EP3772775A1

EP3772775A1 - Electronic remote key

Info

Publication number: EP3772775A1
Application number: EP19465543.7A
Authority: EP
Inventors: Manuel-Ciprian Maritescu-Lungocea; Razvan Bejinaru
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2019-08-07
Filing date: 2019-08-07
Publication date: 2021-02-10

Abstract

An electronic remote key comprises a microcontroller (20), a first antenna (21) electrically coupled to the microcontroller (20), a second antenna (22) electrically coupled to the microcontroller (20), and a decoupling circuit (26) coupled between the first antenna (21) and the microcontroller (20), wherein the decoupling circuit (26) is configured to provide a high impedance at UHF frequencies, thereby decoupling the first antenna (21) from the second antenna (22).

Description

The current invention relates to an electronic remote key, in particular an electronic remote key for a vehicle.
Most vehicles today may be unlocked and remotely started using an electronic remote key. Some "start and stop" access systems are well known in which the user needs to press an unlocking button from the electronic remote key to unlock or lock the vehicle, start the engine of the vehicle, or open a trunk of the vehicle, for example. Such a remote key usually has to be inserted into an immobilizer station located inside the vehicle which recognizes the remote key and allows the user to start the vehicle. Such systems replace the originally known ignition switch systems. Other "start and stop" access systems do not require the user to press a button or to insert the key in an immobilizer in order to unlock or lock the vehicle or to start the engine. Such a "start and stop" access system is called a passive start and entry system. With passive start and entry systems, the vehicle may be unlocked automatically when the key is detected within a certain range from the vehicle. In order to start the vehicle, a start button within the vehicle usually has to be pressed.
Such an electronic remote key communicates with the vehicle using wireless technology. For this reason, an electronic remote key usually comprises two or more different antennas. For example, an electronic remote key may comprise at least one low frequency (LF) antenna and at least one radio frequency (UHF, ultra-high frequency) antenna. If different antennas are mounted on one and the same printed circuit board, however, coupling effects between the different antennas may negatively affect the function of the electronic remote key.
There is a need to provide an electronic remote key that is small in size, may be produced in a cost effective way and has reliable system performance.
This problem is solved by an electronic remote key according to claim 1. Configurations and further developments of the invention are the subject of the dependent claims.
An electronic remote key includes a microcontroller, a first antenna electrically coupled to the microcontroller, a second antenna electrically coupled to the microcontroller, and a decoupling circuit coupled between the first antenna and the microcontroller, wherein the decoupling circuit is configured to provide a high impedance at UHF frequencies, thereby decoupling the first antenna from the second antenna.
Because the first antenna is decoupled from the second antenna, the electronic remote key may be small in size (first antenna and second antenna may be arranged in close proximity to each other) and still provide satisfying system performance.
The electronic remote key may further comprise a printed circuit board, wherein the microcontroller, the first antenna, the second antenna, and the decoupling circuit are arranged on the printed circuit board.
In order to be able to manufacture an electronic remote key that is small in size, the electronic kay may comprise a single printed circuit board which accommodates several antennas and the respective control circuitry.
The first antenna may include at least one coil, and a separate input terminal and a separate output terminal for each of the at least one coil.
Using more than one coil allows each coil to be oriented in a different direction in space. In this way, signals received by the electronic remote key may always be reliably detected, irrespective of how the electronic remote key is oriented in space.
The decoupling circuit may include at least one pair of inductances, each pair comprising two inductances, wherein each of the at least one pair is coupled to a different one of the at least one coil, and wherein for each of the at least one pair of inductances, one inductance is coupled in series with the respective coil and between an input terminal of the respective coil and the microcontroller, and another inductance is coupled in series with the respective coil and between an output terminal of the respective coil and the microcontroller.
The inductances introduce high impedance at UHF frequencies without detuning the LF matching at desired frequencies (e.g., at about 125kHz). With the decoupling circuit arranged between the first antenna and the microcontroller, the first antenna becomes "invisible" for the second antenna and no electromagnetic coupling occurs between the first antenna and the second antenna.
Each of the inductances of the at least one pair of inductances may have an inductivity of between 50nH and 300nH.
In particular, each of the inductances of the at least one pair of inductances may have an inductivity of 100nH.
Each of the inductances of the at least one pair of inductances may have a quality factor of Q > 60 at a frequency of 434MHz.
In this way, any resonances that would occur without the inductances may be reduced or even completely suppressed.
A distance between the first antenna and the second antenna on the printed circuit board may be less than 1 cm.
That is, the antennas may be arranged close to or adjacent to each other, which allows to manufacture a small electronic remote key.
The first antenna may be a low frequency antenna, and the second antenna may be a radio frequency antenna.
Such antennas may be used for sending and receiving different signals for different tasks of the electronic remote key.
The second antenna may be a loop antenna.
Examples are now explained with reference to the drawings. In the drawings the same reference characters denote like features.

