WO2004097749A1

WO2004097749A1 - Transmitting device of an access system provided with a plurality of longwave antennas

Info

Publication number: WO2004097749A1
Application number: PCT/DE2004/000774
Authority: WO
Inventors: Uli Joos; Heinrich Haas
Original assignee: Conti Temic Microelectronic Gmbh
Priority date: 2003-04-25
Filing date: 2004-04-14
Publication date: 2004-11-11

Abstract

In order to operate a transmitting device (1) of an access system, especially a motor vehicle, comprising a plurality of longwave antennas (LF1 .n), said antennas are jointly controlled by means of a central power amplifier (2) and are individually activated by means of a multiplexer device (4). The transmitting device (1) comprises a multiplexer device (4) which is used to individually activate a longwave antenna (LFn) and an amplifier device (2) whereon longwave antennas (LF1...n) are jointly connected to the outlet (LFout) thereof. The multiplexer device (4) is arranged on the mass side of the longwave antennas (LF1 n) facing away from the power amplifier (2). As a result, micro electronic switching equipment with mass related control signals can be controlled in a simple manner and the speed of switching can be increased significantly.

Description

Transmission system of an access system with a number of

Langwe11enantennen

The invention relates to a transmission device with a number of long-wave antennas of an access system of a vehicle, in particular a motor vehicle.

Such an access system, which is often also referred to as a passive entry system, is usually part of a superordinate keyless remote control system which, in addition to automatically unlocking the door of a vehicle, also controls its engine starting system and / or an immobilizer. Such a system comprises, for example, a transmitting or transmitting and receiving device (transponder) integrated in the vehicle key and carried by a person authorized for the vehicle, and a vehicle-based transmitting and receiving device (transceiver).

To determine access authorization to the vehicle, an exchange of security codes or access data based on high-frequency (HF) and / or low-frequency (LF) - and thus short-wave or long-wave - carrier signals takes place between the portable transponder and the vehicle-based transceiver. The location of the transponder is detected using several long-wave antennas arranged in or on the vehicle.

According to a passive remote control system known from DE 101 08 578 AI, the long-wave antennas can be activated sequentially by a vehicle-based control system. In the known system, the transponder responds to such a long-wave-based interrogation signal with a security-coded HF signal to identify the access authorization. If necessary, a vehicle-based control system unlocks the vehicle door so that it can be opened by manually operating the door handle. Through the sequential activation of the long-wave antennas, the energy to be supplied by the vehicle battery for controlling the long-wave antennas can be kept low. However, according to a keyless access system known from DE 198 35 155 AI, the transmit antennas are usually individually controlled by means of separate drivers, which leads to a considerable amount of circuitry, particularly when high demands are placed on a driver output stage.

EP 0741 221 B1 shows a receiving device with a multiplexer for selective reception via several antennas. In addition, for example from DE 19752149 AI transmitting and receiving device (transceiver) are known with an amplifier device, at the output of which several long-wave antennas can optionally be connected via a multiplexer. The multiplexer is formed by switching means which sequentially connect the amplifier device to one of the long-wave antennas. DE 19752149 AI relays are provided as switching means, which, at least for some applications, have an excessive delay time and the costs and the required installation space are disadvantageous.

The invention is therefore based on the object of specifying a particularly suitable transmission device, in particular for the door control of a motor vehicle.

The stated object is achieved according to the invention by the features of claim 1. Advantageous further developments of the

Procedures are the subject of the subclaims referring back to this.

The advantages achieved with the invention consist in particular in that a direct transmission of all long-wave transmission antennas together and their individual activation by means of a multiplexer device result in a reliable transmission drive is achieved with a particularly space-saving or space-saving and thus effective circuit or component arrangement. The direct control of the long-wave transmit antennas achieves on the one hand particularly reliable location detection and on the other hand particularly reliable energy transmission into a transponder, in particular into an intelligent vehicle key.

By arranging the multiplexer device on the ground side of the long-wave antennas facing away from the amplifier device, a significantly faster and at the same time simple transmission device can be created by simply generating control signals with reference to ground and electronic switching means. MOSFET switching transistors are preferably used, since they have an extremely low power loss and enable particularly fast control, in particular also phase modulation.

