Device for supplying electrical power to a capacitive sensor

Abstract

A device for supplying electrical power to a capacitive sensor for detecting proximity or contact between an occupant and a component of a vehicle, said device comprising a microcontroller designed to generate a PWM signal, characterized in that the device comprises a filter arranged to filter the PWM signal generated by the microcontroller and transmit at the output a variable electrical power supply signal of the capacitive sensor.

Description

DESCRIPTION TITLE: Power supply device for a capacitive sensor Technical field of the invention

[0001] The present invention relates to a device for supplying power to a capacitive sensor. This type of sensor can be used to detect the proximity or contact between an occupant and a vehicle component such as a vehicle steering wheel. State of the art

[0002] Capacitive proximity or contact sensors are widely used in motor vehicles, for example to detect the presence of hands on a steering wheel. These capacitive sensors can be supplied with voltage by a periodic power supply signal, for example a sinusoidal signal or a square signal.

[0003] In the prior art, it is known to generate the power supply signal of a capacitive sensor by means of a microcontroller and an ASIC (Application-Specific Integrated Circuit), i.e. an application-specific integrated circuit designed to perform the specific tasks of powering and measuring the capacitive sensor. The design and manufacture of an ASIC can be expensive. Statement of the invention

[0004] An aim of the present invention is to address the drawbacks of the prior art mentioned above and in particular, first of all, to propose a device for generating an electrical supply signal for a simplified and therefore more economical capacitive sensor, not requiring the use of expensive components such as an ASIC.

[0005] For this purpose, a first aspect of the invention relates to a device for supplying electricity to a capacitive sensor for detecting proximity or contact between an occupant and a component of a vehicle, said device comprising a microcontroller arranged to generate a PWM signal, characterized in that the device comprises a filter arranged to filter the PWM signal generated by the microcontroller and transmit as output a variable electrical supply signal for the capacitive sensor.

[0006] The present invention is based on the combination of a microcontroller, or microprocessor or control unit, and a simple filter or filtering circuit. The microcontroller is arranged to generate a PWM signal at its output, which is then filtered by the filter. The output signal of the filter is a variable signal, which is transmitted to the capacitive sensor to power it. The filter is a reconstitution filter for reconstituting an analog signal from the PWM-modulated signal.

[0007] In one embodiment, the device comprises memory means storing predetermined digital values, and wherein the microcontroller is arranged to access the memory means and control the duty cycle of the PWM signal using the predetermined digital values ​​read from the memory means, in order to generate the PWM signal.

[0008] The microcontroller is arranged to generate a PWM signal using predetermined digital values, which it accesses directly in memory, to control the duty cycle of the PWM signal. In operation, the microcontroller will read the predetermined digital values ​​for controlling the duty cycle from memory and uses the read values ​​to set or control the duty cycle of the pulses or pulses of the generated PWM signal. The microcontroller can work in DMA (from the English "Direct Memory Access"), i.e., in direct memory access. In other words, the microcontroller is equipped with a DMA component having direct memory access without requesting a processor or CPU of the microcontroller. More specifically, the DMA component can read data stored in memory, such as the predetermined digital values ​​for controlling the duty cycle, without requesting the processor. Thanks to this, the generation of the PWM signal does not use any computing resources of the processor or CPU. The DMA component can also write or store data, such as measurement data, in memory without using the processor or CPU of the microcontroller. Thanks to this, the acquisition of measurement data does not use any resources of the processor or CPU.

[0009] In one embodiment, said predetermined digital values ​​are obtained by calculation using a function having one or more predetermined characteristics of the power supply of the capacitive sensor, among a frequency characteristic and a signal shape characteristic.

[0010] The function used to precalculate the numerical values ​​can, for example, represent a sinusoidal signal if the capacitive sensor is supplied with a sinusoidal voltage, or a periodic square or triangular signal if the capacitive sensor is supplied with a periodic square or triangular voltage signal. The function can have the same signal shape and frequency characteristics as the predetermined supply signal of the sensor.

[0011] The predetermined frequency characteristic of the capacitive sensor power supply may be between 20 and 200 kHz, between 60 and 200 kHz, between 70 and 200 kHz, between 80 and 200 kHz, between 90 and 200 kHz, or between 100 and 200 kHz. The function used to precalculate the digital values ​​may have the same frequency characteristic.

[0012] In a particular embodiment, the microcontroller is arranged to generate the PWM signal with a frequency equal to N times said predetermined frequency of the electrical supply of the capacitive sensor, N being an integer between 20 and 100, advantageously between 30 and 60, preferably between 35 and 50.

[0013] As purely illustrative and non-limiting examples: - the frequency of the sensor supply signal is equal to 75kHz and the frequency of the PWM signal is equal to 3.6MHz, the factor N between these two frequencies worth 48 (75kHz*48=3.6MHz); or - the frequency of the sensor supply signal is equal to 100kHz and the frequency of the PWM signal is equal to 4MHz, the factor N between these two frequencies being 40 (100kHz*40=4MHz).

[0014] In one embodiment, wherein the memory means stores N pre-calculated digital values ​​over a period of said function.

[0015] Thanks to this, the microcontroller has N sample points over a period of the sensor power supply to reconstruct a PWM modulating signal.

[0016] The filter can be a low-pass filter.

[0017] In one embodiment, the microcontroller comprises an analog-to-digital converter arranged to acquire measurement data from an analog measurement signal of the capacitive sensor, the analog-to-digital converter being arranged to acquire measurement data in a synchronized manner with the generation of the PWM signal.

[0018] Advantageously, the analog-to-digital converter has a sampling frequency that is a submultiple of the PWM signal frequency or is equal to the PWM signal frequency.

[0019] The role of the analog-to-digital converter is to sample an analog measurement signal received from the sensor. Sampling, i.e. the acquisition of measurement data, is performed synchronously with the generation of the PWM signal (i.e., with the generation of PWM pulses or pulses), but not necessarily at the same frequency. A clock signal can be transmitted both to the generator, or generating means, of the PWM signal and to the analog-to-digital converter, to perform the generation of the PWM and the acquisition of measurement data synchronously. Access by the microcontroller to the predetermined digital values ​​in memory allows the microcontroller to generate the PWM signal without requiring any calculations. This greatly reduces the risk of desynchronizing the generation of the PWM and the acquisition of measurement data, which helps to limit or avoid measurement errors.

