METHOD, CIRCUIT AND DEVICE FOR CONTACTLESS COMMUNICATION WITH ACTIVATED TRANSMISSION

Description

Field of invention.

[0001] The invention relates to a method for activated contactless communication as well as a circuit and device for implementing it. It aims in particular to specify the characteristics of the signals, antennas and principle of this new way of using contactless technology. Radiofrequency communication is in principle short-range and carried out by coupling and electromagnetic induction with a range of the order of 0.01 or even 1 m.

[0002] It is particularly used in portable electronic objects, for example memory cards such as SD cards (from the Sandisk company).

[0003] Such cards are currently used in a card interface of mobile phones to carry out a contactless transaction meeting in particular the ISO / IEC 14443 or 15693 standard, since these phones are not equipped with contactless interfaces when leaving the factory. Prior art.

[0004] The current technology ISO / IEC 14443 and NFC, acronym for Near Field communication (proximity radio frequency communication), is based on a principle of retro modulation of a signal emitted by a reader.

[0005] According to this principle, a certain amount of electromagnetic field provided by a reader must be modulated by the proximity contactless chip object also called PICC (Proximity Integrated Circuit Card). In order to comply with the reader's sensitivity, a minimum field amplitude is required to be modulated by the object. This modulation of the reader carrier must generate two sidebands with an amplitude at least equal to 22 / H 0.5< . To meet this condition, it is necessary to have a minimum coupling between the reader and the object. The coupling factor is directly dependent on the antenna surfaces of the reader and that of the contactless object.

[0006] In the case of very small contactless objects, such as a microSD card, the surface area of ​​the radiofrequency antenna is radically too small. Furthermore, such objects are intended to be embedded in a host device such as a mobile phone. This operation further reduces the coupling of the contactless object with the reader due to the metallic environment of the phone.

[0007] Patent EP1801741 (B1) describes a method for generating a self-electromagnetic field by a portable data carrier (transponder), in which the data transmission to a reader is carried out in an activated communication mode and in which the transmission of the object's own electromagnetic field is seen by the reader as a modulation of the reader's field. However, this solution does not appear to be fully described or to function correctly as described.

[0008] Furthermore, teaching this patent is very complicated. Its implementation requires more electronic components, including filters, an oscillator, and an NFC component. In addition, current NFC controllers require two antennas, one dedicated to energy harvesting and the other dedicated to data transmission / reception.

[0009] Patent application EP 1 898 342 describes a radiofrequency transponder used in an inventory control system using several transponders. It comprises a first antenna circuit for reception, a second antenna circuit for transmission. The transmission signal is derived from the reception frequency received by the reception antenna.

[0010] The transponder transmits information by modulating a harmonic transmission frequency derived from the carrier frequency of a reader. This harmonic frequency is a multiple of the carrier frequency without being synchronized with the carrier frequency.

[0011] Patent EP 0 926 855 describes a battery-powered radiofrequency communication transponder. It comprises a circuit capable of switching from a reception mode to a transmission mode and vice versa. The transponder comprises a circuit with a microprocessor, a single capacitor and a single antenna and switching means for forming a parallel LC reception circuit or a series LC transmission circuit depending on the communication mode switched. The transponder responds by modulating an external reader field with which it is coupled.

[0012] Patent EP1898342A2 describes a transponder suitable for use in a cash register or inventory control system which is arranged to transmit by modulating and rebroadcasting a transponder signal frequency derived from a carrier frequency received at a transmitting antenna. The transponder comprises a dual-mode antenna (L4) and circuitry (18) which selectively operates the antenna (L4) to suppress unwanted transmission of the transponder signal frequency when the transponder is not transmitting. A termination circuit (22) is provided which suppresses unwanted transmission of the transponder signal frequency by a demodulator portion of the transponder.

[0013] US6356535B1 describes a communication device that includes: a first antenna operable to receive wireless communication signals; a second antenna having a plurality of conductors, the second antenna operable to transmit wireless communication signals; a connection including a plurality of conductive lines having respective first ends and second ends, the connection coupled to the conductors of the second antenna at the first ends of the lines; and a switch coupled to the second ends of the connection, the switch operable to provide one of selective shorting and isolation of the conductors.

[0014] Patent US5621913A describes a system for wireless communication between a plurality of semiconductor chips.

[0015] The invention aims to find an easier and more advantageous solution to the problem of coupling between a reader and a small object. Summary of the invention.

[0016] The invention proposes to solve this coupling problem by generating independently of the reader at least one of the two sidebands so that the reader can detect the back-modulation signal coming from the contactless object (PICC). The circuit of the invention returns a carrier signal modulated by the charge modulation response signal of the contactless object; Preferably, the modulation of this carrier signal is amplified to feed a transmission antenna.

