Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/27—Adaptation for use in or on movable bodies
  • H01Q1/32—Adaptation for use in or on road or rail vehicles
  • H01Q1/3208—Adaptation for use in or on road or rail vehicles characterised by the application wherein the antenna is used
  • H01Q1/3233—Adaptation for use in or on road or rail vehicles characterised by the application wherein the antenna is used particular used as part of a sensor or in a security system, e.g. for automotive radar, navigation systems
  • H01Q1/3241—Adaptation for use in or on road or rail vehicles characterised by the application wherein the antenna is used particular used as part of a sensor or in a security system, e.g. for automotive radar, navigation systems particular used in keyless entry systems

Definitions

• the present invention relates to a low frequency radio transmission device which incorporates a driving circuit generating an excitation signal from a serial LC type antenna, a hands-free access system incorporating such a device, as well as a driving circuit intended to be used in such a device.
• the invention finds applications, in particular, in hands-free access systems (in English: "passive entry System") in particular for motor vehicles.
• a radio transmission device may comprise a determined number N of transmission antennas, where N is an integer generally greater than unity, and at least one driver circuit (in English: "driver circuit") having the function of generating an excitation signal from the antenna (s) (in English: “driver signal”).
• the drive circuit can be included in a management unit, which can be centralized or decentralized.
• Each transmitting antenna has an inductive coil, which can be tuned or not. Depending on the case, it is said that the antenna is tuned or not.
• a tuned antenna further includes a tuning capacitor.
• the antenna is of the LC series type when the inductor and the capacitor are connected in series. On the contrary, it is of the parallel LC type when the inductor and the capacitor are connected in parallel.
• a non-tuned antenna does not include a tuning capacitor.
• the inductive coil of the antenna is generally connected in series with at least one DC blocking capacitor, and at the very least with stray capacitances. This is why, within the meaning of the invention and in the following, we also speak of an antenna of the LC series type in this case.
• the management unit can be included in a cabin computer ensuring in particular the function of controlling access to the vehicle and / or the function of starting control of the vehicle. vehicle.
• the management unit comprises a control module which generates a data signal, containing the data to be transmitted.
• the transmission antennas are distributed inside the passenger compartment, and / or on the outer periphery of the vehicle.
• the excitation signal delivered to the transmitting antennas is functionally an interrogation signal from an identification member such as a badge or the like, which is worn by a user.
• an identification member such as a badge or the like
• the management unit comprises means for receiving and decoding this response signal in order to authenticate the user. In the event of authentication, the management unit performs certain functions such as unlocking the vehicle doors and / or deactivating a vehicle immobilizer.
• Radio transmission is said to be low frequency (or LF, from the English “Low Frequency”), when the frequency of the interrogation signal is of the order of a few hundred kilohertz (kHz). Under these conditions, the propagation of the radio signal takes place in the near field. Since there is no electromagnetic radiation, compliance with electromagnetic compatibility (EMC) standards poses few problems. Such a transmission must simply comply with the specifications of the standard IETS 300-330 (or EN 300-330) with regard to the spectrum of the signal transmitted. In a classic example in the automotive field, the fundamental frequency of the interrogation signal is equal to 125 kHz.
• the management unit is said to be decentralized when it includes a drive circuit by transmitting antenna, each generating an excitation signal from the corresponding antenna. These circuits are then each arranged near the corresponding transmitting antenna.
• the management unit is said to be centralized when it comprises a single drive circuit, which generates a single antenna excitation signal, as well as switching means making it possible to activate only one (or more) of the antennas. except for the others.
• the excitation signal is then applied to the activated antenna only.
• Figure 1 schematically illustrates the principle of the attack of a serial LC type transmit antenna according to the prior art.
• the transmission antenna EA comprises an inductive coil L in series with a capacitor C.
• the letter L designates both the coil and the value of its inductance.
• the letter C denotes both the capacitor and the value of its capacity.
• this capacitance C corresponds to all the capacitors which exist in series with the coil L, in particular a tuning capacitor (if any), one or more DC blocking capacitors (if any), and the stray capacitances of the coil or other.
