Process for establishing a data link between two processors, specifically within an NFC chipset

A process for establishing a data link between a first processor configured to supply, upon a contact communication port, a first data carrying signal, and a second processor configured to supply, upon a contact communication port, a second data carrying signal is described. The process includes providing a first coupler and a second coupler, establishing a contactless coupling between the first and second couplers and, by the intermediary of the couplers and at least one RF signal, transferring the first data carrying signal to the second processor and transferring the second data carrying signal to the first processor. The second processor is, for example, a secure processor of a SIM card and the first processor is an NFC controller.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate to a process for establishing a data link between two processors.

Embodiments of the present invention also relate, but not exclusively, to Near Field Communication (NFC) technology as well as to NFC chipset structures, i.e., groups of chips including at least one NFC component.

These past few years, industry has greatly invested in research and development of NFC technology in order to integrate NFC controllers within portable objects, such as mobile telephones or equivalent (for example, personal digital assistants (PDAs) equipped with a mobile telephone function). This allows such portable objects to be used for payment or access control (subway, bus, or the like). Furthermore, the user is offered all the other applications of NFC technology, such as the reading of tags or of contactless cards.

Certain applications, such as payment and access control, require a higher level of security. These applications need to be controlled by a secure processor having cryptographic functions for the authentication of the user and/or of the portable object with respect to a transaction terminal. Some mobile telephones already include a secure processor, such as the processor of a Subscriber Identity Module (SIM) card.

An important industrial issue thus arose from the very beginning of NFC technology, i.e., the question of whether the security of NFC applications should be entrusted to the processor of the SIM card or to a second secure processor that would be supplied by the NFC application providers.

Various different NFC chipset architectures dedicated to telephone applications were thus envisaged, some using the processor of the SIM card to manage the NFC applications, others provided with a second secure processor, or a combination of the above two solutions.FIG. 1shows schematically an example NFC chipset architecture using a secure processor of a SIM card to manage the NFC applications. The NFC chipset is integrated in a portable device HD1(“Handheld Device”), for example a mobile telephone, and includes a secure processor SP1of the SIM card, a baseband processor BBP to establish a telephone communication via a cellular telephone network, and an NFC controller designated “NFCC”, equipped with an antenna coil AC0, to receive and emit data by inductive coupling. Processor SP1is linked to controller NFCC as a host processor by the intermediary of a data link functioning according to a specified protocol, for example the Single Wire Protocol (SWP). Baseband processor BBP is also connected to controller NFCC as a host processor, for example by an asynchronous link controlled by Universal Asynchronous Receiver Transmitter (UART) ports. If desired, processor SP1can also be directly linked to baseband processor BBP by a bus ISO 7816.

In such an NFC chipset, secure processor SP1ensures both the secure management of telephone connections with a cellular telephone network CNT and established by the processor BBP, and the security of NFC applications (payment, access control, or the like). During an NFC application, processor SP1links itself to an external device NFCD by the intermediary of controller NFCC and by a contactless communication channel that controller NFCC establishes with the external device by inductive coupling.

A second secure processor can also be connected to controller NFCC as a third host processor to manage other NFC applications. Pursuant to a recent industrial agreement, it was decided that the SIM card will continue to be used to manage NFC applications, which explains the addition of an SWP port within the latest generation SIM cards, also known as “SIM-NFC” cards.

The deployment of NFC applications in mobile telephones is hindered by cost constraints. In fact, the integration of NFC controllers requires substantial modifications of the motherboards of mobile telephones, which in turn implicates considerable industrial investments and a significant increase in the cost price. Therefore, because of these factors, NFC technology remains confidential and will not be integrated within most mobile telephone models until the market demand is sufficient.

In order to offer NFC technology to the user without straining the cost price, an NFC architecture concept has been proposed that consists of “externalizing” the NFC controller by mounting it upon a support distinct from the motherboard of the telephone. This solution is schematically shown inFIG. 2. Processor SP1and baseband processor BBP are mounted within mobile telephone HD1and are conventionally linked by a bus ISO 7816, while the NFC controller is mounted within a distinct portable device HD2, for example a plastic card or sticker designed to be attached to the back of a mobile telephone. A contactless data link is established between processor BBP and the NFC controller, by emitters-receivers WL1, WL2of Wifi or Bluetooth type. This contactless data link allows baseband processor BBP to be used to control NFC applications that are not secure but necessitate a large calculation power (for example, the reading of video or music files).

However, in such an NFC chipset architecture, processor SP1of the SIM card is no longer linked to controller NFCC. A second secure processor SP2is therefore added in device HD2. This second secure processor is connected to controller NFCC and is dedicated to NFC applications.

As the majority of mobile telephones are now equipped with an emitter-receiver of Wifi or Bluetooth type, such an NFC chipset architecture offers the advantage of not requiring any additional material cost for the fabrication of the motherboard of the mobile telephone, and only requires software.

However, the additional cost of emitter-receiver WL2of Wifi or Bluetooth type within portable device HD2is non-negligible, as well as the addition of the second processor SP2to manage secure applications. The electrical consumption of emitter-receiver WL2is also non-negligible and requires the provision, within device HD2, of a specific power source, such as a rechargeable battery and/or photovoltaic cells.