[0017] The invention provides in particular for generating or extracting a communication carrier frequency from the field of a reader received on a data receiving antenna of the contactless object and for transmitting a response by modulating this carrier reinjected into a transmission stage comprising a separate transmission antenna.

[0018] Better communication results are achieved with separate tuning frequencies for the transmitter and receiver resonant circuits.

[0019] To this end, the invention therefore relates to a contactless communication circuit activated according to claim 1.

[0020] According to other characteristics of the circuit: The synchronized transmission means (17) are configured to modulate a carrier signal derived or extracted from an electromagnetic field for receiving data; The circuit is configured to communicate according to at least one of the standards ISO / IEC 14443 or 15693 or 18092. The circuit comprises a contactless chip and a transmission adaptation stage configured to amplify a response signal from the chip before injection into said second transmission antenna; The adaptation stage performs a logic “AND” function to combine a carrier signal and a response signal before amplification; Said antennas are arranged together so that their mutual inductance is minimized, in particular by a spacing or attenuator; Preferably, their mutual inductance is at least partially canceled so as to have a negligible current induction in the reception antenna caused by the transmission antenna;The antennas may partially overlap each other in order to globally cancel the current induced in the receiving antenna by the transmitting antenna; The antenna arrangement makes it possible to minimize a coupling interaction between the antennas, responsible for reciprocal or mutual disturbances. An active current produced in the receiving antenna inadvertently induces a signal in the receiving antenna; This arrangement makes it possible to avoid a processing step and / or electronic filters which could be used alternatively to this preferred arrangement; The receiving antenna is part of a parallel resonance circuit and / or the transmitting antenna is part of a series resonance circuit;The parallel resonance of the receiving circuit allows an increase in the voltage collected by the antenna which is an advantage for data detection, on the other hand the series resonance of the transmitting circuit allows a high current to be injected into the transmitting coil despite a low operating voltage which is the case in particular for a micro SD card; The circuit comprises a contactless chip intended to receive a receiving signal and a reception adaptation stage intended to adapt the reception signal to the characteristics of the chip; The reception adaptation stage can be configured to extract a synchronized carrier signal from the receiving signal; The circuit is integrated in or constitutes an object having a form factor of an integrated circuit card or very reduced such as a micro SD card or other component. The circuit can have at least one connector corresponding to that of an object configured to connect a host device;Thus, devices without a contactless function can be provided with it thanks to the invention. The circuit comprises a PLL phase-locked loop making it possible to artificially maintain the clock of the incident field when the parallel resonant circuit is decoupled; The first and second antennas can constitute a single antenna; The tuning frequencies of the resonant circuits in reception and in transmission are substantially different and respectively centered on 13.56 MHz and 14.4 MHz. ;

[0021] The invention also relates to a contactless communication method activated according to claim 12.

[0022] Thanks to the invention, a good coupling is achieved between a reader and a PICC type object (SD card); In addition, it is easy to implement with a minimum of modification; The invention applies in particular to any chip with a usual dual interface (with or without oscillator). Brief descriptionof the figures.

[0023] There figure 1 illustrates an SD card comprising the circuit according to one embodiment of the invention; The figure 2 illustrates a more detailed view of the RF radio frequency circuit of the previous figure; The Figure 3A illustrates a first embodiment of a reception stage of the figure 2 ; There Figure 3B illustrates a second embodiment of a receiving stage of the figure 2 ; There figure 4 illustrates an embodiment of a transmission stage of the figure 2 ; THE Figures 5 and 6 illustrate a receiving antenna arranged relative to a micro SD card and equivalent circuit values ​​of the antenna; The figure 7 illustrates the level of modulation by the radiofrequency component SE (5); The figure 8 illustrates a filter for extracting the response signal of component 5 from the carrier of the previous figure; The figure 9illustrates a circuit for combining the carrier and the response signal alone; The figure 10 illustrates an LC circuit relating to the transmitting antenna; The figure 11 illustrates values ​​of reactances XL and XC from inductance and capacitance respectively as a function of frequency; The figure 12 illustrates an arrangement of a transmitting antenna relative to a micro SD card and an arrangement of the two antennas between them. The figure 13 illustrates an embodiment of the invention in which the reception and transmission interfaces are operational in turn and which uses particular means for generating a transmitting electromagnetic field synchronized with the reception field of a reader. Detailed description.

[0024] Activated communication means contactless communication in which the response of a transponder is carried out by emitting an electromagnetic field specific to the transponder, preferably amplified. This emission is in fact obtained by emitting at a determined power a carrier signal modulated by a signal from the transponder.

[0025] The energy for amplification and / or operation of the transmitter / receiver transponder is preferably provided by an external energy source separate from the reader.

[0026] Typically, the contactless communication or circuit complies with ISO / IEC 14443 and / or ISO / IEC 15693 or any other protocol relying on an electromagnetic field excitation frequency of 13.56 MHz. The circuit is powered by a current source.

