Passive entry and/or passive go system and associated operating method

Abstract

A passive entry and/or passive go system and am associated operating method is provided. According to an embodiment of the invention, the following steps are performed in an electronic key of the passive entry and/or passive go system: generation of a reference input value, supplying the antenna circuit with the reference input value, measurement of the characteristic parameters, while the antenna circuit is supplied with the reference input value, storage of the characteristic parameters, measurement of a first output value of the antenna circuit, and determination of the field strength from the first output value and the characteristic parameters, whereby an effect of the characteristic parameters on the field strength is compensated. Use, for example, in motor vehicles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 illustrates a block diagram of a passive entry/passive go system for automatic, distance-dependent unlocking and/or locking and for keyless starting of a motor vehicle;

FIG. 2 illustrates a detailed block diagram of a key medium and a base station of FIG. 1; and

FIG. 3 illustrates a detailed block diagram of an antenna circuit of an LF transmitter/receiver of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a passive entry/passive go (PEG) system for automatic, distance-dependent unlocking and/or locking and for keyless starting of a motor vehicle 100.

The PEG system comprises a base station 110, which is placed in motor vehicle 100, and at least one card-shaped, electronic key medium 200 assigned to base station 110.

If a user (not shown) of key medium 200 operates a door handle 120 of motor vehicle 100, this is detected in motor vehicle 100 and reported to base station 110, for example, via a motor vehicle bus system (not shown). Base station 110 thereupon transmits a low-frequency (LF) carrier signal with a frequency of 125 kHz over an LF antenna of base station 110 in the form of a coil 114 to electronic key medium 200. Key medium 200, after receiving the LF carrier signal and a distance determination using the LF carrier signal field strength calculated in the key medium 200, transmits a signal with unlocking information in a UHF frequency range to base station 110, when the determined or calculated distance is within a permissible range. The UHF signal is received by a UHF antenna 115 of base station 110, and when the information transmitted from key medium 200 to base station 110 conforms with the protocol, motor vehicle 100 is unlocked, and the user can sit, for example, on a driver's seat (not shown) of motor vehicle 100.

To start motor vehicle 100, the user presses a start button, whereupon the low-frequency LF carrier signal is again transmitted to key medium 200. After a repeated distance or position calculation in key medium 200, during which it is verified whether the user is sitting in a driver's seat (not shown), a start release is transmitted by key medium 200, again via the UHF channel, to base station 110.

The UHF transmission is based on a far-field coupling and the LF transmission on an inductive or mutual coupling in the near field. If more than one antenna 114 is placed at different positions in motor vehicle 100, apart from a distance measurement, a position measurement relative to motor vehicle 100 can also be made by determining the respective antenna field strength, calculation of the distance to the respective antenna from the field strength, and subsequent triangulation.

FIG. 2 shows a detailed block diagram of key medium 200 and base station 110 of FIG. 1.

Base station 110 comprises an LF transmitter/receiver 111 and LF antenna 114 in the form of a coil, connected to LF transmitter/receiver 111, a UHF transmitter/receiver 113, a UHF antenna 115, connected to UHF transmitter/receiver 113, and a microprocessor 112, which is coupled to LF transmitter/receiver 111 and UHF transmitter/receiver 113 and exchanges data, to be transmitted and received bidirectionally, with the transmitter/receiver.

Key medium 200 comprises an LF transmitter/receiver 201 for a 3D reception, to which antennas 202, 203, and 204 are connected in the form of coils. The antenna coils or symmetry axes in the winding direction of antenna coils 202, 203, and 204 are each perpendicular to one another. The field strengths calculated per antenna can be interpreted as components of a three-dimensional field strength vector, whose contribution has a value dependent on the distance of key medium 200 from transmitting antenna 114 of base station 110, but the value is independent of an orientation of key medium 200 relative to transmitting antenna 114.

For UHF transmission, key medium 200 has a UHF transmitter/receiver 207 and a UHF antenna 208 connected to UHF transmitter/receiver 207.

Furthermore, key medium 200 has a microprocessor 205, which is coupled to LF transmitter/receiver 201 and UHF transmitter/receiver 207 and exchanges data, to be transmitted and received bidirectionally, with the transmitters/receivers, and a battery or an accumulator 206 for supplying power. LF transmitter/receiver 201 in addition outputs a field strength signal, associated with each of antennas 202, 203, and 204, to microprocessor 205.