Figure 1 illustrates in a block diagram different components of an electronic remote key.
Figure 2 schematically illustrates low frequency coils of the electronic remote key in greater detail.
Figure 3 schematically illustrates a matching circuit of the low frequency coils of Figure 2 in detail.
Figure 4 schematically illustrates different components of an electronic remote key that are arranged on a printed circuit board.
Figure 5 schematically illustrates a low frequency matching circuit and a decoupling circuit according to one example.
Figure 6 schematically illustrates in a Cartesian chart the coupling result between LF and UHF antennas.
Figure 7 schematically illustrates in a smith diagram the coupling result between LF and UHF antennas.
Figure 8 schematically illustrates one component of an electronic remote key according to one example.
Figure 9 schematically illustrates in a Cartesian chart the results after applying a decoupling circuit between LF and UHF antennas.
Figure 10 schematically illustrates the results of Figure 9 in a smith diagram.

In the following Figures, only such elements are illustrated that are useful for the understanding of the present invention. The electronic remote key described below may comprise more than the exemplary elements illustrated in the Figures. However, any additional elements that are not needed for the implementation of the present invention have been omitted for the sake of clarity.
Figure 1 illustrates an antenna arrangement that may be arranged in an electronic remote key 10. The electronic remote key 10 may be the key for a vehicle. Signals may be sent between the vehicle and the electronic remote key 10. For example, the electronic remote key 10 may send inquiry signals to the vehicle to indicate the desire of a user to unlock/lock the vehicle. Further, authentication signals may be sent between the electronic remote key 10 and the vehicle, for example, in order to prevent unauthorized users (unauthorized keys) from unlocking or starting the vehicle. Many other signals may be sent between the electronic remote key 10 and the vehicle for many different applications.
The electronic remote key 10, therefore, may comprise different antennas. A first antenna 21 may be a low frequency (LF) antenna, for example. Low frequency signals may be sent at frequencies in the range between 30 to 300kHz, for example. A second antenna 22 may be a radio frequency (RF) or ultra-high frequency (UHF) antenna, for example. Radio frequency signals may be sent at frequencies in the range between 20kHz to 300GHz. The first antenna 21 and the second antenna 22 may be coupled to corresponding circuitries as well as to a microcontroller 20, for example. The circuitries may comprise a low frequency matching circuitry 23 that is coupled to the LF antenna 21, and a radio frequency matching circuitry 24 that is coupled to the RF antenna 22. The low frequency matching circuitry 23 may be coupled to the microcontroller 20 and the radio frequency matching circuitry 24 may be coupled to the microcontroller 20. There may not be a direct connection between the LF matching circuitry 23 and the RF matching circuitry 24. The LF matching circuitry 23 and the RF matching circuitry 24 may only be coupled to each other via the microcontroller 20.
The LF matching circuitry 23 may be coupled between the first antenna 21 and the microcontroller 20. The RF matching circuitry 24 may be coupled between the RF antenna 22 and the microcontroller 20.
The different components are only schematically outlined in Figure 1. However, as is indicated in Figure 1, the LF matching circuitry 23 may comprise a plurality of components such as capacitors, for example. The RF matching circuitry 24 may comprise a plurality of components such as capacitors, resistors and inductors, for example. The precise arrangement of such components of the RF matching circuitry 24 is not relevant for the present invention and is, therefore, not described in further detail herein. The LF matching circuitry 23 is configured to drive the first antenna 21, and the RF matching circuitry 24 is configured to drive the second antenna 22.
The different components of the electronic remote key 10 that are illustrated in Figure 1 may be implemented on one printed circuit board 30. This is schematically illustrated in Figure 4. Figure 4 illustrates a printed circuit board 30 with a microcontroller 20, a first antenna 21, and a second antenna 22 mounted thereon. The LF matching circuitry 23 and the RF matching circuitry 24 have been omitted in Figure 4 for the sake of clarity only. Further, any electrical connections between the microcontroller 20, the first antenna 21 and the second antenna 22 are not specifically illustrated in Figure 4. Figure 4 merely illustrates a possible physical arrangement of the illustrated components on the printed circuit board 30. According to one example, the microcontroller 20 may be arranged essentially in one corner of an essentially rectangular printed circuit board 30. The first antenna 21 may be arranged at an opposite end of the printed circuit board 30 as compared to the microcontroller 20. The second antenna 22 may be a loop antenna, for example, and may extend at least partially along an edge of the printed circuit board 30.
