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

Abstract

Energy-saving device and method for a presence detection system for a motor vehicle. A device (1) for a presence detection system for detecting the presence of a user close to a motor vehicle, configured to: activate a piezoelectric element (230) during a time interval called a "wake-up" time interval (R) to stabilize the piezoelectric element (230), once the piezoelectric element (230) has stabilized, control the voltage supply to an oscillator (120) and supply the oscillator with a reference electrical signal forming a current voltage reference, so that a transceiver circuit (10) transmits a signal during a time interval called a "transmission" time interval (E), measure the frequency of a reflected signal originating from the transmission signal during the transmission time interval (E), measure the frequency of the transmission signal and determine a correction reference based on the measurement of the frequency of the transmission signal, allowing the oscillator (120) of the transceiver circuit (10) to operate at a target frequency value. The invention makes it possible to limit the energy consumption of a transceiver device for detecting the presence of a user close to a motor vehicle.

Description

Technical Field

[0001] The present invention relates to the field of motor vehicles and more particularly to an apparatus and method for a presence detection system for detecting a presence approaching a vehicle. Such a system is particularly intended to allow opening of one or more opening elements of the vehicle, such as a luggage compartment. Prior art

[0002] In motor vehicles, it is known practice to use sensors for detecting the presence of a user approaching the vehicle in order to unlock a door or open a trunk. In the case of a door, the sensor is usually mounted in the door handle. In the case of a trunk, the sensor is usually mounted on the underside of the trunk and the sensor needs to be able to detect the passage of a user's foot in front of the sensor.

[0003] One known sensor solution is based on measuring capacitance, which changes when a user is present near the sensor relative to a reference value that indicates that the user is not near the sensor. However, this type of sensor, known as a "capacitive" sensor, can prove to be inaccurate, reducing its effectiveness and its reliability.

[0004] To remedy this drawback, another known sensor solution is based on radar (acronym for “radio detection and ranging”) technology and consists in transmitting a high-frequency signal with a frequency of, for example, 24 GHz and in measuring the frequency of the reflected signal. To this end, the sensor comprises a microcontroller and a transceiver circuit. The transceiver circuit comprises an antenna and an oscillator for transmitting the high-frequency signal.

[0005] According to current standards, high-frequency signals must be transmitted within a predefined frequency range. In order to avoid that the frequency of the transmitted signal is outside this range, in the prior art, it is known practice to use a phase-locked loop (or PLL). When the circuit is started and before the signal is transmitted, the oscillator is powered during a time period called the "stabilization" period so that its frequency is stabilized. This stabilization is achieved within the transceiver circuit using a phase-locked loop. Another known embodiment for ensuring that the transmission is within the desired frequency range is an embodiment of a frequency closed-loop control using a microcontroller, which controls the power supply to the transceiver circuit, measures the frequency using its own quartz oscillator, checks whether the frequency is actually equal to the value of the target frequency, adjusts the transmission frequency of the oscillator of the radar sensor if necessary, and then measures the transmission frequency again for the purpose of checking. Once this check has been performed, or once the oscillator has been stabilized by the phase-locked loop, the microcontroller controls the transceiver circuit so that it continuously transmits the signal, generating the signal using the oscillator and transmitting the signal using the antenna. The microcontroller then periodically measures the frequency of the Doppler signal originating from the reflected signal, the frequency of the Doppler signal being a function of the frequency shift between the reflected signal and the signal transmitted by the transceiver circuit. A non-zero frequency shift reflects the presence of a user in the immediate vicinity of the sensor. When the frequency of the reflected signal is identical to the frequency of the transmitted signal, this reflects by contrast the absence of movement of the user in front of the sensor. However, continuously transmitting the signal proves to be particularly energy-consuming, which presents a significant disadvantage in motor vehicles.

[0006] In order to at least partially correct this drawback, known practices transmit the signal not continuously but periodically. The evolution of parameters such as the temperature and humidity of the oscillator can modify the transmission frequency of the oscillator and therefore the transmission frequency of the transceiver circuit. Therefore, in the prior art, the frequency of the oscillator of the radar sensor is checked before each signal transmission period and the oscillator of the radar sensor is stabilized. However, the phase of stabilizing the oscillator of the radar sensor and the phase of checking the frequency are particularly energy-consuming. In this case too, repeating this step therefore means a significant consumption of the energy of the sensor.

[0007] The object of the present invention is therefore to at least partially remedy these drawbacks. Summary of the invention

[0008] To this end, a first subject of the invention is a device for a presence detection system for detecting the presence of a user approaching a motor vehicle, the device being intended to be installed in said vehicle and comprising a microcontroller and a transceiver circuit, wherein:

[0009] a transceiver circuit comprising an antenna and an oscillator, wherein the oscillator is configured to receive a supply voltage and a reference electrical signal and to supply a transmission signal when supplied thereto by the supply voltage, the frequency of the transmission signal being a function of a reference formed by characteristics of the reference electrical signal, and wherein the antenna is configured to transmit said transmission signal from the oscillator so as to form a signal transmitted by the transceiver circuit;

[0010] The transceiver circuit is configured to receive, via the antenna, a reflected signal originating from a signal transmitted by the transceiver circuit;

[0011] The microcontroller includes a control unit and a piezoelectric element;