[0027] To the figure 1An example of an embodiment of a contactless communication circuit 1 according to the invention is shown diagrammatically, equipping a memory card 1A. However, any other communicating object can a priori be equipped with it, for example, USB key, PCMCIA card, telephone, PDA, computer.

[0028] The object may or may not be removable from a host device or permanently attached to it, such as soldered to a printed circuit board. The circuit or object may optionally provide for external antenna connections rather than supporting them.

[0029] The memory card 1 comprises in a known manner contact pads 2, a microcontroller 3, a mass memory 4 (NAND) connected to the microcontroller. The card further comprises a communication processing element 5; It is preferably of the dual interface type (configured to manage contact type communication, for example ISO 7816-3 and contactless ISO-14443 (SE)); This component or element 5 (SE) is preferably secured like an integrated circuit chip known in the field of smart cards; It can be provided, where appropriate, with cryptographic and / or anti-fraud, anti-intrusion, etc. functionalities.

[0030] The SE component is connected to the microcontroller 3 by an input / output port; The SE security component is connected to an active CL interface circuit 6; This component 6 receives two antennas 7, 8, respectively for reception and transmission.

[0031] In principle, it is observed that the invention comprises additional RF means 6, 7, 8 added to the contactless element SE in order to compensate for the particularly reduced size of the antenna since it is housed in a micro SD or mini SD card or in an object of substantially equivalent size.

[0032] According to a characteristic of an embodiment of the invention, the transmission means 5, 6, 7, 8 are configured to modulate a carrier signal 25. This carrier signal is here preferably derived or extracted from the magnetic field received from an external reader.

[0033] In the example, the radiofrequency circuit 6 performs functional activities of reception and emission of the electromagnetic field below; It captures in particular the external RF radiofrequency field coming from a contactless reader to, if necessary, make it compatible with the secure component SE (voltage, etc.); It amplifies the response of the secure element SE intended to be listened to by the external reader.

[0034] There figure 2 describes in more detail the SE component (5) and its connections. The SE circuit of this mode includes means of connection to an external energy source.

[0035] In the example, the SE component comprises a contact interface, for example compliant with the ISO-7816 standard symbolized by a connection bundle 9; it comprises a power supply pad Vcc, and pads La, Lb connected respectively to an active interface 6 and to ground. The SE component is configured to modulate an impedance load in response to reception of the contactless frames received on its pads La, Lb.

[0036] The active interface 6 comprises a circuit 16 for conditioning the reception signal SRE and a circuit 17 for generating pulses for transmitting a transmission signal SEE. Each circuit 16, 17 is connected to the pad (La) of the processing component 5.

[0037] According to one embodiment of the invention, the transmission means 5, 17 are configured to modulate a carrier signal. The carrier signal preferably results from a derivation or extraction of the received magnetic field SRE. Clock and reception of data.

[0038] According to one embodiment, the method comprises a step of receiving the carrier frequency generated by the reader; The carrier frequency is received by a dedicated receiving antenna 7. The antenna 7 actually receives the electromagnetic field emitted by the reader comprising the modulated carrier frequency. The frequency is in the example 13.56 MHz but it could be any other depending on the type of communication or protocol based on this frequency of 13.56 MHz of short or medium range less than 10 m, 1 m or 0.1 m or even close to 0.

[0039] However, the invention does not exclude generating a carrier signal otherwise, for example from a clock signal or internal signal of a host device or object.

[0040] This reception stage also aims to collect the data sent by the reader to the contactless object. An electronic stage including a dedicated reception circuit can be developed for this purpose, in particular to adapt the voltage.

[0041] The method can also implement an adaptation step through a reception adaptation stage (16) to adapt the reception signal SRE to the chip 5; The method can cumulatively or alternatively carry out in this stage an extraction of a synchronized carrier signal 25 from the reception signal SRE.

[0042] To the Figure 3A A first detailed embodiment 16B of the stage 16 is illustrated. The reception stage 16A comprises the reception antenna 7 here connected to the pad `La' of the chip via a reception circuit described below.

[0043] The signal received by this antenna can be amplified before extraction of the clock signal corresponding to the carrier signal; For this purpose, the circuit comprises an amplifier 30 connected to the antenna and to the output of this amplifier is connected a clock extractor 31; The clock signal obtained 25 at the output of the extractor is sent by a link (K) to a pulse generator circuit or transmission adaptation stage 17 detailed in figure 4 The output of the clock extractor 31 is also connected to a logic circuit 35 performing an “AND” function.

[0044] Stage 16A here also comprises a demodulator 32a receiving the reception signal SRE amplified by the amplifier 30 connected to a comparison circuit 33a to compare the demodulated signal obtained with a reference voltage (TR).

[0045] Then, the output signal of comparator 33a is combined with the clock signal 25 coming from the clock extractor 31 at a component 35 performing a logical `AND' function; A first branch of the output of component 35 can pass through an amplifier 36 before being injected into the pad `La' of chip 5.