As electronic remote keys 10 are comparably small, also the electronics included in the electronic remote key 10 need to be small. At the same time, a satisfactory performance of the electronic remote key 10 is desired. That is, signals should be transmitted and received reliably without losing any crucial information. To avoid unwanted coupling effects between the first antenna 21 and the second antenna 22, the two antennas 21, 22 may be arranged as far from each other as possible on the printed circuit board 30. However, as electronic remote keys 10, as well as the printed circuit boards 30 inside the electronic remote keys 10 are becoming smaller and smaller, it is also becoming increasingly difficult to maintain a certain distance between the different antennas. In the example of Figure 4 it can be seen that the first antenna 21 and the second antenna 22 may be arranged close to or adjacent each other at least in some parts.
Now referring to Figure 2, an exemplary first antenna 21 is schematically illustrated in greater detail. The first antenna 21 may be a three-dimensional antenna. That is, the first antenna 21 may comprise three different coils, namely a first coil 211, a second coil 222, and a third coil 223. The illustration in Figure 2 is a very simplified illustration. Each of the three coils 221, 222, 223 may be oriented in a different direction in space x, y, z, wherein each direction in space may be perpendicular to the respective other two dimensions. However, it is also possible that the three antennas 221, 222, 223 are not perpendicular to each other. Other angles than right angles between the different antennas 221, 222, 223 are also possible.
A wirelessly transmitted signal generally has three different components in three different directions in space. The signal strength of the different components of a signal may vary considerably. That is, if only one component of a signal is received, the signal strength of this component may not be great enough and information may be lost. With three antennas arranged in three different directions in space, at least one component and possibly all three components may be received regardless of a present orientation of the electronic remote key 10. The different components may be added to each other before retrieving the signal information. In this way, signals generally may be received and their information may be reliably retrieved.
Each of the coils 221, 222, 223 has an input terminal X1, Y1, Z1 and a respective output terminal X2, Y2, Z2. Each coil 221, 222, 223 may be connected to the LF matching circuitry 23 with its input terminal X1, Y1, Z1 as well as with its output terminal X2, Y2, Z2. An exemplary LF matching circuitry 23 is schematically illustrated in Figure 3. The LF matching circuitry 23 may comprise three different sections 41, 42, 43, each section 41, 42, 43 being assigned to one of the coils 221, 222, 223. Each section 41, 42, 43 may comprise two input terminals and two output terminals. A first section 41 may be coupled to the input terminal X1 and the output terminal X2 of the first coil 221 with its two input terminals, for example. Its two output terminals TP300, TP301 may be coupled to the microcontroller 20 (not illustrated in Figure 3), for example. The first section 41 may comprise two capacitors C11, C12, for example. The capacitors C11, C12 may be coupled in parallel between a common node between the input terminal X1 of the first coil 221 and the first output terminal TP300 of the first section 41, and a common node between the output terminal X2 of the first coil 221 and the second output terminal TP301 of the first section 41. The capacitors C11, C12 may be configured to provide LF frequency tuning. Frequency tuning is usually used in order to change the frequency of operation of a system to a desired frequency with mechanical or electrical means. Frequency tuning generally increases the quality of a system. The second section 42 may built correspondingly with regard to the second coil 222, and the third section 43 may be built correspondingly with regard to the third coil 223.
Now referring to Figure 5, a first section 41 of an LF matching circuitry 23 according to one example is schematically illustrated. As has been described above, the two input terminals of the first section 41 are coupled to the input terminal X1 and the output terminal X2 of the respective coil 221. The two output terminals TP300, TP301 of the first section 41 are coupled to the microcontroller 20. In particular, a first output terminal TP300 of the first section 41 may be coupled to a first input terminal IN1 of the microcontroller 20, and the second output terminal TP301 of the first section 41 may be coupled to a second input terminal IN2 of the microcontroller 20. In order to decouple the first antenna 21 from the second antenna 22 (second antenna 22 not specifically illustrated in Figure 5), a decoupling circuit 26 is coupled between the first antenna 21 and the microcontroller 20. In particular, the decoupling circuit 26 may be coupled between the LF matching circuitry 23 and the microcontroller 20. The decoupling circuit 26, as is illustrated in Figure 5, may comprise a first inductance L11 that is coupled between the first output terminal TP300 of the first section 41 and the first input terminal IN1 of the microcontroller 20, and a second inductance L12 is coupled between the second output terminal TP301 of the first section 41 and the second input terminal IN2 of the microcontroller 20.
In the same way, corresponding inductances L21, L22, L31, L32 may be coupled between the outputs TP302, TP303, TP304, TP305 of the second section 42 and the third section 43, and further input terminals IN3, IN4, IN5, IN6 of the microcontroller 20, respectively. The second section 42 and the third section 43, however, are not specifically illustrated in Figure 5.