In the simplest case, an LF data transmission occurs unidirectionally from base station 110 to key medium 200, whereby in this case, unit 111 is only a transmitter and unit 201 only a receiver. Accordingly, the UHF data transmission can occur unidirectionally from key medium 200 to base station 110, whereby in this case, unit 207 is only a transmitter and unit 113 only a receiver. In the shown exemplary embodiment, both the LF data transmission and the UHF data transmission occur bidirectionally.

FIG. 3 shows a detailed block diagram of an antenna circuit 214 of LF transmitter/receiver 201 of FIG. 2. For reasons of clarity, only the antenna circuit which is assigned to antenna 202 is shown in FIG. 3. Antennas 203 and 204 are assigned corresponding antenna circuits (not shown).

Antenna circuit 214 comprises antenna or antenna coil 202, a resistor 212, which represents a parasitic copper resistor of antenna coil 202, and a capacitor 213. Antenna coil 202 and capacitor 213 form a parallel resonant circuit. An output value, which during normal operation is a function of the field strength of the LF carrier signal and a function of characteristic parameters of antenna circuit 214, is applied at the output terminal N1 in the form of an output voltage UAF or UAI. The output voltage UAF or UAI is used as an analog input value for an A/D converter (not shown) of microprocessor 205 and is processed further digitalized in said microprocessor.

The operation of the arrangement shown in FIG. 3 will be described in detail next. In a transmission unit 217 of base station 110, which is shown only as a detail, a signal with a frequency f0 is provided via a driver stage 209. The signal is supplied to a series resonant circuit with transmitting antenna coil 114, a resistor 210, and a capacitor 211. A voltage UQ is induced in antenna coil 202 by a magnetic carrier field generated in transmitting antenna coil 114. The following formulas describe in mathematic terms the coupling between antenna coils 114 and 202. They are derived from the manual Klaus Finkenzeller, RFID-Handbuch [RFID Manual], 3rd ed., HANSER, 2002; see particularly pages 72, 73, and 77.

UQ=ω ₀ *k√{square root over (L1*L2)}*i₁  (1)

In Equation (1), UQ designates a voltage induced in coil 202; ω₀ is the angular frequency assigned to the transmission frequency f0, k is a coupling factor, L1 is an inductance of antenna coil 114, L2 is an inductance of antenna coil 202, and i₁ is a current through transmitting antenna coil 114.

The voltage UQ induced in antenna coil 202 generates the following output voltage UAF:

$\begin{array}{cc}\mathrm{UAF}=\frac{\mathrm{UQ}}{\sqrt{{\left({\omega }_0*R2*C2\right)}^2+{\left(1-{\omega }_0^2*L2*C2\right)}^2}}& \left(2\right)\end{array}$

Equation (2), in comparison with the formula in Finkenzeller, contains the simplified assumption that RL=∞, as a result of which a term with RL is eliminated in the denominator. R2 designates a resistance value of resistor 212 and C2 designates a capacitance of capacitor 213.

Equation (2) shows directly that the output voltage UAF, produced by the field of the carrier signal, is determined by the value R2 of resistor 212, the inductance L2 of receiving coil 202, and the capacitance C2 of capacitor 213. These values therefore form the characteristic parameters of antenna circuit 214.

To determine the characteristic parameters or a measure for the characteristic parameters or a characteristic quantity for the characteristic parameters, which represents their output voltage-relevant properties, antenna circuit 214 is supplied with a reference input value. The reference input value is generated in the form of a reference input voltage UI by a reference input value generating unit in the form of an oscillator 216, which is part of LF transmitter/receiver 201 of FIG. 2. The frequency of the reference input voltage UI is the same as frequency f0 of the carrier signal. The amplitude of the reference input voltage UI is generated precisely with a previously known value.

For measuring the characteristic parameters, a switching unit 215, activated by microprocessor 205, with a first switch 218 and a second switch 219, is activated in such a way that switch 218 is opened and switch 219 is closed. This has the result that antenna circuit 214 is supplied with the reference input value UI as a simulated input voltage. The signal generated by transmitting unit 217 is turned off during the measurement of the characteristic parameters, i.e., UQ=0. Switching unit 215 is part of LF transmitter/receiver 201 of FIG. 2.