• a drive circuit GEN includes a square voltage generator 100. According to Thévenin's model, this generator 100 includes an ideal voltage source 101 in series with an internal resistance Rs. For the sake of simplicity, we consider in what follows that the resistance Rs includes not only the internal resistance of the generator, but also the resistance inherent in the inductive coil L and in the capacitors (if applicable), as well as the resistance of the connections.
• the positive terminal of the voltage source 101 is coupled to a first terminal of the antenna EA via the resistor Rs.
• the negative terminal of the voltage source 101 as well as a second terminal of the antenna EA are coupled to a potential reference, for example mass.
• Source 101 is a voltage source which has a low internal impedance. We denote by U the amplitude of the voltage and i the value of the current which are delivered by the source 101.
• Fo the resonance frequency which satisfies this relation.
• M xi the number of turns of the coil L. Therefore, with constant geometry and current i constant, we increase M to increase the intensity of the radio field and therefore the extent of the dialog area. Nevertheless, the inductance L being proportional to M 2 , the quality factor Q then increases in a manner also proportional to M 2 .
• a transmission device having a high quality factor is thus conventionally obtained, as shown in the graph in FIG. 2 which illustrates the evolution of the current i as a function of the frequency F of the excitation signal generated by the circuit of GEN attack.
• the current i is maximum when the frequency F is equal to the resonant frequency Fo.
• the curve represented is that of a very pointed “bell” function.
• a small variation ⁇ F of the frequency F near the resonance frequency Fo generates a large variation ⁇ i of the current i in the antenna, and therefore a large variation in the extent of the dialog area.
• the values of L and C can vary in an uncontrolled manner.
• a first aspect of the invention thus relates to a low-frequency radio transmission device for a hands-free access system for a motor vehicle, comprising at least one emission antenna of the LC series type, and at least one circuit for attack delivering an antenna excitation signal.
• the drive circuit comprises a current generator for delivering the excitation signal as a current excitation signal.
• the drive circuit further comprises means for determining the internal resistance of the current generator. This reduces the quality factor of the device. Preferably, the resistance is high enough for the quality factor to be less than 10. In the application, a quality factor of the order of 5 is preferred, taking into account the tolerated variation of the extent of the zone. of dialogue.
• a second aspect of the invention relates to a hands-free access system for a motor vehicle, comprising an identification badge worn by a user, and further comprising a low-frequency radio transmission device according to the first aspect, for the emission of a badge interrogation signal.
• a third aspect of the invention relates to a driving circuit intended to be used in a device according to the first aspect.
• - Figure 1 already analyzed, is a diagram illustrating the principle of excitation of an antenna of the LC series type according to the prior art
• - Figure 2 also already analyzed, is a graph of the current in the antenna as a function of the frequency of the excitation signal, in the case of a high quality factor;
• - Figure 4 is a top view "schematic" of a motor vehicle showing the respective range areas, or dialogue areas, transmission antennas in an example of hands-free access system;
• - Figure 5 is a diagram illustrating an embodiment of a hands-free access system according to the invention;
• - Figure 6 is a diagram illustrating the principle of a particular embodiment of a device according to the invention;
• FIG. 7 is a diagram illustrating the principle of excitation of an antenna of LC series type according to the invention
• - Figure 8 is a diagram illustrating a first variant for the excitation of an antenna of the LC series type according to the invention
• FIG. 9 is a diagram illustrating a second variant for the excitation of an antenna of the LC series type according to the invention.
• FIG. 10 is a diagram illustrating a first embodiment of a current generator in a drive circuit according to the invention.
• FIG. 11 is a diagram illustrating a second embodiment of a current generator in a drive circuit according to the invention.
• FIG. 4 a top view of a motor vehicle 10 is shown diagrammatically.
• a hands-free access system for such a vehicle comprises transmission antennas which are arranged inside the passenger compartment and / or outside the vehicle 10. These antennas have the function of ensuring transmission an interrogation signal which is adapted to be received by a system identification member, such as a badge 17 worn by a user, when the badge 17 is located within the range of the signal emitted by one of the antennas (dialog area).
• a system identification member such as a badge 17 worn by a user
• the badge 17 responds by sending a response message, which is received by means of the access system placed on board the vehicle.
• the response message is recognized as valid, it leads to opening the doors ("passive entry” function) and / or unlocking an immobilizer or even starting the vehicle (“passive go” function).