[0020] In one embodiment, an attenuator may be interposed between the microcontroller and the filter.

[0021] Advantageously, the microcontroller may comprise a data processing module arranged to process the measurement data transmitted by the analog-digital converter, in a manner synchronized with the generation of the PWM signal, so as to detect proximity or contact between an occupant and the vehicle component.

[0022] In one embodiment, the device comprises a clock generator arranged to transmit one or more clock signals so as to synchronize the execution of different actions by the device.

[0023] A second aspect of the invention relates to a system comprising an electrical power supply device as previously defined and a capacitive sensor for detecting proximity or contact between an occupant and a component of a vehicle such as a vehicle steering wheel.

[0024] The system may be a motor vehicle or integrated into a motor vehicle.

[0025] A third aspect of the invention relates to a vehicle comprising the system defined above.

[0026] A fourth aspect of the invention relates to a method of supplying electrical power to a capacitive sensor for detecting proximity or contact between an occupant and a component of a vehicle, said method comprising the steps of: - generate a PWM signal using a microcontroller, - transmit the PWM signal from the microcontroller to a filter; - filter the PWM signal using the filter; - transmit a variable output signal from the filter to the capacitive sensor to power said capacitive sensor.

[0027] The above method can correspond to the operation of the previously defined power supply device. Description of figures

[0028] Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the appended drawings, in which:

[0029] [fig. 1] represents a simplified functional block diagram of a device for supplying electricity to a capacitive sensor, according to a particular embodiment;

[0030] [fig. 2] represents a PWM signal generated by a microcontroller of the device of figure 1 and a power supply signal of the sensor obtained by filtering the PWM signal, according to an exemplary embodiment;

[0031] [fig. 3] represents a circuit comprising an attenuator and an active filter, according to a particular embodiment.

[0032] [fig. 4] represents a circuit comprising a passive filter, according to another particular embodiment.

[0033] [fig. 5] represents an output signal of the circuit of figure 3 and an output signal of the circuit of figure 4.

[0034] [fig. 6] represents a flowchart of the steps of a method for generating an electrical power supply signal and acquiring measurement data, corresponding to the operation of the device of figure 1, according to a particular embodiment.

[0035] [fig. 7] represents a table containing sine values ​​of the form sin(2irfo*t) and corresponding sine values, after conversion in number of clock pulses, according to a particular embodiment.

[0036] [fig. 8] represents a sinusoidal curve representing the sine values ​​of the form sin(2irfo*t) of figure 7 and a sinusoidal type curve representing the sine values ​​converted into the number of clock pulses of figure 7 according to a particular embodiment.

[0037] [fig. 9] represents components of a microcontroller which are involved in PWM generation and acquisition of measurement data, according to a particular embodiment.

[0038] Detailed description of embodiment(s)

[0039] The present invention relates to a device or system 1000 for generating an electrical power supply signal for a capacitive sensor 2000, in other words a device for supplying electrical power to the sensor 2000.

[0040] The Capacitive Sensor 2000 is a capacitive sensing system for detecting proximity or contact between a person and an element or organ incorporating the capacitive sensor. For example, it can be integrated into the steering wheel of a vehicle to monitor whether the driver's hand is on the steering wheel and controlling the driving.

[0041] In Figure 1, a purely illustrative and non-limiting example of embodiment of the capacitive sensor 2000 is shown. It comprises for example one or more electrode zones, here two zones 2200, 2300 for carrying out measurements in two distinct zones of the steering wheel, and an optional shielding surface 2100. The zone(s), here 2200 and 2300, can be positioned facing the shielding 2100 so as to create a capacitance referenced C2 between the zone 2200 and the shielding 2100 and another capacitance referenced C3 between the zone 2300 and the shielding 2100. In Figure 1, a reference C4 corresponds to a surface capacitance of a driver's hand(s), the driver's hand(s) being likely to be positioned facing the zone 2200 (i.e., close to and to the right of it), or facing the zone 2300, or facing both areas 2200, 2300. The capacitance C4 in Figure 1 corresponding to the driver's hand(s) is intended to be measured via an interface 1400 which will be described later. The dotted lines between C4 and areas 2200 and 2300 represent the fact that a driver is likely to position a hand facing areas 2200 and / or 2300 and thus create a capacitance C4 between this or these areas and the ground. In Figure 1, a reference C1 represents a capacitance created by placing the surface of the shield 2100 face to face with a surface of the armature 2500.

[0042] An example of a capacitive sensor 2000 is described in document WO201 9224177.

[0043] Any other type of capacitive sensor arranged to be powered by an electrical signal, for example a variable voltage signal, for example sinusoidal or square, could be used. The present invention also applies for example to a capacitive seat sensor for detecting the presence of a person sitting on a seat.

[0044] The power supply device 1000 comprises: - a control unit 1100, such as a microcontroller unit (MCU) or a microprocessor, capable of generating a PWM signal (Pulse-Width Modulation), also called a “PWM”, pulse width modulation, and - a filter 1200 arranged to receive a corresponding input signal PWM signal generated by the microcontroller 1100, optionally attenuated in power, to filter the input signal, and provide a variable output signal intended for the electrical supply of the capacitive sensor 2000.

[0045] A PWM signal consists of a signal of pulses or pulses of fixed frequency and varying pulse width. In other words, the period (time between two successive pulses) remains constant, but the pulse width is modulated. A duty cycle represents the ratio between the duration of a pulse and the period.

[0046] In Figure 1, a simplified schematic representation of some of the components of the control unit or microcontroller 1100 is shown.

[0047] The control unit 1100 is arranged to generate a PWM signal of fixed frequency fpwM and modulate the width of the PWM pulses, i.e., control the duty cycle of the PWM signal, using predetermined digital values ​​read from a memory 1120. The predetermined digital values ​​may be or correspond to digital values ​​of the duty cycle of the PWM.

