Energy-saving device and method for a presence detection system for motor vehicles

Abstract

Device (1) for a system for detecting the presence of a user in the vicinity of a motor vehicle, the device (1) being intended for installation in the vehicle and comprising a microcontroller (20) and a transmitter-receiver circuit (10), wherein: - the transmitter-receiver circuit (10) includes an antenna (110) and an oscillator (120), wherein the oscillator (120) is designed to receive a supply voltage and an electrical setpoint signal and to provide a transmission signal when supplied with the supply voltage, wherein a frequency of the transmission signal is a function of a setpoint formed by a characteristic of the electrical setpoint signal, and wherein the antenna (110) is designed to transmit the transmission signal from the oscillator (120) for the purpose of forming a signal transmitted by the transmitter-receiver circuit (10); - the transmitter-receiver circuit (10) is designed to receive, via the antenna (110), a reflected signal resulting from the signal transmitted by the transmitter-receiver circuit (10); - the microcontroller (20) comprises a control unit (210) and a piezoelectric element (230); - the microcontroller (20) is designed to provide the electrical setpoint signal to the oscillator (120) and to control the supply of the oscillator (120) with the supply voltage such that the transmitter-receiver circuit (10) transmits periodically and during intervals of transmission time (E); and wherein the control unit (210) of the microcontroller (20) is designed to implement the following steps in this order: a) activating (E9) the piezoelectric element (230) during a so-called “wake-up” time interval (R) to stabilize the piezoelectric element (230), b) once the piezoelectric element (230) is stabilized, controlling (E1) the voltage supply of the oscillator (120) and providing an electrical setpoint signal to the oscillator (120) associated with a so-called current setpoint so that the transmitter-receiver circuit (10) transmits a signal (E2) during a transmission time interval (E), c) during the transmission time interval (E): - by means of the stabilized piezoelectric element (230), measuring (E5) the frequency of a Doppler signal resulting from the reflected signal, and - by means of the stabilized piezoelectric element (230), measuring (E3) the frequency of the transmission signal provided at the output of the oscillator (120), d) by means of a comparison between the value of a target frequency and the measurement of the frequency of the transmission signal, determining (E4) a corrected setpoint value, the corrected setpoint value making it possible to reduce a deviation between the value of the target frequency and the measurement of the frequency of the transmission signal when the oscillator (120) is supplied with voltage and receives the corrected setpoint value.

Description

[0001] The invention relates to the field of motor vehicles and, in particular, to a device and method for a presence detection system in the surroundings of a vehicle. The purpose of such a system is, in particular, to enable the opening of one or more doors of the vehicle, for example, the rear trunk.

[0002] In motor vehicles, the use of sensors is common, allowing the detection of a user's presence near the vehicle to unlock the doors or open the rear trunk. In the case of a door, the sensor is generally mounted in the door handle. In the case of a rear trunk, the sensor is generally mounted under the trunk, and the sensor must be capable of detecting the passing of a user's foot in front of the sensor.

[0003] A common sensor solution relies on capacitance measurements that vary when a user is present near the sensor compared to a reference value indicating the absence of a user. However, these types of sensors, known as "capacitive," can be inaccurate, reducing their efficiency and reliability.

[0004] To overcome this disadvantage, another common sensor solution is based on RADAR technology (an acronym for "RADIO DETECTION AND RANGING") and consists of transmitting a high-frequency signal, for example, 24 GHz, and measuring the frequency of the reflected signal. For this purpose, the sensor includes a microcontroller and a transmitter-receiver circuit. The transmitter-receiver circuit includes an antenna and an oscillator for transmitting the high-frequency signal.

[0005] According to current standards, the radio-frequency signal must be transmitted within a predefined frequency range. To prevent the frequency of the transmitted signal from falling outside this range, it is common practice to use a phase-locked loop (PLL). When the circuit is commissioned and before the signal is transmitted, the oscillator is supplied with power for a so-called "stabilization" period to allow its frequency to stabilize. This stabilization is achieved within the transmitter-receiver circuit using the phase-locked loop.Another common implementation for ensuring transmission in the desired frequency range is frequency control with a microcontroller that controls the power supply of the transmitter-receiver circuit, measures the frequency with its own quartz oscillator, checks whether this frequency is equal to a target frequency, adjusts the transmission frequency of the radar sensor's oscillator if necessary, and then measures this transmission frequency again for verification. After this check, or after the oscillator has been stabilized by the phase-locked loop, the microcontroller controls the transmitter-receiver circuit to transmit a continuous signal. The signal is generated using the oscillator and transmitted using the antenna.The microcontroller then periodically measures the frequency of a Doppler signal resulting from the reflected signal. The frequency of the Doppler signal is a function of a frequency offset between the reflected signal and the signal transmitted by the transmitter-receiver circuit. A non-zero frequency shift indicates the presence of a user in the immediate vicinity of the sensor. If the frequency of the reflected signal is identical to that of the transmitted signal, this indicates the absence of any user movement in front of the sensor. However, continuous signal transmission is particularly energy-intensive, which is a major disadvantage in a motor vehicle.

[0006] To at least partially overcome this disadvantage, it is common practice to transmit the signal periodically rather than continuously. Changes in parameters such as oscillator temperature and humidity can alter the transmission frequency of the oscillator and thus of the transmitter-receiver circuit. Therefore, in the current state of the art, the RADAR sensor's oscillator is stabilized and the RADAR sensor's oscillator frequency is controlled before each signal transmission period. However, the stabilization phase of the RADAR sensor's oscillator and the frequency control phase are particularly energy-intensive. Repeating this step, in turn, results in significant energy consumption by the sensor.

