EP1902426B1 - Access control system for a motor vehicle - Google Patents

Abstract

The invention relates to an access control device for a motor vehicle. Said device is composed of at least one transmitter unit arranged in the motor vehicle and at least one receiver unit, which units are controlled by means of at least one microcomputer unit. The receiver unit is used to receive UHF signals and the transmitter unit to transmit low frequency long wave signals. Furthermore, a closing unit is provided which is actuated by means of the microcomputer unit and when a matching code is present the closing device releases the access to the motor vehicle. The transmitter unit has two coupled LC bandpass filters, the first bandpass filter comprising, as a pre-filter, a first coil and a first capacitor group composed of at least one capacitor, and the second bandpass filter comprising the LF-antenna as an inductor and a second capacitor group composed of at least one capacitor. A multiplexer by means of which the antennas are successively connected to the transmitter unit using a multiplex method is provided between the first and second bandpass filters.

Description

The invention relates to an access control system for a motor vehicle according to the preamble of claim 1.

Out DE 102 36 305 A1 is a generic access control system for a motor vehicle known. This has at least one transmission unit arranged in the motor vehicle for the transmission of low-frequency long-wave signals and a plurality of associated LF antennas, which are arranged in the vehicle at exposed locations. In addition, two or more ID-encoders which can be carried by the user are provided, at least one transceiver unit for the vehicle exterior and at least one transceiver unit for the vehicle interior for carrying out a wireless authentication communication with the ID transponders, whereby upon successful authentication of an ID Encoder one or more safety devices are unlocked or locked.

Out DE 100 13 542 A1 a further generic arrangement for an access security system for a motor vehicle is disclosed. This system is particularly suitable for the realization of secure access systems based on chip cards in the field of building security, but can also be used for motor vehicles. The invention is characterized in that the relative orientation or positioning between a data carrier and a base station, which is preferably arranged in a vehicle, signals are obtained, based on which a unique identification is vornehmbar.

The FR-A-2841392 shows an access control device for a motor vehicle with a transmitter for transmitting low-frequency long-wave signals, in which the transmitting unit an antenna with a capacitor can be activated via a multiplexer. In addition, a pre-filter is provided in the transmitting unit. The US 4,806,930 shows a transmitter with an antenna driven by a transistor. At the input of the transistor, an LC element for suppressing unwanted harmonic frequency is provided. The WO 2004/097749 A1 shows a transmitting unit with several antennas, the active antenna is connected to the ground via a multiplexer.

The citation WO2006 / 060974 discloses a transmitting device for a plurality of mutually parallel antennas, which can be supplied independently via a respective supply line, wherein a common exciter circuit and a multiplexer for selective connection of at least one of the antennas is provided, and wherein in each supply line a capacitor is provided in series with the antenna and for each Antenna a controllable switching means is provided, through which the supply line between the capacitor and antenna is connected to reference potential.

Object of the present invention is to show an access control system for a motor vehicle, which is particularly improved in terms of electromagnetic compatibility, the number of components and space requirements should be kept as low as possible.

This object is solved by the features of the independent claims. Advantageous embodiments of the invention will become apparent from the further description, the dependent claims and the accompanying figures.

For this purpose, the LC unit has two coupled LC bandpass filters, the first bandpass as a pre-filter of a first coil and a first capacitor group of at least one capacitor and the second bandpass from the LF antenna as an inductor and a second capacitor group consists of at least one capacitor , This coupled bandpass structure allows a significant reduction of the harmonics and thus a significant improvement of the electromagnetic compatibility even with a rectangular or trapezoidal excitation, as was not usual for access control devices.

Preferably, the first bandpass has a common coil for all antennas, thereby keeping the cost of the pre-filter even with a larger number to be driven separately antennas in limits. For each antenna, a separate capacitor is provided in the pre-filter stage.

In a preferred embodiment, a multiplexer is provided, via which the antennas are connected successively in multiplexing with the transmitting unit, wherein the multiplexer is arranged between the first and second bandpass. Only through the two bandpass filters in succession, it becomes possible to interpose a multiplexer and thereby already transmit a largely harmonics-free signal on the supply line to the antennas.

Preferably, the multiplexer is a shunt multiplexer in which a circuit node between the first to second bandpass for the respective inactive antenna via a controllable transistor is switched to ground potential, while this circuit node for the active antenna is not connected to ground potential and thus the signal from the Transmitter unit passes via the first bandpass to the active antenna.

Preferably, by switching the circuit node of the inactive antennas to ground potential, the capacitors of these inactive antennas are AC-connected in parallel with the capacitor of the active antenna and thus this interconnection of the capacitors gives the first capacitor group.

The access control system generally also has an access unit, which is preferably present in a key or in an access authorization identification unit.

The preferably arranged in the motor vehicle control unit is equipped with at least one transmitter with a low transmission frequency, hereinafter referred to as LF transmitter, which preferably operates in the range of 125 kHz, a control unit and at least one UHF receiver.

The access unit consists of a microcomputer unit, at least one corresponding to the LF transmitter in the motor vehicle LF receiver and at least one UHF transmitter, which in turn corresponds to the UHF receiver in the motor vehicle.

The arranged in the motor vehicle control unit is designed as a control unit, wherein the control unit accesses the LF transmitter whose individual associated antennas are preferably integrated in the door handles of the motor vehicle. In addition, at least one antenna is arranged in the interior of the motor vehicle and in the rear and front bumper. It has proven to be particularly advantageous to arrange the antennas of the LF transmitter at seven points on the vehicle at each exposed point.

The access unit, which is configured in particular as a mobile identification unit, consists of at least one LF receiver, a microcomputer unit and at least one UHF transmitter, which is designed in particular as a UHF transmitter module.

