Contactless communication device using active charge modulation

Abstract

Active Charge Modulation Contactless Communication Device This description relates to an active charge modulation contactless communication device (100), comprising at least: - a receiving circuit (110) configured to receive as input a receive signal from a magnetic field intended to be received by an antenna (102); - a transmitting circuit (116) comprising an output coupled to the antenna and on which a modulation signal in phase with the receive signal is intended to be delivered; - a compensation circuit (118) for a delay in the modulation signal due to the transmission circuit and the amplitude of the receive signal, configured to determine a phase shift value to be applied to an input signal of the transmission circuit to compensate for the delay. Figure for the abbreviation: Fig. 2

Description

Title of the invention: Contactless communication device using active charge modulation. Technical field

[0001] This description relates generally to the field of wireless communications between a reader and a contactless communication device using active charge modulation, in particular between a reader and such a device emulated in card mode (or CE for "Card Emulation"). This description may also relate specifically to the field of contactless communications implemented using NFC (Near Field Communication) technology. Prior art

[0002] Near field communication, or NFC, is a wireless connectivity technology enabling communication over a short distance, for example on the order of ten centimeters, between electronic devices, such as a contactless smart card and a reader, or an EC device (for example a mobile phone or a connected object) and a reader.

[0003] A contactless communication device is a device capable of exchanging information via an antenna with another contactless device, for example a reader, according to a contactless communication protocol.

[0004] An NFC device, which is a contactless device, is a device compatible with NFC technology. NFC technology is an open technology platform standardized in ISO / IEC 18092 and ISO / IEC 21481, but incorporates many existing standards, such as the Type A and Type B protocols defined in ISO 14443, which can be used as communication protocols in NFC technology.

[0005] A CE device can be used to exchange information with another contactless device, for example a contactless reader, using a contactless communication protocol usable in NFC technology.

[0006] During information transmission between a reader and an EC device or an NFC card, the reader generates an electromagnetic field via its antenna, which is generally, according to commonly used standards, a sinusoidal wave with a frequency of 13.56 MHz. Each of the NFC devices (reader and EC device) transmits data using a modulation scheme, for example, amplitude shift keying (ASK).

[0007] Two modes of operation are possible: a passive mode, which corresponds to the mode used by an NFC card, or an active mode, which generally corresponds to the mode used by an CE device.

[0008] In passive mode, also called PLM or Passive Load Modulation, only the reader generates the electromagnetic field, and the card is therefore passive. The card's antenna modulates the electromagnetic field generated by the reader by modifying a load connected to the terminals of the card's antenna. This modifies the output impedance of the reader's antenna due to magnetic coupling between the two antennas. This results in a change in the amplitudes and / or phases of the voltages and currents present at the reader's and card's antennas. Information is thus transmitted from the card to the reader by load modulation of the reader's antenna currents.

[0009] In active mode, also called ALM or Active Load Modulation, both the reader and the CE device generate an electromagnetic field. This operating mode is used when the CE device has its own power source, for example, a battery.

[0010] Generally, an EC device has a smaller antenna than that of an NFC card, and this is why active charge modulation is generally used in such a device.

[0011] During active charge modulation, the electromagnetic fields emitted by the reader and the CE device are in phase with each other so that the detection sensitivity of the device is not reduced. The CE device may, in particular, include a transmission circuit whose output is coupled to the antenna, as well as a phase-locked loop (PLL) used, in particular, to compensate for the propagation delay in the transmission circuit.

[0012] However, the components of the transmission circuit are subject to PVT (Process, Voltage, Temperature) variations that can cause a delay or advance in the signal delivered at the output of the transmission circuit, resulting in a phase shift between the electromagnetic field emitted by the reader and that emitted by the CE device. Variations in the amplitude of the electromagnetic field emitted by the reader and / or in the coupling between the antennas of the reader and the CE device can also contribute to this phase shift, since the signal transmission delay through the transmission circuit also varies according to the amplitude of the received electromagnetic field and therefore the coupling between the antennas of the reader and the CE device.

[0013] There is a need to propose a solution that addresses the problems encountered with existing solutions.