[0012] The microcontroller is configured to supply the reference electrical signal to the oscillator and drive the supply voltage to the oscillator so that the transceiver circuit transmits periodically and during a transmission time interval;

[0013] And wherein the control unit of the microcontroller is configured to implement the following steps in this order:

[0014] a) activating the piezoelectric element during a time interval called a "wake-up" time interval in order to stabilize said piezoelectric element,

[0015] b) once the piezoelectric element has stabilized, controlling the voltage supply to the oscillator and supplying the oscillator with a reference electrical signal associated with a reference called current reference, so that the transceiver circuit transmits a signal during a transmission time interval,

[0016] c) during said transmission time interval:

[0017] - using a stable piezoelectric element, measuring the frequency of the Doppler signal originating from the reflected signal, and,

[0018] - measuring the frequency of said transmission signal supplied at the output of said oscillator using a stable piezoelectric element,

[0019] d) using the comparison between the value of the target frequency and the measurement of the frequency of the transmission signal, determining a correction value of the reference, the correction value of the reference making it possible to reduce the difference 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 said corrected reference.

[0020] In a manner known per se, a Doppler signal represents 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 transceiver circuit. This frequency difference increases with the speed of the target from which the reflected signal reflects. The target is here formed by the user's legs.

[0021] The transceiver circuit and its oscillator are not powered continuously, but intermittently and only during transmission time intervals in order to reduce the power consumption of the device according to the invention.

[0022] The transceiver circuit may be referred to as a "radar circuit".

[0023] The oscillator is configured to receive a supply voltage and a reference electrical signal. Preferably, the supply voltage is a signal that does not vary from one transmission time interval to another transmission time interval. In contrast, the reference electrical signal is a signal that can vary from one transmission time interval to another transmission time interval.

[0024] The characteristics of the reference electrical signal forming the reference may include at least one of the following: voltage value (peak-to-peak value, average value, absolute value, etc. of DC voltage), current value (peak-to-peak value, average value, absolute value, etc. of DC current), output of a digital signal, etc. Therefore, the reference may be a voltage reference, or other types of references that are not voltage references, in particular current references, or digital references, etc.

[0025] During the measuring time interval, the frequency of the signal supplied at the output of the oscillator (transmission signal) is substantially equal to the frequency of the signal transmitted by the transceiver circuit, which is why the measurement of one is substantially equal to the measurement of the other.

[0026] Then, during the subsequent transmission time interval, preferably during the time interval immediately following the transmission time interval in which the corrected reference is determined, the corrected reference can be used as the current reference. In other words, the predetermined reference or the current reference determined in the previous step and in particular during the previous transmission time interval (using the measurement of the frequency of the signal supplied at the output of the oscillator) is then used to control the oscillator. Therefore, the present invention makes it possible to avoid that the transceiver circuit has to perform a frequency check phase before each signal transmission. Therefore, this greatly reduces the power consumption of the device according to the present invention compared to the devices from the prior art. In particular, the present invention makes it possible to dispense with the systematic use of a phase-locked loop at the input of the oscillator to stabilize its frequency to a target frequency before each signal transmission of the transceiver circuit. The present invention requires the implementation of a regular measurement of the frequency of the transmission signal. The frequency of the transmission signal is measured using a piezoelectric element, which must be stabilized in frequency in advance. However, the power consumption of the microcontroller during operation including the piezoelectric element is significantly lower than the power consumption of the transceiver circuit. The piezoelectric element also stabilizes faster than the oscillator. Therefore, the stabilization of the piezoelectric element required for implementing the invention consumes much less energy than the frequency stabilization of the oscillator itself, as implemented in the prior art and in a phase-locked loop. Therefore, the total consumption of the device can be significantly reduced, for example by the order of 30 times, compared to devices from the prior art based on the use of a phase-locked loop before each signal transmission of the transceiver circuit. Moreover, according to the invention, the frequency stabilization of the oscillator is based on a frequency measurement step during the transmission time interval, which is implemented during the transmission of the signal for detecting the presence of the user. Therefore, the frequency stabilization of the oscillator does not increase the total signal transmission duration of the oscillator, making it possible to reduce the electrical energy consumption of the device compared to the prior art.

[0027] Advantageously, the control unit of the microcontroller is configured to use said corrected reference as current reference during subsequent transmission time intervals.Preferably, said subsequent transmission time intervals comprise at least the transmission time intervals immediately following the transmission time interval during which said measurement of the frequency of the transmission signal was performed.

[0028] The control unit may be configured to implement the following sub-steps in step d):

[0029] - comparison of the value of the target frequency and the measurement of the frequency of the transmitted signal;

[0030] - Depending on whether the measure of the frequency of the transmission signal is strictly greater than or strictly less than the value of the target frequency, a delta is added to or subtracted from the current reference in order to obtain said corrected value of the reference.

[0031] When the frequency of the transmission signal is strictly greater than (or less than) the value of the target frequency, the increment is added to (or subtracted from) the current reference, or the increment is subtracted from (or added to) the current reference. Advantageously, the microcontroller then comprises a memory storing data comprising the value of the target frequency and the value of said increment.

[0032] The value of the increment is advantageously recorded during a preliminary calibration phase.

[0033] Additionally or as a variant, the control unit may be configured to implement the following steps in step d):

[0034] - determining said correction value of the reference on the basis of pre-recorded data relating the value of the frequency of the transmission signal to the value of the reference supplied to said oscillator.