[0007] Devices and methods known from the prior art are described, for example, in DE 10 2004 054 667 A1, DE 10 2017 113 730 A1 and US 2018 / 0 170 309 A1.

[0008] The object of the invention is therefore to at least partially remedy these disadvantages.

[0009] To this end, the invention firstly relates to a device for a system for detecting the presence of a user in the vicinity of a motor vehicle, the device being intended to be mounted in the vehicle and comprising a microcontroller and a transmitter-receiver circuit, wherein: - the transmitter-receiver circuit includes an antenna and an oscillator, wherein the oscillator is configured to receive a supply voltage and an electrical setpoint signal and to provide a transmission signal when supplied with the supply voltage, wherein a frequency of the transmission signal is a function of a setpoint formed by a characteristic of the electrical setpoint signal, and wherein the antenna is configured to transmit the transmission signal from the oscillator for the purpose of forming a signal transmitted by the transmitter-receiver circuit, - the transmitter-receiver circuit is designed to receive, via the antenna, a reflected signal resulting from the signal transmitted by the transmitter-receiver circuit, - the microcontroller comprises a control unit and a piezoelectric element, - the microcontroller is designed to provide the electrical setpoint signal to the oscillator and to control the supply of the oscillator with the supply voltage such that the transmitter-receiver circuit transmits periodically and during intervals of transmission time, and wherein the control unit of the microcontroller is designed to implement the following steps in this order: a) Activating the piezoelectric element during a so-called “wake-up” time interval to stabilize the piezoelectric element, b) once the piezoelectric element is stabilized, controlling the voltage supply of the oscillator and providing an electrical setpoint signal to the oscillator, which is associated with a so-called current setpoint, so that the transmitter-receiver circuit transmits a signal during a transmission time interval, c) during the transmission time interval: - by means of the stabilized piezoelectric element, measuring the frequency of a Doppler signal resulting from the reflected signal, and - by means of the stabilized piezoelectric element, measuring the frequency of the transmitted signal provided at the output of the oscillator, d) by means of a comparison between the value of a target frequency and the measurement of the frequency of the transmitted signal, determining a corrected target value, the corrected target value making it possible to reduce a deviation between the value of the target frequency and the measurement of the frequency of the transmitted signal when the oscillator is supplied with voltage and receives the corrected target value.

[0010] The Doppler signal refers, as is well known, to a signal whose frequency is a function of the difference between the frequency of the reflected signal and the frequency of the signal transmitted by the transmitter-receiver circuit. This frequency difference increases with the speed of a target at which the reflected signal is reflected. The target here is the user's leg.

[0011] The transmitter-receiver circuit and its oscillator are not supplied with power permanently, but only intermittently during the transmission time intervals, so that electrical consumption of the device according to the invention is reduced.

[0012] The transmitter-receiver circuit can be called a “RADAR circuit”.

[0013] The oscillator is designed to receive a supply voltage and an electrical setpoint signal. Preferably, the supply voltage is a signal that does not vary from one transmission time interval to the next. Alternatively, the electrical setpoint signal is a signal that can vary from one transmission time interval to the next.

[0014] The characteristic of the electrical setpoint signal constituting a setpoint may comprise at least one of the following characteristics: a voltage value (peak-to-peak value, average value, absolute value of a DC voltage, etc.), a current value (peak-to-peak value, average value, absolute value of a DC current, etc.), an output signal of a digital signal, etc. Thus, the setpoint may be a voltage setpoint or a setpoint of a type other than a voltage setpoint, in particular a current setpoint or a digital setpoint, etc.

[0015] During the measurement time interval, the frequency of the signal provided at the output of the oscillator (transmit signal) is essentially equal to the frequency of the signal transmitted by the transmitter-receiver circuit, so that the measurement of one is essentially the same as the measurement of the other.

[0016] The corrected setpoint can then be used as the current setpoint during a subsequent transmission time interval, preferably during the time interval immediately following the transmission time interval in which the corrected setpoint was determined. The oscillator is then controlled using a predetermined setpoint or a current setpoint determined in a previous step, and in particular during a previous transmission time interval (using a measurement of the frequency of the signal provided at the oscillator output). The invention thus enables the transmitter-receiver circuit to avoid the frequency control phase before each signal transmission. This greatly reduces the electrical consumption of the device according to the invention compared to prior art devices.In particular, the invention eliminates the need for a phase-locked loop at the oscillator input to stabilize its frequency at the target frequency before each signal transmission by the transceiver circuit. The invention requires regular measurements of the transmitted signal frequency. The transmitted signal frequency is measured using the piezoelectric element, which must first be frequency-stabilized. Nevertheless, the power consumption of the microcontroller during operation, including the piezoelectric element, is significantly lower than that of the transceiver circuit. Furthermore, the piezoelectric element stabilizes faster than the oscillator.The stabilization of the piezoelectric element, which is necessary for the implementation of the invention, thus consumes significantly less energy than frequency stabilization of the oscillator itself, as implemented in the prior art using a phase-locked loop. The overall electrical consumption of the device can thus be significantly reduced, for example, by a factor of 30, compared to prior art devices based on the use of a phase-locked loop before each signal transmission by the transmitter-receiver circuit. Furthermore, according to the invention, the frequency stabilization of the oscillator is based on a frequency measurement step performed during the transmission time interval during the transmission of the signal used to detect the presence of a user.Thus, the frequency stabilization of the oscillator does not increase the total duration of the signal transmission by the oscillator, which makes it possible to reduce the electrical energy consumption of the device compared to the state of the art.