The system preferably operates as follows: If the user actuates the door handle or another part on the motor vehicle, a wake-up signal is first sent via the LF transmitter to the access unit. The wake-up signal is necessary because the access unit when not in use at rest, the so-called sleep mode, is located in order to minimize the power consumption of the access unit. The wake-up signal, which was received by the LF receiver of the access unit, now wakes up and in turn transmits its specific identification code via the UHF transmitter.

If this code does not match the code stored in the control unit of the motor vehicle, the door of the vehicle remains locked. However, if the identification code is recognized, the lock of the motor vehicle, or the door lock of the motor vehicle, is unlocked, and the user can open the vehicle.

The control unit which controls the LF transmitter is, as already indicated, preferably in connection with the microcomputer unit, which in turn works together with a driver circuit for operating the transmission antennas for low-frequency signals, adapted for the LF transmitter. At the same time, however, the microcomputer unit also controls the UHF receiver, especially since unlocking of the at least one access opening to the motor vehicle takes place only after receipt of the UHF signal and receipt of the authentication. The microcomputer unit and the driver circuit for the LF transmitters and the LF antennas generate a transmission signal which consists of a high frequency carrier in the long wave range with a nominal frequency of 125 kHz. The high frequency carrier is amplitude modulated. The resulting AM signal includes a bit string transmission for transmitting the wake-up signal to the access unit. With ideal transmission, a square wave signal is modulated to the amplitude of the radio frequency carrier. To transmit such a signal over long wave requires various measures, in particular with regard to the frequency spectrum, since sidebands as well as harmonic components of the carrier must not exceed certain predetermined values due to the radio admission of the radio determination.

The LF transmitter further cooperates with a pulse width modulator, a driver, a pre-filter, at least one LF transmission antenna, and a rectifier and control filter circuit located in the feedback region. It has proven advantageous to effectively use an antenna current of 1.41 amps at a range of 1.5 m of the LF signal around the antenna (s). In order now to achieve this current independently of the battery voltage of the motor vehicle and other disturbing factors, the modulation signal supplied by the microcomputer unit is changed by the pulse width modulation unit in the pulse width ranges such that the Antenna resonant circuit is supplied via an amplifier circuit just with so much energy or is triggered, so that the above-mentioned required antenna current flows. By a broad pulse clock, the energy supply increases and the current increases, with a narrow pulse the energy supply decreases and the current falls. Once the setpoint current value has been reached, only little energy needs to be supplied to the antenna so that the setpoint current is maintained. The pulse width modulated signal is fed into the antenna via an amplifier circuit and a double Pi band pass filter acting as a transmitter. The current through the bandpass filter is determined by means of a peak-value rectifier. The recovered voltage is proportional to the transmit antenna current. In order to ensure now a continuous antenna current, the supplied pulse width modulation width of the signal is incrementally adjusted via the microcomputer unit. The incremental adaptation is done in a ratio of 1 to N, where N is the number of modulation increases in progress. It has proven to be advantageous to leave at least four pulses unchanged. As soon as a desired current flow has settled in the antenna during the feedback and return measurement, the incremental control is fixed by the microcomputer unit to the desired value.

To generate a transmission signal without interfering harmonics, the transmit antenna (s) and the pre-filter are used. This pre-filter is designed as a double-circuit pre-filter and thus achieves that even the third harmonic in the first circuit is attenuated by 45 dB. In this way, the connection from the control unit to the transmitting antenna is not subjected to unnecessary harmonics. The second transmission circuit consists of an inductor and a capacitor. This series resonant circuit is tuned to the resonance frequency of 125 kHz, just the transmission frequency.

In the following, the invention will now be described in more detail with reference to embodiments and figures.

FIG. 1

einen schematischen Aufbau der wesentlichen Elemente des Zugangskontrollsystems;

FIG. 2

einen schematischen Aufbau des Steuergerätes des Zugangskontrollsystems;

FIG. 3

einen weiteren schematischen Aufbau des Steuergerätes;

FIG. 4

eine schematische Darstellung der Funktionsweise der Pulsweitenmodulations-Regelung; und

FIG. 5

einen weiteren schematischen Aufbau des Steuergerätes mit Integration eines digitalen Bausteines;

FIG. 6

einen weiteren schematischen Aufbau des Steuergerätes mit Integration eines digitalen Bausteines;

FIG. 7

einen weiteren vereinfachten schematischen Aufbau des Steuergerätes mit Integration eines digitalen Bausteines.

Fig. 8

Funktionsweise der gekoppelten Bandpassfilter sowie des Shunt- Multiplexers

It shows:

FIG. 1

a schematic structure of the essential elements of the access control system;

FIG. 2

a schematic structure of the control unit of the access control system;

FIG. 3

a further schematic structure of the control unit;

FIG. 4

a schematic representation of the operation of the pulse width modulation control; and

FIG. 5

a further schematic structure of the control unit with integration of a digital module;

FIG. 6

a further schematic structure of the control unit with integration of a digital module;

FIG. 7

another simplified schematic structure of the control unit with integration of a digital block.

Fig. 8

Functionality of the coupled bandpass filter and the shunt multiplexer

In the figures, the same reference numerals are used for identical components or groups in all figures. This is for easier understanding of the description

This in FIG. 1 illustrated access control system consists of the two essential units 1, 7, wherein the first unit 1 in the motor vehicle and the second unit 7, the access unit, preferably arranged in a key or in an access authorization identification unit for the vehicle or integrated.