[0014] One embodiment overcomes all or part of the drawbacks of known solutions and proposes a contactless communication device using active load modulation, comprising at least:

[0015] - a receiving circuit configured to receive as input a receive signal from of a magnetic field intended to be received by an antenna;

[0016] - a transmission circuit comprising an output coupled to the antenna and on which a modulation signal in phase with the received signal is intended to be delivered;

[0017] - a circuit for compensating for a delay in the modulation signal due to the circuit transmission and the amplitude of the received signal, configured to determine a phase shift value to apply to an input signal of the transmission circuit to compensate for the delay.

[0018] According to a particular embodiment, the device further comprises a phase-locked loop configured to receive as input a first clock signal delivered at the output of the receiving circuit and the phase shift value, and to deliver on a first output the input signal of the transmission circuit.

[0019] According to a particular embodiment, the compensation circuit includes at least one circuit for measuring a phase difference between the input signal of the transmission circuit and a delayed signal corresponding to the input signal of the transmission circuit delayed by said delay.

[0020] According to a particular embodiment, the measuring circuit comprises at least:

[0021] - a counting trigger circuit comprising a first input configured to receive at least the input signal from the transmission circuit and a second input configured to receive at least the delayed signal, and configured to output a counting trigger signal having a first value for a duration equal to the delay and a second value, different from the first value, outside of this duration;

[0022] - a counter comprising a clock input coupled to an output of the circuit counting trigger, and a data input coupled to a second phase-locked loop output on which a periodic signal of frequency equal to a multiple of that of the input signal of the transmission circuit is intended to be delivered;

[0023] - a calculation circuit configured to determine the phase shift value as a function of a value of a counting signal intended to be delivered by the meter.

[0024] According to a particular embodiment, the transmission circuit includes a controlled switch whose output corresponds to the output of the transmission circuit.

[0025] According to a particular embodiment, the transmission circuit includes a control input configured to receive a signal controlling the emission or not of a signal on the output of the transmission circuit, and includes a delay circuit having an input coupled to the input of the transmission circuit, an output coupled to the second input of the counting trigger circuit and which is configured to apply a delay of equal value to that due to the transmission circuit.

[0026] According to a particular embodiment, the receiving circuit comprises at least:

[0027] - a variable gain amplifier configured to receive as input the signal from reception ;

[0028] - a sinusoidal signal to square wave converter, comprising an input coupled to an output of the variable gain amplifier, and an output corresponding to an output of the receiving circuit.

[0029] According to a particular embodiment, a contactless communication method between a reader and a device is proposed, comprising at least the implementation of the following steps:

[0030] - detection of a magnetic field by the device;

[0031] - when a magnetic field is detected by the device, emission of a first clock signal by the receiving circuit of the device receiving an input signal from the magnetic field;

[0032] - measurement, by the device's compensation circuit, and compensation of the delay of the modulation signal due to the transmission circuit and the amplitude of the received signal in a signal applied to the input of the device's transmission circuit, the compensated delay depending on the amplitude of the received signal and a target amplitude of the modulation signal intended to be delivered at the output of the transmission circuit;

[0033] - application, by the transmission circuit of the device, of the modulation signal on the antenna.

[0034] According to a particular embodiment, the emission of the first clock signal by the receiving circuit of the device is followed by a start and locking of the phase-locked loop on the first clock signal.

[0035] According to a particular embodiment, the method further comprises, between the emission of the first clock signal and the application of the phase shift value:

[0036] - a measurement of the receiving power;

[0037] - a pre-programming of a power of transmission circuit components depending on the measured reception power.

[0038] According to a particular embodiment, the method further comprises, before measuring and compensating for the delay, applying a control signal to a control input of the controlled switch of the transmission circuit or to the control input of the transmission circuit such that no signal is delivered at the output of the transmission circuit.