[0017] Advantageously, the control unit of the microcontroller is configured to use the corrected setpoint as the current setpoint during a subsequent transmission time interval. Preferably, the subsequent transmission time interval comprises at least the transmission time interval immediately following the transmission time interval in which the transmission signal frequency measurement is performed.

[0018] The control unit may be designed to carry out the following substeps in step d): - Comparing the value of the target frequency with the frequency measurement of the transmitted signal, - depending on whether the measurement of the frequency of the transmitted signal is clearly higher or clearly lower than the value of the target frequency, adding or subtracting an increment to / from the current setpoint to obtain the corrected setpoint.

[0019] If the frequency of the transmitted signal is clearly above (or below) the target frequency, an increment is added (or subtracted) to (from) the current setpoint, or a subtraction (or addition) is performed from (to) the current setpoint. Advantageously, the microcontroller then includes a memory that stores data including the target frequency value and the increment value.

[0020] The value of the increment is advantageously stored during a pre-calibration phase.

[0021] Additionally or alternatively, the control unit may be designed to perform the following step in step d): - determining the corrected setpoint from pre-stored data relating the value of the frequency of the transmitted signal and the value of the setpoint provided to the oscillator.

[0022] The pre-stored data may comprise a table of values and / or a curve and / or a function relating the value of the frequency of the transmitted signal and the value of the setpoint supplied to the oscillator.

[0023] Advantageously, the microcontroller then includes a memory that stores the pre-stored data relating the value of the frequency of the transmitted signal and the value of the setpoint provided to the oscillator.

[0024] The pre-stored data relating the value of the frequency of the transmitted signal and the value of the setpoint supplied to the oscillator are advantageously stored during a pre-calibration phase.

[0025] Advantageously, the piezoelectric element is a quartz clock generator, which enables the precise measurement of the signal transmission frequency.

[0026] Preferably, the duration of the wake-up time interval is between 100 µs and 10 ms, preferably between 500 µs and 5 ms.

[0027] Preferably, during an initialization phase after switching on the device and before the first transmission time interval by the transceiver circuit, the microcontroller can supply voltage to the oscillator during a so-called "stabilization" time interval in order to stabilize it at the desired transmission frequency (preferably the target frequency) and thus determine an initial setpoint. In particular, the control unit is advantageously designed to implement the following steps during an initialization phase after switching on the device and before a first transmission time interval: - Controlling the voltage supply of the oscillator during a so-called “stabilization” time interval, - during the stabilization time interval, controlling a stabilization, at the target frequency, of the transmission signal provided at the output of the oscillator and thereby determining an initial value of the current setpoint that enables the oscillator to be stabilized at the target frequency.

[0028] Alternatively, the microcontroller is adapted to measure the temperature in the device, preferably at the oscillator, and to select a predetermined setpoint (or initial value of the current setpoint) to stabilize the oscillator in frequency (preferably the target frequency) at the measured temperature. This predetermined value can, for example, be listed in a table stored in a memory area, in particular a memory area of the microcontroller. In this embodiment, the device according to the invention includes a temperature sensor, the sensitive element of which is advantageously arranged on the oscillator and which is designed to provide a measurement signal to the microcontroller.

[0029] According to one aspect of the invention, the microcontroller is capable of varying the period of the transmission and measurement time intervals, i.e. a ratio between a repetition rate of the transmission time intervals and a repetition rate of the measurement steps of the frequency of the transmission signal, in particular depending on the operating mode of the vehicle (normal operation or idle state), in order to avoid that the microcontroller measures the frequency of the transmitted signal at each transmission time interval, which enables further energy saving.

[0030] Preferably, the device according to the invention further comprises a battery and a switch, wherein the battery is adapted to provide the supply voltage to the oscillator, wherein the switch is connected between the battery and the oscillator, and wherein the switch is controlled by the microcontroller such that the transmitter-receiver circuit transmits periodically and during the transmission time intervals.

[0031] Preferably, the control unit of the microcontroller is further configured to detect the presence of a user at the device when the frequency of the reflected signal differs from the frequency of the transmitted signal. This detection utilizes the measurement of the frequency of the Doppler signal. If the frequency of the reflected signal is equal to the frequency of the signal transmitted by the transmitter-receiver circuit (and thus the frequency of the transmitted signal at the oscillator output), the frequency of the Doppler signal is zero, meaning there is no movement of a target located at the device. This infers the absence of a user at the device.If the frequency of the reflected signal differs from the frequency of the signal transmitted by the transmitter-receiver circuit (and thus from the frequency of the transmitted signal at the oscillator output), the frequency of the Doppler signal is non-zero, reflecting the movement of a target, such as the user's foot. This infers the presence of a user at the device.

[0032] Preferably, the frequency of the transmission signal is a function of a voltage of the electrical setpoint signal, the setpoint thus forming a voltage setpoint.

[0033] The invention also relates to a device for detecting the presence of a user in the vicinity of a motor vehicle, the device being designed to be mounted in the vehicle and comprising a microcontroller and a transmitter-receiver circuit, the transmitter-receiver circuit including an antenna and an oscillator and being adapted to periodically transmit, during a transmission time interval and via the antenna, a signal having a target frequency from the oscillator and to receive a reflected signal resulting from the signal transmitted via the antenna, the microcontroller comprising a control unit and a piezoelectric element, the control unit being adapted to: - Activating the piezoelectric element during a so-called “wake-up” time interval to stabilize the piezoelectric element, - once the piezoelectric element is stabilized, controlling the voltage supply of the oscillator from a predetermined voltage setpoint to the stabilized frequency of the piezoelectric element (which allows the oscillator of the transmitter-receiver circuit to operate at the target frequency value) so that the transmitter-receiver circuit transmits a signal during a so-called "transmit" time interval, - during the transmission time interval: - Measuring the frequency of a reflected (Doppler) signal resulting from the transmitted signal, and - Measuring the frequency of the transmitted signal, - Determining a new voltage setpoint from the measurement of the frequency of the transmitted signal, which enables the oscillator of the transmitter-receiver circuit to operate at the target frequency value of the signal, and - Detecting the presence of a user at the device when the frequency of the reflected signal differs from the frequency of the transmitted signal.