The preferably arranged in the motor vehicle unit 1 is a control unit 2, which with at least one LF transmitter 4 with a low transmission frequency, a so-called LF transmitter, which preferably in the range of 125 kHz operates, a microcomputer unit 5, and at least one UHF receiver 6 is equipped. An LF transmitter 4 is in each case preferably arranged in each of the door handles 3 of the motor vehicle or on these.

The access unit 7, in turn, consists of a microcomputer unit 10, at least one LF receiver 9 corresponding to the LF transmitter 4 in the motor vehicle, and at least one UHF transmitter 11, which in turn corresponds to the UHF receiver 6 in the motor vehicle, as well as one not currently to be explained Unit 8, which serves for example for coding the transmission signals. The LF receiver 9 is optimized for the transmission characteristic of the LF transmitter 4 and the UHF receiver 6 to the transmission characteristic de UHF transmitter 11th

Of course, there is a power supply unit in the access unit 7, which supplies the units and electrical components with the necessary energy. This power supply unit is charged at each startup of the motor vehicle via the electrical system, for example via the unit. 8

In addition, the unit 1 is associated with at least one further LF antenna in the interior of the motor vehicle and in the rear and front bumper of the motor vehicle. It has proved to be particularly advantageous to arrange the antennas 4 at seven locations on the vehicle at respectively exposed points.

If the user actuates one of the door handles 3 or another part on the motor vehicle, a wake-up signal is initially sent to the access unit 7 via all LF transmitters 4-one after the other. The wake-up signal is necessary because the access unit 7 when not in use in the idle state, the so-called sleep mode, is located in order to keep the power consumption of the access unit 7 as low as possible. By the wake-up signal, which was received by the LF receiver 9 of the access unit 7, the microcomputer unit 10 is awakened in the access unit 7, which in turn sends the specific identification code to the control unit 2 via the UHF transmitter 11. If this code does not match the code stored in the control unit 2, the door of the vehicle remains locked. Will the identification code but recognized, the lock of the motor vehicle, or the door lock of the motor vehicle, unlocked, and the user can open the vehicle.

Based on FIG. 2 the functional principle of the control unit 2 will be described in more detail. The control unit 2, which via the microcomputer unit. 5 drives the LF transmitter 4, has a driver circuit 12 for operating the LF transmission antennas 13, wherein in FIG. 2 only one antenna is shown for clarity, for low-frequency signals, adapted for the LF transmitter 4, on. The other LF transmission antennas 13 are parallel to in FIG. 2 switched transmitting antenna and are controlled via a multiplexer in succession. At the same time, however, the microcomputer unit 5 also controls the UHF receiver 6, especially since unlocking of the at least one access opening to the motor vehicle takes place only after receipt of the UHF signal and receipt of the authentication. The UHF receiver 6 in turn has a UHF receiving antenna 14 for receiving the UHF signals.

The microcomputer unit 5 and the drive circuit 12 for the LF transmitters 4 and the LF antennas 13 generate a transmission signal which consists of a high frequency carrier in the long wave range with a nominal frequency of 125 kHz. The high frequency carrier is amplitude modulated. The resulting AM signal includes a bit string transmission for transmitting the wake-up signal to the access unit 7. In ideal transmission, a square wave signal is modulated to the amplitude of the radio frequency carrier. To transmit such a signal over long wave requires various measures, in particular with regard to the frequency spectrum, since sidebands as well as harmonic components of the carrier must not exceed certain predetermined values due to the radio admission of the radio determination.

The LF transmitter 4 is further connected to a pulse-width modulator, a pre-filter and a rectifier and control filter circuit located in the feedback region.

In FIG. 3 this is shown in more detail. It has proven advantageous to effectively use an antenna current of 1.41 amps at a range of 1.5 m of the LF signal around the antenna (s) 13. To now this current independent of the power supply 19, the battery voltage of the Motor vehicle, and other disturbing factors to achieve, the modulation signal supplied by the microcomputer unit 5 is changed by the pulse-width modulation unit 15 in the pulse width ranges such that the antenna resonant circuit 13 is supplied via an amplifier circuit just with so much energy or triggered , so that the above-mentioned required antenna current flows. By a broad pulse clock, the energy supply increases and the current increases, with a narrow pulse the energy supply decreases and the current falls. Once the desired current value has been reached, only little energy needs to be supplied to the antenna 13 so that the desired current is maintained. The pulse width modulated signal is fed to the LF transmission antenna 13 via a driver 12 and a double Pi band pass filter (L1, C1, Lant, C2) acting as a transmitter. The current is determined by a band-pass filter via a peak-value rectifier 17. The recovered voltage is proportional to the transmit antenna current. In order to ensure a continuous antenna current, the supplied pulse width modulation width of the signal is incrementally adjusted via the microcomputer unit 5. The incremental adjustment is done in a ratio of 1 to N, where N is the number of modulation increases in progress. It has proved to be advantageous to leave at least four pulses unchanged. As soon as a desired current flow has settled in the antenna during the feedback and return measurement, the incremental control is fixed by the microcomputer unit 5 to the desired value.

The LF transmission antenna 13 is designed as a long wave antenna. The entire transmission device comprises an amplifier device in the form of a central amplifier whose operating voltage is supplied to the power supply 19. At the output of the amplifier, the LF transmission antenna 13 is connected directly. The LF transmission antennas 13 are supplied by a multiplexer or a multiplexer, in FIG. 3 not shown - individually activated and thereby switched on in a certain order and time sequence and thus activated one after the other.

In the ground branch of the multiplexer in FIG. 2 not shown multiplexer is a resistor, in particular a shunt, connected for current measurement, which is part of a current control. The current control comprises a current detector in the form of an overcurrent comparator. This measures the transmission current conducted via the LF transmission antennas 13 and the multiplexer.