An output voltage UAF arising at output terminal N1 of antenna circuit 214 can be calculated using the following equation:

$\begin{array}{cc}\mathrm{UAF}=\frac{\mathrm{UI}}{\sqrt{{\left({\omega }_0*R2*C2\right)}^2+{\left(1-{\omega }_0^2*L2*C2\right)}^2}}& \left(3\right)\end{array}$

If a quotient is formed from the first output value UAF and the second output value UAI, the following equation results:

$\begin{array}{cc}\frac{\mathrm{UAF}}{\mathrm{UAI}}=\frac{\frac{\mathrm{UQ}}{\sqrt{{\left({\omega }_0*R2*C2\right)}^2+{\left(1-{\omega }_0^2*L2*C2\right)}^2}}}{\frac{\mathrm{UI}}{\sqrt{{\left({\omega }_0*R2*C2\right)}^2+{\left(1-{\omega }_0^2*L2*C2\right)}^2}}}=\frac{\mathrm{UQ}}{\mathrm{UI}}& \left(4\right)\end{array}$

If Equation (4) is solved for UQ, we obtain:

$\begin{array}{cc}\mathrm{UQ}=\mathrm{UI}*\frac{\mathrm{UAF}}{\mathrm{UAI}}& \left(5\right)\end{array}$

A distance x of the transmitting antenna or transmitting coil 114 of receiving antenna or receiving coil 202 can be calculated from the calculated voltage UQ using the following Equation (6):

$\begin{array}{cc}x=\sqrt{{\left(\sqrt[3]{\frac{r_{L2}^2*r_{L1}^2}{2*\sqrt{r_{L2}*r_{L1}}*\frac{\mathrm{UQ}}{{\omega }_0*\sqrt{L1*L2}*i_1}}}\right)}^2-r_{L2}^2}& \left(6\right)\end{array}$

where r_L1 is a radius of transmitting antenna coil 114 and r_L2 a radius of receiving antenna coil 202. Equation (6) applies to air coils as transmitting antenna 114 and receiving antenna 202. If no air coils are used, Equation (6) can be modified accordingly. For this purpose, the coupling factor dependent on the distance x (by transformation of Equation (1))

$k\left(x\right)=\frac{\mathrm{UQ}}{{\omega }_0*\sqrt{L1*L2}*i_1}$

in Equation (6) is to be replaced by a coupling factor valid for an employed coil type. For this purpose, reference is again made, for example, to Finkenzeller, see particularly page 108, or the data book: ATMEL, Data Book 2001, ICs for wireless control systems, pages 326ff.

In summary, the field strength or the distance is determined as follows:

In a first step, switching unit 215 is activated by microprocessor 205 such that antenna circuit 214 is supplied with the reference input value UI. The reference input value UI can be permanently active or activated solely for the measuring process. Here, it should be known or made certain that the carrier signal is not active.

Next, the arising output voltage UAI is measured and stored.

After storage of output voltage UAI generated by turning on reference voltage source 216, switching unit 215 is activated by microprocessor 205 in such a way that antenna circuit 214 is decoupled from the reference input value UI. The now arising output voltage UAF is produced by the field of the carrier signal at antenna coil 202.

The actual field strength, i.e., the field strength at which an effect of the characteristic parameters is compensated, is calculated by forming the ratio of UAF and UAI and multiplying by the known voltage UI.

For the final distance measurement, the specific field strengths, determined as described above, of antennas 202, 203, and 204 are superposed for calculating a total field strength, which is independent of the orientation. The distance is finally calculated using Equation (6) from the total field strength calculated by conventional vector calculus.

The measurement of the voltage UAI can be measured cyclically or triggered by certain events, as a result of which a change in the characteristic parameters of the antenna circuit, for example, due to a temperature drift, is taken into account.

It is understood that a current may also be used instead of the reference input value in the form of the voltage UI. For this purpose, switch 218 must remain closed in switching unit 215 during the measurement of the characteristic parameters and a reference current source supplies its current to a connection node between resistor 212 and capacitor 213.

In LF transmitter/receiver 201 of FIG. 2, other circuit parts can be provided in addition to antenna circuit 214. For example, an integrated circuit can be provided, which is designed for coupling to antenna circuit 214. The integrated circuit can then take over, for example, the evaluation of the output voltage UAF or UAI instead of microprocessor 205. In other words, the entire evaluation of the output voltage UAI and UAF occurs in the integrated circuit, as a result of which the evaluation in microprocessor 205 is simplified, because specific information is no longer necessary there. Furthermore, switching unit 215 and reference input value generating unit 216 can also be part of the integrated circuit.