Generally speaking, the decoupling circuit that is arranged between the first antenna 21 and the microcontroller 20 is configured to introduce a high impedance at UHF frequencies without detuning the LF matching at frequencies of about 125kHz. With the decoupling circuit 26 arranged between the first antenna 21 and the microcontroller 20, the first antenna 21 becomes "invisible" for the second antenna 22 and no electromagnetic coupling occurs between the first antenna 21 and the second antenna 22.
Figure 6 schematically illustrates in a Cartesian chart an attenuation of the first antenna 21 and the second antenna 22 in the arrangement of Figure 1. As can be seen, there is a resonance in the respective bands at a frequency of 433.92 MHz. On the horizontal axis, a frequency is indicated in a range from 100MHz up to 1GHz. On the vertical axis an attenuation is indicated in a range from -800 to +1200.
Figure 7 schematically illustrates the attenuation of the second antenna 22 in a smith diagram. In this smith diagram the resonance at 433.92MHz is also clearly visible.
This unwanted in-band resonance drastically impacts the performance of the second antenna 22, thereby significantly reducing the overall radiation efficiency of the electronic remote key 10. A matching circuit 24 arranged between the second antenna 22 and the microcontroller 20 in this case shows a comparably low radiated power due to this parasitic resonance induced by the capacitive coupling with the first antenna 21.
Figure 8 exemplarily illustrates an arrangement that is similar to the arrangement of Figure 5. The arrangement in Figure 8, however, exemplarily illustrates the second section 42 of the LF matching circuitry 23 instead of for the first section 41 (see Figure 5). In addition to the elements already discussed with respect to Figure 5 above, further pins (terminals) of the microcontroller 20 are exemplarily illustrated. Some of the pins of the microcontroller 20 (e.g., pins VSS1, VDDC) may be coupled to a ground potential GND, for example. An additional capacitor C402 is illustrated that is coupled between one of the pins VDDC and a ground potential GND.
In order to transmit at maximum power, the second antenna 22 (e.g., radio frequency RF antenna) may be matched to a 50 Ohm point and should ideally be as stable as possible. The second antenna 22 may be configured to act as a small loop antenna having a comparably small real part impedance. A small impedance for a loop antenna is generally considered to have a real part maximum of 20 Ohms. The imaginary part generally need not be considered in this context. However, according to one example, the imaginary part may be essentially defined as j ^∗100. Using a loop antenna having a comparably large real part impedance of, e.g., 60 Ohms, generally requires significant layout modifications in order to match it to a 50 Ohm point.
The cause of the resonance as depicted in Figures 6 and 7 is an electromagnetic coupling between at least one of the coils 221, 222, 223 of the first antenna 21 and the second antenna 22. An electromagnetic coupling between the antennas 21, 22 may occur, for example, if the antennas 21, 22 are arranged in close proximity to each other (e.g., distance between antennas 21, 22 < 1cm).
By arranging at least one inductance L11, L12 (L21, L22, L31, L32) in series with the respective coil 221 (222, 223) and between the respective input terminal X1 (Y1, Z1) and output terminal X2 (Y2, Z2) of the first antenna 21 and the microcontroller 20, respectively, this resonance may be reduced or even completely suppressed. Each inductance L11, L12 (L21, L22, L31, L32) may have an inductivity of between 50nH and 300nH, e.g., 100nH. The inductances L11, L12 (L21, L22, L31, L32) may be SMD-type coils with a high quality factor at the desired UHF frequency (ultra-high frequency). According to one example, each of the inductances L11, L12 (L21, L22, L31, L32) may have a quality factor of Q > 60 at the desired frequency of 434MHz. Other quality factors at other desired frequencies, however, are also possible.
In some applications, due to a different physical arrangement (different layout) of the different antennas 21, 22 and coils 221, 222, 223 on the printed circuit board 30, not all of the at least one coil 221, 222, 223 of the first antenna 21 may couple with the second antenna 22. Therefore, it may not be necessary to provide additional inductances L11, L12 (L21, L22, L31, L32) for all of the coils 221, 222, 223.
Additional inductances L11, L12 (L21, L22, L31, L32) may only be provided for those coils 221, 222, 223 of the first antenna 21 that couple with the second antenna. It may be determined by means of respective testing and analyzing during design of the transponder unit which of the coils 221, 222, 223, if any, couples with the second antenna 22.
Now referring to Figures 9 and 10, similar curves to those curves of Figures 6 and 7 are illustrated for an electronic remote key 10 comprising the arrangement that has been described with respect to Figures 5 and 8, respectively. As can be seen in Figures 9 and 10, with the described decoupling of the antennas 21, 22, the resonance that was clearly visible in the curves of Figures 6 and 7 has been eliminated. In this way, the overall system performance of the electronic remote key 10 is increased significantly.