During operation of the unit 1, the driver 12, which is driven on the input side with a low-frequency trigger signal, generates on the output side a square-wave voltage, which directly serves for the joint control of the LF transmission antennas 13 via the amplifier output. In this case, the LF transmission antennas 13 are switched in succession to the driver 12 by means of the multiplexer in a predeterminable time sequence. As a result, a particularly low-loss control is achieved. Advantageously, the driver 12 is designed as a push-pull stage.

The transmitted current conducted via the respectively activated LF transmission antenna 13 is measured as described. The overcurrent comparator compares the transmission current with a predetermined reference value. When the reference value is exceeded, a current limitation of the transmission current to the predefinable reference value, which represents the setpoint value of the current regulation, takes place by means of a current regulation. For this purpose, the overcurrent comparator generates on the output side a control or trigger signal, which is supplied to the input of the driver 12 for controlling the output power of the output stage. As a result, the actual value of the transmission current is adjusted to the setpoint.

Each LF transmitting antenna 13 is designed as a transmitting coil Lant, which is tuned by means of a series-connected capacitor C2 to series resonance.

For a simple and energy-saving control, the pulse width modulation drive signal is generated by the pulse width modulator 15 to the driver 12. In order to generate a transmission signal without interfering harmonics, the prefilter 16 is used. With this double-circuit filter can be achieved that even the third harmonic in the first circle is attenuated by up to 45 dB.

The result of the first circle and the second circle is a double-Pi bandpass filter (consisting of a pre-circle 1 with L1, C1 and from a second filter circle 2 from LAnt, C2).

At the input of the rectifier 17 thus creates an AC voltage across the series resistor R. This is an illustration of the current flowing through the LF transmission antenna 13. Via a rectifier 17, this voltage is rectified. The rectified voltage is applied to the output of the rectifier 17 and serves as an input signal of the control filter 18th

A timebase generator generates a 125 kHz periodic rectangular digital signal. Via this signal, a ramp is again generated via the positive edge and transferred to the inverted input of a comparator. The non-inverted input of this comparator receives from the control filter 18 a dependent of the amplitude of the antenna current voltage transmitted.

The nominal value of the antenna current or the field strength is predetermined via the measuring point M. An operational amplifier serves as a control filter. Assuming that the antenna current increases, the AC voltage at the input of the rectifier 17 will increase. Thus, the DC voltage at the output of the rectifier 17 will be proportionally larger. As a result, the inverted input of the operational amplifier in the control filter 18 is given a more positive voltage than the voltage setpoint at the measuring point M at the non-inverted input. This voltage difference is integrated. Thus, the output voltage of the control filter 18 decreases. The output voltage of the control filter 18 is supplied to the pulse width modulator 15. This narrows the positive pulse because the energy at the dual-Pl bandpass filter has become less. This has the consequence that the voltage at the input of the rectifier 17 has become smaller. The difference between the actual value and the setpoint is reduced, so that the correct value is regulated.

Based on the flowchart FIG. 4 the procedure of the regulation will be described in more detail.

Thus, for a restart or an undefined operating state, for example, after a certain transmission time, the actual value U_correction adjusts as quickly as possible to the reference variable, the integration filter is preset to a coarse value U0 during the phase P1. This is done by means of the signal LF_DC_FILT_VAL_UPO (cf. Figure 3 ) until LF_FILT_SETUP_UPO = LOW.

To quit the presetting and to activate the PWM, after the enable, the signals LF_MODULATION_UPO and LF_FILT_SETUP_UPO = HIGH are switched through (FILT_OUT_VAL_HLD_UPO = LOW). i.e. the control behavior in phase P2 becomes active as above.

Thus, in phase P2.1, the carrier signal is transmitted unmodulated (PWM out) and the current through the antenna (I_antenna) is detected and readjusted, as can be seen from the fluctuations in U_correction.

In the subsequent transmission phase P3.1 signal FILT_OUT_VAL_HLD_UPO = HIGH and thus the PWM ratio is held until the data transmission cycle is completed.

From this point on data bits can be transmitted via 100% modulation of the carrier. Since turning on or off the carrier is far above the time constant of the carrier is avoided by the previous measures and a correspondingly sized duration of a data transfer cycle that a beating of U_Korrektur and thus the carrier amplitude takes place.

After the predetermined duration P3 of a data transmission cycle, the control loop is restored

In order to operate the transmission circuit with low loss over a wide range of operating voltages, a PWM signal generator is provided for generating a pulse width modulated signal of predetermined clock frequency, wherein the clock frequency of the PWM (ground) signal is greater, preferably a multiple of the frequency of the digital signal. For the transmission of the digital signal, the digital signal is superimposed on the PWM signal, ie there is a correspondingly lower-frequency amplitude modulation on the PWM fundamental signal. The PWM signal controls semiconductor switches in switching operation, the transmit antenna being connected upstream of the bandpass pre-filter.

In FIG. 5 and 6 a further embodiment is shown, in which a majority of the elements of the invention, in particular the unit 1, have been replaced by a digital control and an electronic digital module. The microcomputer unit 5, consisting of a computer unit 5_1 and the associated peripheral 5_2 accepts the control digitally.