The execution of the multiplexer in SMART-MOSFET technology also leads to a resistance of the arrangement against short circuits of the antenna line.

Through the use of a power amplifier with a limited rise time and optimized saturation behavior, a particularly low-loss control with simultaneous limitation of the electromagnetic radiation to a permissible value is achieved without additional filter measures at the amplifier output.

Furthermore, the direct control of the long-wave transmission antennas formed from transmission coils in series resonance by means of a trapezoidal or rectangular voltage means that the circuitry and thus the cost are particularly low, especially since several transmitters can be controlled from a central control device and the transmission antennas can be connected directly to the amplifier output. In addition, by regulating the sinusoidal transmission current with a limitation of its peak value by means of a rapid current cut-off and synchronization by pulse width modulation at the control input of the amplifier, its output power is stably adjusted to a particularly high power value. As a result, the output stage of the amplifier can be operated in a saturated manner, so that only a low power loss occurs in its driver or driver stage.

An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. In it show:

1 shows schematically in a block diagram the circuit of a transmission device with a single amplifier and a number of transmission antennas,

2 shows a comparatively detailed circuit of the block diagram according to FIG. 1,

3 shows a signal diagram to illustrate the functioning of a current control of the transmitting device, and

4 shows a circuit principle of the amplifier of the transmission device.

Corresponding parts are provided with the same reference symbols in all figures.

1 shows schematically in a block diagram a transmission device 1 which is, for example, part of a door control of an access system of a motor vehicle. The transmitting device 1 comprises an amplifier device in the form of a central amplifier 2, the operating voltage U _B of which is supplied by the vehicle battery (not shown). A number of long-wave transmit antennas LFι ... _n, hereinafter referred to as antennas, are connected directly and jointly to the output LF _ou t of the amplifier 2. The antennas LFι ... _n are individually activated by a multiplexer device or a multiplexer 4 and thereby in a specific order and time sequence activated and thus activated one after the other. For this purpose, the multiplexer device 4 connected downstream of the antennas LFι ... _{n is} connected to ground GND.

A shunt 8 for current measurement, which is part of a current control 10, is connected in the ground branch 6 of the multiplexer 4. The current control 10 comprises a current detector 12 in the form of an overcurrent comparator, one input - here the (+) input - a reference signal I _Ref and the other input - here the (-) input - one via the antennas LFι ... _n and the multiplexer 4 guided transmission current I _{LF is} supplied.

On the output side, the current detector 12 is connected to an input Ei of a control logic 14, at the second input E of which a low-frequency clock signal LF _c i _{k is carried} at a frequency of expediently 125 kHz. On the output side, the control logic 14 is connected to a control input P _{n of} the amplifier 2.

When the transmitting device 1 is in operation, the amplifier 2, which is driven on the input side with the low-frequency trigger signal LF _CLK, generates a trapezoidal or rectangular voltage on the output side, which voltage is used directly via the amplifier output LF _out to jointly control the antennas LFι ... _n . The antennas LFι ... _{n are} connected to the amplifier 2 in succession in a predefinable time sequence by means of the multiplexer 4. This results in a particularly low-loss control.

The transmission current I _L F conducted via the respectively activated antenna LF _n is detected on the base side of the multiplexer 4 by means of the shunt 8 and is fed to the (-) input of the current detector 12 referred to below as an overcurrent comparator. The overcurrent comparator 12 compares the transmission current I _LF with the reference value I _Ref . If the reference value I _Rβf is _exceeded , the current control 10 is used to limit the current of the transmission current I _LF to the predefinable reference value I _Ref , which represents the setpoint of the current control 10. For this purpose, the overcurrent comparator 12 generates a control or trigger signal S _τ on the output side, which is fed via the control logic 14 to the input P _{n of} the amplifier 2 for controlling the output power of its output stage. As a result, the actual value of the transmission current I _{LF is} adapted to the target value I _Ref with a good approximation, with good quality of the transmission device 1 acting as the transmission circuit.

As can be seen from the comparatively detailed circuit according to FIG. 2, each long-wave transmission antenna LF _{n is designed} as a transmission coil L _n , which is tuned for series resonance by means of a capacitor C _{n connected} in series therewith. The multiplexer 4, which is directly connected to the antennas LF _n directly driven by the amplifier 2 by means of a trapezoidal or rectangular voltage, is expediently designed in MOSFET technology.