BRIEF SUMMARY OF THE INVENTION

Thus, embodiments of the present invention relate to a device and a process for achieving, in a simple and low-cost manner, a contactless data link between two processors, specifically between an NFC controller and a host processor of the NFC controller.

Embodiments of the present invention also relate to a device and a process for achieving an NFC chipset architecture in which an NFC controller is mounted upon a support distinct from that receiving the host processor, but in which a data link is established between the host processor and the NFC controller.

More particularly, embodiments of the present invention relate to a process for establishing a data link between a first processor and a second processor. The process includes, by the intermediary of a contact communication port of the first processor, emitting a first data carrying signal in the form of a first modulated signal; by the intermediary of a contact communication port of the second processor, emitting a second data carrying signal in the form of a second modulated signal; providing a first coupler and connecting the first coupler to the contact communication port of the first processor; providing a second coupler and connecting it to the contact communication port of the secure processor; establishing a contactless coupling between the first and second couplers; and by way of the couplers and of at least one RF signal, transferring the first data carrying signal to the contact communication port of the second processor and transferring the second data carrying signal to the contact communication port of the first processor.

According to one embodiment, the process includes, by way of the first coupler, receiving or sensing the first modulated signal, extracting from the first modulated signal the first data carrying signal and transferring the first data carrying signal to the second coupler by way of the RF signal; by way of the second coupler, receiving or sensing the second modulated signal, extracting from the second modulated signal the second data carrying signal and transferring the second data carrying signal to the first coupler by way of the RF signal or another RF signal, and receiving the first data carrying signal and supplying to the contact communication port of the second processor a third modulated signal that emulates the first modulated signal; and by way of the first coupler, receiving the second data carrying signal and supplying to the contact communication port of the first processor a fourth modulated signal that emulates the second modulated signal.

According to one embodiment, the process includes, by way of the first coupler, emitting the RF signal and modulating the RF signal such that the RF signal has a parameter that is modulated as a function of the first data carrying signal; by way of the second coupler, demodulating the RF signal in order to recover the first data carrying signal, and injecting in the RF signal a backscattered signal that has a parameter that is modulated as a function of the second data carrying signal; and by way of the first coupler, sensing the backscattered signal and demodulating the backscattered signal in order to recover the second data carrying signal.

According to one embodiment, the process includes, by ways of the second coupler, emitting the RF signal and modulating the RF signal such that the RF signal has a parameter that is modulated as a function of the second data carrying signal; by way of the first coupler, demodulating the RF signal in order to recover the second data carrying signal, and injecting in the RF signal a backscattered signal that has a parameter that is modulated as a function of the first data carrying signal; and by way of the second coupler, sensing the backscattered signal and demodulating the backscattered signal in order to recover the first data carrying signal.

According to one embodiment, the process includes, by way of the first coupler, emitting a first RF signal and modulating the first RF signal such that RF signal has a parameter that is modulated as a function of the first data carrying signal; by way of the second coupler demodulating the first RF signal in order to recover the first data carrying signal, and emitting a second RF signal and modulating the second RF signal such that the RF signal has a parameter that is modulated as a function of the second data carrying signal; and by way of the first coupler, demodulating the second RF signal in order to recover the second data carrying signal.

According to one embodiment, the first modulated signal is an electrically modulated voltage and the second modulated signal is a current signal modulated in the presence of the said electrically modulated voltage.

According to one embodiment, the first processor is an NFC controller that includes, in addition to the contact communication port, a contactless interface circuit functioning by inductive coupling, and the second processor is a host processor of the NFC controller.

According to one embodiment, the second processor is a secure processor of a SIM card.

According to one embodiment, the contactless coupling is an inductive coupling, an electrical field coupling, or a capacitive coupling.

Embodiments of the invention also relate to a process for conducting a transaction between the host processor of an NFC controller and an NFC device. The process includes establishing a data link between the host processor and the NFC device by way of the NFC controller, in which establishing a data link between the host processor and the NFC device includes establishing a data link between the host processor and the NFC controller according to the above-mentioned process.

Embodiments of the present invention also relate to a data processing and transfer device including a first processor configured to supply, upon a contact communication port, a first data carrying signal in the form of a first modulated signal, and a second processor configured to supply, upon a contact communication port, a second data carrying signal in the form of a second modulated signal. The device includes a first coupler connected to the contact communication port of the first processor, a second coupler connected to the contact communication port of the second processor. The couplers are coupled by a contactless coupling, and the first coupler is configured to receive or sense the first modulated signal, extract from the first modulated signal the first data carrying signal and transfer the first data carrying signal to the second coupler, by way of an RF signal. The second coupler is configured to receive or sense the second modulated signal, extract from the second modulated signal the second data carrying signal and transfer the second data carrying signal to the first coupler, by way of the RF signal or of another RF signal, and receive the first data carrying signal, and supply to the contact communication port of the second processor a third modulated signal that emulates the first modulated signal. The first coupler is also configured to receive the second data carrying signal and supply to the contact communication port of the first processor a fourth modulated signal that emulates the second modulated signal.