The LF transmitter is shown with 8 transmitting antennas Ant1 to Ant8. The control of the pulse width modulation is performed directly by the microcomputer unit 5 via one of its output ports QPWM. About the microcomputer unit 5 either the pulse width modulation can be controlled digitally, or, with knowledge of the parameters, calculated directly and set directly. Via the output port CLK, a clock signal is output, which provides the timing for the entire peripheral circuitry. at FIG. 5 the antenna current of each of the LF transmission antennas Ant1 to Ant8 is fed via a demultiplexer 21 on a line and compared via a comparator with the nominal antenna current. The result of the comparison is supplied to the microcomputer unit 5 via the input port COMP. The multiplexer 20 and the demultiplexer 21 are controlled in parallel by the microcomputer unit 5. In addition, a bin to 1 of 8 decoder 21_1 is provided. In FIG. 6 the demultiplexer is inexpensively replaced by a respective diode D1 to D8.

The digital control takes place via the input values which are present at the input port COMP. There, the comparison value between the actual antenna current and the preset setpoint is available. Depending on this result, the microcomputer unit 5 controls the driver 12 via the output port QPWM and thus the pulse width.

The already described control can also be bypassed by calculating the respective values in advance.

This can be calculated from the equations as follows:

• wobei PWM_nS der Wert der Dauer der Pulsbreite in nsec,
• Linear_Fakt das Produkt des Quadrats des Antennenstromes mit dem elektrischen Widerstand der Antenne und
• U_Batt die Versorgungsspannung ist.

The rms value of the current of the LF transmitting antenna 13 can be calculated as follows: $$\mathrm{I\_Ant\_eff}:=\left[\mathrm{<figure-callout\; id="2"\; label="sin\; \pi "\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">sin\; </figure-callout>}\left[\left(\frac{\pi }{}\right)\right]\left[\left(\frac{}{2}\right)•\left(\frac{\mathrm{PWM\_nS}}{4000}\right)\right]\right]•\left(\frac{1}{\sqrt{\mathrm{8th}}}\right)•\mathrm{Linear\_Fakt}•\mathrm{u\_Batt}$$

• where PWM_nS is the value of the duration of the pulse width in nsec,
• Linear_Fakt the product of the square of the antenna current with the electrical resistance of the antenna and
• U_Batt is the supply voltage.

Somit kann digital der gewünschte Wert errechnet und direkt eingestellt werden.If, on the other hand, one knows the rms value of the antenna current, or if one wants to set this, then the pulse width in nsec is calculated as follows: $$\mathrm{PWM\_nS}:=\left[\mathrm{asin}\left[\frac{\mathrm{I\_Ant\_eff}•\left(\sqrt{\mathrm{8th}}\right)}{\left(\mathrm{Linear\_Fakt}•\mathrm{u\_Batt}\right)}\right]\right]•\left[\frac{1}{\left(\mathrm{\pi }•0.5\right)}\right]•4000$$

Thus, the desired value can be calculated digitally and set directly.

In FIG. 7 in this figure, the structure of the invention is shown using an embodiment with three antennas. The microcontroller 5_1 outputs the corresponding signal to the antennas Ant_01 to Ant_03, wherein the signals are supplied via the driver 12 to the multiplexer 20, which is designed as a shunt multiplexer. By this arrangement and wiring and the structure according to FIG. 7 can be obtained in a particularly simple manner, the DC voltage. This voltage represents an image of the current in the antennas or the antenna and thus enables ideal control of the antenna and optimization of the antenna current. By the in FIG. 7 selected structure can be arranged in an advantageous manner, the resonance capacitors C_Ant_01 to C_Ant_03 and the capacitors C1_VK to C3_VK on a board, only the antennas are to be arranged in an exposed position. This also makes it possible to obtain the voltage U DC, which is an image of the antenna current.

It is due to the build up FIG. 7 no expensive electronic design and effort to drive to gain the voltage U DC. If one now chooses the capacitors C1_VK and C_Ant_01 such that they are the same, the result for the voltage across these capacitors is a phase rotation of 180 ° degrees. This has the advantage that harmonics are avoided.

Based on Fig. 8 again, the particularly preferred embodiment of the transmitting unit consisting of two coupled LC bandpass filters and the interposed shunt multiplexer 20 will be explained in more detail.

The first bandpass forms the pre-filter from the first coil L1 and a first capacitor group. It is Ant_01 active and the other two antennas Ant_02 and Ant_03 inactive.

Since the multiplexer 20 is configured as a shunt multiplexer, in each case the switching node between the first and second band pass for the respectively inactive antennas Ant_02 and Ant_03 is switched to ground potential via a controllable transistor. In this case, preferably CMOS semiconductors are used as the transistor, which enable a very fast switching of the transmitting antennas, in particular switching times of less than 400 μS. In contrast to mechanical switching relays, there is an additional advantage in the almost unlimited life and reliability of the multiplexer systems, since only semiconductors are used.

By switching the respective circuit nodes of the inactive antennas Ant_02, Ant_03 to ground potential by means of the switches S2, S3, the capacitors C2_VK, C3_VK of these inactive antennas are alternately connected in parallel to the capacitor C1_VK of the active antenna Ant_01 and thus results in this parallel connection of the capacitors C1 VK, C2 VK, C3 VK the first capacitor group. The directly connected in series capacitor C1_VK can therefore be significantly smaller dimensions, which leads to significant cost savings, especially in systems with a larger number of separate antennas.

The second bandpass consists of the LF antenna Ant_01 as inductance and a second capacitor group of at least one capacitor, here C Ant 01.