[0034] The invention also relates to a motor vehicle comprising at least one device as disclosed above.

[0035] The invention further relates to a method for detecting the presence of a user in the vicinity of a motor vehicle using a device according to one of the preceding claims, the method comprising the following steps: a) during a so-called “wake-up” time interval, activation of the piezoelectric element by the control unit for the purpose of stabilising the piezoelectric element, b) once the piezoelectric element is stabilized, and using the microcontroller, controlling the voltage supply of the oscillator and providing an electrical setpoint signal to the oscillator associated with the current setpoint so that the transmitter-receiver circuit transmits a signal during a transmission time interval, c) during the transmission time interval: - Measuring, by the microcontroller, the frequency of the Doppler signal resulting from the reflected signal, and - Measuring, by the microcontroller, the frequency of the transmission signal provided at the output of the oscillator, d) by means of a comparison between the value of a target frequency and the measurement of the frequency of the transmission signal, determining, by the microcontroller, a corrected setpoint, the corrected setpoint making it possible to reduce a deviation between the value of the target frequency and the measurement of the frequency of the transmission signal when the oscillator is supplied with voltage and receives the corrected setpoint.

[0036] Advantageously, the method according to the invention also includes a step of detecting the presence of a user at the device when the frequency of the reflected signal differs from the frequency of the transmitted signal.

[0037] Preferably, the piezoelectric element is a quartz clock.

[0038] Preferably, the duration of the wake-up time interval is between 100 µs and 10 ms, preferably between 500 µs and 5 ms.

[0039] The invention also relates to a method for detecting the presence of a user in the vicinity of a motor vehicle with a device as disclosed above, the method comprising the following steps: - Activation, by the control unit, of the piezoelectric element during a so-called “wake-up” time interval to stabilize the piezoelectric element, - once the piezoelectric element is stabilized, controlling, by the microcontroller, the voltage supply of the oscillator from a predetermined voltage setpoint to the stabilized frequency of the piezoelectric element, so that the transmitter-receiver circuit transmits a signal during a so-called "transmit" time interval, - during the transmission time interval: - Measuring, by the microcontroller, the frequency of a reflected signal resulting from the transmitted signal, and - Measuring, by the microcontroller, the frequency of the transmitted signal, - Determining, by the microcontroller, a new voltage setpoint from the measurement of the frequency of the transmitted signal, which allows the oscillator of the transmitter-receiver circuit to operate at the target frequency value of the signal, - Detecting the presence of a user at the device when the frequency of the reflected signal differs from the frequency of the transmitted signal.

[0040] Further features and advantages of the invention will become apparent from the following description. This is for illustrative purposes only and should be read in conjunction with the accompanying drawings: Fig. Figure 1 shows schematically an embodiment of the device according to the invention. Fig. Figure 2 shows schematically an example of the operation of the device according to the invention. Fig. Figure 3 shows schematically an embodiment of the method according to the invention.

[0041] The device according to the invention is intended to be mounted in a motor vehicle for the purpose of detecting the presence of a user in the vicinity of the vehicle, in particular the presence of a foot or a hand of the user.

[0042] Fig. Figure 1 shows an embodiment of the device 1 according to the invention. The device 1 comprises a transceiver circuit 10 and a microcontroller 20, both powered by a battery 2 of the vehicle, as well as a switch 30 mounted between the battery 2 and the transceiver circuit 10 and suitable for being controlled by the microcontroller 20 to supply or not supply the transceiver circuit 10 with electrical energy.

[0043] The transmitter-receiver circuit 10 comprises an antenna 110 and an oscillator 120.

[0044] The transmitter-receiver circuit 10 is adapted to periodically transmit a signal at a predetermined frequency from the oscillator 120 and via the antenna 110 during a so-called "transmission" time interval, and to receive a reflected signal resulting from the signal transmitted via the antenna 110. For this purpose, the oscillator 120 is configured to receive a supply voltage from the battery 2 when the switch 30 is closed and to receive no supply voltage when the switch 30 is open. Furthermore, the oscillator 120 is configured to have its oscillation frequency controlled by an electrical setpoint signal provided by the microcontroller 20. In particular, the oscillation frequency of the oscillator 120, and thus the frequency of the transmission signal output by the oscillator 120, is a function of a setpoint formed by a characteristic of the electrical setpoint signal.In the following, but not by way of limitation, this setpoint is a voltage setpoint formed by the absolute value of the voltage of the electrical setpoint signal (a DC voltage that assumes a fixed value during a considered transmission time interval). Oscillator 120 can, for example, be configured to operate at a target frequency of 24.2 GHz, as is common for civil radar applications. The output of the oscillator is connected to antenna 110 for the purpose of transmitting a signal through transceiver circuit 10.

[0045] In this example and advantageously, the transmitter-receiver circuit 10 also comprises a switch 115 connected between the output of the oscillator 120 and the antenna 110 and suitable to be controlled by the microcontroller 20.

[0046] In this case, and advantageously, the transceiver circuit 10 further comprises a frequency divider 130 connected to the microcontroller 20, through which the microcontroller 20 measures the frequency of the transmission signal at the output of the oscillator. The frequency divider 130 serves to reduce a measured value of the frequency of the transmission signal provided by the oscillator in order to bring this value into a digitally usable range for the microcontroller. In this example, and not by way of limitation, the frequency divider 130 divides the transmission frequency by 220 = 1048576. The transceiver circuit 10 further includes a circuit (not shown) designed to receive a reflected signal received by the antenna 110 and forward this signal to the microcontroller 20.