For this purpose, the multiplexer 4 in each antenna branch AZi to AZ _n comprises a power transistor (MOSFET) which is controlled on the gate side by means of a corresponding control signal M _c for activating the respective antenna LF _n . Accordingly, only each controlled power transistor performs the multiplexer 4 to the (entire) transmitting current I _LF as a result of actuation of the in the corresponding antenna branch AZ _n arranged LF antenna _n by means of the trapezoidal generated by the amplifier 2 or the rectangular voltage. The implementation of the multiplexer 4 in SMART-MOSFET technology advantageously leads to a resistance of the arrangement against short-circuits of the antenna line thanks to integrated current and voltage monitoring. With conventional MOSFETs particularly fast controls, for example for a fast phase modulation, can be achieved. In principle, several antennas can also be operated simultaneously, in which case only the total current would be regulated. The control logic 14 is constructed according to FIG. 2 from a logic AND gate or gate 16 and a switching mechanism 18, hereinafter referred to as a PWM latch. This is expediently designed as an edge-controlled D flip-flop (latch flip-flop) which, according to the signal diagram in FIG. 3, triggers on the positive edge of the clock signal LF _clk . This PWM latch thus serves for the synchronization of the control or regulating signal S _τ with the clock LF _c ι _k and for pulse width modulation (PWM) of the input signal Pι _{n of} the amplifier 2. This results in the regulation of the sinusoidal transmission current I _LF - and thus the regulation of the transmission power - through a peak value limitation of the transmission current I _F by means of a fast current cut-off and a pulse width modulation synchronization.

For this purpose, the control signal S _τ supplied by the overcurrent comparator 12, which is formed by comparing the transmission current I _LF measured in the ground or ground branch 6 of the multiplexer 4 with the setpoint or reference value I _R8f , used to control the PWM latch 18.

As illustrated in FIG. 3, the overcurrent comparator 12 does not trigger and the PWM latch 18 remains set for the period designated ti (Qa _tc = high) as long as the reference value R _{Ref specifying} the maximum value of the transmission current I _{LF is} not exceeded , The input clock LF _c i _k (50% duty cycle) is thus present at the input Pι _{n of} the amplifier 2 and its output stage controls the full output power.

Exceeded, however, the transmitter current I _LF predetermined by the reference value I _ref maximum or peak value, so the overcurrent compensator switch 12 and the control signal generated by S _τ is - in the illustrated time period t ₂ - the PWM latch 18 back (Qatc = low ). As a result of the linkage with the clock signal LF _c ι _k serving as the input clock by means of the AND gate 16, the pulse width at the input Pι _n of Amplifier 2 modulated such that the maximum or peak value of the transmission current I _LF corresponds at least approximately to the reference or setpoint I _Ref . This short-circuit protection means that the transmitting device 1 can be used not only in a door control system, but rather also in a central control system which, in addition to the access system, also includes an engine start control and / or an immobilizer of the vehicle.

The amplifier 2 can be deactivated via an ENABLE input E _βb ι, so that the power consumption in the idle state of the _{transmitting device} 1 is negligible.

According to the illustration in FIG. 4, the amplifier 2 is designed as a source follower and thus as a power amplifier with MOS field-effect transistors (MOSFETs) in a drain circuit. This design of the amplifier 2 and thus the common driver output stage for all transmission antennas LFι ... _n limits the rise time of the rectangular or trapezoidal output voltage at the output LF _{out of} the amplifier 2 or its output stage. This keeps the electromagnetic radiation and thus the electromagnetic compatibility (EMC) particularly low. A further limitation of the electromagnetic radiation or EMC is expediently achieved by a suitable edge shaping of the preferably rectangular output voltage (LF _out ).

For this purpose, the input signal PWMi _n supplied by the control logic 14 of the control device 10 to the input Pi _{n of} the power amplifier 2 is converted into reference currents via a buffar B1 and two base circuits formed by the resistor R2 and the transistor T1 as well as the resistor R3 and the transistor T2. These are mirrored with current mirrors SS1, SS2 respectively at the highest and lowest potential (+ VH = U _B + 5V), (- VH = -5V). The current mirrors connected to the respective voltage supplies + VH and -VH of the amplifier 2 SSI and SS2 are current-controlled current sources which transfer the current impressed on the input side into the capacitor C1.