The first bandpass is thus formed by the coil L1 and the coupling capacitors C2_VK, C3_VK of the currently unused antennas Ant_02, Ant_03. These capacitors are grounded through the CMOS multiplexer switches.

$$\begin{array}{l}\mathrm{Impedanz\; Auswertung\; der\; Inaktiven\; Antenne\; Nr}.3\mathrm{Bezeichnung},\mathrm{Z\_Ant\_}03\mathrm{\_Ausgeschalet}:\\ \mathrm{Z\_Ant\_}03\mathrm{\_Ausgeschaltet}:=\sqrt{\mathrm{RS\_Ant\_}{03}^2+{\left[\mathrm{L\_Ant\_}03•2•\mathrm{\pi Freq}-\left[\frac{1}{\left(\mathrm{C\_Ant\_}03\right)•2•\pi •\mathrm{Freq}}\right]\right]}^2}\end{array}$$

The non-active antennas consist of respectively associated Rs_Ant_xx, L_Ant_xx and C_Ant_xx. The impedance for the inactive antennas is shown in Equation 1 b and 1 c. $$\begin{array}{l}\mathrm{Impedance\; Evaluation\; of\; the\; Inactive\; Antenna\; No}.2\mathrm{description}.\mathrm{Z\_A}\ddot{\mathrm{n}}\mathrm{t\_}02\mathrm{\_Ausgeschal}\dot{\mathrm{e}}\mathrm{t}:\\ \mathrm{Z\_Ant\_}02\mathrm{\_Switched\; off}:=\sqrt{\mathrm{<figure-callout\; id="02"\; label="RS\_Ant\_"\; filenames="imgf0007.png"\; state="\{\{state\}\}">RS\_Ant\_</figure-callout>}{02}^2+{\left[\mathrm{<figure-callout\; id="02"\; label="L\_Ant\_"\; filenames="imgf0007.png"\; state="\{\{state\}\}">L\_Ant\_</figure-callout>}02•2•\mathrm{\pi Freq}-\left[\frac{1}{\left(\mathrm{<figure-callout\; id="02"\; label="C\_Ant\_"\; filenames="imgf0007.png"\; state="\{\{state\}\}">C\_Ant\_</figure-callout>}02\right)•2•\pi •\mathrm{<figure-callout\; id="2"\; label="Freq"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Freq</figure-callout>}}\right]\right]}^2}\end{array}$$

$$\begin{array}{l}\mathrm{Impedance\; Evaluation\; of\; the\; Inactive\; Antenna\; No}.3\mathrm{description}.\mathrm{Z\_Ant\_}03\mathrm{\_Ausgeschalet}:\\ \mathrm{Z\_Ant\_}03\mathrm{\_Switched\; off}:=\sqrt{\mathrm{RS\_Ant\_}{03}^2+{\left[\mathrm{L\_Ant\_}03•2•\mathrm{\pi Freq}-\left[\frac{1}{\left(\mathrm{C\_Ant\_}03\right)•2•\pi •\mathrm{<figure-callout\; id="2"\; label="Freq"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Freq</figure-callout>}}\right]\right]}^2}\end{array}$$

The second bandpass is the active antenna (in the Fig. 8 Ant_01). This antenna is tuned to the transmission frequency, the impedance being determined by RS_Ant_01, C_Ant_01 and C1_VK. The impedance calculation of this active antenna is shown under 1 a. $$\begin{array}{l}\mathrm{Impedance\; Evaluation\; of\; the\; active\; antenna\; No}.1\mathrm{description}.\mathbf{<figure-callout\; id="01"\; label="Z\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">Z\_Ant\_</figure-callout>}\mathbf{<figure-callout\; id="01"\; label="01\; \_Active\; Z\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">01\; </figure-callout>}\mathbf{\_Active}& \\ \mathrm{Z\_Ant\_}01\mathrm{\_Active}:=\sqrt{\mathrm{<figure-callout\; id="01"\; label="RS\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">RS\_Ant\_</figure-callout>}{01}^2+{\left[\mathrm{<figure-callout\; id="01"\; label="L\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">L\_Ant\_</figure-callout>}01•2•\mathrm{\pi Freq}-\left[\frac{1}{\left[\frac{\left(\mathrm{C}1\mathrm{\_Vk}•\mathrm{C\_Ant\_}01\right)}{\left(\mathrm{C}1\mathrm{\_Vk}+\mathrm{<figure-callout\; id="01"\; label="C\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">C\_Ant\_</figure-callout>}01\right)}\right]•2•\pi •\mathrm{<figure-callout\; id="2"\; label="Freq"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Freq</figure-callout>}}\right]\right]}^2}\end{array}$$

Since the semiconductor multiplexers in the switched state not the theoretical zero ohms, but some milli ohms have, created by the apparent current through C2_VK and C3_VK at the multiplexers, a residual voltage of several mV. Since the two tuning capacitors are connected in parallel by the multiplexers in the two non-active antennas, but doubles the capacity of the tuning capacitor of these inactive antennas.

As a result, the two inactive antennas are strongly detuned with respect to the transmission frequency, thus preventing crosstalk by increasing the series impedance at the transmission frequency (see equation 1 b or 1 c above).