[0047] The microcontroller 20 enables the control of the transmitter-receiver circuit 10 and comprises a control unit 210, a memory area 220 and a piezoelectric element 230.

[0048] The control unit 210 is adapted to activate the piezoelectric element 230 during a so-called "wake-up" time interval to stabilize the piezoelectric element 230. Preferably, the duration of the wake-up time interval is between 0.1 and 1 ms. The piezoelectric element 230 serves as a clock for performing frequency measurements within the microcontroller 20.

[0049] The control unit 210 is suitable for controlling the voltage supply to the oscillator 120 (here by closing the switch 30) after the piezo element has stabilized and for providing the oscillator with an electrical setpoint signal. A characteristic of the electrical setpoint signal, here an absolute voltage value, forms a predetermined setpoint, here a predetermined voltage setpoint. The predetermined voltage setpoint advantageously enables the oscillator 120 to operate at the target frequency value of the signal to be transmitted. In practice, the operating conditions (in particular the temperature of the oscillator 120) can cause a frequency drift of the signal transmitted by the oscillator at a constant value of the voltage setpoint. For the sake of clarity, a current voltage setpoint is therefore defined, which designates the voltage setpoint provided to the oscillator 120 at a specific time.The current voltage setpoint allows the oscillator 120 to operate at the target frequency value of the signal to be transmitted under initial operating conditions. After a certain period of operation of the device 1, the current voltage setpoint no longer allows the oscillator 120 to operate precisely at the target frequency value of the signal to be transmitted, because the operating conditions of the device 1 have changed. The oscillator 120 is then operated at a value that deviates slightly from the target frequency, for example, above or below the target frequency. The voltage supply to the oscillator 120 enables the transmission of a signal via the antenna 110 during a so-called "transmit" time interval.

[0050] In this preferred example, the piezoelectric element 230 is in the form of a quartz clock capable of oscillating very precisely at the desired frequency value to enable the measurement of the desired frequency values, including the frequency of the transmitted signal at the output of the oscillator 120.

[0051] The control unit 210 is adapted to measure the frequency of a Doppler signal resulting from the reflected signal during a transmission time interval. Measuring the frequency of a Doppler signal in connection with detecting the presence of a user on a vehicle is a common technique that will not be described further here. Simply put, the Doppler signal is formed using a multiplier that receives at its input, on the one hand, the reflected signal of frequency f0 and, on the other hand, a portion of the signal of frequency fl provided at the output of the oscillator 120. At its output, it provides a signal, one component of which has the frequency |f0-fl|. Using frequency filtering, this component is isolated and forms the Doppler signal.The device 1 comprises various elements, not shown, which allow the measurement of a Doppler signal, in particular the multiplier, and a coupler arranged at the output of the oscillator 120 and capable of directing most of the signal to the antenna 110 and a small part of the signal to the multiplier.

[0052] In parallel, the control unit 210 is able to measure the frequency of the signal transmitted by the antenna 110 during the same transmission time interval and determine a new setpoint (here, a new voltage setpoint) corresponding to the measured frequency of the transmitted signal, so that the oscillator 120 can be operated at the target frequency during the next transmission. In practice, the control unit measures the frequency of the signal at the output of the oscillator 120, upstream of the antenna 110, the frequency of the signal transmitted by the antenna being substantially equal to the frequency of the signal transmitted by the oscillator 120 when the switch 115 is closed. The new setpoint can be referred to as the "corrected setpoint." This is the setpoint value that allows the oscillator to operate at the target frequency value under the current operating conditions.

[0053] The measurement of the frequency of the transmitted signal can advantageously be carried out using a counter (not shown), which is controlled, for example, by the control unit 210 and is electrically connected to the frequency divider 130. The counter uses the piezoelectric element 230 as a clock generator. According to the invention, the piezoelectric element 230 must therefore be frequency-stabilized before measuring the frequency of the transmitted signal.

[0054] The predetermined setpoint may have been determined in the previous transmission time interval or in any previous transmission time interval. The newly obtained setpoint is then used as the setpoint in subsequent transmission time intervals. Preferably, a new setpoint is determined periodically, for example, every three or four transmission time intervals.

[0055] During an initialization phase after switching on the device 1 and before the first transmission time interval by the transmitter-receiver circuit 10, the microcontroller 20 may be able to supply voltage to the oscillator 120 and provide it with an electrical setpoint signal during a so-called "stabilization" time interval in order to stabilize the oscillator at the desired transmission frequency (referred to herein as "target frequency") and thus determine an initial setpoint.

[0056] Alternatively, the microcontroller 20 may be capable of measuring an initial temperature inside the device 1, preferably at the oscillator 120, and deriving an initial setpoint therefrom in order to stabilize the oscillator 120 at the measured temperature at the desired transmission frequency (referred to here as the target frequency). Advantageously, this variant uses a table stored in a memory that relates setpoints and temperature values for the operation of the oscillator 120 to the target frequency. The memory is, for example, the memory area 220 of the microcontroller 20 or an auxiliary memory (not shown).In one embodiment, the microcontroller 20 is capable of changing the period of the transmission and measurement time intervals, in particular depending on the operating mode of the vehicle (normal mode or idle mode), in order to avoid the microcontroller 20 measuring the frequency of the transmitted signal at each transmission time interval, thus enabling further energy savings. In particular, the period of the transmitted signal by the transmitter-receiver circuit (via the oscillator 120 and the antenna 110), as well as the period of measurement of the frequency of the signal transmitted by the transmitter-receiver circuit, can be adjusted according to the fluctuations in temperature and humidity. For example, if the temperature and humidity change little or not at all and / or the vehicle is in idle mode, the microcontroller 20 can increase the transmission period (i.e.In some cases, the microcontroller can reduce the transmission period (i.e., reduce the repetition rate of the transmission time intervals) and also not measure the frequency of the transmitted signal with each transmission. However, if the temperature and humidity are changing rapidly and / or the vehicle is in normal operating mode, the microcontroller can reduce the transmission period (i.e., increase the repetition rate of the transmission time intervals) and additionally measure the frequency of the transmitted signal with each transmission.