The (mirrored) reference currents charge the capacitor Cl via the cascode stages formed by the diode Dl and the transistor T3 or the diode D2 and the transistor T4, the potential at the capacitor Cl alternating between approximately the potentials + VH and -VH. The rate of rise of the charging voltage across the capacitor C1 is set with the resistors R2, R3 and with the capacity of the capacitor C1. With a network formed from the transistors T5, T6 and the diodes D3, D4 and the resistors R4, R5, R6, the voltage ramp at the capacitor C1 can additionally be slowed down in the range of the supply voltages + VH and -VH (edge shaping).

The illustrated interconnection of transistors T7 to T10 with resistors R7 to RIO forms a current amplifier which decouples the voltage across capacitor C1 and drives an output stage driver T15, T16. For this purpose, the transistors TU and T12 and the resistor R11 form a switchable current source, the output current of which is mirrored at the highest or lowest potential + VH or -VH with the two current mirrors SS3 and SS4 and via which through the diode D5 and the transistor T13 or the diode D6 and the transistor T14 formed cascode stage is coupled out. The current mirrors with cascode (SS1, D2, T4; SS2, D1, T3; SS3, D6, T14; SS4, D5, T13) offer the advantage of high output resistances and large amplifications in the respective driver stages T7 to T10 and T15, T16 of the amplifier device second

The decoupled symmetrical current flows through a network formed by the diodes D7, D8 and the resistors R12, R13 and thus generates an offset voltage for driving the control inputs of the output stage of the amplifier 2. The output stage is in through MOS field-effect transistors T17 and T18 Source follower configuration formed so that the offset voltage drives their gates. Due to the constant current supply to this network D7, R12; D8, R13, the gate voltage offset remains constant over the entire range of control, only the center voltage at the resistors R12 and R13 having to be controlled by the current amplifier T7 to T10, R7 to RIO.

If the resistors R12 and R13 are replaced by a network with temperature-dependent resistors, in particular by NTC resistors with a negative temperature coefficient, the offset can be influenced in such a way that the cross current in the output or output stage formed by the MOSFETs T17 and T18 over a wide temperature range remains almost constant. Alternatively, this property can also be achieved by controlling the respective reference current as a function of the temperature. For this purpose, either the resistor R11 can be replaced by a temperature-dependent resistor or the base voltage at the transistor TU can be modulated by an external control device.

The offset voltage directly controls the respective gate of the output stage transistors T17 and T18 via the emitter follower formed by the transistors T15 and T16. A network formed by the resistor R14 and the capacitor C2 ensures that the gates of the output transistors T17 and T18 can be moved dynamically in both directions. Instead of this network R14, C2, alternatively, complementary followers can also be used to control the final stage transistors T17, T18. A clamping network formed by the diodes D9 to D12 ensures that, in the event of a short circuit at the amplifier output LFout, the maximum permissible gate-source voltage of the output transistors T17, T18 is not exceeded and is therefore not destroyed. The currents in the output paths of the output stage transistors T17 and T18 are measured via operational amplifiers OPV1 and OPV2 connected to resistors R15 and R16 and monitored for diagnostic purposes. The output stage formed by the two output transistors T17 and T18 can be thermally destroyed in the event of a short circuit or an overload at the output LF _out and before an excessive cross-current in the output stage T17, by a suitable combination of the current values detected in this case with the transmission current I _LF , T18 are protected.

The 5V ENABLE input used to deactivate the power amplifier 2 switches off the current sources of the base circuit comprising the transistor T1 and of the network comprising the transistor T1 and of the switchable current source having the transistor T1. In the deactivated state of the power amplifier 2 (ENABLE = low) these current sources are deactivated and the output stage transistors T17, T18 are thus switched to high resistance.

By the current measurement in the initial or final stage transistors T17 and T18 generated diagnostic signals hsai _a g or LS _d i _a g a control device (not shown) are supplied to the t power amplifier 2 at short circuit or overload on the output LF _ou and / or against protects increased cross flow.