[0046] A second branch of the output of component 35 can pass through an inverter then an amplifier 36 before being connected to the 'Lb' pad of the chip.

[0047] To the Figure 3B A second embodiment 16B of this stage 16 is illustrated, in which the component 5 used is still a chip with a dual contact and contactless interface (combi). The same numbers from one figure to another represent identical or substantially similar elements.

[0048] In this variant, the clock extraction circuit 31 also connects to a phase shifter 34 before acting on the analog / digital converter 32b.

[0049] The receiving stage or circuit 16B is on the one hand connected to the receiving antenna 7 connected here to the pad `La' of the chip. The circuit 16B can include a capacitor 13 arranged across the pads 'La' and 'Lb' of the chip. This capacitance makes it possible to have a good quality factor. The resonant circuit of the receiving antenna is implemented on the principle of a parallel circuit.

[0050] Unlike circuit 16A, demodulator 32a is replaced by an analog / digital converter 32b, comparator 33a is replaced by a digital comparator 33b with a digital reference value (DR) and pad 'Lb' is connected to ground instead of receiving the inverted "AND" circuit output signal amplified by an inverter 37 and an amplifier 36 respectively.

[0051] In addition, this circuit includes a phase shifter 34 on an output branch of the clock extractor 31. This phase shifter then connects to the analog / digital converter 32b.

[0052] Thus, these stages 16A or 16B each allow the clock signal 25 to be extracted and the signal to be adapted to the chip 5. After reception and amplification, the carrier signal is directed to the RF input of the Combi chip 5 using the interface pads La / Lb. An additional capacitor 18 can be added to the interface in order to adapt the input impedance.

[0053] The electronic stages 16A and 16B operate as follows: The SRE signal received by the antenna 7 can be quite weak given the small coupling surface of the antenna 7 in a medium such as a mini SD card.

[0054] This signal is amplified by the amplifier 30 before being demodulated by the demodulator 32a or analog / digital converter 32b; A useful signal extracted and calibrated by the comparator is combined by the (AND) gate 35 with the clock signal extracted by the clock extractor 31. At the output of the gate 35, the reconditioned radiofrequency signal is injected into the component 5, having been previously amplified in differential mode using the inverter 37 and the amplifiers 36.

[0055] At the same time, the Vcc supply of the ISO 7816 contact-side chip can be deactivated by a suitable circuit (not shown) during the presence of an SRE electromagnetic field. This latter circuit can be included in circuit 16A or 16B. Actuation can be manual.

[0056] The latter may preferably have their components (30, 36, 32a...) supplied with voltage by a power supply coming from the contacts 2 in relation to a host device.

[0057] Circuit 16B operates in much the same way; however, phase shifter 34 allows the acquisition triggers of the radiofrequency signal to be precisely adjusted in order to convert the envelope of the signal received into a digital signal by converter 32b.

[0058] The “Combi” chip 5 can be powered by its ISO / IEC 7816 Vdd and Vss contact pads and may or may not use energy provided to it by the field depending on the use and the electronic assembly of the invention. The chip can also be powered by a voltage that would be generated like the RF field or by the circuit 16 itself which would be powered by the contacts 2 of a host device.

[0059] The advantage of this last option is for component 5 to have its power supply managed by stage 16 depending on the presence or absence of the field and, if necessary, to reset chip 5.

[0060] At this point, the VLab voltage amplitude is at least 3.3 Vpp (Volts peak-peak). This value is necessary for the example chip to detect the 13.56 MHz clock and be able to extract data from the reader.

[0061] As an example, the following table shows the voltage required by two current chips, for example P5CD072 from Philips / NXP or 66CLX800 from Infineon, to detect the clock and data coming from the external field. Chip Contactless chip Vcc = 3v Contactless chip Vcc = 2.7v Vmin (Vpp) 3,48 3,53 Vmax (Vpp) 6,87 6,22 Duty Cycle (%) 7,7 7,7 Antenna of reception (fig. 5, 6).

[0062] The dimension of the receiving antenna 7 is as large as possible within the limit of the available surface in the object. Within the framework of an available surface on a micro SD card, the results below were retained. The inductance is preferably selected so as to be tuned by an additional capacitor of low value in order to limit the size of the capacitor.

[0063] The receiving antenna can for example have an area of ​​5 x 5 mm 2< and comprise 4 to 6 turns. The antenna can be tuned to 13.56 MHz with a quality factor Q of 10. A parallel circuit can be selected so as to obtain a maximum voltage across the antenna circuit. The following antenna characteristics were selected with the equivalent circuit of the figure 6 with L: 663 nH and R: 1.59 KΩ; C not being applicable.

