Presence detection sensor for a motor vehicle

Abstract

Disclosed is a detection sensor for detecting the presence of an item of user equipment through near-field communication for a motor vehicle, the sensor including an antenna, an impedance matcher, a driver module for driving the antenna and a microcontroller, which is configured to control the driver module, the impedance matcher being able to match the output impedance of the driver module to the impedance of the antenna while amplifying the power supplied by the driver module. The sensor includes a resistive module, mounted between the driver module and the impedance matcher, configured to stabilize the value of the input power of the impedance matcher.

Claims

1. A detection sensor to detect a presence of an item of user equipment through near-field communication, said detection sensor being configured to be mounted in a motor vehicle, the detection sensor comprising: an antenna; a driver module configured to drive the antenna; an impedance matcher configured to match the output impedance of the driver module to the impedance of the antenna and configured to amplify the voltage and the current supplied by the driver module; a resistive module mounted between the driver module and the impedance matcher, the resistive module comprising at least one resistor configured to stabilize the value of the input power of the impedance matcher; and a microcontroller configured to control the driver module.

2. The sensor as claimed in claim 1, wherein the resistive module has a resistance value between plus or minus 80% of the value of the real part of the matching impedance of the impedance matcher.

3. The sensor as claimed in claim 2, wherein the resistive module has a resistance value between 1 and 100 ohms.

4. The sensor as claimed in claim 2, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

5. A motor vehicle comprising at least one sensor as claimed in claim 2.

6. A method for stabilizing power supplied by the driver module to the impedance matcher of the detection sensor as claimed in claim 1 for a motor vehicle, the method comprising: stabilizing the power by the resistive module of the detection sensor, the resistive module connected between the driver module and the impedance matcher.

7. The sensor as claimed in claim 1, wherein the resistive module has a resistance value between the value of the real part minus 40% and the value of the real part plus 40% of the matching impedance of the impedance matcher.

8. The sensor as claimed in claim 7, wherein the resistive module has a resistance value between 1 and 100 ohms.

9. The sensor as claimed in claim 7, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

10. A motor vehicle comprising at least one sensor as claimed in claim 7.

11. The sensor as claimed in claim 1, wherein the resistive module has a resistance value between the value of the real part minus 20% and the value of the real part plus 20% of the matching impedance of the impedance matcher.

12. The sensor as claimed in claim 11, wherein the resistive module has a resistance value between 1 and 100 ohms.

13. The sensor as claimed in claim 11, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

14. The sensor as claimed in claim 1, wherein the resistive module has a resistance value equal to the value of the real part of the matching impedance of the impedance matcher.

15. The sensor as claimed in claim 14, wherein the resistive module has a resistance value between 1 and 100 ohms.

16. The sensor as claimed in claim 14, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

17. The sensor as claimed in claim 1, wherein the resistive module has a resistance value between 1 and 100 ohms.

18. The sensor as claimed in claim 17, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

19. The sensor as claimed in claim 1, wherein the microcontroller, the driver module, and the impedance matcher are mounted on a printed circuit board.

20. A motor vehicle comprising at least one sensor as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the invention will become apparent from the following description, which is given with reference to the appended figures, which are given by way of non-limiting examples and in which identical references are given to similar objects.

(2) FIG. 1 describes one embodiment of a detection sensor according to the invention.

(3) FIG. 2 illustrates an equivalent circuit diagram of the driver module, of the resistive module and of the impedance matcher of the sensor of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The sensor according to the invention is intended to be mounted in a vehicle, in particular a motor vehicle, to detect the presence of an item of user equipment through near-field communication (or NFC) in order to activate a function of the vehicle such as, for example, the opening of an opening element of the vehicle. The item of user equipment may in particular be a fob or a smartphone able to communicate with the sensor over an NFC communication link. Preferably, but non-limitingly, the detection sensor according to the invention is intended to be mounted in a door handle of a motor vehicle.

(5) FIG. 1 shows an example of a sensor 1 according to the invention. The sensor 1 comprises a microcontroller 10, a driver module 20, a resistive module 30, an impedance matcher 40 and an antenna 50.

(6) The microcontroller 10 is configured to control the driver module 20, in particular by configuring its registers with the aid of a digital link, in a manner known per se. The driver module 20 is configured in particular to encode the physical layer of the NFC communication.

(7) The impedance matcher 40 is configured to match the output impedance of the driver module 20 to the impedance of the antenna 50 while amplifying the voltage and the current supplied by said driver module 20 through a resonance effect.

(8) The antenna 50 is for example in the form of an inductive coil and is connected by both its terminals to the impedance matcher 40. The antenna 50 allows a magnetic field to be generated, the intensity of which is proportional to the power supplied by the impedance matcher 40, which will serve to excite the antenna of a fob or of a smartphone located nearby.

(9) Both terminals of the antenna 50 are also each connected to an analog input of the microcontroller 10 via a voltage-dividing capacitive bridge 60. This capacitive bridge 60 allows the voltage potential seen at the terminal of the antenna 50 to which it is connected to be reduced in order to transform the voltage defined across the terminals of the antenna 50, which is for example of the order of 50 V, into a voltage the value of which, which is lower, comes within the operating range of the microcontroller 10, for example between 0 and 5 V. The driver module 20 comprises an analog-to-digital converter 210 which is configured to transform this reduced voltage, designated image voltage in the present document, which is defined between the two analog input terminals RFI1, RFI2 of the driver module 20, into a numerical value representative of said voltage and between 0 and (2.sup.n?1), where n is a natural number representing the number of digital bits over which the voltage values are coded.