According to one embodiment, the first coupler is configured to emit the RF signal and modulate the RF signal such that the RF signal has a parameter that is modulated as a function of the first data carrying signal. The second coupler is configured to inject in the RF signal a backscattered signal that has a parameter that is modulated as a function of the second data carrying signal, demodulate the RF signal in order to recover the first data carrying signal. The first coupler is also configured to sense the backscattered signal and demodulate the backscattered signal in order to recover the second data carrying signal.

According to one embodiment, the second coupler is configured to emit the RF signal and modulate the RF signal such that the RF signal has a parameter that is modulated as a function of the second data carrying signal. The first coupler is configured to demodulate the RF signal in order to recover the second data carrying signal, and inject in the RF signal a backscattered signal that has a parameter that is modulated as a function of the first data carrying signal. The second coupler is also configured to sense the backscattered signal and demodulate the backscattered signal in order to recover the first data carrying signal.

According to one embodiment, the first coupler is configured to emit a first RF signal and modulate the first RF signal such that it has a parameter that is modulated as a function of the first data carrying signal. The second coupler is configured to demodulate the first RF signal in order to recover the first data carrying signal, and emit a second RF signal and modulate the second RF signal such that the second RF signal has a parameter that is modulated as a function of the second data carrying signal. The first coupler is also configured to demodulate the second RF signal in order to recover the second data carrying signal.

According to one embodiment, the first modulated signal is an electrically modulated voltage and the second modulated signal is a current signal modulated in the presence of the electrically modulated voltage.

According to one embodiment, the first processor is an NFC controller also includes a contactless interface circuit functioning by inductive coupling, and the second processor is a host processor of the NFC controller.

According to one embodiment, the first processor is an NFC controller also includes a contactless interface circuit functioning by inductive coupling, and the second processor is a baseband processor for a cellular telephone network.

According to one embodiment, the first processor is a baseband processor for a cellular telephone network, and the second processor is a secure processor of a SIM card.

According to one embodiment, the contactless coupling is an inductive coupling, an electrical field coupling, or a capacitive coupling.

Embodiments of the present invention also relate to a data processing and transfer device including a processor configured to supply, on at least one contact communication port, a first data carrying signal in the form of a first modulated signal. The device includes at least one coupler connected to the contact communication port of the processor, is configured for contactless coupling with another coupler, and is configured to receive or sense the first modulated signal, extract from the first modulated signal the first data carrying signal and transfer the first data carrying signal to the other coupler, by way of an RF signal; receive, by way of the other coupler, a second data carrying signal, by way of the RF signal or of another RF signal, and supply to the contact communication port of the processor a second modulated signal.

According to one embodiment, the coupler is configured to emit the RF signal and modulate the RF signal such that the RF signal has a parameter that is modulated as a function of the first data carrying signal, and sense a backscattered signal and demodulate the backscattered signal in order to recover the second data carrying signal.

According to one embodiment, the coupler is configured to receive and demodulate the RF signal in order to recover the second data carrying signal, and inject in the RF signal a backscattered signal that has a parameter that is modulated as a function of the first data carrying signal.

According to one embodiment, the coupler is configured to emit the RF signal and modulate the RF signal such that the RF signal has a parameter that is modulated as a function of the first data carrying signal, and receive and demodulate another RF signal in order to recover the second data carrying signal.

According to one embodiment, the first modulated signal is an electrically modulated voltage and the second modulated signal is a current signal modulated in the presence of the said electrically modulated voltage, or vice-versa.

According to one embodiment, the processor is an NFC controller also including a contactless interface circuit functioning by inductive coupling.

According to one embodiment, the processor is a secure processor of the SIM card.

According to one embodiment, the processor is a baseband processor for a cellular telephone network.

According to one embodiment, the contactless coupling is an inductive coupling, an electrical field coupling or a capacitive coupling.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 5Ashows an example embodiment of a data link between two processors PROC1, PROC2, by two contactless couplers CP1, CP2. Processors PROC1, PROC2were initially designed to be connected by a wire data link. To this effect, processor PROC1is provided with a contact communication port P1and processor PROC2is provided with a contact communication port P2, ports P1and P2able to be interconnected. Processor PROC1emits upon port P1a digital signal TX1carrying data DTX1, in the form of a modulated signal Sm11(TX1). Similarly, processor PROC2emits upon port P2a digital signal TX2carrying data DTX2, in the form of a modulated signal Sm21(TX2).

The form, nature and type of modulation of modulated signals Sm11and Sm21are conventionally determined by a physical protocol layer, such as a Layer 1 Protocol for Open Systems Interconnection, or OSI model. The form or profile of signals TX1, TX2(the coding of data DTX1, DTX2) is determined by the physical layer protocol while the data DTX1, DTX2that the signals TX1, TX2contain and arrangement (dividing into frames; start of frame fields, end of frame fields, correction codes, and the like) are defined by a data link layer protocol (or Layer 2 of the OSI model, as well as higher layer protocols (application data).

It is reminded here that the physical layer protocol of a data transmission is generally in charge of the activation, maintenance, and deactivation of the physical link between the elements. The physical layer protocol determines the electrical specifications (voltage and current levels, timing, and coding of the voltage and current levels), the mechanical specifications (physical contacts) and the functional specifications (data flow). It also defines the initial establishment of the communication and the end of the communication. In addition, the data link layer protocol is responsible for the physical addressing of data through the frames and a Link Protocol Data Unit (LPDU). The data link layer protocol is also in charge of error notifications, frame status commands and flow control.