[0064] The antenna performance measured with such an antenna with the equivalent scheme of the figure 6 are given in the table below. Ls = 663 nH; Rs = 1.59 KΩ; C1 = 180 pF; C2 = 18 pF; Rc = 270 KΩ; Cp = 9.5 pF; Rp = 1 MΩ. Field strength Contactless chip Vcc = 2.7v 1.5 A / m 1.01 Vpp 4.5 A / m 3.00 Vpp 7.5 A / m 5.09 Vpp

[0065] The expected voltage with this antenna is greater than 1Vpp (Volt peak to peak). The minimum field creates a voltage greater than 1Vpp, not enough to allow the combi 5 chip to detect the signal. This is why, in the example embodiment with a micro SD card, an amplification stage has preferably been introduced. This amplification stage for clock reception is here greater than 10 dB, the voltage gain being equal to 3. This amplification may not be necessary in other circumstances or for other chips.

[0066] The output level of the conditioning stage 16 is between 3 Vpp and 14 Vpp. The gain can be between 5 and 20 dB.

[0067] The chip power-down or RESET function can also be triggered by any means, such as a switch in the host device or on the chip's power circuit. The chip resets automatically when powered on. Side band and modulation (fig. 7-10).

[0068] In the example ( Fig. 9 ), when the combi chip 5 receives the carrier signal (or the carrier) as well as the data signal, through its La / Lb pads, it generates a charge modulation signal in order to transmit a response to the device or terminal in communication with it. The amplitude of the modulation signal Vmod is here approximately half the amplitude of the carrier VLAB when the capacitor is well adapted.

[0069] A 10 to 60pF capacitor across the La and Lb points of the chip can be used for this purpose. This value may vary depending on the type of chip. This gives the VLAB and Vmod voltages equal to 3.3 Volts peak-peak and 1.6 Volts peak-peak respectively.

[0070] At this stage, two options are considered. The first, simpler, is to use this signal as it is presented and then, preferably, to amplify it in a high-power amplification stage before injecting the signal into a transmission adaptation or activation circuit 17 before the transmitting antenna 8. Different amplification means known to those skilled in the art can be used.

[0071] In another example ( Fig. 8 ) according to a second option, the carrier signal for transmission is suppressed in order to preserve the digital data 25. For this purpose, one can use for example a low-pass filter 27 of the figure 8 .

[0072] Afterwards ( Fig. 9 ), a modulation is preferably carried out at 100% by combining the data signal 25 with a carrier 26 at 13.56 MHz. This can be achieved using the logic (AND) gate 38 or an amplifier buffer 42 or a transistor circuit performing the same function. After power amplification, the resulting signal 29 is used to feed the output antenna 8.

[0073] Thus, rather than amplifying the assembly comprising the carrier 25 and the signal 26 or the carrier alone 25 even when there is no signal, the invention provides for amplifying the signal and the carrier only when there is a response signal. For example, here on the figure 9The useful signal 29 is amplified when the data signal is at a high level. When there is no signal, (data line at zero or near zero level), no signal comes out of gate 38. There is no unnecessary amplification and energy loss of the carrier alone before feeding the transmit antenna.

[0074] There figure 4 illustrates a preferred option of relatively simple implementation allowing to obtain good results and partly implementing the second option; According to this preferred option, the adaptation stage 17 comprises an “AND” logic gate 38 or equivalent circuit for combining a carrier signal 26 ( fig.9 ) and a response signal 25 or emission from chip 5 before amplification.

[0075] In more detail in circuit 17, the `La' pad of chip 5 is connected to a demodulator 39 (which can be of the same type as circuit 27 or 32a) to receive a modulated response signal from chip 5; Then, the output of demodulator 39 connects a comparator 41 which compares the received voltage level with a reference voltage level (TRE) in order to digitize the useful signal. The output of comparator 41 carrying the useful response signal from chip 26 is connected to one of the inputs of component 38 performing the logical 'AND' function to combine the carrier signal 25 with the response signal 26 from the chip.

[0076] The carrier 25 comes from point K of the reception and extraction adaptation stage 16A or 16B; The carrier is injected via a connection to the other input terminal of the component 38 performing the logic 'AND' function; The clock signal is preferably phase-shifted by a phase-shifter 40 so as to optimally synchronize or align the clock signals with the carrier of the radiofrequency signal generated by a reader device in order to produce maximum retro-modulation. The transmission frequency of the circuit of the invention is therefore synchronized in phase with the frequency of the field emitted by the reader.

[0077] The circuit 17 preferably comprises a buffer or amplifier circuit 42 for amplifying the signal 29 at the output of the component 38 before injecting it into the transmitting antenna 8. The antenna circuit used forms a series resonant circuit with a capacitor 43.

[0078] Certain components of stage 17 can preferably be supplied with voltage, for their operation, by a power source coming from the host device via the contacts 2. Other sources known to those skilled in the art are not excluded.