[0035] The pre-recorded data may comprise a function and / or a curve and / or a table of values ​​relating the value of the frequency of the transmission signal to the value of a reference supplied to the oscillator.

[0036] Advantageously, the microcontroller then comprises a memory storing said pre-recorded data relating the value of the frequency of the transmission signal to the value of the reference supplied to the oscillator.

[0037] Said pre-recorded data relating the value of the frequency of the transmission signal to the value of the reference supplied to the oscillator are advantageously recorded in a preliminary calibration phase.

[0038] Advantageously, the piezoelectric element is a quartz clock, which allows the transmission frequency of the signal to be measured accurately.

[0039] Preferably, the duration of the wake-up time interval is between 100 μs and 10 ms, preferably between 500 μs and 5 ms.

[0040] Preferably, in an initialization phase after powering up the device and before the first transmission time interval of the transceiver circuit, the microcontroller is capable of supplying a voltage to the oscillator during a time interval called a "stabilization" time interval in order to stabilize the oscillator at the desired transmission frequency (preferably the target frequency) and thus determine an initial reference value. In particular, the control unit is advantageously configured to implement the following steps in an initialization phase after powering up the device and before the first transmission time interval:

[0041] - driving the voltage supply to the oscillator during a time interval called a "stabilization" time interval;

[0042] - During the stabilization time interval, the transmission signal supplied at the output of the oscillator is driven to stabilize at the target frequency and thus an initial value of the current reference for stabilizing the oscillator at the target frequency is determined.

[0043] As a variant, the microcontroller is capable of measuring the temperature inside the device, preferably measuring the temperature in the oscillator, and is capable of selecting a predetermined reference value (or an initial value of the current reference) in order to stabilize the oscillator in terms of frequency (preferably the target frequency) at the measured temperature. The predetermined value can be listed, for example, in a table stored in a memory area, in particular in a memory area of ​​the microcontroller. In this embodiment, the device according to the invention comprises a temperature sensor, the sensitive element of which is advantageously arranged in the oscillator and is configured to supply a measurement signal to the microcontroller.

[0044] According to one aspect of the invention, the microcontroller is able to modify the time period of the transmission and measurement time intervals, that is, the ratio between the repetition frequency of the transmission time interval and the repetition frequency of the step of measuring the frequency of the transmission signal, in particular based on the operating mode of the vehicle (normal mode or standby mode), so as to avoid the microcontroller measuring the frequency of the signal transmitted in each transmission time interval, thereby making it possible to save more energy.

[0045] Preferably, the device according to the present invention further comprises a battery and a switch, wherein the battery is configured to supply said supply voltage to the oscillator, the switch is connected between the battery and the oscillator, and the switch is driven by the microcontroller such that the transceiver circuit transmits periodically and during transmission time intervals.

[0046] Preferably, the control unit of the microcontroller is also configured to detect the presence of a user in front of the device when the frequency of the reflected signal is different from the frequency of the transmitted signal. The detection uses a measurement of the frequency of the Doppler signal. When the frequency of the reflected signal is equal to the frequency of the signal transmitted by the transceiver circuit (and therefore equal to the frequency of the transmitted signal at the output of the oscillator), the frequency of the Doppler signal is zero, which reflects that the target located in front of the device has not moved. It is inferred that there is no user in front of the device. When the frequency of the reflected signal is different from the frequency of the signal transmitted by the transceiver circuit (and therefore different from the frequency of the transmitted signal at the output of the oscillator), the frequency of the Doppler signal is non-zero, which reflects the movement of the target, such as the user's feet. The presence of the user in front of the device is inferred.

[0047] Preferably, the frequency of the transmission signal is a function of the voltage of the reference electrical signal, said reference thus forming a voltage reference.

[0048] Another subject of the invention is a detection device for detecting the presence of a user close to a motor vehicle, the device being designed to be installed in said vehicle and comprising a microcontroller and a transceiver circuit comprising an antenna and an oscillator and being able to transmit, during transmission time intervals and periodically via said antenna, a signal at a target frequency from said oscillator and to receive a reflected signal originating from the signal transmitted via said antenna, the microcontroller comprising a control unit and a piezoelectric element, the control unit being able to:

[0049] - activating the piezoelectric element during a time interval called the "wake-up" time interval in order to stabilize said piezoelectric element,

[0050] - once the piezoelectric element has stabilized, controlling the supply of voltage to the oscillator based on a predetermined voltage reference at the stabilized frequency of the piezoelectric element (allowing the oscillator of the transceiver circuit to operate at the value of the target frequency), so that the transceiver circuit transmits signals during time intervals called “transmission” time intervals,

[0051] - During the transmission time interval:

[0052] - measure the frequency of the reflected (Doppler) signal from the transmitted signal,

[0053] - measure the frequency of the transmitted signal,

[0054] - based on the measurement of the frequency of the transmitted signal, determining a new voltage reference allowing the oscillator of the transceiver circuit to operate at the target frequency value of the signal,

[0055] - Detecting the presence of a user in front of the device when the frequency of the reflected signal is different from the frequency of the transmitted signal.

[0056] The invention also relates to a motor vehicle comprising at least one device as described above.