[0057] The control unit 210 is configured to measure the frequency of the Doppler signal obtained from the signal transmitted by the transceiver circuit 10 and reflected (or backscattered) by a user (e.g., their moving foot). Preferably, the control unit 210 is capable of detecting the presence of a user at the device 1 if the frequency of the reflected signal differs from the frequency of the transmitted signal (Doppler signal frequency not equal to zero). Alternatively, the presence detection is implemented in an additional device.

[0058] To perform all these functions, the microcontroller 20 is able to implement a list of instructions stored in its memory area 220.

[0059] The invention will now be described in its implementation with reference to the Fig. 2 and Fig. 3 described. Fig.Figure 2 shows an example of the operation of the device 1, in which the upper diagram shows the evolution of the intensity of the current consumed by the device 1, the middle diagram shows the periodic transmission time intervals E of the transmitter-receiver circuit 10 and the lower diagram shows an initialization phase P1 and a measurement phase P2 including periodic idle state intervals V, wake-up time intervals R and measurement time intervals M (of the period T).

[0060] First, upon starting up device 1, the microcontroller goes through an initialization phase P1, during which it opens switch 115 (to prevent a signal at the output of oscillator 120 from being transmitted to antenna 110), closes switch 30 (to supply voltage to oscillator 120), and then applies an electrical setpoint signal to the input of oscillator 120, forming a setpoint. During this initialization phase P1, microcontroller 20 searches for the setpoint value necessary for oscillator 120 to transmit at a target frequency. The target frequency lies within the frequency range permitted by the standard and is, for example, 24.2 GHz. During this time, oscillator 120 must stabilize its frequency for a non-zero time interval.To stabilize the oscillator 120 so that the signal transmitted (by the oscillator 120 and thus not by the transmitter-receiver circuit 10) is at the desired target frequency, the microcontroller 20 sets the input setpoint of the oscillator 120, possibly by trial and error or by closed-loop control. The setpoint is formed here, but not limited to, by a voltage. Alternatively, it can also be formed by any characteristic of an electrical signal other than its voltage, for example, its current. Once the oscillator 120 is stabilized, the microcontroller 20 stores the setpoint defined at the oscillator input in its memory area 220 as the start setpoint or initial setpoint.The microcontroller 20 can then optionally close switch 115 to check the influence of the connection to the antenna 110 on the frequency of the oscillator 120 and further adjust the initial setpoint. In fact, the frequency of the oscillator 120 can be influenced, in particular, by the connection of the antenna 110 to the oscillator 120. It should be noted that during the initialization phase P1, no signal is transmitted by the transceiver circuit 10 (or only at the end of the initialization phase P1, when the frequency of the oscillator 120 has stabilized and the switch 115 is closed). In fact, during this initial setpoint search phase, the transmission frequency could be outside the permissible range. Nevertheless, the transceiver circuit 10 is supplied with power during this initialization phase P1 (the switch 30 is closed).After completion of the initialization phase P1, the device 1 operates in a so-called "measurement" phase P2. This measurement phase P2 is repeated periodically. In a step E1 of the measurement phase P2, the microcontroller 20 first closes switch 115, keeps switch 30 closed, and applies the starting setpoint determined in the initialization phase P1 to the input of oscillator 120. The oscillator 120 is thus immediately ready for operation. In fact, it then directly emits a signal that essentially oscillates at the target frequency for which it was precalibrated in the initialization phase P1. If the operating conditions, such as temperature and / or humidity, have not changed since the initialization phase P1, the signal transmitted by oscillator 120 oscillates exactly at the target frequency. Alternatively, these operating conditions may have changed since the initialization phase P1.In this case, the setpoint defined in the initialization phase P1 no longer corresponds to a transmission at the target frequency, and the signal transmitted by oscillator 120 oscillates at a frequency different from the target frequency. After applying the starting setpoint to the input of oscillator 120, in a step E2, transceiver circuit 10 transmits a signal via antenna 110 during a first so-called "transmission" time interval E. One function of the signal transmitted by transceiver circuit 10 is to detect a nearby user. The signal transmitted by transceiver circuit 10 corresponds to the signal provided by oscillator 120, which is then transmitted by antenna 110. This signal therefore oscillates essentially at the same frequency as the oscillator when switch 115 is closed.

[0061] During the transmission of the signal by the transceiver circuit 10, the control unit 210 of the microcontroller 20 measures the frequency of the signal transmitted by the transceiver circuit 10 in a step E3. In practice, this measurement is performed on the signal transmitted by the oscillator 120 via the frequency divider 130. The frequency divider 130 reduces the frequency of the signal transmitted by the oscillator 120 to a value that can be measured in the microcontroller 20. The frequency measurement uses a counter of the microcontroller 20 and a clock generator, which here is formed by the piezoelectric element 230.