[0079] The circuit 17 operates as follows. After the chip has received at its points La, Lb radiofrequency frames SRE preferably reconditioned beforehand, the response of the chip by load modulation is received and demodulated in the demodulator 39; Then a useful signal is digitized by the threshold comparator 41 before being injected into the circuit (ET) 38 and combined with a carrier 25 extracted or derived from the received field SRE coming from the point K. If necessary, the circuit 17 can include a clock extractor similar to 31 sampling the signal as in figures 16A or 16B.

[0080] The response signal 29 resulting from the circuit 38 is then preferably amplified by the amplifier 42 before being injected into the series resonance transmitting antenna 8. Power of output buffer amplification.

[0081] In order to compensate for the small surface area of ​​the transmitting antenna in the SD card (or other substrate), an output buffer amplifier 42 can be used, which preferably delivers a minimum current of 60 to 80 mA under the supplied supply voltage. Good results are obtained with a power greater than 200 mW.

[0082] An advantage of this treatment is in particular to limit the energy consumption at the amplification level when there is no response signal from chip 5. It is in fact useless to amplify the carrier signal alone when there is no response or signal to be transmitted in the intended application. Output antenna & tuning frequency (fig. 10, 11).

[0083] The antennas 7, 8 comprise, in the example, turns arranged flat on the same substrate (or two separate substrates) as illustrated in the figures 3 and 13 in particular. Any means known to those skilled in the art for producing an antenna can be used, such as etching, ultrasonic wire inlay, etc.

[0084] When the system is powered by a low voltage (3.3 V), the output antenna is designed to achieve series resonance. When the system is powered by a high current, the voltage across the entire LC circuit will be relatively low, when a high voltage is present on each L and C component.

[0085] The curve illustrated in the figure 11 represents values ​​obtained from reactance XL as a function of inductance and thus values ​​of reactance XC as a function of a capacitor according to frequency by applying the formulas below. Xc = 1 2 ⋅ π ⋅ f ⋅ C X L = 2 ⋅ π ⋅ f ⋅ L

[0086] At the point of intersection between the two curves, the reactances XL and XC are equal. F is the series resonant frequency of the circuit.

[0087] At this point, the voltage across the LC circuit ( Fig. 10 ) is minimal when the current intensity is maximum. Since the magnetic flux is directly dependent on the current intensity, this series resonance is a means of creating a high magnetic field on the transmitting antenna 8 even though it is powered by a low voltage.

[0088] This provides a way to increase the signal strength of transponder 5 despite the small size of the antenna on the substrate. Characteristics of the transmitting antenna (fig. 12).

[0089] According to the embodiment of the invention, the circuit comprises separate receiving and transmitting antennas; the antennas are arranged together so that their mutual inductance is minimal or at least partially cancels out. Preferably, the arrangement is chosen so as to have a minimal current induction in the receiving antenna, in particular lower than the gain threshold of the receiving stage 16. For example, with a gain of 3, provision is made to arrange the antennas together so as to have a voltage lower than 300 mV).

[0090] In one variant (not shown), the antennas are protected from each other by being spaced apart from each other and / or by shielding.

[0091] In another variant, the antennas overlap and electronic protection means such as filters configured to avoid mutual disturbances are provided.

[0092] In the advantageous embodiment, the dimension of the transmitting antenna 8 is larger than the receiving antenna. The antenna is for example located on the rear side of the µSD as illustrated in figure 12 . Its characteristics used in the example are: L = 1.05 µH; R = 939 Ω; C = 2.69 pF.

[0093] In order to avoid crosstalk between the antennas due to unavoidable coupling between them, the antennas are arranged in such a way that the mutual inductance between the two antennas is reduced to a minimum. Various solutions are possible, including isolating one antenna from the other, deactivating one antenna while the other is active and vice versa.

[0094] According to a preferred embodiment, this minimized mutual induction characteristic is achieved by overlapping or superimposing the two antennas. The larger receiving antenna 7 in the example is arranged to have substantially a portion disposed outside the outer periphery of the transmitting antenna; Preferably the receiving antenna 7 is substantially mounted half on one side and inside the periphery of the transmitting antenna 8 and half outside the periphery of the transmitting antenna.

[0095] Thus, thanks to this particular arrangement, we have two antennas whose mutual inductance resultant is globally zero or at least minimized.

[0096] When the transmitting antenna emits an electromagnetic field, a part of the flux F passes in a direction X through a part A of the antenna 7 located opposite the inside of the transmitting antenna 8 generating an induced current (i) in the antenna 7; At the same time, another part of the flux F passes through a part B of the antenna 7 located outside the surface of the transmitting antenna 8 in a direction Y opposite to X generating an induced current (j) opposite to (i).

[0097] Thus, by a partial overlap of the antennas, at least the value of a disturbance caused by the transmitting antenna 8 on the receiving antenna 7 is reduced.