[0057] The invention also relates to a method for detecting the presence of a user approaching a motor vehicle based on a device as described above, said method comprising the following steps:

[0058] a) during a time interval called a "wake-up" time interval, the control unit activates the piezoelectric element in order to stabilize said piezoelectric element,

[0059] b) once the piezoelectric element has stabilized, the microcontroller controls the voltage supply to the oscillator and supplies the oscillator with a reference electrical signal associated with said current reference, so that the transceiver circuit transmits a signal during a transmission time interval,

[0060] c) during said transmission time interval:

[0061] - a microcontroller measures the frequency of a Doppler signal originating from said reflected signal, and

[0062] - the microcontroller measures the frequency of the transmission signal supplied at the output of the oscillator,

[0063] d) Using the comparison between the value of the target frequency and the measurement of the frequency of the transmission signal, the microcontroller determines a correction value of the reference which makes it possible to reduce the difference 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 said corrected reference.

[0064] Advantageously, the method according to the invention also comprises a step of detecting the presence of a user in front of the device when the frequency of the reflected signal differs from the frequency of the transmitted signal.

[0065] Preferably, the piezoelectric element is a quartz clock.

[0066] Likewise preferably, the duration of the wake-up time interval is between 100 μs and 10 ms, preferably between 500 μs and 5 ms.

[0067] The invention also covers a method for detecting the presence of a user approaching a motor vehicle based on a device as described above, the method comprising the following steps:

[0068] - the control unit activates the piezoelectric element during a time interval called a "wake-up" time interval for stabilizing said piezoelectric element,

[0069] - once the piezoelectric element has stabilized, the microcontroller controls the voltage supply to the oscillator based on a predetermined voltage reference at the stable frequency of the piezoelectric element, so that the transceiver circuit transmits a signal during a time interval called a "transmit" time interval,

[0070] - During the transmission time interval:

[0071] - the microcontroller measures the frequency of the reflected signal from the transmitted signal,

[0072] -The microcontroller measures the frequency of the transmitted signal,

[0073] - based on the measurement of the frequency of the transmitted signal, the microcontroller determines a new voltage reference allowing the oscillator of the transceiver circuit to operate at the target frequency value of the signal,

[0074] - Detecting the presence of a user in front of the device when the frequency of the reflected signal is different from the frequency of the transmitted signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Other features and advantages of the present invention will become more apparent from reading the following description. This description is purely illustrative and should be read with reference to the accompanying drawings, in which:

[0076] [ Figure 1 ] Figure 1 An embodiment of the device according to the invention is schematically shown.

[0077] [ Figure 2 ] Figure 2 An example of the operation of the device according to the invention is schematically shown.

[0078] [ Figure 3 ] Figure 3 An embodiment of the method according to the invention is schematically shown. DETAILED DESCRIPTION

[0079] The device according to the invention is intended to be installed in a motor vehicle in order to detect the presence of a user close to said vehicle, in particular the presence of a foot or a hand of said user.

[0080] Figure 1 An embodiment of a device 1 according to the invention is shown. The device 1 comprises a transceiver circuit 10 and a microcontroller 20, both powered by a battery 2 of the vehicle, and a switch 30, connected between the battery 2 and the transceiver circuit 10 and controllable by the microcontroller 20 in order to supply or not supply electrical energy to said transceiver circuit 10.

[0081] Transceiver circuit 10

[0082] The transceiver circuit 10 includes an antenna 110 and an oscillator 120 .

[0083] The transceiver circuit 10 is capable of periodically transmitting a signal of a predetermined frequency from said oscillator 120 and via said antenna 110 during time intervals called "transmission" time intervals, and receiving reflected signals originating from the signal transmitted via the antenna 110. To this end, the oscillator 120 is configured to receive a supply voltage from the battery 2 when the switch 30 is closed, and is configured not to receive any supply voltage when the switch 30 is open. In addition, the oscillator 120 is configured so that its oscillation frequency is driven using a reference electrical signal supplied by the microcontroller 20. In particular, the oscillation frequency of the oscillator 120 and therefore the frequency of the transmission signal supplied at the output of the oscillator 120 is a function of a reference formed by the characteristics of the reference electrical signal. In the following, but not by way of limitation, the reference is a voltage reference (DC voltage, taking a fixed value during the considered transmission time interval) formed by the absolute value of the voltage of the reference electrical signal. The oscillator 120 can, for example, be designed to operate at a target frequency of 24.2 GHz in a manner known per se for civil radar applications. The output of the oscillator is connected to the antenna 110 for transmission of signals by the transceiver circuit 10 .

[0084] In this example and advantageously, the transceiver circuit 10 also comprises a switch 115 connected between the output of the oscillator 120 and the antenna 110 and controllable by the microcontroller 20 .

[0085] Here and advantageously, the transceiver circuit 10 also comprises a frequency divider 130 connected to the microcontroller 20 and by means of which the microcontroller 20 measures the frequency of the transmission signal at the output of the oscillator. The frequency divider 130 makes it possible to reduce the measured value of the frequency of the transmission signal supplied by the oscillator in order to bring this value into a range that the microcontroller can use numerically. In this example, and without limitation, the frequency divider 130 divides the transmission frequency by 2 20 =1048576. The transceiver circuit 10 further includes a circuit, not shown, configured to receive the reflected signal received by the antenna 110 and transmit the signal to the microcontroller 20.