Instead of interconnecting ports P1and P2, couplers CP1, CP2are interposed between ports P1, P2. Coupler CP1includes a port Pa connected to port P1and coupler CP2includes a port Pb connected to port P2. Coupler CP1includes a contactless coupling M1and coupler CP2includes a contactless coupling M2. Couplings M1, M2are, for example, inductive couplings, electrical field couplings, or capacitive couplings. The couplings M1, M2allow data to be transferred from coupler CP1to coupler CP2and vice-versa, by the intermediary of at least one RF carrier.

Each coupler CP1, CP2includes an emulation interface I11, I21respectively, for emulation of the physical layer protocol used by processors PROC1, PROC2and a contactless coupling interface I12, I22connected to couplings M1, M2. Emulation interface I11is connected to port Pa of coupler CP1. The emulation interface I11receives or senses signal Sm11emitted by port P1of processor PROC1, extracts from signal Sm11the data carrier signal TX1and supplies the data carrier signal to coupling interface I12. Coupling interface I12transfers signal TX1to coupling interface I22by the intermediary of couplings M1, M2.

Emulation interface I21is connected to port Pb of coupler CP2. The emulation interface121receives or senses signal Sm21emitted by port P2of processor PROC2, extracts from signal Sm21the data carrier signal TX2and supplies the data carrier signal to coupling interface I22. Coupling interface I22transfers signal TX2to coupling interface I12by the intermediary of couplings M1, M2.

Emulation interface I11also supplies to port P1of processor PROC1a signal S22(TX2) that conveys data carrier signal TX2and emulates signal S21(TX2) emitted by processor PROC2, while respecting the physical layer protocol for which port P1is configured, so that processor PROC1can function as if the processor PROC1was connected directly to processor PROC2and as if the processor PROC1received signal S21(TX2).

Emulation interface I21also supplies to port P2a signal S12(TX1) that conveys data carrier signal TX1and emulates signal S11(TX1) emitted by processor PROC1, while respecting the physical layer protocol for which port P2is configured, so that processor PROC2can function as if ports P1and P2were directly interconnected and as if the processor PROC2received signal S11(TX1).

Couplers CP1, CP2are therefore “transparent” with respect to processors PROC1, PROC2. The couplers CP1, CP2ensure a Layer 1, or physical layer, coupling by exchanging signals TX1, TX2without the addition of their own data link layer protocol (i.e., without the addition of start or end of frame data, without error correction, or the like). As it will later be described with the aid of examples, couplers CP1, CP2use a contactless physical layer protocol of their own to exchange signals TX1, TX2, wherein this protocol includes the utilization of at least one RF carrier. This physical layer protocol can nevertheless be restored to its simplest expression. For example, in an embodiment, the physical layer protocol does not include any connection or disconnection conventions of the contactless physical layer between couplers CP1, CP2.

Couplers CP1, CP2allow for the realization of original chipset architectures in the NFC domain or in the mobile telephone domain, for example, the architecture shown inFIG. 5B. In this application example, processor PROC1is an NFC controller designated “NFCC”. Processor PROC2is a secure processor designated “SP1” of a SIM card. Controller NFCC is configured as a master device to manage a Single Wire Protocol (SWP) connection via port P1. Port P1is therefore here a port with a single connection point forming an input/output of bidirectional (full-duplex) data. Similarly, processor SP1is configured as a slave device to manage an SWP connection via port P2. It will be noted that for reasons of simplicity of the figure, the connection to ground between processors NFCC and SP1is not shown.

Controller NFCC also includes a contactless interface circuit NFCI connected to an antenna coil AC0. Controller NFCC is configured to communicate with an external device NFCD, for example, a payment terminal, an access control terminal, an automatic teller machine, an electronic access gate, or the like. Controller NFCC is, for example, the controller “MicroRead” commercialized by the applicant, compatible with various protocols (e.g., ISO 14443 A&B, ISO 15693, ISO 18092), offering a communication distance on the order of 10 centimeters (cm), and including UART ports to connect host processors and an SWP interface port to connect a host processor of a SIM-NFC type card.

Thanks to couplers CP1, CP2, a contactless link is thus established between ports P1, P2. Master port P1supplies a modulated voltage Vs1(TX1) to coupler CP1, and emulation interface I21of coupler CP2supplies to slave port P2a modulated voltage Vs2(TX1) that emulates voltage Vs1and conforms to the SWP physical layer protocol. Port P2supplies a modulated current Is1(TX2) to coupler CP2, and interface I11of coupler CP1supplies to port P1a modulated current Is2(TX2) that emulates current Is1(TX2) and conforms to the SWP physical layer protocol. Controller NFCC and processor SP1can therefore exchange data as if their ports P1, P2were directly interconnected.