[0048] The control unit 1100 comprises hardware and / or software means 1110 for synchronizing or triggering actions in the system 1000, and in particular for generating the PWM signal. For example, the control unit 1100 may comprise a dedicated peripheral, such as a timer peripheral, and / or an emulation program for generating the PWM signal. For the sake of clarity, the reference 1110 will be referred to hereinafter as the “timer module”.

[0049] The power supply device 1000 may also comprise a clock generator 1150 for generating a clock signal h at a fixed clock frequency fh. In a particular embodiment, the clock generator 1150 may be internal to the control unit 1100. Alternatively, it could be external to the control unit 1100. The clock generator makes it possible to synchronize the tasks or actions executed by different modules of the power supply device 1000, as will be explained later.

[0050] In one embodiment, the clock frequency fh is a multiple of the frequency fpwM of the PWM signal.

[0051] The memory 1120, or the memory means, stores predetermined digital values ​​for controlling the duty cycle of the PWM signal and thus controlling the pulse width modulation of the PWM signal, preferably without calculation or with very little calculation. These predetermined digital values ​​stored in memory 1120 correspond here to values PWM duty cycle values ​​between 0 and 1, or between 0% and 100% when the duty cycle is expressed as a percentage. They are precalculated and stored in the memory 1120, so that they can be directly read and used by the control unit 1100 to control the duty cycle when generating a PWM signal.

[0052] The digital values ​​stored in the memory 1120 may be precalculated by the control unit 1100. Alternatively, they may be precalculated by any other means, for example a calculation unit external to the device 1000, then transmitted to the control unit 1100 and stored in the memory 1120.

[0053] The power supply of the capacitive sensor 2000 has predetermined characteristics or parameters. In one embodiment, these predetermined characteristics may include: - a voltage or current supply; - a variable power supply, for example periodic or alternating with a given frequency fo; - a power signal shape, for example sinusoidal, square or triangular; - amplitude and / or power supply characteristics.

[0054] In one embodiment, the predetermined digital PWM duty cycle control values ​​are obtained from a function F representing a signal having the same frequency and shape characteristics as the predetermined frequency and shape characteristics of the power supply of the capacitive sensor 2000.

[0055] The predetermined frequency characteristic fo of the power supply of the sensor 2000 may be between 20 and 200 kHz, between 60 and 200 kHz, between 70 and 200 kHz, between 80 and 200 kHz, between 90 and 200 kHz, or between 100 and 200 kHz. The function F used to precalculate the digital PWM duty cycle values ​​has the same frequency fo as the predetermined frequency of the power supply of the sensor 2000.

[0056] The predetermined shape characteristic of the power supply of the sensor 2000 may be a sinusoidal signal shape. In this case, the function F represents a sinusoidal signal. For example, the power supply of the capacitive sensor 2000 is a sinusoidal voltage supply of frequency fo, and the function F is a sine function of frequency fo of the form sin(2irfo*t) where t represents an instant.

[0057] Alternatively, the predetermined shape characteristic of the power supply of the sensor 2000 may be a square or triangular signal shape. In this case, the function F represents a periodic square or triangular signal of frequency fo.

[0058] In a particular embodiment, the digital values ​​precalculated by the function F may be modified by one or more mathematical operations preserving the frequency and shape characteristics of the signal, so as to obtain digital values ​​between 0 and 1 which may represent PWM duty cycle values. These mathematical operations may comprise at least one of the following operations: - scaling (i.e., multiplication of the numerical values ​​precalculated by the function F by a fixed non-zero scalar); and - an offset in English (i.e., adding a fixed offset value to the numerical values ​​precalculated by the F function).

[0059] For example, if the function F is a sine or sine function with a predefined phase or phase shift (e.g., a cosine function), the values ​​precalculated using the function F are comprised of numerical sine values ​​between -1 and +1. In this case, an offset by adding the offset value +1 and a scaling by multiplying by the scalar 0.5 can be applied to the numerical values ​​provided by the function F in order to obtain values ​​between 0 and 1 corresponding to duty cycle values.

[0060] The digital values ​​thus predetermined or precalculated using the function F and optionally one or more mathematical operations preserving the frequency and shape characteristics of the signal, represent PWM duty cycle values ​​and can be stored in the memory 1120 to control the duty cycle of the generated PWM signal. In a particular, non-limiting embodiment, these predetermined digital values ​​representing PWM duty cycle values ​​can be converted into a number of "docks" or clock pulses. In this case, the memory 1120 can store digital values ​​representing PWM duty cycle values ​​expressed in numbers of docks or clock pulses, as will be described in more detail later.

[0061] In a particular embodiment, the predetermined digital values ​​stored in the memory 1120 comprise a series or sequence of digital values ​​which correspond to a succession of instants distributed over a period T of the signal F, in other words over a period of the power supply of the sensor 2000, with x=1 / fo. For example, these instants are uniformly distributed 0, At, 2At, ..., T in the period T. The frequency fpwM of the PWM signal generated by the control unit 1100 may be equal to N times the predetermined frequency fo of the power supply of the sensor 2000. In this case, the number of digital values ​​precalculated over a period T and stored in memory 1120 may be equal to N.

[0062] The predetermined digital PWM duty cycle control values, stored in memory 1120, can be precalculated as follows: - N numerical values ​​are calculated using the function F over a period T, for example using the function sin(2irfo*t) for times t such as 0, At, 2At, ..., T; and - one or more mathematical operations preserving the frequency and shape characteristics of the signal, such as scaling (i.e., multiplication by a fixed non-zero scalar) and / or an offset (i.e., addition of a fixed offset value) can then be applied to the numerical values ​​provided by the F function, so as to obtain numerical values ​​between 0 and 1 (or between 0% and 100% when expressed as percentages) representing duty cycle values.

[0063] These pre-calculated digital values ​​can be stored in memory 1120 to control the PWM duty cycle.