[0098] The disturbance induced in the receiving antenna by the transmitting antenna cancels itself out at least to a large extent. The resultant can be substantially zero overall depending on the appropriate positioning of the antennas and their characteristics. The effectiveness of self-cancellation can depend on the immediate environment outside the antenna, such as, for example, the metallic environment of a telephone or device hosting the object 1. The antennas can be on the same face of a substrate while being isolated from each other or on opposite faces. The antennas can also be arranged on separate supports parallel to each other.

[0099] The invention may provide for implementing the following elements for the described advantages: Means for recovering or extracting the carrier from the received magnetic field to enable an active modulation function without an oscillator with conventional contactless (non-NFC) chips; an arrangement of separate antennas with zero or almost zero mutual inductance simplifying the circuit; The implementation of two kinds of resonance (preferably parallel type for reception) and preferably serial type for transmission, for better efficiency; A level 16 matching circuit connected to the combi chip 5 allowing the use of existing chips, in particular dual interface chips (bank combi) which are already certified and without any modification for simplification and industrial convenience; In particular, the use of the La / Lb antenna interface of the existing combi chip (in particular from the company Infineon SLE 66CLX800PE) is provided for modulating / demodulating;Furthermore, the invention does away with the need for an NFC-type chip or component, in particular with an integrated oscillator. For example, a contactless chip meeting the ISO / IEC 14443 and / or ISO / IEC 15693 standard can be used. The circuit may comprise a detector configured to provide a signal representative of the presence of an external magnetic field and trigger an operating mode from among at least a contact mode and a contactless mode. Alternatively, one and / or the other of the antennas of the circuit may already be integrated into a host device, the circuit of the invention without the antennas simply being connected to one of the antennas via a connector (not shown) for greater adaptability of the circuit to host devices. ; Thus, the invention provides any communication device or apparatus comprising the circuit described above, whether in removable form or not.

[0100] To the figure 13A preferred embodiment of the invention is illustrated in which the transmitting / receiving circuits are uncoupled from each other; the components referenced in the same manner being identical or similar to those of the other figures.

[0101] The communication circuit 1 of the invention here comprises a transmission 17A / reception 16C interface (or stage) connected to two antennas 7 and 8. This transmission / reception stage comprises a control block 59 for dynamic decoupling of the antennas 7 and 8 and / or their respective resonant circuit 8, 43 and 7, 13. This control block comprises connections coming from the two stages 17B and 17A, in particular a connection 60 with the PLL block 58.

[0102] The communication circuit 1 comprises a parallel resonant receiving circuit, consisting of an antenna 7 tuned by the capacitor 13 to the carrier frequency. The antenna 7 is connected to the device 16C.

[0103] A series resonant transmission circuit comprises an antenna 8 tuned by the capacitor 43 substantially to the carrier frequency 13.56 Mhz (or to a different frequency 14.4 Mhz according to a preferred mode below).

[0104] In order to avoid any inductive coupling between the reception circuit 7, 13 and the transmission circuit 8, 43, which could considerably alter the performance of each of the circuits depending on the positioning of the antennas relative to each other, each resonant circuit (7, 13) and (8, 43) is deliberately and alternately decoupled.

[0105] According to the present invention, the communication circuit is arranged to deactivate the first receiving resonant circuit 7, 13 with the first antenna 7 while the second transmitting resonant circuit 8, 43 with the second antenna 8 is active and vice versa.

[0106] According to this principle, in this embodiment: An analog switch SW2c is placed in the communication circuit and allows the reception antenna 7 to be decoupled from the tuning capacitor 13 and the rest of the circuit; And two analog switches SW2a and SW2b allow the reception antenna 7 to be decoupled from the rest of the circuit 16C, 17A; The transmission antenna 8 is placed in series with the tuning capacitor 43, the whole being connected to the stage 17A by possibly removable pin connections or by soldering.

[0107] An analog switch SW1 placed in stage 17B makes it possible to decouple the transmission antenna from the rest of the transmission circuit (A), in particular at the level of one of the output amplifiers or buffers 36.

[0108] Note that in an alternative embodiment, it is possible not to have the analog switch SW1; The opening of the resonant circuit can for example be carried out by placing at least one of the output buffers 36 in high impedance mode (HiZ).

[0109] The device operates as follows under the control of control block 59 common to both stages 16C and 17A: In reception mode (default mode or idle in this example), the analog switch SW1 is open to decouple the series resonant circuit 8, 43. The analog switches SW2a, SW2b, SW2c are closed to receive the maximum SEE field. In transmission mode, the analog switch SW2a, SW2b, SW2c are open to decouple the parallel resonant circuit 7, 13. The analog switch SW1 is closed to transmit the maximum SEE field.

[0110] This embodiment therefore allows deactivation of the reception circuit during the transmission of frames, which implies the temporary loss of the clock signal of the incident field. However, in the context of a contactless communication type device activated according to the invention, it is necessary for the device to remain synchronized with the field clock so that it can transmit synchronous frames.