• the interrogation signal is a low frequency signal (LF signal), for example equal to 125 kHz
• the response signal is a radiofrequency signal (RF signal, from the English "Radiofrequency"), for example of frequency equal to 433 MHz (megahertz).
• LF signal low frequency signal
• RF signal radiofrequency signal
• Hand access systems Free compliant with this example are commonly called LF / RF systems in the jargon of the skilled person.
• the transmission of the response signal by the badge (RF signal) must comply with the specifications of the IETS 300-330 standard (or EN 300-330).
• the hands-free access system comprises five external transmission antennas, arranged at the external periphery of the vehicle, and which are associated with five dialogue zones 11 to 15 respectively.
• the dialogue extend from, respectively, the left front door, the left rear door, the luggage compartment, the right rear door, and the right front door.
• the external transmitting antennas are dedicated to the "passive entry” function.
• the system comprises a single internal transmitting antenna arranged inside the passenger compartment of the vehicle, which is associated with a dialog box 16 (represented by a closed broken line in the figure) corresponding the interior volume of the passenger compartment of the vehicle.
• the internal transmit antennas are dedicated to the "passive go" function.
• FIG. 5 there is shown schematically an example of a hands-free access system according to the invention.
• the system comprises a cabin CU computer placed at a strategic location in the vehicle 10.
• the CU computer is powered by the vehicle battery 20.
• the system further comprises a determined number P of external transmit antennas EA1, EA2, ..., EAp, where P is an integer. These antennas are arranged at the outer periphery of the vehicle 10, for example at the doors and the luggage compartment. They have first and second terminals connected to the CU computer.
• the system also includes one (or more) LSW switch (s) which is connected to the CU computer, such as an unlocking button. This switch can be actuated from outside the vehicle 10 by the user.
• LSW switch LSW switch
• the system can also include a number NP of internal transmitting antennas EAp + 1, EAp + 2, ..., EAn, where N is an integer greater than P, arranged inside the passenger compartment of the vehicle . These antennas have first and second terminals connected to the CU computer. In the example illustrated in Figure 4, P is equal to 5 and N is equal to 6 (NP is therefore equal to unity).
• the system also includes an SSW switch such as a start button, which can be operated by the user while inside the vehicle 10 only.
• the external transmission antennas EA1 to EAp are LC type series antennas comprising an inductive coil (of inductance L) constituted by a winding wound around a ferrite rod in series with a capacitor (of capacity C) constituted by stray capacitances or by voluntarily added capacitors.
• the internal transmit antennas EAp + 1 to EAn are for example air coils (loop antennas) of the LC series type, comprising an inductive coil (of inductance L) constituted by a certain number of turns arranged on an appropriate support, in series with a capacitor (of capacity C) constituted by the parasitic capacities or by capacitors voluntarily added.
• the antennas may further include a tuning capacitor, arranged in series with the inductive coil.
• DC blocking capacitors can be arranged in series with the antennas. For each antenna, the value of the capacitance of the capacitor C shown in the figure then includes the value of these capacitors.
• the external transmission antennas EA1 to EAp have the function of transmitting an interrogation signal 41 outside the vehicle, under the control of the computer CU, when the switch LSW is actuated.
• the internal transmission antennas EAp + 1 to EAn have the function of transmitting the interrogation signal 41 inside the vehicle, under the control of the computer CU when the switch SSW is actuated.
• the system also includes Q actuators A1, A2 Aq, such as electric motors or the like associated in certain cases with an electromechanical and / or electro-pneumatic mechanism, where Q is a determined whole number. These actuators are controlled by the CU computer to perform certain functions such as unlocking the doors and / or deactivating a vehicle immobilizer 10.
• the system comprises a reception antenna 31 placed in the vehicle 10 and coupled to the computer CU via reception means 30.
• the antenna 31 has the function of receiving a response signal 42 which is transmitted by the badge 17 upon reception of the interrogation signal 41 emitted by one of the external transmitting antennas EA1 to EAp, or by one of the internal transmitting antennas EAp + 1 to EAn.
• the badge 17 includes a control unit 176 such as a microcontroller. It also comprises a reception antenna 172 for receiving the interrogation signal 41, which is coupled to the control unit 176 via reception means 171. It further comprises a transmission antenna 174, which is coupled to the control unit 176 by transmission means 173. Control unit 176 and means 171 and 173 are supplied by an accumulator 175 such as a battery.