(10) Thus, for example, in the case of an 8-bit converter, used as standard in detection sensors for a motor vehicle given its low cost and its simplicity, the value of the image voltage, which is analog, is transformed into a numerical value between 0 and 255.

(11) Such a converter 210 is configured to operate in an analog operating range so that any instance of the voltage value received at the input of the converter 210 exceeding the upper limit of the operating range is attributed the maximum numerical value, for example 255 in the preceding example, or a little less according to the type of converter 210 (for example 230 for a converter 210 operating over eight bits) because of a limitation caused by certain components.

(12) In this case, the converter 210 is said to be saturated and it is then no longer possible to distinguish the values of the image voltage which are higher than the upper limit of the operating range of the converter 210 from each other. The voltage defined across the terminals of the antenna 50 must therefore vary little, along with the image voltage, the value of which must therefore remain within the operating range of the driver module 20 for the numerical values, which are utilized by the microcontroller 10, to be pertinent.

(13) To do this, and avoid such saturation of the converter 210, the sensor 1 comprises a resistive module 30 connected between the driver module 20 and the impedance matcher 40.

(14) This resistive module 30 has a resistance value, in ohms, which allows the value of the input power of the impedance adapter 40, supplied by the driver module 20 via said resistive module 30, to be stabilized.

(15) In this preferred example, the resistive module 30 comprises a resistor on each input terminal of the impedance matcher 40. As a variant, the resistive module 30 could comprise one or more than two resistors. FIG. 2 shows an example of an equivalent electrical circuit representing the driver module 20 connected to the resistive module 30, represented by the equivalent resistor Rs, and to the impedance matcher 40, represented by the impedance Z.

(16) The power at the input of the impedance matcher 40, denoted P_matching, is then given by the following formula:

(17) $\mathrm{P\_matching}=\frac{Z*V{d}^2}{{\left(Rs+Z\right)}^2}$ where Vd is the amplitude of the voltage signal oscillating at the operating frequency, of 13.56 MHz in NFC, supplied by the driver module 20.

(18) In order to stabilize the input power P_matching of the impedance matcher 40, it is necessary to make its derivative tend toward zero when the impedance Z varies:

(19) $\frac{dP\mathrm{matching}}{\mathrm{dz}}.fwdarw.0.$

(20) Making the assumption that the derivative is zero, then:

(21) $\frac{dPmatching}{dz}=0$

(22) Thus, by differentiating

(23) $\frac{Z*V{d}^2}{{\left(Rs+Z\right)}^2}$
with respect to Z, what is obtained is:

(24) $\frac{dPmatching}{dz}=\frac{R{s}^2-Z^2}{{\left(Rs+Z\right)}^4}*V{d}^2$

(25) It is then observed that

(26) $\frac{dP\mathrm{matching}}{a_Z}=0$
when Rs=Z, Z being the target impedance corresponding to the value of the output voltage of the driver module 20 divided by the intensity value supplied by the driver module 20.

(27) Table 1 shows an example of a test varying the value of the impedance of the impedance matcher 40 for a real target impedance value equal to 50 ohms and an Rs value equal to the value of the target impedance:

(28) TABLE-US-00001 TABLE 1 Z 50 45 40 35 30 25 20 15 10 N (Rs = 0 ?) 190 200 212 227 245 255 255 255 255 N (Rs = 50 ?) 190 189 189 187 184 179 172 160 142

(29) In this example, it is observed that the numerical value of the image voltage given by the converter 210 is identical in the presence or in the absence of the resistive module 30 (Rs=0 or Rs=50 ohms) when the impedance value is equal to the target impedance of 50 ohms. When the impedance value of the impedance matcher 40 is varied, it is observed that the converter 210 is saturated when Z is lower than or equal to 25 ohms in the absence of the resistive module 30 but that it is not saturated in the presence of the resistive module 30. In this example, it is observed, by contrast, that the numerical value of the image voltage given by the converter 210 decreases with the value of the impedance in the presence of a resistive module 30 the resistance value of which is equal to the target impedance. This results in a drop in sensitivity but the converter 210 is not saturated.

(30) Table 2 shows an example of a test varying the value of the impedance of the impedance matcher 40 for a real target impedance value equal to 50 ohms and an Rs value equal to 20 ohms:

(31) TABLE-US-00002 TABLE 2 Z (Im(Z) = 0) 50 45 40 35 30 25 20 15 10 N ( Rs = 0 ?) 190 200 212 227 245 255 255 255 255 N ( Rs = 20 ?) 190 194 198 202 206 209 210 207 198

(32) In this example, it is observed that the numerical value of the image voltage given by the converter 210 is identical in the presence or in the absence of the resistive module 30 (Rs=0 or Rs=50 ohms) when the impedance value is equal to the target impedance of 50 ohms. When the impedance value of the impedance matcher 40 is varied, it is observed that the converter 210 is saturated when Z is less than or equal to 25 ohms in the absence of the resistive module 30 but that it is not saturated in the presence of the resistive module 30. It is observed that the numerical value of the image voltage given by the converter 210 varies and increases slightly up to 210 when the value of the impedance decreases in the presence of a resistive module 30 the resistance value of which is lower than the target impedance value.

(33) The presence of a resistive module 30 allows the input power P_matching of the impedance matcher 40, and therefore the power delivered to the antenna 50, to be stabilized, which reduces the amplitude of the variations in the voltage defined across the terminals of the antenna 50 and therefore in the image voltage, allowing the converter 210 to operate within its operating range without being saturated and with significant stability.