[0111] For this purpose, the device according to this preferred embodiment may preferably have a phase-locked loop PLL (Phase Locked Loop) 58 placed here downstream of the clock extraction circuit 31 making it possible to artificially preserve the clock of the incident field when the parallel resonant circuit is decoupled.

[0112] In addition, in order to limit a possible desynchronization of the PLL over time, linked to the loss of clock (reference signal of the PLL), the device can preferably voluntarily deactivate a Phase / Frequency detector PFD of the PLL during the transmission mode, which then runs in free mode.

[0113] For example, a response signal from the SE chip reaches the control block which is detected to disable the PFD phase detector in transmit mode.

[0114] The logic control block 59 is capable of inhibiting reception and transmission by acting on the switches as explained above. The switches SW2a, SW2b, SW2c can be by default closed (in reception mode) while SW1 is in the open position, then when a response is transmitted by the SE chip, the control block detects a response signal from the chip and can cause a transmission configuration below.

[0115] The control block 59 controls the switching of the switches SW1 and (SW2a, SW2b, SW2c) to be respectively in closed and open position, controls the deactivation of the Phase / Frequency detector PFD of the PLL component 58 during the transmission mode, and allows the supply of the carrier frequency of the PLL block 58 to generate pulses.

[0116] At the end of transmission, control block 59 operates in the opposite direction to above and places the switches in the default position for a reception mode.

[0117] Furthermore, advantageously, the inventors have found that the tuning frequencies of the receiving circuit and the transmitting circuit should preferably be different, respectively centered on 13.56 MHz for reception and on 14.4 MHz for transmission so as to promote communication.

Claims

1. Activated contactless communication circuit (1) comprising means for receiving and transmitting a data-carrying electromagnetic field (5, 6, 7, 8), a first resonant circuit (7, 13) with a first antenna (7) for receiving data and a second resonant circuit (8, 43) with a second antenna (8) for transmitting data, said first and second resonant circuits being different from one another, characterized in that said circuit (1) is designed to carry out phase synchronization, by changing the phase of a transmission frequency, so that said data transmission is carried out at a transmission frequency that is phase-synchronized with the frequency of the receiving electromagnetic field, and characterized in that said circuit (1) is arranged so as to deactivate the first resonant circuit with first antenna while the second resonant circuit with the second antenna is active and vice versa.

2. Communication circuit according to the preceding claim, characterized in that the synchronized transmission means (17) are designed to modulate a carrier signal derived from or extracted from a data-receiving electromagnetic field.

3. Circuit according to claim 1, characterized in that it is designed to communicate a contactless transponder response according to at least one of the ISO / IEC 14443 or 15693 or 18092 standards.

4. Circuit according to any of the preceding claims, characterized in that said antennas are arranged with respect to each other in such a way that the mutual inductance thereof is minimized by the spacing or attenuator thereof or at least partially canceled out, so as to have negligible current induction in the receiving antenna caused by the transmitting antenna.

5. Circuit according to the preceding claim, characterized in that the two antennas (7, 8) partially face one another, being arranged in particular on two substantially parallel horizontal planes.

6. Circuit according to any of the preceding claims, characterized in that the receiving antenna (7) forms part of a parallel resonance circuit and / or the transmitting antenna (8) forms part of a series resonance circuit.

7. Circuit according to the preceding claim, characterized in that the series resonance antenna circuit preferably produces a minimum current of 60 to 80 mA with the provided supply voltage.

8. Circuit according to any of the preceding claims, characterized in that it comprises a contactless chip designed for receiving a reception signal and a reception adaptation stage (16) for adapting the reception signal to the chip and / or for extracting a synchronized carrier signal from the reception signal.

9. Circuit according to any of the preceding claims, characterized in that it is integrated in or constitutes an object having the form factor of an integrated circuit card or micro SD card.

10. Circuit according to claim 1, characterized in that it comprises a PLL phase-locked loop which makes it possible to artificially conserve the incident field clock when the parallel resonant circuit (7, 13) is decoupled.

11. Communication device or apparatus comprising the circuit according to any of the preceding claims.

12. Method for activated contactless communication comprising steps of receiving and transmitting an electromagnetic field carrying data, the data receiving step being carried out by a first resonant circuit (7, 13) with a first antenna (7) and the data transmitting step being carried out by a second resonant circuit (8, 43) with a second antenna (8), said first and second resonant circuits being different from one another, characterized in that it comprises a phase synchronization step changing the phase of a transmission frequency so that said data transmission is carried out at a frequency that is phase-synchronized with the frequency of the receiving electromagnetic field, and characterized in that said circuit (1) is arranged so as to deactivate the first resonant circuit with first antenna while the second resonant circuit with the second antenna is active and vice versa.