• the transmission antenna 174 has the function of transmitting the response signal 42, under the control of the control unit 176, when a valid interrogation signal 41 is received by the reception antenna 172 and decoded by unit 176.
• FIG. 6 illustrates an example of a management unit for managing the transmission of the interrogation signal by a determined number N of antennas of a device according to the invention, for example in a system according to FIG. 5 .
• the management unit 500 delimited by a discontinuous closed line, is centralized. It comprises a single drive circuit GEN, which generates a single signal excitation of the antennas, as well as switching means making it possible to activate only one (or more) of the antennas except the others.
• the management unit 500 comprises a control module CTRL, the drive circuit GEN, and the switching means DEMUX.
• the circuit GEN receives a data signal Sd delivered by the module CTRL, and generates the excitation signal SC.
• the switching means DEMUX are for example a demultiplexer having an input IN, and N outputs respectively OUT1 to OUTn.
• the excitation signal SC is delivered on a respective first terminal of each of the antennas EA1 to EAn, via a respective first link whose length can reach a few meters.
• the switching means DEMUX are arranged between a respective second terminal of each of the antennas EA1 to EAn, on the one hand, and a reference potential, for example the ground, on the other hand.
• the input IN of the DEMUX demultiplexer is connected to ground.
• the outputs OUT1 to OUTn of the demux multiplexer DEMUX are connected to said respective second terminal of each of the antennas, respectively EA1 to EAn, via a respective second link whose length is substantially identical to that of the first link, that is to say that is, up to a few meters.
• the demux multiplexer DEMUX comprises a determined number N of switches, respectively SW1 to SWn, which are each arranged between the input IN and one of the outputs OUT1 to OUTn, respectively.
• the CTRL control module generates a SEL selection signal which is delivered to the DEMUX demultiplexer. This signal has the function of controlling the closing of only one of the switches SW1 to SWn, that is to say the selection of only one of the outputs OUT1 to OUTn of the demux multiplexer DEMUX which is coupled to the input IN via one of said switches.
• the selection signal SEL makes it possible to activate only one of the antennas EA1 to EAn, the others being deactivated. It will be noted that it is not excluded that, in certain applications, several transmitting antennas are activated simultaneously.
• Such an arrangement of the switching means results in a switching of the transmitting antennas "by cold spot".
• the electrical links connecting the drive circuit GEN to the antennas which are deactivated, although being in open circuit, are permanently subjected to the excitation signal SC. Since these links can be more or less strongly coupled to ground via parasitic capacitances, there is a risk that one or more deactivated antennas are nevertheless crossed by the current of the excitation signal, and emit the interrogation signal at a frequency offset from the fundamental frequency of the excitation signal.
• the excitation signal SC of the antennas is a signal LF preferentially sinusoidal or quasi-sinusoidal.
• the low level of harmonics of such an excitation signal makes it possible to avoid the aforementioned risk of accidental resonance of the antenna. This avoids the risk of erratic operation of the hands-free access system.
• the management unit 500 is advantageously included in the cabin computer CU.
• the antenna EA is an antenna of the LC series type, that is to say comprising an inductive coil L in series with a capacitor C, tuning capacitance and / or to one or more capacitors for blocking the DC.
• the inductive coil L of the antenna EA is not tuned, that is to say that it is not connected in series with a tuning capacitor.
• a drive circuit GEN delivers an excitation signal SC for the excitation of the antenna EA, as a current excitation signal.
• This drive circuit comprises a current generator 600 which, according to the Norton model, comprises an ideal current source 601 in parallel with an internal resistance Ri.
• the positive terminal of the current source 601 is coupled to a first terminal of the antenna EA.
• the negative terminal of the current source 601 as well as a second terminal of the antenna EA are coupled to ground.
• the current generator delivers a current lo.
• the excitation signal SC is preferably a sinusoidal or quasi-sinusoidal signal. Indeed, as has already been said above, this characteristic makes it possible to limit the effects on the operation of the system, of the parasitic coupling of the connections to ground.
• a centralized management unit has been described above with reference to the diagram in FIG. 6.
• the drive circuit GEN may also include means arranged to increase the value of the internal resistance Ri of the current generator 600.