[0039] According to a particular embodiment, the method further comprises, after the measurement and compensation of the delay, the application of the control signal to the control input of the controlled switch of the transmission circuit or to the control input of the transmission circuit such that the modulation signal is delivered on the output of the transmission circuit. Brief description of the drawings

[0040] These features and advantages, as well as others, will be described in detail in the following non-limiting descriptions of specific embodiments, in connection with the accompanying figures, among which:

[0041] - Fig. 1 schematically represents an example of a communication device contactless by active charge modulation communicating with a contactless reader, according to a particular embodiment;

[0042] - [Fig.2] schematically represents details of the realization of a first example of a contactless communication device using active load modulation, according to a particular embodiment;

[0043] - [Fig. 3] schematically represents details of the realization of a second example of a contactless communication device using active load modulation, according to a particular embodiment;

[0044] - Figure 4 schematically represents steps in an example of a process communication of a contactless communication device by active charge modulation with a reader, according to a particular embodiment;

[0045] - [Fig. 5] schematically represents details of the realization of the second example of a contactless communication device using active load modulation, according to a particular embodiment;

[0046] - Figure 6 schematically represents an example of the implementation of a counter of a phase-locked loop of a contactless communication device using active load modulation, according to a particular embodiment;

[0047] - Figure 7 schematically represents an example of the implementation of a circuit of a counting trigger and a counter forming part of a contactless communication device by active load modulation, according to a particular embodiment;

[0048] - [Fig. 8] represents a timing diagram of examples of signals used in the circuits of the [Fig.7]. Description of the implementation methods

[0049] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0050] For the sake of clarity, only the steps and elements necessary for understanding the described embodiments and examples have been shown and are detailed. In particular, the implementation of the various elements and circuits (variable gain amplifier, sinusoidal-to-square wave converter, phase-locked loop, calculation circuits, delay circuits, flip-flops, counters, etc.) of the device is not detailed. A person skilled in the art will be able to implement the various functions of the device in detail from the functional description given here.

[0051] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0052] Unless otherwise specified, the expressions "approximately", "roughly", and "on the order of" mean within 10%, preferably within 5%.

[0053] An example of a contactless communication device 100 by active charge modulation according to a particular embodiment is described below in relation to [Fig.1],

[0054] Device 100 is NFC-type, that is, it is configured to use a communication protocol compatible with NFC technology. In the example described, device 100 corresponds to a card-mode emulated device (CE). In [Fig. 1], device 100 is shown communicating with an NFC-type contactless reader 200.

[0055] In the described embodiment, the device 100 includes an antenna 102 intended to exchange data with an antenna 202 of the reader 200 via the emission of electromagnetic fields by these antennas 102, 202 and the magnetic coupling of these antennas 102, 202.

[0056] In the particular configuration shown in [Fig.1], the device 100 further includes an adaptation circuit 104 coupled between the antenna 102 and the other elements of the device 100. The circuit 104 can be used in particular to adapt the impedance of the antenna 102 to interface the input and output signals of the antenna 102.

[0057] The device 100 further includes a receiving circuit 110 configured to receive as input a receive signal from a magnetic field intended to be received by the antenna 102. In [Fig. 1], the receive signal is called "RFI" and corresponds to a sinusoidal signal. The frequency of the RFI signal is, for example, equal to 13.56 MHz.

[0058] In a particular configuration corresponding to that shown in [Fig. 1], the receiving circuit 110 comprises at least:

[0059] - a variable gain amplifier, or VGA, 112 configured to receive as input the RFI signal;

[0060] - a sinusoidal signal to square wave converter 114, comprising an input coupled to an output of the VGA 112, and an output on which a first clock signal is intended to be delivered.

[0061] In this particular configuration, the signal emitted at the output of converter 114 corresponds to a square signal of greater amplitude than that of the RFI signal, that is to say, it corresponds to the transformation of the RFI signal into an amplified square signal with a gain greater than 1.

[0062] Alternatively, the receiving circuit 110 may include additional and / or different elements than those in the embodiment example of [Fig.1].

[0063] The device 100 further includes a transmission circuit 116 comprising an output coupled to the circuit 104 and which is intended to deliver on this output a modulation signal called "RFO" to the antenna 102. This RFO signal includes information intended to be transmitted by the device 100 to the reader 200. The RFO signal is intended to be in phase with the RFI signal.

[0064] The device 100 further includes a compensation circuit 118 for a delay ΔTX of the RFO signal due to the transmission circuit 116, including the delay due to PVT variations of the components of the transmission circuit 116, and to the amplitude of the RFI signal. When the device 100 is in communication with the reader 200, the amplitude of the RFI signal can be directly proportional to that of the electromagnetic field received by the antenna 102 and therefore to the coupling between the antennas 102 and 202. The compensation circuit 118 is configured to determine, at each startup of the device 100, a phase shift value to be applied to an input signal of the transmission circuit 116 to compensate for the delay ΔTX.