The equation for the crosstalk suppression can be found under 1e. $$\begin{array}{l}\mathrm{U\_}\ddot{\mathrm{U}}\mathrm{review\; suppression}\ddot{\mathrm{u}}\mathrm{Imedance\; uncertainty\; of\; the\; non-active\; antenna}\\ \mathrm{Full}\ddot{\mathrm{a}}\mathrm{if\; equation}\mathrm{:}\mathrm{C}\mathrm{1}\mathrm{\_VK}\mathrm{=}\mathrm{C}\mathrm{2}\mathrm{\_VK}\mathrm{=}\mathrm{C}\mathrm{3}\mathrm{\_VK\; and\; <figure-callout\; id="01"\; label="C\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">C\_Ant\_</figure-callout>}\mathrm{01}\mathrm{=}\mathrm{C\_Ant\_}\mathrm{02}\mathrm{=}\mathrm{C\_Ant\_}\mathrm{03}\\ \mathrm{U\_Uebersprechung\_Unterdruekung}\mathrm{:}\\ \mathrm{U\_Uebersprechung\_Unterdrueckung}\mathrm{=}\sqrt{\frac{\left[\mathrm{<figure-callout\; id="01"\; label="RS\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">RS\_Ant\_</figure-callout>}{\mathrm{01}}^{\mathrm{2}}\mathrm{+}{\left[\mathrm{<figure-callout\; id="01"\; label="L\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">L\_Ant\_</figure-callout>}\mathrm{01}\mathrm{•}\mathrm{2}\mathrm{•}\mathit{\pi }\mathrm{Freq}\mathrm{-}\left[\frac{\mathrm{1}}{\left(\mathrm{C}\mathrm{1}\mathrm{\_Vk}\right)\mathrm{•}\mathrm{2}\mathrm{•}\pi \mathrm{•}\mathrm{<figure-callout\; id="2"\; label="Freq"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Freq</figure-callout>}}\right]\right]}^{\mathrm{2}}\right]}{\mathrm{<figure-callout\; id="01"\; label="RS\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">RS\_Ant\_</figure-callout>}{\mathrm{01}}^{\mathrm{2}}\mathrm{+}\left[\mathrm{<figure-callout\; id="01"\; label="L\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">L\_Ant\_</figure-callout>}\mathrm{01}\mathrm{•}\mathrm{2}\mathrm{•}\mathit{\pi }\mathrm{Freq}\mathrm{-}\left[\frac{\mathrm{1}}{\left[\frac{\left(\mathrm{C}\mathrm{1}\mathrm{\_Vk}\mathrm{•}\mathrm{C\_Ant\_}\mathrm{01}\right)}{\left(\mathrm{C}\mathrm{1}\mathrm{\_Vk}\mathrm{+}\mathrm{<figure-callout\; id="01"\; label="C\_Ant\_"\; filenames="imgf0005.png,imgf0006.png"\; state="\{\{state\}\}">C\_Ant\_</figure-callout>}\mathrm{01}\right)}\right]\mathrm{•}\mathrm{2}\mathrm{•}\pi \mathrm{•}\mathrm{Freq}}\right]\right]}}\end{array}$$

$$\begin{array}{c}\mathrm{I\_Uebersprechung\_Inaktiv\_Ant\_}03\mathrm{:}\mathrm{=}\frac{\mathrm{U\_Uebersprechung}}{\sqrt{\left[\mathrm{RS\_Ant\_}{\mathrm{03}}^{\mathrm{2}}\mathrm{+}{\left[\mathrm{L\_Ant\_}03\mathrm{•}\mathrm{2}\mathrm{•}\mathit{\pi }\mathrm{Freq}\mathrm{-}\left[\frac{\mathrm{1}}{\left(\mathrm{C}\mathrm{3}\mathrm{\_Vk}\right)\mathrm{•}\mathrm{2}\mathrm{•}\pi \mathrm{•}\mathrm{Freq}}\right]\right]}^{\mathrm{2}}\right]}}\end{array}$$

The actual crosstalk current for the inactive antennas can be found under 1f and 1g. $$\begin{array}{l}\mathrm{Evaluation\; equation\; current}\ddot{\mathrm{u}}\mathrm{Termination\; for\; the\; <figure-callout\; id="2"\; label="Inative\; Antenna"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Inative\; Antenna</figure-callout>}\mathrm{2}\mathrm{I\_Uebersprchung\_Inaktiv\_Ant\_}\mathrm{02}\mathrm{:}\\ \mathrm{U\_Uebersprechung}\mathrm{=}\mathrm{30}\mathrm{•}{\mathrm{10}}^{\mathrm{-}\mathrm{3}}\mathbf{U\_Uebersprechung}\mathbf{:}\mathbf{Voltage\; at\; the\; switched\; multiplexer}\\ \mathrm{I\_Uebersprechung\_Inaktiv\_Ant\_}\mathrm{02}\mathrm{:}\mathrm{=}\frac{\mathrm{<figure-callout\; id="02"\; label="U\_Uebersprechung\; RS\_Ant\_"\; filenames="imgf0007.png"\; state="\{\{state\}\}">U\_Uebersprechung\; </figure-callout>}}{\sqrt{\left[\mathrm{RS\_Ant\_}\right]}}\end{array}$$

$$\begin{array}{c}\mathrm{I\_Uebersprechung\_Inaktiv\_Ant\_}03\mathrm{:}\mathrm{=}\frac{\mathrm{U\_Uebersprechung}}{\sqrt{\left[\mathrm{RS\_Ant\_}{\mathrm{03}}^{\mathrm{2}}\mathrm{+}{\left[\mathrm{L\_Ant\_}03\mathrm{•}\mathrm{2}\mathrm{•}\mathit{\pi }\mathrm{Freq}\mathrm{-}\left[\frac{\mathrm{1}}{\left(\mathrm{C}\mathrm{3}\mathrm{\_Vk}\right)\mathrm{•}\mathrm{2}\mathrm{•}\pi \mathrm{•}\mathrm{<figure-callout\; id="2"\; label="Freq"\; filenames="imgf0001.png,imgf0007.png"\; state="\{\{state\}\}">Freq</figure-callout>}}\right]\right]}^{\mathrm{2}}\right]}}\end{array}$$

Practical measurements have shown that crosstalk is on the order of less than 0.05% (-66dB), i. a transmission current in the 2000mA active antenna produces a crosstalk current of less than 1 mA in the non-active antennas.

When changing the active antenna to Ant_02 or Ant_03, the calculation principle remains the same.