[0064] In a particular embodiment, the pre-computed digital values ​​may be converted into numbers of clock pulses or docks. The clock frequency fh is here a multiple of the frequency fpwM of the PWM signal, in other words: fh=M*fpwM, where M is a natural integer preferably greater than 5, more preferably greater than 10, more preferably greater than 20. In this case, the precalculated numerical values ​​between 0 and 1 (or between 0% and 100% expressed as percentages), representing duty cycle values, can be converted into a number of clock pulses or clock ticks or docks by multiplying by the multiple M. For example, a duty cycle value of 1 or 100% is converted into a number of docks equal to M, a duty cycle value of 0.5 or 50% is converted into a number of docks equal to M / 2, ... The numbers of docks or clock pulses can be rounded to the nearest integer.

[0065] Optionally, one can also convert the integer rounding values ​​of dock numbers back to the corresponding sine values ​​by dividing the integer rounding values ​​determined by M.

[0066] As previously explained, the memory 1120 stores predetermined or precalculated digital PWM duty cycle control values ​​for controlling the PWM duty cycle of the PWM signal generated by the control unit 1100 preferably without calculation or with very little calculation. These predetermined digital PWM duty cycle control values ​​stored in memory 1120 may comprise at least one of following types of values: - sine values ​​calculated using the F function, for example sin(2irfo*t); - the sine values ​​calculated using the F function and modified by scaling and offset to be between 0 and 1; - sine values ​​calculated using function F, modified by scaling and offset, and converted to numbers of docks or clock pulses; - the whole rounding values ​​of these values ​​converted into dock numbers; - sine values ​​corresponding to the integer rounded values ​​of dock numbers.

[0067] The memory 1120 may be internal to the control unit 1100. Alternatively, the memory 1120 may be external to the control unit 1100, and the latter may have access to the memory 1120.

[0068] As a purely illustrative and non-limiting example, Figure 7 illustrates an example of predetermined or precalculated values ​​for controlling the duty cycle of the PWM signal generated by the control unit 1100. In this exemplary embodiment, the parameters used are as follows: - the frequency of the power supply signal of the capacitive sensor 2000 fo is equal to 100 kHz; - the frequency fpwM of the PWM signal is equal to 4MHz; and - the clock frequency fh is equal to 100 MHz (25*4MHz, in other words M=25).

[0069] In this figure 7, a table is shown containing the following values: i) sine values ​​calculated by the function F of the form sin(2irfo*t) in the third column; ii) the sine values ​​i) modified by adding the offset value +1 and scaled by multiplication by the scalar 0.5 in the fourth column “Sine after scaling and offset” (these values ​​are between 0 and 1 and represent PWM duty cycle values ​​between 0% and 100%); iii) the modified sine values ​​ii) then converted into number of docks or clock pulses by multiplication by M=25 in the fifth column “Corresponding number of docks”; iv) the integer rounding values ​​of values ​​iii) in the sixth column “Integer rounding of number of docks”; v) the sine values ​​corresponding to the integer rounding values ​​iv) in the sixth column, here obtained by dividing values ​​iv) by M=25.

[0070] Figure 8 illustrates: - the sinusoidal curve representing the function of the form sin(2irfo*t) and - the sinusoidal (or approximately sinusoidal) type curve based on the values ​​of sine v) in the seventh column of the table in Figure 7.

[0071] The control unit 1100 may also comprise an analog-to-digital converter 1130 arranged to acquire measurement data from an analog measurement signal transmitted by the capacitive sensor 2000. The analog-to-digital converter 1130 is arranged to acquire measurement data in a manner synchronized with the generation of the PWM signal. To sample an analog measurement signal received from the sensor 2000, the analog-to-digital converter 1130 operates with a sampling frequency f e which can be a submultiple of the frequency fpwM of the PWM signal or be equal to the frequency fpwM of the PWM signal.

[0072] The control unit 1100 may comprise a data processing module 1140, connected to the analog-to-digital converter 1130, arranged to process measurement data received from the analog-to-digital converter 1130 so as to detect proximity or contact between a person and an element or device incorporating the capacitive sensor 2000, for example a vehicle steering wheel. processing module 1140 is arranged to process the measurement data in a synchronized manner with the generation of the PWM signal by the control unit 110, so as to detect proximity or contact between an occupant and the vehicle component. It can be implemented by at least one processor or CPU.

[0073] Alternatively, the analog-to-digital converter 1130 and / or the processing module 1140 could be external to the control unit 1100.

[0074] Advantageously, the clock generator 1150 can be connected - directly or indirectly - to different components of the system such as the timing module 1110, the analog-to-digital converter 1130, and / or the processing module 1140. In operation, the clock generator 1150, possibly in cooperation with the timing module 1110, can generate one or more synchronous clock or timing signals. These different clock signals can comprise the clock signal h of frequency fh and one or more other clock signals, derived from the signal h, of frequency equal to a multiple or a sub-multiple of the frequency fh. Thus, each of these different clock signals can have a clock frequency fh, or a frequency equal to a multiple of the clock frequency fh (i.e., fh*n where n is a natural number), or a frequency equal to a submultiple of the clock frequency fh (i.e., fh / m where m is a natural number).Advantageously, there is no time lag or phase shift between the different clock signals of different frequencies.

[0075] For example, the clock module 1150 can transmit the clock signal h of frequency fh to the module 1110, a clock signal of frequency equal to fh or to an integer subdivision of fh can be transmitted by the module 1110 to the analog-to-digital converter 1130, and a clock signal of frequency equal to fh or to an integer multiple of fh can be transmitted to the processing module 1140 by the clock module 1150, as will be described later. The clock module 1150 makes it possible to synchronize the tasks or actions executed by the system 1000, such as the PWM generation by the module (1110), the analog-digital conversion (1130) - via the channel 1112 of the module 1110 which is clocked or paced by the clock module 1150 -, and the data processing (1140), as will be explained later in the description of the method.

[0076] As previously indicated, the power supply device 1000 comprises a filter 1200 whose role is to filter the PWM signal to generate a variable electrical power supply signal for the capacitive sensor 2000. The filter 1200 can be arranged to receive the PWM signal generated by the control unit 1100, filter it by blocking or attenuating predetermined frequencies, and transmit a variable output signal intended to power the capacitive sensor 2000.