[0062] In step E4, microcontroller 20 determines a corrected setpoint, also referred to as the new setpoint or "real-time" setpoint. The real-time setpoint is determined from the frequency measurement of the transmitted signal. This would allow oscillator 120 of transceiver circuit 10 to operate approximately at the exact value of the target frequency when oscillator 120 receives the real-time setpoint. Therefore, at a next transmission time interval, oscillator 120 can approach operation at the exact value of the target frequency when oscillator 120 receives the real-time setpoint. This real-time setpoint is stored in memory area 220.

[0063] In practice, the real-time setpoint can be obtained simply by comparing the target frequency with the frequency measured in step E3. If the target frequency is higher than the frequency measured in step E3, an increment is added to or subtracted from the current setpoint (i.e., the setpoint present at the oscillator input during step E3). If, on the other hand, the target frequency is lower than the frequency measured in step E3, an increment is subtracted from or added to the current setpoint. The value of the increment is advantageously determined in a pre-calibration step. While this solution does not necessarily ensure operation at the exact target frequency at all times, it prevents excessive frequency drift from accumulating over time. This ensures that the oscillator 120 is always within a desired frequency band.

[0064] Alternatively, the real-time setpoint can be determined using a table of values and / or a curve and / or a function that relates the value of the frequency of the signal transmitted by the oscillator 120 (or the transmitter-receiver circuit) to the setpoint at the oscillator input. The data used (table of values and / or curve and / or function) are advantageously determined in a pre-calibration step.

[0065] During this transmission time interval E, the control unit 210 of the microcontroller 20 also measures the frequency of the Doppler signal obtained from the reflected signal in a step E5 in parallel to steps E3 and E4.

[0066] At the end of the transmission time interval E and in step E6, the microcontroller 20 stops supplying voltage to the oscillator 120 so that it stops operating and the transceiver circuit 10 stops outputting the signal, thus saving the vehicle's electrical energy. To this end, the microcontroller 20 controls the opening of switch 30 and the opening of switch 115. It also stops supplying a setpoint value to the input of the oscillator 120.

[0067] In an optional step E7, the control unit 210 detects the presence of a user in the vicinity of the device 1. This detection is based on detecting a difference between the frequency of the reflected signal and the frequency of the signal transmitted by the transmitter-receiver circuit (Doppler effect), equivalent to a nearby user movement, for example, passing a foot. When the control unit 210 detects the presence of a user in the vicinity of the device 1, it activates a vehicle function, such as unlocking the door in which the device 1 is mounted.

[0068] After completion of steps E6 and, if applicable, E7, the microcontroller 20 enters a sleep state for a sleep interval V in which it consumes little electrical energy.

[0069] In a step E8, shortly before the start of the next transmission time interval E, the control unit 210 of the microcontroller 20 wakes up. It then controls, in a step E9, the voltage supply to the piezoelectric element 230 during a so-called "wake-up" time interval R, which allows the piezoelectric element 230 to stabilize, with the switch 115 and the switch 30 still open.

[0070] At the end of this wake-up time interval R and in a step E10, the control unit 210 closes the switch 30 and the switch 115 so that a signal is sent from the transmitter-receiver circuit 10 during a new transmission time interval E.

[0071] The microcontroller 20 then repeats steps E3 to E10 periodically as long as the device 1 is in operation, using, at each transmission time interval E, a previously defined setpoint (either defined during the initialization phase, in particular for the first transmission time interval, or defined and stored in memory during a previous transmission time interval, in particular the transmission time interval immediately preceding the transmission time interval under consideration).

[0072] It should be noted that, alternatively, steps E3 and E4 may be performed not systematically in each transmission time interval E, but at longer time intervals. Indeed, when the temperature and humidity levels vary very slowly or not at all, it may be advantageous to maintain the same setpoint for several consecutive transmission time intervals E to avoid measuring the frequency of the transmitted signal and calculating a new real-time setpoint at each transmission time interval E, thus saving electrical energy.

[0073] It should also be noted that the device 1 can be in operation both during normal operation of the vehicle (on-board electrical system activated, for example engine started) and when the vehicle is at rest (on-board electrical system in rest, engine switched off).

[0074] The invention is not limited to the examples described above and also includes many variations, including but not limited to: - Variants in which the oscillator is not controlled by an absolute value of the voltage of an electrical setpoint signal, but by any other characteristic of this signal, such as an absolute value of the current, an average value of current or voltage, etc., - variants without switch 115, whereby the initialisation phase can be carried out with a sufficiently low power in an environment that temporarily allows transmission outside the authorised frequency band, - Variants in which the control of the switch 30 is replaced by a control of the battery itself, - Variants where the step of detecting a user is performed outside the microcontroller using the Doppler frequency measurement provided by it, etc.