The shown embodiments enable a precise, long-term stable field strength or distance measurement, without a laborious calibration being necessary during a manufacturing process.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

1. A method for operating a passive entry and/or a passive go system, the system having a base station that is provided in a motor vehicle and at least one electronic key assigned to the base station, the method comprising: generating a carrier signal by the base station;receiving the carrier signal at least one antenna of an antenna circuit of the electronic key, the antenna circuit generating an output value, which is a function of a field strength of the carrier signal and a function of characteristic parameters of the antenna circuit;determining, in the electronic key, a distance between the base station and the electronic key based on the field strength; andoperating functions of the system are carried based on the determined distance,wherein, in the electronic key, the method further comprises: generating a reference input value;supplying the antenna circuit with the reference input value;measuring the characteristic parameters while the antenna circuit is supplied with the reference input value;storing the characteristic parameters;measuring a first output value of the antenna circuit; anddetermining the field strength from the first output value and the characteristic parameters, wherein an effect of the characteristic parameters on the field strength is compensated.

2. The method according to claim 1, wherein the functions of the system comprise an unlocking, a locking, and/or starting of the motor vehicle as a function of the determined distance.

3. The method according to claim 1, wherein the reference input value is generated in the form of a reference input voltage and/or a reference input current with a predefined reference frequency and reference amplitude, wherein a second output value is measured at an applied reference input value, and wherein the characteristic parameters are determined from the second output value.

4. The method according to claim 3, wherein, to determine the field strength, a quotient is formed from the first output value and the second output value.

5. The method according to claim 3, wherein the reference frequency is set equal to a frequency of the carrier signal.

6. The method according to claim 3, wherein the reference frequency is derived from a frequency of the carrier signal.

7. The method according to claim 1, wherein a distance between the antenna and a transmitting antenna of a transmitter of the carrier signal is determined based on the determined field strength.

8. The method according to claim 7, wherein the field strength is determined at a second antenna and at a third antenna, and a distance between the antennas and a transmitting antenna of a transmitter of the carrier signal is determined from the determined field strengths.

9. The method according to claim 1, wherein the antenna and a transmitting antenna of a transmitter of the carrier signal are coupled mutually.

10. The method according to claim 1, wherein a parallel resonant circuit or a series resonant circuit is formed by the antenna circuit.

11. The method according to claim 1, wherein the frequency of the carrier signal is within a range of 50 KHz to 150 KHz or within a range of 5 MHz to 25 MHz.

12. A passive entry and/or passive go system comprising: a base station for placement in a motor vehicle;at least one electronic key, which is assigned to the base station; andat least one antenna circuit arranged on the electronic key, the electronic key including at least one antenna and an output terminal at which an output value is applied in the form of an output voltage and/or an output current, which is a function of the field strength and a function of characteristic parameters of the antenna circuit,wherein the electronic key comprises: a reference input value generating unit for generating a reference input value in the form of a reference input voltage and/or a reference input current with a known reference frequency and reference amplitude andan activatable switching unit, which is coupled to the antenna circuit and the reference input value generating unit and which supplies the antenna circuit with the reference input value as a function of the activation state or decouples the antenna circuit from the reference input value.

13. The passive entry and/or passive go system according to claim 12, wherein the reference input value generating unit is an oscillator.

14. The passive entry and/or passive go system according to claim 12, wherein the key medium comprises an evaluation unit, which is designed in such a way that it evaluates an output value when a reference input value is not applied and an output value when a reference input value is applied for determining the field strength.

15. The passive entry and/or passive go system according to claim 12, wherein the antenna circuit has an antenna coil and a capacitor, which together form a parallel resonant circuit.

16. The passive entry and/or passive go system according to claim 15, wherein the switching unit has a first switch, which is looped between a terminal of the capacitor and a reference potential, and a second switch, which is looped between the terminal of the capacitor and a terminal of the reference input value generating unit at which the reference input value is applied.

17. The passive entry and/or passive go system according to claim 12, wherein the antenna circuit is designed for mutual coupling with a transmitting antenna of a transmitter of the carrier signal.

18. The method according to claim 8, wherein at least one of the antennas is perpendicular to an adjacent antenna.