[0065] In the particular configuration shown in [Fig. 1], the device 100 further includes a phase-locked loop, or PLL, 120 for synchronizing the RFO signal with the received RFI signal, and thus compensating for delays related to signal processing in the various circuits and elements of the device 100. This PLL 120 is configured to receive as input the first clock signal delivered by the receiving circuit 110 as well as the phase shift value determined by the compensation circuit 118, and to deliver on a first output the input signal of the transmitting circuit 116. Thus, the PLL 120 is configured here to take into account the phase shift value determined by the compensation circuit. 118 so that the signal delivered at the output of the PLL 120 to the transmission circuit 116 no longer has any phase shift, or delay, related to the transmission circuit 116 and the amplitude of the RFI signal.

[0066] In the diagram of [Fig. 1], only some of the elements of the device 100 are shown. The device 100 includes, in addition to those visible in [Fig. 1], other circuits and elements not described here, such as the modulation and demodulation circuits for the data received and transmitted by the device 100.

[0067] In the configuration shown in [Fig.1], the device 100 further includes a battery 122 intended to electrically supply the various circuits and components of the device 100.

[0068] A first, more detailed embodiment of device 100 is described below in relation to [Fig. 2]. In [Fig. 2], only some of the components and circuits of device 100 are shown and described below. For example, compared to [Fig. 1], antenna 102 and circuit 104 of device 100 are not shown in [Fig. 2].

[0069] In the described embodiment, the compensation circuit 118 includes a circuit for measuring a phase difference between the input signal of the transmission circuit 116, obtained at the output of the PLL 120, and a delayed signal corresponding to the input signal of the transmission circuit 116 delayed by the delay ôTX.

[0070] In a particular configuration corresponding to that shown in [Fig.2], this measuring circuit comprises:

[0071] - a counting trigger circuit 128 comprising a first input on to which the input signal of the transmission circuit 116 is intended to be applied, a second input to which the delayed signal (input signal of the transmission circuit 116 delayed by the delay ôTX) is intended to be applied, and configured to deliver at output a counting trigger signal having a first value for a duration equal to the delay ôTX and a second value, different from the first value, outside of this duration;

[0072] - a 130 counter comprising a clock input coupled to a circuit output 128, and a data input coupled to a second output of the PLL 120 on which a periodic signal of frequency equal to a multiple of that of the input signal of the transmission circuit 116 is intended to be delivered;

[0073] - a calculation circuit 132 configured to determine the phase shift value at apply according to a value of a counting signal intended to be delivered by counter 130, the output of counter 130 being coupled to an input of the calculation circuit 132.

[0074] The value of the frequency of the periodic signal delivered on the second output of the PLL 120 may depend on the components of the PLL 120, and for example on the frequency of operation of an oscillator present in the PLL 120. For example, the frequency of the receive signal and the frequency of the input signal of the transmit circuit 116 may be equal to 13.56 MHz, and the frequency of the periodic signal delivered on the second output of the PLL 120 may be equal to approximately 868 MHz (64*13.56 MHz).

[0075] The measurement circuit is therefore configured to measure the phase difference between the input signal of the transmission circuit and the delayed signal, which is representative of the delay ôTX, via a count whose result is representative of this phase difference and therefore of this delay ôTX which depends in particular on the PVT variations of the components of the transmission circuit 116 and the amplitude of the RFI reception signal.

[0076] In the example of [Fig. 2], the various elements and components of the transmission circuit 116 generating the delay ôTX are symbolized by a single component, referenced as 135. In this first embodiment of the device 100, the transmission circuit 116 also includes a controlled switch 137, one output of which corresponds to the output of the transmission circuit 116. The output of component 135 is coupled to the input of the controlled switch 137 as well as to the second input of the circuit 128. Depending on the value of the control signal, called "EN" in [Fig. 2], applied to the controlled switch 137, the RFO signal is delivered or not at the output of the transmission circuit 116.