[0086] Microcontroller 20

[0087] The microcontroller 20 makes it possible to control the transceiver circuit 10 and comprises a control unit 210 , a memory area 220 and a piezoelectric element 230 .

[0088] The control unit 210 can activate the piezoelectric element 230 during a time interval called a "wake-up" time interval in order to stabilize said piezoelectric element 230. Preferably, the duration of the wake-up time interval is between 0.1 and 1 ms. The piezoelectric element 230 is used as a clock for frequency measurements implemented with the microcontroller 20.

[0089] Once the piezoelectric element has stabilized, the control unit 210 is able to control the voltage supply to the oscillator 120 (here via the closing switch 30) and supply the oscillator with a reference electrical signal. The characteristics of the reference electrical signal, which is here an absolute voltage value, form a predetermined reference, here a predetermined voltage reference. The predetermined voltage reference advantageously allows the oscillator 120 to operate at the target frequency value of the signal to be transmitted. In practice, the use conditions (in particular the temperature of the oscillator 120) may cause a frequency drift of the signal transmitted by the oscillator, in the case of a constant value of the voltage reference. For the sake of clarity, a definition of a current voltage reference is therefore given that represents the voltage reference delivered to the oscillator 120 at a given time. The current voltage reference allows the oscillator 120 to operate at the target frequency value of the signal to be transmitted under the initial use conditions. After a certain period of use of the device 1, due to changes in the use conditions of the device 1, the current voltage reference no longer allows the oscillator 120 to operate precisely at the target frequency value of the signal to be transmitted. The oscillator 120 then operates at a slightly offset value relative to the target frequency, for example greater than or less than the target frequency. For its part, the supply of voltage to the oscillator 120 allows the transmission of signals via the antenna 110 during time intervals known as “transmission” time intervals.

[0090] In the preferred example, the piezoelectric element 230 is in the form of a quartz clock, which makes it possible to oscillate very accurately at a desired frequency value, thereby making it possible to measure a desired frequency value, in particular the frequency of the transmission signal at the output of the oscillator 120 .

[0091] The control unit 210 is able to measure the frequency of the Doppler signal originating from the reflected signal during the transmission time interval. Measuring the frequency of the Doppler signal in the context of detecting the presence of a user in front of the vehicle is a well-known technique and will not be described further here. It can be stated simply that the Doppler signal is formed using a multiplier which receives at its input a frequency f ○ and on the other hand receives the frequency f supplied at the output of the oscillator 120 ⊥ and supplies a signal at the output, one of the components of which is at a frequency |f ○ -f T |. This component forming the Doppler signal is isolated using a frequency filter. The device 1 has various elements, not shown, allowing said measurement of the Doppler signal, in particular said multiplier, and a coupler, which is arranged at the output of the oscillator 120 and is able to direct the majority of the signal to the antenna 110 and a smaller portion of the signal to the multiplier.

[0092] In parallel, during this same transmission time interval, the control unit 210 is also able to measure the frequency of the signal transmitted by the antenna 110 and determine a new reference (here a new voltage reference) based on the frequency of the transmission signal thus measured, allowing the oscillator 120 to operate at the target frequency in 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, it being understood that when the switch 115 is closed, the frequency of the signal transmitted by the antenna is substantially equal to the frequency of the signal transmitted by the oscillator 120. The new reference value may be referred to as a "corrected value of the reference". This is the value of the reference that allows the oscillator to operate at the value of the target frequency under the current conditions of use.

[0093] Advantageously, the frequency of the transmitted signal can be measured using a counter (not shown), which is driven, 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. According to the invention, the piezoelectric element 230 should therefore be stable in frequency before the measurement of the frequency of the transmitted signal.

[0094] The value of the predetermined reference may have been determined in a previous transmission time interval or in any previous transmission time interval. Next, the obtained new reference is used as a reference in a subsequent transmission time interval. Preferably, a new value of the reference is determined periodically, for example every 3 or 4 transmission time intervals.

[0095] During an initialization phase after power-up of the device 1 and before the first transmission time interval of the transceiver circuit 10, the microcontroller 20 may be able to supply a voltage to the oscillator 120 and, during a time interval called a “stabilization” time interval, supply a reference electrical signal thereto in order to stabilize the oscillator at the desired transmission frequency (herein called the target frequency) and thus determine an initial reference value.

[0096] As a variant, the microcontroller 20 may be able to measure the initial temperature inside the device 1, preferably in the oscillator 120, and to deduce from it an initial reference value for stabilizing the oscillator 120 in terms of frequency at the desired transmission frequency (here called the target frequency) at the measured temperature. This variant advantageously uses a table stored in a memory, linking reference values ​​and temperature values, for the operation of the oscillator 120 at the target frequency. The memory is, for example, a memory area 220 of the microcontroller 20 or an added memory not shown. In one embodiment, the microcontroller 20 is able to modify the time periods of the transmission and measurement time intervals, in particular based on the operating mode of the vehicle (normal mode or standby mode), so as to avoid the microcontroller 20 measuring the frequency of the signal transmitted in each transmission time interval, thereby making it possible to save more energy. In particular, the transmission time periods of the signals of the transceiver circuit (via the oscillator 120 and the antenna 110) and the measurement time periods of the frequencies of the signals transmitted by the transceiver circuit can be adapted based on changes in temperature and humidity. For example, if the temperature and humidity do not change or change only slightly and / or if the vehicle is in standby mode, the microcontroller 20 may increase the transmission time period (that is, reduce the repetition frequency of the transmission time interval) and also not measure the frequency of the signal transmitted in each transmission. In contrast, if the temperature and humidity change rapidly and / or if the vehicle is in normal operating mode, the microcontroller may reduce the transmission time period (that is, increase the repetition frequency of the transmission time interval) and also measure the frequency of the signal transmitted in each transmission.