As an application example, a contactless data link CDL1is established between controller NFCC and external device NFCD to carry out a transaction with the aid of secure processor SP1. The latter can secure all or some of the transaction, at least the secure phases of the transaction, such as the authentication of processor SP1with respect to device NFCD and/or the authentication of device NFCD with respect to processor SP1. To this effect, a data link is established between controller NFCC and host processor SP1. The data link includes a link SWP1in conformance with the SWP specifications between controller NFCC and coupler CP1, a contactless link CPL between the two couplers CP1, CP2, and a link SWP2in conformance with the SWP specifications between coupler CP2and processor SP1. Processor SP1can therefore exchange data with external device NFCD by the intermediary of a resulting data link that includes the two contactless links CDL1, CPL and the two wire links SWP1, SWP2. Link CDL1differs from link CPL in that it has its own data link layer (for example, ISO 14443 A&B, ISO 15693, or ISO 18092). The management of the data link layer of link CDL1is performed by controller NFCC, which is designed to this effect.

Embodiments of couplers CP1, CP2provided to be connected to SWP ports will be described hereinafter.

As a reminder, the SWP protocol is described in the proposed industrial technical specification ETSI TS 102 613. The timing diagrams ofFIGS. 4A,4B show modulated signals intervening in a conventional SWP link such as that shown inFIG. 3, in which ports P1and P2of controller NFCC and of processor SP1are interconnected. Voltage Vs1(TX1) emitted by host port P1conveys signal TX1. The latter includes data DTX1coded in the following manner: when DTX1=0, signal TX1is at 1 during a fourth of the clock period, and is at 0 during the rest of the clock period. When DTX1=1, signal TX1is at 1 during three-fourths of the clock period, and is at 0 during the last fourth of the clock period. Signal TX1at 1 corresponds to a value of voltage Vs1between two high voltages VHmax and VHmin. Signal TX1at 0 corresponds to a value of voltage Vs1between two low voltages VLmax and VLmin. Current Is1(TX2) is a current consumed or drawn by port P2in the presence of voltage Vs1, and is not an emitted current. Current Is1(TX2) is therefore a backscattered signal that needs to be sensed. Current Is1(TX2) conveys signal TX2. The latter includes data DTX2coded in the following manner: when DTX2=1, signal TX2is at 1. When DTX2=0, signal TX2is at 0. Seen from the side of the master receiver (here the controller NFCC), TX2=1 corresponds to a current value between two high currents IHmax and IHmin, and TX2=0 corresponds to a current value between two low currents ILmax and ILmin. When TX2=1, the duration of the emission of current Is1during period T can be equal to a fourth of a period or to three-fourths of a period because it depends on the duration of voltage Vs. Still as a reminder,FIG. 3shows schematically an example of a backscatter circuit BM1that could be provided within host processor SP1to draw current Is1. Backscatter circuit BM1is of an open drain type and includes, for example, a switch SW1that links port P1to ground by means of a resistor R1, switch SW1being controlled by signal TX2.

Coupler CP1includes an RF modulator designated MCT1, a demodulator DCT1and a current modulation emulation circuit BM2. Modulator MCT1includes a first input receiving voltage Vs1(TX1) and connected to port P1, a second input receiving an RF signal S1(f1) of a frequency f1supplied by an oscillator (not shown), and an output supplying to antenna coil AC1an RF antenna signal Vac. Signal Vac is the result of the modulation of signal S1(f1) by voltage Vs1, for example, an amplitude modulation, and has a modulated parameter, here its amplitude, that conveys data carrier signal TX1. Antenna coil AC1thus emits a modulated magnetic field H1of frequency f1. To avoid interferences with the magnetic field emitted by interface NFCI of controller NFCC, frequency f1is preferably different than that used by controller NFCC (FIGS. 5A,5B). If this latter is for example 13.56 MHz (ISO 14443 A&B, ISO 15693, ISO 18092), frequency f1is for example chosen to be greater than a hundred MHz.

Demodulator DCT1is connected to antenna coil AC1and is configured to extract, after filtering of the RF carrier, from antenna signal Vac a backscatter signal Im1(TX2) conveying signal TX2and emitted by coupler CP2. The output of demodulator DCT1supplies signal TX2to the current modulation emulation circuit BM2. Circuit BM2has here the same structure as circuit BM1of processor SP1(Cf.FIG. 3orFIG. 6), and includes a switch SW2linking port Pa to ground by way of a resistor R2. Switch SW2is controlled by signal TX2supplied by demodulator DCT1. Controller NFCC thus sees modulated current Is2(TX2), which emulates current Is1(TX2), appear upon port P1.

Antenna signal Vac is reflected by inductive coupling with antenna coil AC2of coupler CP2. This latter includes an RF demodulator DCT2, an amplifier TAMP, a current sense circuit CSCT and a load modulation circuit LM1. Demodulator DCT2has one input connected to antenna coil AC2to receive modulated antenna signal Vac, and an output supplying data carrier signal TX1to amplifier TAMP. In the embodiment where modulator MCT1performs a simple amplitude modulation of signal Vac, demodulator DCT2can simply include a half-wave rectifying diode and a capacitor C1that filters the RF carrier of frequency f1in order to conserve only the envelope of signal Vac, corresponding to the profile of voltage Vs1, that is signal TX1.