[0077] During the operation of the device 100, initially, the switch 137 is controlled so that it is in an open state so that the RFO signal is not delivered at the output of the transmission circuit 116, i.e. no modulation signal is delivered by the transmission circuit 116. The signal obtained at the output of the component 135 is only injected into the measurement circuit so that the delay ôTX is calculated or measured. After the calculated phase shift value, called "Ç>Offset" on [Fig.2], is applied by the PLL 120 to the input signal of the transmission circuit 116, the switch 137 can be controlled so that it is in a closed state and the RFO modulation signal is emitted at the output of the transmission circuit 116. The RFO modulation signal obtained at the output of the transmission circuit 116 is well phase-shifted so as to compensate for the delay ôTX (compensation symbolized by the indication "-ôTX" at the output of the circuit 132).

[0078] Alternatively, the function performed by the measuring circuit could be achieved using circuits and components different from those described above. Furthermore, one or more components other than the controlled switch 137 described above can be used to perform a similar function, namely, enabling or disabling the RFO signal at the output of the transmission circuit 116.

[0079] The features and variants previously described in connection with device 100 of [Fig.1] can be applied to device 100 according to this first embodiment shown in [Fig.2].

[0080] A second embodiment of device 100 is described below with reference to [Fig. 3]. In [Fig. 3], only some of the components and circuits of device 100 are shown and described below. For example, compared to [Fig. 1], antenna 102 and circuit 104 of device 100 are not shown in [Fig. 3].

[0081] In the transmission circuit 116 of the device 100 according to the second embodiment, the controlled switch 137 is not present, the interruption or not of the output of the transmission circuit 116 being controlled directly by the control signal "EN" applied to the component 135.

[0082] In this second embodiment, the transmission circuit 116 includes a delay circuit 139 reproducing the delay ôTX due to the various elements and components of the transmission circuit 116 and symbolized by component 135. The input of the delay circuit 139 is coupled to the input of the transmission circuit 116, and therefore to the first output of the PLL 120, and the output of the delay circuit 139 is coupled to the second input of the circuit 128.

[0083] During operation of device 100, initially, component 135 is controlled (via the "EN" signal) so that the RFO signal is not delivered at the output of the transmission circuit 116; that is, no modulation signal is delivered by the transmission circuit 116. The signal obtained at the output of the delay circuit 139 is injected into the measurement circuit so that the delay ôTX is calculated. After the calculated phase shift value is applied by the PLL 120 to the input signal of the transmission circuit 116, component 135 can be controlled so that the modulation signal RFO is emitted at the output of the transmission circuit 116. The modulation signal RFO obtained at the output of the transmission circuit 116 is then correctly phase-shifted to compensate for the delay ôTX (compensation symbolized by the indication "-ôTX" at the output of circuit 132).

[0084] In addition, one or more different components of the delay circuit 139 described above can be used to perform an analogous function, namely to reproduce the transmission delay of the transmission circuit 116.

[0085] The features and variants previously described in connection with device 100 of [Fig.1] or [Fig.2] can be applied to device 100 according to this second embodiment shown in [Fig.3].

[0086] Fig. 4 schematically represents the steps of an example of a communication process between device 100 and reader 200.

[0087] Device 100 may be in an inactive state (step 400).

[0088] During a step 402, the device 100 checks whether a magnetic field corresponding to that emitted by a reader is detected.

[0089] In the absence of such a magnetic field, the device 100 is maintained in an inactive state (return to step 400).

[0090] In the presence of such a magnetic field, the first clock signal is delivered by the receiver circuit 110, which receives as input the signal from the magnetic field received by the antenna 102. The PLL 120 starts and then locks onto this first clock signal (step 404). This locking of the PLL ensures a fixed and known frequency of the oscillator, for example, equal to 64*13.56 MHz, and thus provides a precise time base for the measurement.

[0091] The received power is measured in order to determine the coupling coefficient between the reader 200 and the device 100 (step 406). This measurement of the received power is, for example, carried out with an element not shown in Figures 1 to 3 and which may correspond to an analog-to-digital converter (ADC) whose output is coupled to a digital circuit configured to analyze the amplitude of the received signal.

[0092] Depending on the amplitude measured in the previous step, the power of elements 135 and 139 can be pre-programmed so as to apply to the RFO modulation signal the appropriate power to respond to the reader 200 (step 408).

[0093] The delay measurement ôTX is then performed in order to remove the phase shift corresponding to the PLL 120 setpoint (step 410). Thus, the delay of the modulation signal due to the transmission circuit 116 and the amplitude of the received signal is compensated in the signal applied to the input of the transmission circuit 116.