[0077] In a particular embodiment, the filter 1200 is a low-pass filter arranged to pass the low frequencies of the PWM signal while blocking or attenuating the higher frequencies. It may be an active filter or a passive filter. Figure 3 represents an exemplary embodiment of a circuit comprising an active filter 1200. Figure 4 represents another exemplary embodiment of a circuit comprising a passive filter 1200, in this case an RC filter.

[0078] The filter 1200 is arranged to filter the PWM signal and extract therefrom a signal which corresponds to a modulating or modulating signal or initiating signal of the PWM signal.

[0079] The filter 1200 may be external to the control unit 1100. It is connected to an output port of the control unit 1100, intended to transmit the PWM signal.

[0080] In a particular embodiment, the filter 1200 makes it possible to produce or create a variable voltage signal, for example a sinusoidal or substantially sinusoidal or sinusoidal type voltage, at the output of the filter 1200, to electrically supply the sensor 2000.

[0081] Optionally, the device 1000 may also comprise an attenuator 1300, or attenuation device, for reducing the power of the PWM signal generated by the control unit 1100. The attenuated PWM signal at the output of the attenuator 1300 may have a predetermined power depending on the power supply characteristics of the capacitive sensor 2000, and thus be adapted to power the capacitive sensor 2000. For example, the attenuator 1300 may be arranged to reduce the voltage of the PWM signal (i.e., the high voltage of the pulses or pulses) to a target voltage value within a range of values ​​accepted by the capacitive sensor 2000. The attenuator 1300 may be interposed between an output of the control unit 1100 and the input of the filter 1200.

[0082] The 1300 attenuator can be programmable or adjustable to adjust the signal attenuation according to the characteristics of the capacitive sensor 2000.

[0083] The attenuator 1300 and the filter 1200 may be combined in a single circuit or device. As an illustrative example, the circuit shown in Figure 3 incorporates an attenuator 1300 and a filter 1200.

[0084] The device 1000 may also comprise, in a known manner, an analog input interface 1400 of the capacitive sensor 2000, also called a “front end” in English. The input interface 1400 may be interposed between the control unit 1100 and the capacitive sensor 2000. It may also be connected to a reference potential, for example to ground. The input interface 1400 is configured to: - receive the analog power supply signal from the sensor 2000, for example a voltage signal, from the output of the filter 1200; - supplying the capacitive elements of the capacitive sensor 2000 with the received power supply signal; - receive one or more analog measurement signals from the capacitive sensor 2000, for example one or more current signals; - optionally, carry out one or more processing operations and / or of conditioning the analog measurement signal; - retransmit the analog measurement signal, possibly processed and / or conditioned, to the analog-digital converter 1130 of the control unit 1100.

[0085] The interface 1400 may be connected by an electrical connection, for example by a wire, to each of the hardware elements 2200, 2300, 2100 and 2500 of the capacitive sensor 2000. For the sake of clarity, these connections are not shown in FIG. 1.

[0086] The operations of processing and / or conditioning the analog measurement signal coming from the sensor 2000 may include: - filtering using a filter such as an anti-aliasing filter; and / or - a current / voltage conversion, for example to convert a measured current signal into a voltage signal if the analog-to-digital converter operates on voltage; and / or - multiplexing of measurement zone inputs.

[0087] We will now describe a method of supplying electricity to the capacitive sensor 2000, according to a particular embodiment, corresponding to the operation of the supply device 1000 and represented in FIG. 6.

[0088] As previously indicated, the power supply of the capacitive sensor 2000 has predetermined characteristics, for example frequency, signal shape (sinusoidal signal, square signal, etc.), power and / or amplitude, type (voltage or current), etc.

[0089] For example, the power supply of the sensor 2000 may be a sinusoidal voltage supply of frequency fo.

[0090] When performing steps E1 to E1 1 described below, the clock generator 1 150 generates one or more clock signals. A clock signal h of fixed frequency fh can be transmitted to the module 1 1 10. This clock signal h or a clock signal derived from h of frequency equal to a integer subdivision of the frequency fh can be transmitted to the analog-to-digital converter 1 130, for example via a channel 11 12 of the module 1 1 10 as described later. The clock signal h or a clock signal derived from h with a frequency equal to a multiple of the frequency of the clock signal h can be transmitted to the processing module 1 140. In other words, the clock generator 1150 in cooperation with the timing module 1 1 10 provides the timing to the module 1 1 10 for PWM generation, to the analog-to-digital converter 1 130 for data acquisition, and to the processing module 1 140. The clock signal h times the actions or tasks respectively executed by these different entities 1 1 10, 1130, 1 140 so as to synchronize them.

[0091] During a step E1, the microcontroller 1100 generates a PWM signal of fixed frequency fpwM, under control of the clock signal h.

[0092] The frequency fpwM can be a submultiple of the clock frequency fh or be equal to the clock frequency fh.

[0093] Furthermore, the frequency fpwM may be equal to N times the predetermined frequency fo of the power supply of the sensor 2000.

[0094] The predetermined frequency characteristic fo of the power supply of the sensor 2000 may be between 20 and 200 kHz, between 60 and 200 kHz, between 70 and 200 kHz, between 80 and 200 kHz, between 90 and 200 kHz, or between 100 and 200 kHz.

[0095] The number N is an integer which can be between 20 and 100, advantageously between 30 and 60, preferably between 35 and 50.

[0096] As purely illustrative and non-limiting examples: - the predetermined frequency fo of the power supply of the sensor 2000 is equal to 75 kHz, the number N is equal to 48, the frequency fpwM of the PWM signal is equal to 3.6 MHz (75 kHz * 48), and the clock frequency fh is equal to 90 MHz (3.6 MHz * 25); or - the predetermined frequency fo of the power supply of the sensor 2000 is equal to 100 kHz, the number N is 40, the frequency ÏPWM of the PWM signal is equal to 4MHz (100kHz*40), and the clock frequency fh is equal to 100MHz (4MHz*25).