LIST OF REFERENCE NUMBERS

1

unit

2

control unit

3

Door handle (e)

4

LF-transmitters

5

Microcomputer unit

6

UHF receiver

7

access unit

8th

unit

9

LF receiver

10

Microcomputer unit

11

UHF Transmitter

12

driver

13

LF transmission antenna

14

UHF receiving antenna

15

Pulse width modulator

16

prefilter

17

rectifier

18

rule filter

19

power supply

20

multiplexer

21

demultiplexer

22

Mass (reference)

5_1

computer unit

5_2

periphery

21 _1

Am to 1 of 8 decoders

RM1 to RM8

resistance

D1 to D8

diode

Ant1 to Ant 8

LF transmission antennae

Ans_0 to Ant_03

LF transmission antennae

C1_VK to C3_VK

capacitors

C_Ant_01 to C_Ant_03

capacitors

U DC

tension

CLK

Clock

COMP, COMP 1

input port

QPWM

output port

Claims (10)

1. Access control device for a motor vehicle, consisting of at least one transmitting unit (4) for the transmission of low-frequency long-wave signals and a plurality of associated LF antennas (13) that are arranged in exposed places in the vehicle, said transmitting unit (4) being arranged in the motor vehicle, wherein

   - the transmitting unit (4) has two coupled LC band-pass filters, wherein

   - the first band-pass filter, as a preliminary filter, consists of a first coil (L1) and a first capacitor group consisting of at least one capacitor (C1 VK, C2 VK, C3 VK,...), and

   - the second band-pass filter consists of the LF antenna (Lant), as an inductor, and a second capacitor group consisting of at least one capacitor (C2, C Ant 01, C Ant 02,...), and

   - the first band-pass filter has a coil (L1) common to all antennas and has a separate capacitor (C1 VK, C2 VK,...) for each antenna.
2. Access control device according to claim 1, characterized in that a multiplexer (20) is provided via which the antennas (13) are connected to the transmitting unit (4) one after the other by means of the multiplex method, wherein the multiplexer (20) is arranged between the first band-pass filter and the second band-pass filter.
3. Access control device according to claim 1, characterized in that the first band-pass filter has a coil (L1) common to all antennas and has a separate capacitor (C1 VK, C2 VK, C3 VK) for each antenna and that, by the switching (S2, S3) of the circuit node of the inactive antennas (Ant_02, Ant_03) to ground potential, the capacitors (C2 VK, C3 VK) of these inactive antennas are connected in a parallel alternating-voltage connection with the capacitor (C1 VK) of the active antenna (and_01) and thus this parallel connection of the capacitors (C1 VK, C2 VK, C3 VK) makes the first capacitor group.
4. Access control device according to one or several of the preceding claims, characterized in that the transmitting unit (4) operates at a carrier frequency of 125 kHz.
5. Access control device according to one or several of the preceding claims, characterized in that the antenna current in the antennas (13) is controlled by means of a pulse-width modulation.
6. Access control device for a motor vehicle, consisting of at least one transmitting unit (4) for the transmission of low-frequency long-wave signals and a plurality of associated LF antennas (13) that are arranged in exposed places in the vehicle, said transmitting unit (4) being arranged in the motor vehicle, wherein the transmitting unit (4) has two coupled LC band-pass filters, wherein

   - the first band-pass filter, as a preliminary filter, consists of a first coil (L1) and a first capacitor group consisting of at least one capacitor (C1 VK, C2 VK, C3 VK,...), and

   - the second band-pass filter consists of the LF antenna (Lant), as an inductor, and a second capacitor group consisting of at least one capacitor (C2, C Ant 01, C Ant 02,...), wherein the antenna current in the antennas (13) is controlled by means of a pulse-width modulation and a microcomputer unit (5) controls the pulse durations of the pulse-duration modulator (15) in dependence on the antenna current by increasing the pulse durations when the current is too low and decreasing the pulse durations when the antenna current exceeds a desired value.
7. Access control device according to claim 6, characterized in that the microcomputer unit (5) changes the pulse durations incrementally.
8. Access control device according to any one of the preceding claims, characterized in that the microcomputer unit (5) determines the antenna current by means of a band-pass filter.
9. Access control device according to any one of claims 6 to 8, characterized in that the microcomputer unit (5) calculates the root mean square of the current in the LF transmitting antenna (13) according to $$\mathit{I\_Ant\_eff}:=\left[\sin \left[\left(\frac{\pi }{2}\right)•\left(\frac{\mathit{PWM\_nS}}{4000}\right)\right]\right]•\left(\frac{1}{\sqrt{8}}\right)•\mathit{Linear\_Fakt}•\mathit{U\_Batt}$$

   

   wherein PWM_nS is the value of the pulse duration in nsec,

   Linear_Fakt is the product of the square of the antenna current with the electrical resistance of the antenna,

   U_Batt is the supply voltage, and

   I_Ant_eff is the root mean square of the antenna current.
10. Access control device according to any one of claims 6 to 8, characterized in that the microcomputer unit (5) calculates the pulse durations of the pulse-width modulator (15) in nsec, if the desired root mean square of the antenna current is known, according to $$\mathrm{PWM\_nS}:=\left[\mathrm{asin}\left[\frac{\mathit{I\_Ant\_eff}•\left(\sqrt{8}\right)}{\left(\mathit{Linear\_Fakt}•\mathit{U\_Batt}\right)}\right]\right]•\left[\frac{1}{\left(\pi •0.5\right)}\right]•4000$$

    

    wherein PWM_nS is the value of the pulse duration in nsec,

    Linear_Fakt is the product of the square of the antenna current with the electrical resistance of the antenna,

    U_Batt is the supply voltage, and

    I_Ant_eff is the root mean square of the antenna current.

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