[0097] 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) from the user (e.g. his moving feet). Preferably, when the frequency of the reflected signal is different from the frequency of the transmitted signal (non-zero frequency of the Doppler signal), the control unit 210 is then able to detect the presence of a user in front of the device 1. As a variant, the presence detection is implemented in an added device.

[0098] In order to perform all these functions, the microcontroller 20 is able to implement a list of instructions stored in its memory area 220 .

[0099] accomplish

[0100] Now refer to Figure 2 and 3 , the present invention is described in terms of its implementation. Figure 2An example of the operation of the device 1 is shown, wherein the top graph shows the evolution of the current intensity consumed by the device 1, the middle graph shows the periodic transmission time interval E of the transceiver circuit 10 and the bottom graph shows the initialization phase P1 and the measurement phase P2, comprising periodic standby V, wake-up R and measurement M time intervals (of the time period T).

[0101] First, when the device 1 is started, the microcontroller performs an initialization phase P1 in which it opens the switch 115 (so as to prevent the signal at the output of the oscillator 120 from being transmitted to the antenna 110), closes the switch 30 (so as to supply the oscillator 120 with voltage), and then applies a reference electrical signal forming a reference at the input of the oscillator 120. During this initialization phase P1, the microcontroller 20 searches for the value of the reference required for the oscillator 120 to transmit at the target frequency. The target frequency is within the frequency range authorized by the standard and has a value of, for example, 24.2 GHz. In doing so, the oscillator 120 will need to be stable in frequency during a non-zero time interval. In order to stabilize the oscillator 120 so that the signal transmitted (by the oscillator 120 and therefore by the transceiver circuit 10) is at the desired target frequency, the microcontroller 20 adjusts the reference at the input of the oscillator 120 by trial and error or, if necessary, by closed-loop control. Here, the reference is formed by a voltage, but is not limited thereto. As a variant, it can be formed by any characteristic of the electrical signal other than its voltage, such as its current. Once the oscillator 120 has stabilized, the microcontroller 20 records the reference defined at the input of the oscillator in its memory area 220 as a starting reference or initial reference. The microcontroller 20 can then optionally close the switch 115 in order to check the influence of the connection to the antenna 110 on the frequency of the oscillator 120 and to refine the initial reference value even more. In particular, the frequency of the oscillator 120 can be particularly affected by the connection of the antenna 110 to the oscillator 120. It should be noted that in the initialization phase P1, there is no transmission of signals of the transceiver circuit 10 (or only at the end of the initialization phase P1, once the frequency of the oscillator 120 has stabilized and when the switch 115 is closed). In particular, in this phase of searching for the initial reference, the transmission frequency may be outside the authorized range. However, during this initialization phase P1 (switch 30 closed), power is still supplied to the transceiver circuit 10.

[0102] Once the initialization phase P1 is over, the device 1 operates in a phase called the "measurement" phase P2. This measurement phase P2 will be repeated periodically. In step E1 of the measurement phase P2, the microcontroller 20 first closes the switch 115, keeps the switch 30 closed, and applies the starting reference determined during the initialization phase P1 at the input of the oscillator 120. The oscillator 120 is therefore directly operable. Specifically, it then directly transmits a signal that oscillates substantially at the target frequency, for which it is pre-calibrated in the initialization phase P1. When the use conditions such as temperature and / or humidity have not changed since the initialization phase P1, the signal transmitted by the oscillator 120 oscillates precisely at the target frequency. As a variant, the use conditions may have changed since the initialization phase P1. In this case, the reference defined in the initialization phase P1 no longer corresponds to the transmission at the target frequency, and the signal transmitted by the oscillator 120 oscillates at a frequency different from the target frequency. Once a starting reference has been applied at the input of the oscillator 120, in step E2, the transceiver circuit 10 transmits a signal via the antenna 110 during a first time interval called "transmission" time interval E. One function of the signal transmitted by the transceiver circuit 10 is the function of detecting nearby users. The signal transmitted by the transceiver circuit 10 corresponds to the signal supplied by the oscillator 120 and then transmitted by the antenna 110. Therefore, this signal oscillates substantially at the same frequency as the oscillator, the switch 115 is closed.

[0103] During the transmission of the signal by the transceiver circuit 10, the control unit 210 of the microcontroller 20 measures in step E3 the frequency of the signal transmitted by the transceiver circuit 10. In practice, the 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, here formed by the piezoelectric element 230.

[0104] In step E4, the microcontroller 20 determines a correction value of the reference, also called a new reference or a "real-time" reference. The real-time reference is determined based on a measurement of the frequency of the transmission signal. If the oscillator 120 is supplied with the real-time reference, it will allow the oscillator 120 of the transceiver circuit 10 to operate close to the exact value of the target frequency. Therefore, if the oscillator 120 is supplied with the real-time reference, it will allow the oscillator 120 to operate close to the exact value of the target frequency in subsequent transmission time intervals. The real-time reference is stored in the memory area 220.