[0094] An RFO signal, in phase with the field of the reader 200, is then obtained at the output of the transmission circuit 116 and applied to the antenna 102, allowing communication between the device 100 and the reader 200 (step 412).

[0095] The second embodiment of device 100 is described below with reference to [Fig. 5]. In [Fig. 5], only a portion of the components and circuits of device 100 are shown and described below. Compared to device 100 previously described with reference to [Fig. 3], an embodiment of the PLL 120 is detailed in [Fig. 5].

[0096] In the example of [Fig.5], the PLL 120 includes a counter 140, an oscillator 142, a filter 144, a subtractor 146 and an adder 148.

[0097] In this example, the counter 140 has a clock input coupled to the output of the receiver circuit 110, a data input coupled to an output of the oscillator 142 which corresponds to the second output of the PLL 120 previously described in connection with [Fig. 3], and an output coupled to a negative input of the subtractor 146 and on which a counting value is delivered. The counter 140 also delivers, on another output, the input signal of the transmitting circuit 116.

[0098] A target phase value, called " <ptarget », est appliquée sur une entrée positive du soustracteur 146. Cette valeur <ptarget peut correspondre à une valeur prédéterminée, par exemple mémorisée dans un registre du dispositif 100, et qui correspond par exemple au déphasage attendu en considérant le retard dû aux différents éléments et circuits du dispositif 100 sans prendre en compte le retard dû aux variations PVT du circuit de transmission 116 et à l’amplitude du signal de réception.

[0099] The output of the subtractor 146 is coupled to a first input of the adder 148 and the phase shift value <pOffset est appliquée sur une deuxième entrée de l’additionneur 148.

[0100] The output of the adder 148 is coupled to the input of the filter 144, and the output of the filter 144 is coupled to the input of the oscillator 142.

[0101] According to one example, the oscillator 142 can be of the DCO type, or "Digital Controlled Oscillator" in English (oscillator controlled by digital input).

[0102] According to one example, the frequency of the periodic signal delivered by the oscillator 142 can be about 868 MHz (64*13.56 MHz), and those of the input signal of the transmission circuit 116 delivered by the counter 140 and of the reception signal and of the first clock signal are 13.56 MHz.

[0103] Alternatively, the PLL 120 may include circuits and / or components different from those described above and shown in [Fig.5].

[0104] An example of an embodiment of the counter 140 is shown in [Fig.6].

[0105] In this example, the counter 140 has an input 149 to which the output signal of the oscillator 142 is applied. As shown in [Fig. 6], the counter 140 also has several frequency dividers 150 connected in series such that the output of each divider is connected to the clock input of the next divider. In this example, the output signal of the oscillator 142 is applied to the clock input of the first divider 150. Furthermore, the output signal of one of the dividers 150 corresponds to the input signal of the transmitter circuit 116. In this example, the frequency dividers 150 are configured to divide the frequency of the signal received at their input by a factor of 2.Thus, in the example described, given that the ratio between the frequency of the periodic signal delivered by the oscillator 142 and that of the input signal of the transmission circuit 116 is equal to 64, the input signal of the transmission circuit 116 is obtained at the output of the 6th divider 150 (26 = 64). Furthermore, in a particular configuration, each of the dividers 150 configured to divide the frequency of the signal received at its input by a factor of 2 can be formed by a D flip-flop whose output is fed back to its input via an inverter.

[0106] In this example, the counter 140 further comprises several flip-flops 152 (3 D flip-flops in [Fig. 6]) connected in series such that the output of each flip-flop 152 is connected to the data input of the next flip-flop 152. The output signal of the oscillator 142 is applied to the clock input of each flip-flop 152. The first clock signal delivered by the receiver circuit 110 is applied to the data input of the first flip-flop 152. These flip-flops 152 prevent metastability from occurring in the counter 140.

[0107] In the described embodiment, the counter 140 also includes other D flip-flops 154 connected in series such that the clock inputs of these flip-flops 154 are connected to each other. The first of these flip-flops 154 receives on its clock input the output signal of the last of the flip-flops 152, and on its data input the output signal of the oscillator 142. The other flip-flops 154 receive on their data input the output signals of the dividers 150. The output signals of the flip-flops 154 together form the counting signal (called "cnt_out" in [Fig. 6]) which is encoded in binary form in this example (the output signal of each of the flip-flops 154 corresponding to one bit of this counting signal).