By using such a power amplifier 2 with a limited rise time and particularly favorable saturation behavior, the electromagnetic radiation is limited to reliable values without additional filter measures at the output LF _out . In this case, the slew rate of the rectangular or trapezoidal output voltage of the power amplifier 2 can be largely reduced by avoiding an impairment of the properties of the transmission current control 10 by symmetrical design of the switching edges. With this active influence on the switching edges, the e- minimized electromagnetic radiation of the transmission amplifier 1 and thus the transmission device 1.

Overall, the amplifier properties are particularly favorable, while avoiding an ineffective increase in the total expenditure, by using only a single power amplifier 2 for jointly controlling the multiple long-wave transmit antennas LFι ... _n . In particular, by actively influencing the switching edges, that is to say the rise time limitation and the edge shaping of the rectangular or trapezoidal output voltage of the power amplifier 2, the transmitter device 1 can be operated in a motor vehicle without additional filter expenditure. The electromagnetic radiation is kept particularly low.

Compared to a sinusoidal control of a transmission device in the long-wave range, the transmission coil of which is operated in parallel or series resonance, the control method described is by means of rectangular or trapezoidal output voltage with regard to the resulting low circuit complexity and the low power loss in the power output stage T17, T18 of the power amplifier 2 particularly advantageous.

Complex regulation of the transmission power and the use of a power output stage for each transmission stage or each transmission branch are also not necessary. The reason for this is that the output stage T17, T18 of the power amplifier 2 is operated in a saturated manner and therefore only a small power loss occurs in the output stage driver T15, T16. In addition, the transmission current I _{LF can} be regulated by means of pulse width modulation, which further reduces the circuitry. Because the antennas LFι ... _{n are} connected directly to the output LF ₀ T _{J of} the power amplifier 2, several transmitters can be controlled from a central control unit. Here, the

Control effort in particular also reduced by using a power multiplexer 4. LIST OF REFERENCE NUMBERS

1 transmitter

2 amplifiers

4 multiplexers

6 ground branch

8 shunt

10 current control

12 current detector / comparator

14 control logic

16 AND gates

18 rear derailleur / PWM latch

AZ _n antenna branch

B buffer

C capacitor

D diode

_An entrance

E _Θ bl ENABLE input HSdiag diagnostic signal

LF _n transmitting antenna

LSdiag diagnostic signal

I _LF transmit current / actual value

I _{Re £} reference current / setpoint L _n transmitter coil

LF _n transmitting antenna

LFout output

LFci clock signal

M _c control signal Pi _n control input

R resistance

S _τ trigger signal

SS current mirror

T transistor / MOSFET U _B operating voltage

VH supply voltage / potential

Claims

claims

1. Transmitting device (1) for an access system, in particular a vehicle, - with a number of long-wave antennas (LFι ... _n ) and with an amplifier device (2), at the output (LFout) of which the long-wave antennas (LFι ... _n ) are connected together with a multiplexer device (4) for activating a single long-wave antenna (LF _n ), characterized in that the multiplexer device (4) on the ground side of the long-wave antennas (LFι ... _n ) facing away from the amplifier device (2) is arranged.

2. Transmitting device according to claim 1, wherein each long-wave antenna (LFι ... _n ) has a MOSFET switching transistor for optional switching in the multiplex.

3. Transmitting device according to claim 2, wherein the MOSFET switching transistors are driven by a ground-related voltage signal at the gate.

4. Transmitting device according to claim 2 or 3, wherein the MOSFET switching transistors are smart MOSFETs.

7. Transmitting device according to claim 6, wherein each long-wave antenna (LFι ... _n ) with a capacitor (Cι ... _n ) tuned to series resonance transmitter coil (Lι ... _n ).

8. Transmitting device according to claim 6 or 7, with one of the amplifier device (2) upstream on the input side and the multiplexer device (4) downstream control device (10) for limiting the transmission current (I _F ) •

9. Transmitting device according to one of claims 6 to 7, with a control device (2) connected on the output side to a control input (Pι _n ) of the amplifier device (2), which has a first input (Ei) for a clock signal (LF _c ι _k ) and one second input (E ₂ ) for a control signal (S _τ ).