[0097] The step E1 of generating the PWM signal comprises a step E1 A of reading a predetermined digital value in the memory 1120 and a step of controlling the duty cycle of the PWM signal using the digital value read in the memory 1120, which are executed iteratively so as to read in a loop the successive values ​​of the sequence of N predetermined digital values ​​stored in the memory 1120. In this case, the control unit 1100 reads a predetermined digital value in the memory 1120 during the step E1 A, then applies a duty cycle equal to or corresponding to the predetermined digital value read to generate a pulse or pulse. The execution of the steps E1 A-E1 B is controlled, punctuated by the clock signal of frequency fpwM. Steps E1 A-E1 B are repeated at the frequency fpwM, so as to read in a loop one by one the values ​​of the sequence of N predetermined digital values ​​in the memory 1120.The microcontroller 1100 can operate in DMA (Direct Memory Access), or direct memory access, by means of a Direct Memory Access (DMA) component 1160 described later, to read the values ​​in the memory 1120. Thanks to this, the control of the generation of the PWM signal takes up no or little processor resources and / or requires no calculation or very limited calculations. Direct memory access allows the microcontroller 1100 to retrieve the digital values ​​in memory 1120 and send them to the module 1110 which can generate the PWM pulses by using the values ​​received from the memory 1120, without calculation or with very little calculation, to set or control the duty cycle.

[0098]

[0099] In a particular embodiment, the PWM signal is a voltage signal. As a purely illustrative and non-limiting example, the high voltage of the PWM pulses or pulses may be equal to 3.3V.

[0100] During a step E2, the control unit 1100 transmits the generated PWM signal to the filter 1200, here via the attenuator 1300.

[0101] In a step E3, the PWM signal is attenuated by the attenuator 1300. The attenuator 1300 reduces the power of the PWM signal without modifying the shape and frequency characteristics of the signal. In the case of a voltage PWM signal, the high voltage of the pulses or pulses is reduced to a target voltage value equal to a predetermined supply voltage of the sensor 2000 or within a predetermined range of accepted supply voltages of the sensor 2000. For example, this target voltage value is less than or equal to 1 V. However, step E3 is optional. For example, if the voltage of the PWM pulses at the output of the control unit 1100 has an accepted value for supplying the sensor 2000, it is not necessary to attenuate the PWM signal.

[0102] During a step E4, in a particular embodiment, the filter 1200 filters the PWM signal and transmits a variable output signal to the sensor 2000 to power it. The filter 1200 can allow low frequencies of the PWM signal to pass while blocking or attenuating higher frequencies. It makes it possible to extract from the received PWM signal a signal corresponding to a modulating signal or modulating signal or initiating signal of the PWM. The signal obtained by filtering has the same frequency and shape characteristics as the function F used to precalculate the digital values ​​stored in the memory 1120, which are the predetermined frequency fo and shape characteristics (sinusoidal, square, etc.) of the power supply of the capacitive sensor 2000.

[0103] In the case of a voltage PWM signal, the signal after filtering is a voltage signal.

[0104] Figure 2 represents an example of a PWM signal generated by the control unit 1100 and a signal S obtained after filtering, at the output of the filter 1200. The ordinate axis represents the voltage and the abscissa axis represents the time. It will be noted that, in Figure 2, the signal S has been resynchronized with the PWM signal (i.e., slightly shifted in time to be synchronized with the PWM signal) by removing a delay introduced by the filter 1200. In this exemplary embodiment, the predetermined digital values ​​stored in the memory 1120 which control the duty cycle of the pulses of the PWM signal are precalculated using a sine function F of frequency fo. The signal S after filtering represents a sine function of frequency fo.

[0105] Figure 5 shows two other illustrative examples of signals S1 and S2 obtained after filtering a PWM signal, such as that shown in Figure 2, respectively by the filtering circuit of Figure 3 and by the RC filter of Figure 4. The filtering circuit of Figure 3 integrates an attenuator and an active filter. It allows the output amplitude of the signal to be adjusted using the attenuator and to filter by significantly reducing EMC (electromagnetic compatibility) emissions. The RC filter also allows the sinusoidal initiator signal to be reconstituted.

[0106] During a step E5, the output signal S of the filter 1200 is transmitted to the capacitive sensor 2000 via the analog input interface 1400. The interface 1400 supplies capacitive elements C1 to C4 of the sensor 2000 with the signal S obtained after filtering.

[0107] During a step E6, the capacitive sensor 2000 provides an electrical measurement signal, for example a current signal. In operation, all or part of the capacitive elements C1 to C4 shown in FIG. 1 are excited by the voltage signal S, and the sensor 2000 can for example be crossed by a current I passing through the capacitor C4 in the case where a hand is positioned in front of the zone 2200 and / or 2300. In the example of FIG. 1, the sensor 2000 transmits to the analog interface input 1400 an analog signal of the current I passing through the capacitor C4.

[0108] The analog measurement signal from the sensor 2000 (here, a current I, extracted by the sensor 2000) is transmitted to the analog-to-digital converter 1130, via the analog interface or front end 1400, during a step E7. During step E7, if the analog-to-digital converter 1130 operates in voltage, the extracted analog current signal (i.e., the signal at the output of the sensor 2000) can be converted into a voltage before transmission to the analog-to-digital converter 1130. Furthermore, during step E7, the analog measurement signal can be filtered with the anti-aliasing filter of the interface 1400, in a known manner.

[0109] During a step E8, the analog-to-digital converter 1130 operates with a sampling frequency f eto sample the analog measurement signal received from the sensor 2000 and convert it into measurement data (i.e., digital data). The converter 1130 performs the action of sampling the analog measurement signal under the control of the clock generator 1150, so as to synchronize the acquisition of measurement data and the generation of the PWM pulses. The sampling frequency fe may be equal to the frequency fpwM of the PWM signal or be a submultiple thereof, in other words f e = fpwM / n, where n= 1, 2, 3, ....

[0110] The number of sampling points NP e per period T of the power supply signal of the sensor 2000 (eg, one period of a sinusoid) can be obtained by the following relation: [Math 1 ] fe = f0* NP e NPe is equal to the ratio of the sampling frequency f eof the analog-to-digital converter 1 130 and the frequency f0 of the sensor supply signal 2000.