Amplifier TAMP thus receives signal TX1of which the profile corresponds to the profile of voltage Vs1, and supplies voltage Vs2(TX1) that emulates voltage Vs1(TX1). Amplifier TAMP is, for example, a regulated voltage amplifier having a threshold voltage Vt and a switching hysteresis to generate net voltage edges between VHmax and VHmin, as well as when processor SP1consumes current Is1(TX2) on port P2.

The current sense circuit CSCT is arranged between the output of amplifier TAMP and port Pb of the coupler, which is connected to port P2of processor SP1. Circuit CSCT is provided to sense current Is1drawn by processor SP2and to extract from current Is1the data carrier signal TX2, which circuit CSCT provides to load modulation circuit LM1.

It will be noted here that since Is1is a backscatter current of which the duration depends upon the duration of voltage Vs2(that is ¼ or ¾ of period T), the profile of current Is(TX2) and the profile of signal TX2can be appreciably different. InFIG. 6, it can be seen that TX2is applied by processor SP1upon a control terminal of switch SW2(for example the gate of a metal-oxide-semiconductor (MOS) transistor. In an embodiment, the duration of TX2can thus be a complete clock cycle while the duration of current Is1is only one-fourth or three-fourths of the clock period, depending upon the duration of voltage Vs2. In other embodiments, the duration of TX2can be chosen by convention to be three-fourths of the clock cycle, or even less (a duration of ¼ of the clock cycle allows for the transfer of data DTX2). Therefore, when it is indicated in this description and in the claims that coupler CP2is configured to “sense the modulated signal Is1and to extract from the modulated signal Is1the data carrier signal TX2”, this indication is approximate and the said extraction of the data carrier signal can correspond to several embodiments:the extracted signal TX2is, in reality, not exactly identical to the initial signal TX2(such as applied to the switch SW1) and its profile corresponds to the profile of current Is1; orthe extracted signal TX2is identical to the initial signal TX2and its profile does not correspond to the profile of current Is1. In this case, circuit CSCT needs to be configured to prolong the duration of signal TX2=1 in such a manner that to cover the duration of signal TX2provided by convention, for example, three-fourths of the clock cycle.

Finally, load modulation circuit LM1includes, for example, a switch SW3that links a terminal of antenna coil AC2to ground, by the intermediary of a resistor R3. Switch SW3is controlled by signal TX2supplied by the current sense circuit CSCT and causes a backscatter current Im1(TX2) to appear within antenna signal Vac. The backscatter current is reflected by inductive coupling in antenna coil AC1and is recovered by demodulator DCT1.

FIG. 7shows the profile of antenna signal Vac as a function of modulated signals Vs1(TX1) and Is1(TX2). It can be seen that signal Vac is doubly modulated, its envelope is the same as voltage Vs1(TX1), but has sub-modulations of amplitude Vmax, Vmin that are functions of current Is1(TX2). In order that these sub-modulations do not modify the amplitude of the emulated voltage Vs2supplied to processor SP1, amplifier TAMP can be configured to have a threshold voltage Vt that is inferior to the amplitude modulation extremes Vmax, Vmin, which only depend upon current Is1.

This embodiment of couplers CP1, CP2, functioning by inductive coupling, can be transformed into a capacitive coupling embodiment by replacing antenna coils AC1, AC2with capacitive coupling plates, or transformed into an electrical field coupling embodiment by replacing antenna coils AC1, A2by electrical field antennas. In these implementation variations, the modulation of signal S1by means of voltage Vs1to supply signal Vac, can be done in various other manners, notably by phase modulation (Binary Phase Shift Keying (BPSK)), by frequency modulation (Frequency Shift Keying (FSK)), or the like. Equally, the emission of signal TX2by charge modulation via load modulation circuit LM1, can be performed in numerous other ways, notably by phase modulation of a sub-carrier, frequency modulation by two sub-carriers, or the like.

FIG. 8shows an embodiment of couplers CP1, CP2according to the principle of electrical field coupling. Antenna coils AC1, AC2are replaced by electrical field antennas A1, A2, for example, dipolar antennas. Modulator MCT1of coupler CP1is replaced by a modulator MCT2that receives, instead of signal S1, an RF signal S2of which the frequency f2is situated in the UHF domain, for example a frequency on the order of several hundred megahertz to several gigahertz. Modulator circuit MCT2supplies to antenna A1an antenna signal SA1that is modulated as a function of signal Vs1(TX1) and is reflected within antenna A2by electrical coupling.

Load modulation circuit LM1of coupler CP2is replaced by a backscatter circuit BSM1that modulates the reflection coefficient of antenna A2in order to perform a backscattering. More particularly, circuit BSM1receives signal TX2as supplied by the current sense circuit CSCT and converts signal TX2into a modulation of the reflection coefficient of antenna A2. This causes a backscattered signal Ir(TX2) to appear within antenna A1, and the backscattered signal is mixed with antenna signal SA1.

Finally, demodulator DCT1of coupler CP1is replaced by a demodulator DCT3configured to extract the backscattered signal Ir1, and the RF demodulator DCT2of coupler CP2is replaced by an RF demodulator DCT4configured to filter the frequency f2and extract signal TX1from antenna signal SA1.