[0105] In practice, the real-time reference can be obtained simply by comparing the target frequency with the frequency measured in step E3. If the target frequency is greater than the frequency measured in step E3, the increment is added to the current reference (i.e. the reference applied at the input of the oscillator during said step E3), or the increment is subtracted from the current reference. Conversely, if the target frequency is less than the frequency measured in step E3, the increment is subtracted from said current reference, or the increment is added to said current reference. Advantageously, the value of the increment is determined in a preliminary calibration step. This solution does not necessarily always allow operation exactly at the target frequency, however, but it does avoid the accumulation (buildup) of excessive frequency drifts over time. It is thus ensured that the oscillator 120 always transmits within the desired frequency band.

[0106] As a variant, the real-time reference can be obtained using a table and / or a curve and / or a function of values ​​relating the value of the frequency of the signal transmitted by the oscillator 120 (or the transceiver circuit) to the value of the reference at the input of the oscillator. The data used (table and / or curve and / or function of values) are advantageously determined in a preliminary calibration step.

[0107] During this transmission time interval E, in parallel with steps E3 and E4 , the control unit 210 of the microcontroller 20 also measures in a step E5 the frequency of the Doppler signal obtained using the reflected signal.

[0108] 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 transmitting signals, thus saving the vehicle's electrical energy. To this end, the microcontroller 20 drives the opening of the switch 30 and the opening of the switch 115. It also stops sending a reference to the input of the oscillator 120.

[0109] In an optional step E7, the control unit 210 detects the presence of a user close to the device 1. This detection is based on detecting the difference between the frequency of the reflected signal and the frequency of the signal transmitted by the transceiver circuit (Doppler effect), which is synonymous with the movement of a nearby user, for example the passage of a foot. When the control unit 210 detects the presence of a user close to the device 1, it activates a function of the vehicle, such as, for example, unlocking an opening element in which the device 1 is installed.

[0110] Once steps E6 and possibly E7 have been completed, the microcontroller 20 puts itself in a standby state during a standby interval V during which it consumes almost no electrical energy.

[0111] In step E8, the control unit 210 of the microcontroller 20 wakes up just before the start of the subsequent transmission time interval E. Then, in step E9, it controls the supply of voltage to the piezoelectric element 230 during a time interval called the “wake-up” time interval R, allowing the piezoelectric element 230 to stabilize, the switches 115 and 30 still being open.

[0112] 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 during a new transmission time interval E, a signal is transmitted by the transceiver circuit 10 .

[0113] The microcontroller 20 then cyclically executes steps E3 to E10 again, as long as the device 1 is operable to use a previously defined reference in each transmission time interval E, the previously defined reference (defined in an initialization phase, in particular for the first transmission time interval, or defined in a previous transmission time interval and stored (memorized) in a memory, in particular the transmission time interval directly preceding the transmission time interval under consideration).

[0114] It should be noted that, as a variant, steps E3 and E4 may not be implemented systematically in each transmission time interval E, but in a more time-spaced manner. In particular, if the temperature and humidity levels vary very slowly or do not vary, it may be advantageous to keep the same reference for a number of consecutive transmission time intervals E in order to avoid measuring the frequency of the transmission signal and calculating a new real-time reference in each transmission time interval E, thus saving electrical energy.

[0115] It should also be noted that the device 1 is operable during normal operation of the vehicle (the vehicle's electrical system is activated, e.g. the engine is started) and during operation in a standby mode of the vehicle (the vehicle's electrical system is in standby mode, engine off).

[0116] The present invention is not limited to the above examples and also covers many variations, including:

[0117] - a variant in which the oscillator is not controlled by the absolute value of the voltage of the reference electrical signal, but by any other characteristic of said signal, such as the absolute current value, the average current or voltage value, etc.;

[0118] - Variant, without switch 115, the initialization phase can be implemented in an environment where: temporary authorization is given for transmission outside the authorized band with sufficiently low power;

[0119] - a variant in which the drive of the switch 30 is replaced by the drive of the battery itself;

[0120] - A variant in which the step of detecting the user is performed external to said microcontroller, using Doppler frequency measurements or the like supplied by said microcontroller.

