) of the radiofrequency antenna (102) being electrically connected to the anode of the first diode (D1) and the second end (104) of the radiofrequency antenna (102) being electrically connected to the anode of the second diode (D2).

3. Electronic card according to claim 2, characterized in that the active device (106) comprises a first terminal and a second terminal, the first terminal of the active device (106) being electrically connected both to the cathode of the first diode (D1) and to the cathode of the second diode (D2).

4. Electronic card according to claim 3, characterized in that the radiofrequency antenna (102) further comprises an intermediate connection point (105) located between its first end (103) and its second end (104), the intermediate connection point (105) being electrically connected to the second terminal of the active device (106).

5. Electronic card according to one of claims 2 to 4, characterized in that the first diode (D1) is identical to the second diode (D2).

6. Electronic card according to any one of claims 1 to 5, characterized in that the electronic circuit (107) comprises a smoothing capacitor (C), the smoothing capacitor being connected in parallel with the active device (106).

7. Electronic card according to any one of claims 2 to 6, characterized in that the radiofrequency antenna comprises a first winding (102a) between the intermediate connection point (105) and its first end (103), and a second winding (102b) between the intermediate connection point (105) and its second end (104), the electronic circuit (107) comprising a first tuning capacitor (A1) configured to vary the resonant frequency of the first winding (102a) of the radiofrequency antenna (102) and / or a second tuning capacitor (A2) configured to vary the resonant frequency of the second winding (102b) of the radiofrequency antenna (102).

8. Electronic card according to one of claims 1 to 7, characterized in that it further comprises an RFID module and an RFID antenna electrically connected to said RFID module, integrated in the body.

9. Electronic card according to any one of claims 1 to 8, characterized in that the at least one active device (106) comprises at least one light-emitting diode and / or an OLED and / or a biometric sensor, for example a fingerprint sensor.

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