In the embodiment shown inFIG. 6, antenna coil AC1emits the magnetic field H1, and in the embodiment shown inFIG. 8, antenna A1emits the electrical field E1. Coupler CP1is therefore active and coupler CP2is passive in these two embodiments. In other embodiments, it can be provided that coupler CP2is active and coupler CP1is passive. The provision of the RF emission from the coupler CP2side of the device can be advantageous in certain applications such as that shown inFIG. 5B. Indeed, in this application coupler CP2can be arranged in a mobile telephone (HD1) with a powerful battery allowing the RF signal to be generated without the available energy reserve being greatly affected. On the contrary, in other applications, as will be described later in relation withFIG. 13, coupler CP2is arranged in proximity to the battery of a mobile telephone.

FIG. 9shows an embodiment in which coupler CP1is passive and coupler CP2is active and emits the electrical field E1. Signal TX1is transmitted to coupler CP2by backscattering while signal TX2is transmitted to coupler CP1by active emission of the electrical field E1.

This embodiment requires a particular precaution so that the transmission by backscattering of all the rising edges of signal TX1is not omitted. According to the SWP protocol, these edges are in fact used as a clock signal by processor SP1. To this effect, coupler CP2is equipped with an RF modulator MCT3that receives signal TX2(such as supplied by the circuit CSCT) and supplies to antenna A2an uninterrupted antenna signal SA2. Antenna signal SA2does not have a modulation period where its amplitude is zero. Moreover, signal TX2is preferably transmitted by using an RF modulation technique by phase shifting BPSK (a single carrier) or of RF frequency modulation FSK (two carriers). These techniques avoid the creation in the carrier of amplitude modulation holes, which could alter the reception of the clock edges.

Modulator MCT3shown inFIG. 9is of the FSK type. It receives two carriers S2(f2), S3(13) of frequencies f2and f3respectively, and which are situated in the UHF domain, for example. Values 0 and 1 of signal TX2are coded in the form of frequency modulation either by direct coding (the 0 being coded by the frequency f1, the 1 by frequency f2, or reciprocally) or by Manchester type coding (the 0 being coded by an alternating f1-f2of two frequencies, the 1 being coded by an inverse alternating f2-f1, or reciprocally).

A backscattering circuit BSM2is arranged here within coupler CP1. Circuit BSM2receives voltage Vs1(TX1) and converts it into a modulation of the reflection coefficient of antenna A1, causing a backscattering signal Ir(TX1) to appear in antenna A2. The backscatter signal mixes with antenna signal SA2. Demodulator DCT3is here arranged in coupler CP2, and is configured to filter and demodulate the backscattered signal generated by circuit BSM2. The demodulator DCT3output supplies signal TX1to amplifier TAMP, the output of which supplies signal Vs2(TX1) to port P2of processor SP1. Finally, an RF demodulator DCT5is arranged in coupler CP1to decode the FSK modulation (detection of jumps of frequencies f1-f2or f2-f1) and to extract from it signal TX2, which is then applied to the current modulation emulation circuit BM2.

FIG. 10shows the profile of antenna signal AC2as a function of the modulated signals Vs1(TX1) and Is1(TX2). As desired, signal AC2is uninterrupted and has the frequency f1when Is1=1 and the frequency f2when Is2=0 (direct coding). The amplitude of signal AC2is modulated as a function of voltage Vs1(TX1), as an effect of the backscattering circuit BSM2. The amplitude of signal SA2has here a lower maximum value when Vs1=1 and a higher maximum value when Vs1=0.

FIG. 11shows an embodiment in which the two couplers are active. Coupler CP1includes an RF emitter-receiver TR1that emits an electrical field E1and coupler CP2includes an RF emitter-receiver TR2that emits an electrical field E2. This embodiment does not require backscattering because each coupler modulates the electrical field that it emits as a function of the signals TX1, TX2to be emitted. Thus, emitter-receiver TR1receives voltage Vs1(TX1) and applies to antenna A1an antenna signal SA3that it modulates as a function of signal TX1(amplitude modulation, of phase or of frequency), so that the antenna emits the electrical field E1. Emitter-receiver TR2receives signal TX2such as supplied by the current sense circuit CSCT and applies to antenna A2an antenna signal SA4that is modulated as a function of signal TX2, so that the antenna emits the electrical field E2. Emitter-receiver TR1also receives electrical field E2and demodulates electrical field E2to supply signal TX2to the current modulation emulation circuit BM2. Reciprocally, emitter-receiver TR2receives electrical field E1and demodulates electrical field E1to supply signal TX1to amplifier TAMP.

Each antenna A1, A2thus receives the antenna signal SA3, SA4, one being supplied thereto, the other being received by coupling. The differentiation of fields E1, E2and of the corresponding antenna signals SA3, SA4can be done either in the frequency domain or in the time domain. In the first case, signals SA3, SA4have different frequencies and can be separated by an appropriate filtration. Different antennas could also be provided in each coupler to emit field E1or E2on the one hand, and to receive field E2or E1emitted by the other coupler on the other hand. In this second case, fields E1, E2are emitted in alternation, and the transmission of signals TX1, TX2is conducted in a unidirectional mode (half-duplex) instead of being done in a bidirectional mode (full-duplex). Emitter-receiver TR2is silent while emitter-receiver TR1emits field E1, and then performs the demodulation of the received antenna signal SA3. Then, emitter-receiver TR1is silent while emitter-receiver TR2emits field E2, and then performs the demodulation of the received antenna signal SA4.