Claims

1. A device (1) for a presence detection system for detecting the presence of a user approaching a motor vehicle, the device (1) being intended to be installed in the motor vehicle and comprising a microcontroller (20) and a transceiver circuit (10), wherein: The transceiver circuit (10) comprises an antenna (110) and an oscillator (120), wherein the oscillator (120) is configured to receive a supply voltage and a reference electrical signal and to supply a transmission signal when it is supplied with the supply voltage, the frequency of the transmission signal being a function of a reference formed by a characteristic of the reference electrical signal, and wherein the antenna (110) is configured to transmit the transmission signal from the oscillator (120), thereby forming a signal transmitted by the transceiver circuit (10); The transceiver circuit (10) is configured to receive, via the antenna (110), a reflected signal originating from a signal transmitted by the transceiver circuit (10); The microcontroller (20) comprises a control unit (210) and a piezoelectric element (230); The microcontroller (20) is configured to supply a reference electrical signal to the oscillator (120) and drive the supply voltage to the oscillator (120) so that the transceiver circuit (10) transmits periodically and during a transmission time interval (E); And wherein the control unit (210) of the microcontroller (20) is configured to implement the following steps in this order: a) activating the piezoelectric element (230) during a time interval called a "wake-up" time interval (R) in order to stabilize said piezoelectric element (230), b) once the piezoelectric element (230) has stabilized, controlling (E1) the supply of voltage to the oscillator (120) and supplying the oscillator (120) with a reference electrical signal associated with a reference called current reference, so that the transceiver circuit (10) transmits (E2) a signal during a transmission time interval (E), c) during said transmission time interval (E): - using a stable piezoelectric element (230), measuring the frequency (E5) of a Doppler signal originating from said reflected signal, and - using a stable piezoelectric element (230), measuring the frequency (E3) of the transmission signal supplied at the output of the oscillator (120), d) using the comparison between the value of the target frequency and the measurement of the frequency of the transmission signal, determining (E4) a correction value of the reference, the correction value of the reference making it possible to reduce the difference 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 said corrected reference.

2. The device (1) according to claim 1, wherein: The control unit (210) of the microcontroller (20) is configured to use the corrected reference as a current reference during a subsequent transmission time interval (E).

3. The device (1) according to claim 1 or 2, wherein: The control unit (210) is configured to implement the following sub-steps in step d): - comparison of the value of the target frequency and the measurement of the frequency of the transmitted signal; - Depending on whether the measure of the frequency of the transmission signal is strictly greater than or strictly less than the value of the target frequency, a delta is added to or subtracted from the current reference in order to obtain said correction value of the reference.

4. The device (1) according to claim 1 or 2, wherein: The control unit (210) is configured to implement the following steps in step d): - determining said correction value of the reference on the basis of pre-recorded data relating the value of the frequency of the transmission signal to the value of the reference supplied to the oscillator (120).

5. The device (1) according to claim 1 or 2, wherein: The piezoelectric element (230) is a quartz clock.

6. The device (1) according to claim 1 or 2, wherein: The duration of the wake-up time interval is between 100 μs and 10 ms.

7. The device (1) according to claim 1 or 2, wherein: The control unit (210) is configured to implement the following steps in an initialization phase (P1) after the device (1) is powered on and before a first transmission time interval (E): - driving the voltage supply to the oscillator (120) during a time interval called a "stabilization" time interval; - During the stabilization time interval, driving the stabilization of the transmission signal supplied at the output of the oscillator (120) at the target frequency and thus determining an initial value of a current reference for stabilizing the oscillator (120) at the target frequency.

8. The device according to claim 1 or 2, wherein: The microcontroller (20) is configured to measure the temperature inside the device (1) and to infer therefrom an initial value of a current reference for stabilizing the oscillator (120) at a target frequency at the measured temperature.

9. The device according to claim 8, wherein: Measuring the temperature inside the device (1) is measuring the temperature in the oscillator (120).

10. The device (1) according to claim 1 or 2, wherein: The microcontroller (20) is configured to modify the ratio between the repetition frequency of the transmission time interval and the repetition frequency of the step (E3) of measuring the frequency of the transmission signal, in particular based on the operating mode of the vehicle, so as to avoid the microcontroller (20) measuring the frequency of the transmission signal in each transmission time interval (E).

11. The device (1) according to claim 1 or 2, further comprising a battery (2) and a switch (30), the battery (2) being configured to supply the supply voltage to the oscillator (120), the switch (30) being connected between the battery (2) and the oscillator (120), and the switch (30) being driven by the microcontroller (20) so that the transceiver circuit (10) transmits periodically and during a transmission time interval (E).

12. The device (1) according to claim 1 or 2, wherein: The control unit (210) of the microcontroller (20) is also configured to detect (E7) the presence of a user in front of the device (1) when the frequency of the reflected signal is different from the frequency of the transmitted signal.

13. The device (1) according to claim 1 or 2, wherein: The frequency of the transmission signal is a function of the voltage of the reference electrical signal, said reference thus forming a voltage reference.

14. A motor vehicle comprising at least one device (1) according to any one of the preceding claims.

15. A method for detecting the presence of a user approaching a motor vehicle based on a device (1) according to any one of claims 1 to 13, the method comprising the following steps: a) during a time interval called a "wake-up" time interval (R), the control unit (210) activates the piezoelectric element (230) in order to stabilize said piezoelectric element (230), b) once the piezoelectric element (230) has stabilized, the microcontroller (20) controls the voltage supply to the oscillator (120) and supplies the oscillator with a reference electrical signal associated with the current reference, so that the transceiver circuit (10) transmits a signal during a transmission time interval (E), c) during said transmission time interval (E): - a microcontroller (20) measures the frequency of a Doppler signal originating from said reflected signal, and - the microcontroller (20) measures the frequency of the transmission signal supplied at the output of the oscillator (120), d) using the comparison between the value of the target frequency and the measurement of the frequency of the transmission signal, the microcontroller (20) determines a correction value of the reference which makes it possible to reduce the difference 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 said corrected reference.

16. The method according to claim 15, characterized in that It also comprises the step of detecting the presence of a user in front of the device (1) when the frequency of the reflected signal is different from the frequency of the transmitted signal.

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