[0108] Alternatively, the counter 140 can be made with elements and / or components different from those described above and shown in [Fig.6].

[0109] An example of an embodiment of the counting trigger circuit 128 and the counter 130 is shown in [Fig.7]. A timing diagram of the signals used in these circuits 128, 130, during the determination of a phase shift value to be applied to the input signal of the transmission circuit 116 to compensate for the delay ôTX, is also shown in [Fig.8].

[0110] In figures 7 and 8, the following legends are used:

[0111] - SG_FIRST: output signal of PLL 120, corresponding to the input signal of the transmission circuit 116;

[0112] - SG_SECD: output signal of transmission circuit 116, i.e. including the delay ôtTX;

[0113] - Window: counting trigger signal;

[0114] - WIND0W_EN: activation signal for the counting trigger circuit 128;

[0115] - DCO: output signal of oscillator 142;

[0116] - Gated DCO: Gate output signal AND counter 130 shown on the [Fig.7];

[0117] - DFLL_counter: output signal of counter 130;

[0118] - Delay_meas_done: signal delivered at the output of circuit 128 indicating that the The counting is complete and can be read at the output of circuit 130;

[0119] - RN: signal resetting the D flip-flops when its value is in the 0 state, and leaving operate the D flip-flops on each clock edge when its value is in state 1;

[0120] - Rni: signal indicating the end of measurement.

[0121] In [Fig.7], the "Dff" blocks correspond to D flip-flops, and the " / 2" blocks correspond to frequency dividers applying a division factor equal to 2.

[0122] The operating details of circuits 128 and 130 shown in [Fig. 7] are not described here; those skilled in the art will understand the operation of these circuits from the components and wiring visible in [Fig. 7] and from the timing diagram in [Fig. 8]. Furthermore, the signals in the timing diagram in [Fig. 8] are shown schematically and not to scale relative to each other, both for the amplitudes and the durations of the different parts of these signals.

[0123] In the various embodiments, the proposed device 100 can, each time the device is used to communicate with a reader, compensate for the delay due to variations in the PVT of the transmission circuit 116 of the device 100 and to the amplitude of the received signal at the input of the receiving circuit 110. The various elements of the device 100 can, in particular, allow:

[0124] - a synchronization of a clock signal (first clock signal in the (description above), corresponding for example to a square wave signal, without variation in delay with a reception signal, corresponding for example to a sinusoidal signal, whose amplitude can vary;

[0125] - a delay measurement between the input and output signals of the transmitting circuit 116;

[0126] - the use of a PLL as an accurate time base to achieve automatically a measurement and correction of the delay occurring in the device.

[0127] In all embodiment examples, the proposed device can facilitate contactless communication between the device and a reader, allowing the device to have a small antenna and / or low power and / or a large distance between the device and the reader.

[0128] In all embodiment examples, the compensation of the delay by the device can be carried out without using an external device to measure the delays, and / or without having to deliver one or more measurement signals at the output, this compensation being able to be carried out within the device.

[0129] In all embodiments, the device may include counters to automatically perform delay measurements.

[0130] In all embodiments, thanks to the delay compensation achieved, the phase of the signal emitted by the device remains stable even when the amplitude of the magnetic field received by the device varies, which results in a magnetic field in which the amplitude levels are clearly distinct and different from each other.

[0131] In all embodiment examples, it is possible that the measurement of the delay ôTX is continued even after the transmission circuit 116 emits the RFO signal, which allows the measurement of this delay ôTX to be refined.

[0132] In the above description, device 100 corresponds to a contactless communication device using active charge modulation which, during communication with a reader, is emulated in card mode. Device 100 may have functionalities other than those described above. Device 100 may correspond, for example, to a mobile phone or a connected object such as a watch.

[0133] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0134] Finally, the practical implementation of the described examples of realization and variants is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A contactless communication device (100) using active charge modulation, comprising at least: - a receiving circuit (110) configured to receive as input a receive signal from a magnetic field intended to be received by an antenna (102); - a transmitting circuit (116) comprising an output coupled to the antenna (102) and on which a modulation signal in phase with the receive signal is intended to be delivered; - a compensation circuit (118) for a delay of the modulation signal due to the transmitting circuit (116) and the amplitude of the receive signal, configured to determine a phase shift value to be applied to an input signal of the transmitting circuit (116) to compensate for the delay.