FIGS. 12A,12B show the transmission of signals TX1, TX2in alternating unidirectional mode and show respectively the antenna signal SA3(TX1) and the antenna signal SA4(TX2). Signal SA4is emitted during the first half-period of signal Vs1(TX1), clock period T being supplied by signal Vs. Signal SA3is emitted during the second half-period of the clock. The emission of signals TX1, TX2can be performed in any known manner, for example by Manchester coding by an RF signal with a single carrier, as shown inFIGS. 12A,12B. In this case, signal TX1=0 is coded during the second half-period by an absence of field E1emission during a fourth of a period, followed by a field emission during the remaining fourth of a period. Inversely, signal TX1=1 is coded during the second half-period by a field emission during a fourth of a period, followed by an absence of field emission during the remaining fourth of a period. In a similar manner, signal TX2=0 is coded during the first half-period by an absence of field E2emission during a fourth of a period, followed by a field emission during the remaining fourth of a period. Signal TX2=1 is coded during the first half-period by a field emission during a fourth of a period, followed by an absence of field emission during the remaining fourth of a period.

FIG. 13shows, very schematically, an application example of couplers CP1, CP2in a mobile telephone HD1. The telephone includes a motherboard PCB upon which is mounted the baseband processor BBP, the secure processor SP1of the SIM card, the coupler CP2and the coupling means M2. Processor SP1is connected to baseband processor BBP and to coupler CP2by the intermediary of a SIM card insertion slot and an electrical connector, which are not shown here for reasons of simplicity. The telephone also includes a removable battery BT forming a portable support HD2. Battery BT receives controller NFCC and its antenna coil AC0, as well as coupler CP1. Antenna coil AC0is optionally arranged upon a ferrite layer FLR, which is magnetically conductive in order to isolate the battery and the motherboard PCB from the magnetic field generated by the antenna coil. Coupling M1is arranged on the rear face of battery BT in order to be opposite coupling M2. Couplings M1, M2are, for example, capacitive coupling plates or antenna coils. Thus, processor SP1can establish a data link (for example by SWP) with controller NFCC, by the intermediary of couplers CP1, CP2.

This application example has the advantage of allowing the integration of an NFC controller in a mobile telephone without substantial modifications of the architecture of the motherboard of the telephone—only coupler CP2and coupling means M2need to be added. Mobile telephone batteries can thus be commercialized with an NFC fitting.

With reference toFIG. 5B, the utilization of couplers CP1, CP2to link processor SP1and controller NFCC does not exclude the provision of a wireless link between baseband processor BBP and controller NFCC by emitter-receivers WL1, WL2such as Wifi or Bluetooth type. Processor SP1also can be linked to baseband processor BBP via a bus ISO 7816.

It will clearly appear to the skilled person that couplers according to the invention are susceptible of numerous variations and embodiments. As previously indicated, the data transfer by coupling, by means of an RF carrier, can be based upon various known modulation techniques, that is to say amplitude modulation, phase modulation (BPSK), frequency modulation (FSK), etc.

In the previously described figures, the current sense circuit CSCT includes a resistor Ri with a low value, to transform current Is1into a voltage, as well as a differential amplifier Ai connected to the terminals of resistor Ri. The output of the amplifier supplies signal TX2. Other embodiments of circuit CSCT can be provided by the skilled person, notably embodiments including a current mirror and not introducing any loss of voltage proportional to the current traversing circuit CSCT.

Couplers according to embodiments of the invention are also susceptible of various other applications. For example, as shown inFIG. 14, contactless couplers CP1′-CP2′ can be used to link baseband processor BBP to controller NFCC. Coupler CP1′ is connected to a UART port of controller NFCC and emulates an asynchronous bus UART1while coupler CP2′ is connected to a UART port of baseband processor BBP and emulates an asynchronous bus UART2, such that processors BBP and NFCC exchange data as if their UART ports were directly linked by a wire link.

As shown inFIG. 15, contactless couplers CP1″, CP2″ can also be used in a “non-NFC” application, for example, to link processor SP1of the SIM card to baseband processor BBP, with emulation of the bus ISO 7816 by the couplers. In this case, coupler CP1″ is connected to the I/O port of baseband processor BBP and emulates a link ISO 7816(1) and coupler CP2″ is connected to the I/O port of processor SP1and emulates a link ISO 7816(2), such that processors SP1and BBP exchange data as if directly linked by a wire bus ISO 7816.

FIG. 16shows an NFC chipset including processors SP1, BBP and controller NFCC, as well as the previously described couplers SP1, SP2, SP1′, SP2′, SP1″, SP2″. Baseband processor BBP is mounted upon a first portable support HD1, controller NFCC is mounted upon a second portable support HD2and processor SP1is mounted upon a third portable support HD3. Processor SP1is linked to controller NFCC by the intermediary of couplers CP1, CP2and a bus SWP. Controller NFCC is linked to processor BBP by the intermediary of couplers CP1′, CP2′ and an asynchronous bus of UART type. Processor BBP is linked to processor SP1by the intermediary of couplers CP1″, CP2″ and a bus ISO 7816.