[0111] Let us take the purely illustrative and non-limiting example of a sampling frequency f e equal to the frequency fpwM of the PWM signal divided by 4. In this case: - if the predetermined frequency fo of the sensor power supply 2000 is equal to 75 kHz and the frequency fpwM of the PWM signal is equal to 3.6 MHz, then the sampling frequency fe of the analog-to-digital converter 1130 is equal to 900 kHz (3.6 MHz / 4), which makes it possible to obtain 12 sampling points (NP e =12) over a period T of the power supply of the sensor 2000 (75kHz*12=900kHz); - if the predetermined frequency fo of the sensor 2000 power supply is equal to 100 kHz and the frequency fpwM of the PWM signal is equal to 4 MHz, then the sampling frequency fe of the analog-to-digital converter 1130 is equal to 1 MHz (4 MHz / 4), which makes it possible to obtain 10 sampling points (NP e =10) over a period T of the power supply of the sensor 2000 (100kHz*10=1 MHz).

[0112] The sampling points of the analog measurement signal (i.e., the measurement data) are acquired synchronously with the generation of PWM pulses. The device 1000 excites the capacitive elements of the sensor 2000 and reads the measurement data at the same time, synchronously, which allows reliable measurements to be obtained. This synchronization is achieved by means of the clock module or clock generator 1150 which allows the distribution of clock or timing signals synchronized at identical frequencies or at frequencies derived from the clock frequency fh by multiplication by an integer n or division by an integer m. between them by an integer multiplication or division factor, both to the module 1110 generating the PWM signal and to the analog-to-digital converter 1130.

[0113] The measurement data acquired by the digital-analog converter 1130 are written, stored in the memory 1121 by the DMA component 1160, during a step E9. In Figure 6, step E10 illustrates the operation of acquiring and writing the measurement data in the memory 1121. The measurement data stored in the memory 1121 are accessible to the processing module 1140, which is responsible for processing them to detect the proximity or contact between the vehicle component integrating the sensor 2000 and a person, for example to detect whether a driver has his hands on the steering wheel, during a step E11. The processing of the measurement data E11 is carried out synchronously with the generation of the PWM signal and the acquisition of the measurement data.

[0114] By precomputing and storing the predetermined digital values ​​to control the generation of the PWM signal, the generation of the PWM signal only requires access to the memory 1120 to retrieve the precomputed values, and does not use any processor and / or computing resources. As a result, the PWM signal pulses can be generated without lag (i.e., instantaneously or quasi-instantaneously) at a rate given by the clock signal h. The clock signal h sets the pace for the generation of the PWM pulses or pulses, without any time lag.

[0115] The same clock signal of frequency fh or a clock signal of frequency equal to an integer subdivision of fh also paces the acquisition of the measurement data by the analog-to-digital converter 1130 at a frequency which is a submultiple of the frequency fpwM of the PWM or is equal to the frequency fpwM of the PWM. This acquisition rhythm is carried out by the channel 1112 of the module 1110 from the clock signal fh. This makes it possible to generate pulses or pulses and to read or acquire the measurement data synchronously with the generation of pulses (at the same frequency or at different frequencies). The sampling of the measured signal (i.e., the digital reading of the measured analog signal) is carried out synchronously with the generation of PWM pulses. This makes it possible to measure without error an amplitude variation and / or a phase shift between an applied input signal (i.e., the power signal applied to the sensor 2000) and an output signal. of the sensor 2000. These two input and output signals of the sensor 2000 are preferably synchronous to obtain a correct, non-erroneous measurement.

[0116] If the generation of the PWM signal used computing resources, there would be a risk of desynchronizing the analog-to-digital converter 1130 and the PWM generation, in other words desynchronizing the reading or acquisition of the measurement data and the generation of the PWM pulses, which could cause measurement errors.

[0117] Referring to Figure 6, the power supply device 1000 uses the DMA component 1160 in the microcontroller 1100 to synchronously: - generate the PWM signal - for example by a channel 11 1 1 of the module 1110 - this PWM signal making it possible to generate the sinusoidal power supply signal after filtering; and - acquire and store measurement data via the Analog to Digital Converter (ADC) 1130 which is clocked, paced, controlled - for example by another channel, namely channel 1112, of the module 1110.

[0118] We will now describe in more detail the DMA operation of the microcontroller 1100, in particular for the generation of the sinusoidal supply signal and the acquisition of measurement data, according to a particular embodiment.

[0119] Figure 9 schematically and simplifiedly represents components of the microcontroller 1100 which are involved in the generation of the PWM signal, precursor of the sinusoidal power supply signal, and in the acquisition of measurement data at the output of the capacitive sensor 2000. These components include: - at least one 1125 memory; - the DMA 1160 component; - the timing module 1 1 10.

[0120] The microcontroller 1100 also includes the analog-to-digital converter, ADC, 1130 and the processing module 1140. The processor or CPU of the processing module 1140 may control the operation of the components and / or peripherals of the microcontroller 1100.

[0121] The memory 1125 can be shared and accessible by the CPU - or processing module 1140 - and by the DMA component 1160. It can include: - memory 1120 storing the sinusoidal values ​​for the PWM duty cycle control, preferably a single period of sinusoidal values, and - a memory 1 121 storing the measurement data of the CAN converter 1 130.

[0122] Memories 1120 and 1121 may be separate or integrated.

[0123] The DMA component 1160 is a hardware element capable of direct memory access, i.e. without requesting the processor or CPU 1140 of the microcontroller 1100. It operates independently of the processor 1140, allowing generation of a PWM signal at a PWM frequency (for example, 3.6 MHz), and acquisition of measurement data at a sampling frequency fe independently of the processor 1140. It reads the sinusoidal values ​​in the memory 1120 to transmit them to the module 1110, more specifically to the channel 11111 of the module 1110, and controls the acquisition and storage of the data by the CAN 1130 in the memory 1121.

[0124] Module 1 1 10, connected to clock 1 150, provides signals through both channels 1 1 1 1 and 1 1 12 to coordinate PWM generation and data acquisition. In one embodiment, data is acquired synchronously with PWM generation, either at the same frequency or at an integer division of the frequency.