Claims

[1] Device (1) for a system for detecting the presence of a user in the vicinity of a motor vehicle, the device (1) being intended to be mounted in the vehicle and comprising a microcontroller (20) and a transmitter-receiver circuit (10), wherein: - the transmitter-receiver circuit (10) includes an antenna (110) and an oscillator (120), wherein the oscillator (120) is designed to receive a supply voltage and an electrical setpoint signal and to provide a transmission signal when supplied with the supply voltage, wherein a frequency of the transmission signal is a function of a setpoint formed by a characteristic of the electrical setpoint signal, and wherein the antenna (110) is designed to transmit the transmission signal from the oscillator (120) for the purpose of forming a signal transmitted by the transmitter-receiver circuit (10); - the transmitter-receiver circuit (10) is designed to receive, via the antenna (110), a reflected signal resulting from the signal transmitted by the transmitter-receiver circuit (10); - the microcontroller (20) comprises a control unit (210) and a piezoelectric element (230); - the microcontroller (20) is designed to provide the electrical setpoint signal to the oscillator (120) and to control the supply of the oscillator (120) with the supply voltage such that the transmitter-receiver circuit (10) transmits periodically and during intervals of transmission time (E); and wherein the control unit (210) of the microcontroller (20) is designed to implement the following steps in this order: a) activating (E9) the piezoelectric element (230) during a so-called “wake-up” time interval (R) to stabilize the piezoelectric element (230), b) once the piezoelectric element (230) is stabilized, controlling (E1) the voltage supply of the oscillator (120) and providing an electrical setpoint signal to the oscillator (120) which is associated with a so-called current setpoint so that the transmitter-receiver circuit (10) transmits a signal (E2) during a transmission time interval (E), c) during the transmission time interval (E): - by means of the stabilized piezoelectric element (230), measuring (E5) the frequency of a Doppler signal resulting from the reflected signal, and - by means of the stabilized piezoelectric element (230), measuring (E3) the frequency of the transmission signal provided at the output of the oscillator (120), d) by means of a comparison between the value of a target frequency and the measurement of the frequency of the transmission signal, determining (E4) a corrected setpoint value, wherein the corrected setpoint value makes it possible to reduce a deviation between the value of the target frequency and the measurement of the frequency of the transmission signal when the oscillator (120) is supplied with voltage and receives the corrected setpoint value. [2] Device (1) according to claim 1, wherein the control unit (210) of the microcontroller (20) is designed to use the corrected setpoint as the current setpoint during a subsequent transmission time interval (E). [3] Device (1) according to claim 1 or 2, wherein the control unit (210) is designed to carry out the following substeps in step d): - Comparing the value of the target frequency with the frequency measurement of the transmitted signal; - depending on whether the measurement of the frequency of the transmitted signal is clearly higher or clearly lower than the value of the target frequency, adding or subtracting an increment to / from the current setpoint to obtain the corrected setpoint. [4] Device (1) according to claim 1 or 2, wherein the control unit (210) is designed to carry out the following sub-step in step d): - determining the corrected setpoint from previously stored data relating the value of the frequency of the transmitted signal and the value of the setpoint supplied to the oscillator (120). [5] Device (1) according to one of the preceding claims, wherein the piezoelectric element (230) is a quartz clock. [6] Device (1) according to one of the preceding claims, wherein the duration of the wake-up time interval is between 100 µs and 10 ms. [7] Device (1) according to one of the preceding claims, wherein the control unit (210) is designed to carry out the following steps during an initialization phase (P1) after switching on the device (1) and before a first transmission time interval (E): - controlling the voltage supply of the oscillator (120) during a so-called “stabilization” time interval, - during the stabilization time interval, controlling a stabilization, at the target frequency, of the transmission signal provided at the output of the oscillator (120) and thereby determining an initial value of the current setpoint that enables the oscillator (120) to be stabilized at the target frequency. [8] Device according to one of claims 1 to 6, wherein the microcontroller (20) is designed to measure a temperature inside the device (1), preferably at the oscillator (120), and to derive therefrom an initial value of the current setpoint, which makes it possible to stabilize the oscillator (120) at the measured temperature at the target frequency. [9] Device (1) according to one of the preceding claims, wherein the microcontroller (20) is designed to change a ratio between a repetition rate of transmission time intervals and a repetition rate of transmission signal frequency measuring steps (E3), in particular depending on an operating mode of the vehicle, in order to avoid that the microcontroller (20) measures the frequency of the transmitted signal at each transmission time interval (E). [10] Device (1) according to one of the preceding claims, further comprising a battery (2) and a switch (30), wherein the battery (2) is designed to provide the supply voltage to the oscillator (120), wherein the switch (30) is connected between the battery (2) and the oscillator (120), and wherein the switch (30) is controlled by the microcontroller (20) such that the transmitter-receiver circuit (10) transmits periodically and during the transmission time intervals (E). [11] Device (1) according to one of the preceding claims, wherein the control unit (210) of the microcontroller (20) is further configured to detect (E7) the presence of a user at the device (1) when the frequency of the reflected signal differs from the frequency of the transmitted signal. [12] Device (1) according to one of the preceding claims, wherein the frequency of the transmission signal is a function of a voltage of the electrical setpoint signal, the setpoint thus forming a voltage setpoint. [13] Motor vehicle comprising at least one device (1) according to one of the preceding claims. [14] A method for detecting the presence of a user in the vicinity of a motor vehicle by a device (1) according to any one of claims 1 to 12, the method comprising the following steps: a) during a so-called “wake-up” time interval (R), activating the piezoelectric element (230) by the control unit (210) for the purpose of stabilising the piezoelectric element (230), b) once the piezoelectric element (230) is stabilized, and using the microcontroller (20), controlling the voltage supply of the oscillator (120) and providing an electrical setpoint signal to the oscillator associated with the current setpoint so that the transmitter-receiver circuit (10) transmits a signal during a transmission time interval (E), c) during the transmission time interval (E): - measuring, by the microcontroller (20), the frequency of the Doppler signal resulting from the reflected signal, and - measuring, by the microcontroller (20), the frequency of the transmission signal provided at the output of the oscillator (120), d) by means of a comparison between the value of a target frequency and the measurement of the frequency of the transmission signal, determining, by the microcontroller (20), a corrected setpoint value, wherein the corrected setpoint value makes it possible to reduce a deviation between the value of the target frequency and the measurement of the frequency of the transmission signal when the oscillator (120) is supplied with voltage and receives the corrected setpoint value. [15] Method according to claim 14, characterized by that it further includes a step of detecting the presence of a user at the device (1) when the frequency of the reflected signal differs from the frequency of the transmitted signal.

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