• the diagram in FIG. 8 symbolically illustrates such a attack circuit variant
• an additional resistance Rp has been symbolically connected in series with the internal resistance Ri of the current generator 600.
• the resistance Rp makes it possible to determine the value of the internal resistance Ri.
• the physical presence of a component corresponding to such additional resistance Rp is not compulsory.
• a high value of the internal resistance of the current generator 600 can be obtained by an adapted architecture of the generator.
• the value of the current lo is chosen taking into account the internal resistance of the current generator 600, so as to obtain an excitation current of desired amplitude in the antenna EA.
• the quality factor of the device is less than 10.
• it is arranged so that it is of the order of 5.
• the diagram of FIG. 9 illustrates another variant in which the drive circuit GEN comprises a voltage follower stage 602 disposed at the output of the current generator 600 and having a determined current gain Gi.
• the gain Gi is greater than unity (Gi> 1).
• This variant is recommended in the case where a high excitation current is required, that is to say in applications requiring a high emission power.
• Such a stage makes it possible to limit the value of the current lo and therefore makes it possible to limit the heat losses in the current generator 600.
• the current source 601 and the internal resistance Ri are then seen from the side of the load (the antenna EA) , as a current source Gi x lo, and as a resistance Ri / Gi, respectively.
• the voltage follower stage 602 is arranged between a terminal 603 brought to the potential of the supply voltage Vbatt delivered by the battery, on the one hand, and the ground on the other hand. It is for example a push-pull power stage in class B. This is however only a preferred example but in no way limitative.
• the current generator 600 comprises for example a voltage generator followed by a transconductance amplifier.
• FIG. 10 a first exemplary embodiment of such a current generator 600 is shown.
• the current generator 600 comprises a low frequency sinusoidal oscillator 71, delivering a sinusoidal signal Sm, which is a signal LF having a frequency Fo. It further comprises an amplifier 74 with variable gain, one input of which receives the signal Sm and the output of which delivers the excitation signal SC.
• Amplifier 74 is a transconductance amplifier.
• the signal Sm which it receives is a voltage signal
• the signal which it delivers is a current signal, namely the current noted lo in FIGS. 7 to 9. This current excites the inductive coil of the antenna which is activated.
• a control input of amplifier 74 receives the data signal Sd, which is a square LF signal.
• the signal Sd contains the data to be transmitted in the form of Manchester coding.
• the gain of the amplifier 74 is for example equal to zero when the signal Sd is in the low state and it has a non-zero value when the signal Sd is in the high state.
• the signal lo thus corresponds to the signal Sm modulated by the signal Sd.
• the current generator 600 comprises a low frequency oscillator 72 generating a square signal Sck, which is an LF signal having a fundamental frequency Fo which is for example equal to 125 kHz.
• the signal Sck is a clock signal delivered by an output of a microcontroller included in the control circuit CTRL.
• the signal Sck is filtered by a low-pass filter 73 to generate the signal Sm.
• the signal Sm is then a quasi-sinusoidal signal, which is an LF signal having a fundamental frequency Fo.
• the filter 73 is at least third order. Its cut-off frequency is for example equal to 80 kHz or 100 kHz.
• the rest of the current generator 600 is identical to the circuit according to the first embodiment, according to the diagram in FIG. 10.
• the signal Sck can be modulated in pulse width, which makes it possible to control the drive current of the antennas, that is to say the current flowing in the activated antenna.

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• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Lock And Its Accessories (AREA)
• Details Of Aerials (AREA)
• Near-Field Transmission Systems (AREA)

Applications Claiming Priority (3)

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• 2002
  • 2002-06-24 FR FR0207792A patent/FR2841393B1/fr not_active Expired - Fee Related
• 2003
  • 2003-06-20 JP JP2004514965A patent/JP4221362B2/ja not_active Expired - Fee Related
  • 2003-06-20 DE DE60321464T patent/DE60321464D1/de not_active Expired - Lifetime
  • 2003-06-20 AU AU2003255686A patent/AU2003255686A1/en not_active Abandoned
  • 2003-06-20 EP EP03760762A patent/EP1516389B1/de not_active Expired - Lifetime
  • 2003-06-20 WO PCT/FR2003/001903 patent/WO2004001897A1/fr not_active Ceased

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