2. Device (100) according to claim 1, further comprising a phase-locked loop (120) configured to receive as input a first clock signal delivered at the output of the receiving circuit (110) and the phase shift value, and to deliver on a first output the input signal of the transmission circuit (116).

3. Device (100) according to any one of the preceding claims, wherein the compensation circuit (118) comprises at least one circuit for measuring a phase difference between the input signal of the transmission circuit (116) and a delayed signal which is the input signal of the transmission circuit (116) delayed by said delay.

4. Device (100) according to claims 2 and 3, wherein the measuring circuit comprises at least: - a counting trigger circuit (128) comprising a first input configured to receive at least the input signal from the transmission circuit (116) and a second input configured to receive at least the delayed signal, and configured to output a counting trigger signal having a first value for a duration equal to the delay and a second value, different from the first value, outside of this duration; - a counter (130) comprising a clock input coupled to an output of the counting trigger circuit (128), and a data input coupled to a second output of the phase-locked loop (120) on which a periodic signal of frequency equal to a multiple of that of the input signal of the transmission circuit (116) is intended to be delivered; - a calculation circuit (132) configured to determine the phase shift value as a function of a value of a counting signal intended to be delivered by the counter (130).

5. Device (100) according to any one of claims 3 or 4, wherein the transmission circuit (116) includes a controlled switch (137) having an output which is the output of the transmission circuit (116).

6. Device (100) according to claim 4, wherein the transmission circuit (116) includes a control input configured to receive a signal controlling the emission or not of a signal on the output of the transmission circuit (116), and includes a delay circuit (139) having an input coupled to the input of the transmission circuit (116), an output coupled to the second input of the counting trigger circuit (128) and which is configured to apply a delay of equal value to that due to the transmission circuit (116).

7. Device (100) according to any one of the preceding claims, wherein the receiving circuit (110) comprises at least: - a variable gain amplifier (112) configured to receive the receiving signal as input; - a sinusoidal signal to square wave converter (114), comprising an input coupled to an output of the variable gain amplifier (112), and an output corresponding to an output of the receiving circuit (110).

8. A contactless communication method between a reader (200) and a device (100) according to any one of the preceding claims, comprising at least the implementation of the following steps: - detection (402) of a magnetic field by the device (100); - when a magnetic field is detected by the device (100), emission (404) of a first clock signal by the receiving circuit (110) of the device (100) receiving at input a reception signal from the magnetic field; - measurement (410), by the compensation circuit (118) of the device (100), and compensation of the delay of the modulation signal due to the transmission circuit (116) and to the amplitude of the reception signal in a signal applied at the input of the transmission circuit (116) of the device (100), the compensated delay depending on the amplitude of the reception signal and on a target amplitude of the modulation signal intended to be delivered at the output of the transmission circuit (116) and being obtained by adjusting the power of the components (135) of the transmission circuit (116); - application (412), by the transmission circuit (116) of the device (100), of the modulation signal on the antenna (102).

9. A method according to claim 8, wherein the device (100) has all the features of claim 2, and wherein the transmission (404) of the first clock signal by the receiving circuit (110) of the device (100) is followed by a start and locking of the phase-locked loop (120) on the first clock signal.

10. A method according to any one of claims 8 or 9, further comprising, between the emission (404) of the first clock signal and the application of the phase shift value (410): - a measurement of the received power (406); - a preprogramming (408) of a power of components of the transmission circuit (116) as a function of the measured received power.

11. A method according to any one of claims 8 to 10, wherein the device (100) comprises all the features of any one of claims 5 or 6, and further comprising, prior to the measurement (410) and the delay compensation, the application of a control signal to a control input of the controlled switch (137) of the transmission circuit (116) or to the control input of the transmission circuit (116) such that no signal is delivered at the output of the transmission circuit (116).

12. A method according to claim 11, further comprising, after measurement (410) and delay compensation, the application of the control signal to the control input of the controlled switch (137) of the transmission circuit (116) or to the control input of the transmission circuit (116) such that the modulation signal is delivered on the output of the transmission circuit (116).

Images