List of reference signs

10: electronic key
20: microcontroller
21: first antenna
22: second antenna
23: LF matching circuit
24: RF matching circuit
26: decoupling circuit
30: printed circuit board
41: first section
42: second section
43: third section
L11, L12: inductances
X1, Y1, Z1: input terminals of first antenna
X2, Y2, Z2: output terminals of first antenna
C11, C12, C402: capacitors
TP300 - TP305: output terminals of LF matching circuit
IN1, IN2: input terminals of microcontroller

Claims

An electronic remote key (10) comprising
a microcontroller (20);
a first antenna (21) electrically coupled to the microcontroller (20);
a second antenna (22) electrically coupled to the microcontroller (20); and
a decoupling circuit (26) coupled between the first antenna (21) and the microcontroller (20), wherein
the decoupling circuit (26) is configured to provide a high impedance at UHF frequencies, thereby decoupling the first antenna (21) from the second antenna (22).
The electronic remote key (10) of claim 1, further comprising a printed circuit board (30), wherein the microcontroller (20), the first antenna (21), the second antenna (22), and the decoupling circuit (26) are arranged on the printed circuit board (30).
The electronic remote key (10) of claim 1 or 2, wherein the first antenna (21) comprises
at least one coil (221, 222, 223); and

a separate input terminal (X1, Y1, Z1) and a separate output terminal (X2, Y2, Z2) for each of the at least one coil (221, 222, 223).
The electronic remote key (10) according to any of claims 1 to 3, wherein the decoupling circuit (26) comprises at least one pair of inductances (L11, L12), each pair comprising two inductances, wherein each of the at least one pair is coupled to a different one of the at least one coil (221, 222, 223), and wherein for each of the at least one pair of inductances (L11, L12), one inductance (L11) is coupled in series with the respective coil (221, 222, 223) and between an input terminal (X1, Y1, Z1) of the respective coil (221, 222, 223) and the microcontroller (20), and another inductance (L12) is coupled in series with the respective coil (221, 222, 223) and between an output terminal (X2, Y2, Z2) of the respective coil (221, 222, 223) and the microcontroller (20).
The electronic remote key (10) according to claim 4, wherein each of the inductances (L11, L12) of the at least one pair of inductances (L11, L12) has an inductivity of between 50nH and 300nH.
The electronic remote key (10) of claim 5, wherein each of the inductances (L11, L12) of the at least one pair of inductances (L11, L12) has an inductivity of 100nH.
The electronic remote key (10) of any of claims 4 to 6, wherein each of the inductances (L11, L12) of the at least one pair of inductances (L11, L12) has a quality factor of Q > 60 at a frequency of 434MHz.
The electronic remote key (10) of any of claims 2 to 7, wherein a distance between the first antenna (21) and the second antenna (22) on the printed circuit board (30) is less than 1 cm.
The electronic remote key (10) of any of claims 1 to 8, wherein
the first antenna (21) is a low frequency antenna; and

the second antenna (22) is a radio frequency antenna.
The electronic remote key (10) of any of claims 1 to 9, wherein the second antenna (22) is a loop antenna.