[0125] The system generates several periods of the sinusoidal signal by cyclically reading the values ​​from the 1120 memory, while synchronously acquiring the measurement data. The first two periods are generally ignored to achieve electronic stability.

[0126] The system executes a measurement process enabling a measurement or detection action to be carried out by the capacitive sensor 2000. This measurement process can last a few hundred microseconds, for example approximately 300 microseconds, and be repeated periodically according to a periodicity of for example between 2 ms and 500 ms, preferably between 5 ms and 100 ms, on command from the processor 1140.

[0127] The measurement process may include: 1. Activation, made by the CPU 1 140, of the channels 1 11 1 and 1 1 12, triggering respectively the DMA 1 160 for the PWM generation and the CAN 1 130 for the acquisition, and simultaneous start of the PWM generation and the data acquisition. 2. PWM generation by cyclic reading of the sinusoidal values ​​from the memory 1120 via the DMA 1160, repeated over several cycles. During each reading cycle, the DMA component 1160 successively reads the sinusoidal values ​​from the memory 1120 at the PWM frequency (for example 3.6 MHz) and transmits them to the module 1110 to generate a sinusoidal signal period. The cycles are repeated in order to generate a continuous sinusoidal signal over several periods. 3. Synchronous sampling of the measurement signal by the CAN 1 130 and storage of the data in the memory 1 121 via the DMA 1160. The CAN 1 130 samples the measurement signal, at the output of the capacitive sensor 2000, at the sampling frequency fe (for example, 900 kHz) and the DMA component 1160 stores the measured values ​​directly in memory 1121, without involving the processor 1140. Sampling and storage in memory 1121 are synchronous with the PWM generation by channel 11111 module 1110.

[0128] This process allows a defined number of measurement points to be acquired (e.g., 360 measurement points can be acquired with 30 reading cycles, a PWM frequency of 3.6 MHz, and a sampling frequency fe of 900 MHz). The number of reading cycles is determined according to the desired number of measurement values, with a maximum of 1024 values ​​per run for example.

[0129] DMA 1160 signals the end of the process to processor 1140.

[0130] The processor 1140 processes the data from the memory 1121 to extract the sensing information, such as the phase and amplitude of the output signal from the sensor 2000.

[0131] Industrial application

[0132] A feeding device according to the present invention, and its manufacture, are capable of industrial application.

[0133] It will be understood that various modifications and / or improvements obvious to those skilled in the art may be made to the various embodiments of the invention described in the present description without departing from the scope of the invention.

Claims

CLAIMS

1. Device (1000) for supplying electricity to a capacitive sensor (2000) for detecting proximity or contact between an occupant and a component of a vehicle, said device comprising a microcontroller (1100) arranged to generate a PWM signal, characterized in that the device (1000) comprises a filter (1200) arranged to filter the PWM signal generated by the microcontroller (1100) and transmit as output a variable signal for supplying electricity to the capacitive sensor (2000).

2. A device according to claim 1, comprising memory means (1120) storing predetermined digital values, and wherein the microcontroller (1100) is arranged to access the memory means (1120) and control the duty cycle of the PWM signal using the predetermined digital values ​​read from the memory means (1120), in order to generate the PWM signal.

3. Device according to claim 2, wherein said predetermined digital values ​​are obtained by calculation using a function (F) having one or more predetermined characteristics of the power supply of the capacitive sensor (2000), among a frequency characteristic (fo) and a signal shape characteristic.

4. Device according to claim 3, wherein said function (F) represents a sinusoidal signal or a periodic square signal or a periodic triangular signal.

5. Device according to claim 3 and 4, wherein said predetermined frequency characteristic (fo) of the power supply of the capacitive sensor (2000) is between 20 and 200 kHz, between 60 and 200 kHz, between 70 and 200 kHz, between 80 and 200 kHz, between 90 and 200 kHz, or between 100 and 200 kHz.

6. Device according to one of claims 3 to 5, in which the microcontroller (1100) is arranged to generate the PWM signal with a frequency (fpwM) equal to N times said predetermined frequency (fo) of the electrical supply of the capacitive sensor (2000), N being an integer between 20 and 100, advantageously between 30 and 60, preferably between 35 and 50.

7. Device according to claim 6, in which the memory means (1120) stores N precalculated digital values ​​over a period of said function (F).

8. Device according to one of claims 1 to 7, in which the filter (1200) is a low-pass filter.

9. Device according to one of claims 1 to 8, in which the microcontroller (1100) comprises an analog-digital converter (1130) arranged to acquire measurement data from an analog measurement signal of the capacitive sensor (2000), the analog-digital converter (1130) being arranged to acquire measurement data in a synchronized manner with the generation of the PWM signal.

10. The device of claim 8, wherein the analog-to-digital converter (1130) has a sampling frequency (f e ) which is a submultiple of the frequency (fpwM) of the PWM signal or is equal to the frequency (fpwM) of the PWM signal.

11. Device according to one of claims 1 to 10, comprising an attenuator (1300) interposed between the microcontroller (1100) and the filter (1200).

12. Device according to one of claims 1 to 11, in which the microcontroller (1100) comprises a data processing module (1140) arranged to process the measurement data acquired by the analog-digital converter (1130), in a synchronized manner with the generation of the PWM signal, so as to detect proximity or contact between an occupant and the vehicle component.

13. Device according to one of claims 1 to 12, comprising a clock generator (1150) arranged to transmit one or more clock signals so as to synchronize the execution of different actions by the device.

14. System comprising an electrical power supply device (1000) according to one of claims 1 to 13 and a capacitive sensor (2000) for detecting proximity or contact between an occupant and a component of a vehicle such as a vehicle steering wheel.

15. Method for supplying electrical power to a capacitive sensor (2000) for detecting proximity or contact between an occupant and a component of a vehicle, said method comprising the steps of: - generating (E1) by a microcontroller (1100) a PWM signal, - transmitting the PWM signal from the microcontroller (1100) to a filter (1200); - filter (E4) the PWM signal using the filter (1200); - transmitting (E5) a variable output signal from the filter (1200) to the capacitive sensor (2000) to supply said capacitive sensor (2000).

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