Search

US-12620992-B2 - Capacitive sensor with optimized noise immunity

US12620992B2US 12620992 B2US12620992 B2US 12620992B2US-12620992-B2

Abstract

Disclosed is a capacitive proximity sensor including a microcontroller which is configured to perform measurements in a repetitive predetermined sequence, the sequence including a series of N consecutive measurements, N being a natural integer greater than or equal to three, wherein, with the period between two consecutive analog-to-digital conversions of the first measurement of the series being called a reference period, the period between two analog-to-digital conversions of a measurement m of the series, m being a natural integer included between 2 and N, is defined as being equal to the reference period plus the product of and a predetermined additional unitary period. The additional unitary period is equal to half the period needed to shift a noise sensitivity peak of the sensor by half its frequency width.

Inventors

  • Xavier Hourne
  • Cédric VERGNIERES
  • Julien GALAUP

Assignees

  • Vitesco Technologies GmbH

Dates

Publication Date
20260505
Application Date
20220222
Priority Date
20210302

Claims (20)

  1. 1 . A capacitive proximity sensor comprising: a detection circuit comprising a detection capacitor, a storage capacitor, and switches; and a microcontroller which is configured to control the switches of the detection circuit in order to perform measurements to detect whether or not a human is present in proximity to the sensor, each of the measurements comprising an alternation of a first acquisition phase and a second acquisition phase over a constant period, said first acquisition phase comprising charging of the detection capacitor then the discharging of the detection capacitor into the storage capacitor in order to obtain a voltage value across the terminals of the storage capacitor by analog-to-digital conversion, said second acquisition phase comprising charging of the storage capacitor then the discharging of the storage capacitor into the detection capacitor in order to obtain a voltage value across the terminals of the detection capacitor by analog-to-digital conversion, the microcontroller configured to perform measurements in a repetitive being predetermined sequence, said sequence comprising a series of N consecutive measurements, N being a natural integer greater than or equal to three, wherein a reference period is defined as being between two consecutive analog-to-digital conversions of the first measurement of the series, another period between two analog-to-digital conversions of a measurement m of the series, m being a natural integer comprised between 2 and N, is defined as being equal to the reference period plus the product of (m−1) and a predetermined additional unitary period, the additional unitary period being equal to half a period needed to shift a noise sensitivity peak associated with the sensor.
  2. 2 . The sensor as claimed in claim 1 , wherein the series comprises between four and eight measurements in order to obtain enough measurements outside of the noise peaks.
  3. 3 . The sensor as claimed in claim 1 , wherein each series comprises exactly eight measurements.
  4. 4 . The sensor as claimed in claim 1 , wherein the reference period is comprised between 80 us and 140 μs.
  5. 5 . The sensor as claimed in claim 1 , wherein the additional unitary period is comprised between 1% and 10% of the reference period.
  6. 6 . A vehicle comprising the sensor as claimed in claim 1 .
  7. 7 . A method for detecting a human presence in proximity to the sensor as claimed in claim 1 , the method, implemented by said sensor, comprising: performing the series of measurement steps performed in the predetermined sequence comprising the series of N consecutive measurements.
  8. 8 . The method as claimed in claim 7 , wherein the additional unitary period is comprised between 1% and 10% of the reference period.
  9. 9 . A non-transitory computer-readable medium on which is stored a set of program code instructions which, when executed by one or more processors of the microcontroller of the sensor of claim 1 , configure the one or more processors to implement a method for detecting a human presence in proximity to the sensor, the method, implemented by said sensor, comprising: performing the series of measurements performed in the predetermined sequence comprising the series of N consecutive.
  10. 10 . The sensor as claimed in claim 1 , wherein the additional unitary period is comprised between 3% and 5% of the reference period.
  11. 11 . The method as claimed in claim 7 , wherein the additional unitary period is comprised between 3% and 5% of the reference period.
  12. 12 . The sensor as claimed in claim 2 , wherein each series comprises exactly eight measurements.
  13. 13 . The sensor as claimed in claim 2 , wherein the reference period is comprised between 80 us and 140 μs.
  14. 14 . The sensor as claimed in claim 3 , wherein the reference period is comprised between 80 μs and 140 μs.
  15. 15 . The sensor as claimed in claim 2 , wherein the additional unitary period is comprised between 1% and 10% of the reference period.
  16. 16 . The sensor as claimed in claim 3 , wherein the additional unitary period is comprised between 1% and 10% of the reference period.
  17. 17 . The sensor as claimed in claim 4 , wherein the additional unitary period is comprised between 1% and 10% of the reference period.
  18. 18 . A vehicle comprising the sensor as claimed in claim 2 .
  19. 19 . A vehicle comprising the sensor as claimed in claim 3 .
  20. 20 . A vehicle comprising the sensor as claimed in claim 4 .

Description

This application is the U.S. national phase of International Application No. PCT/EP2022/054327 filed Feb. 22, 2022, which designated the U.S. and claims priority to FR 2101990 filed Mar. 2, 2021, the entire contents of each of which are hereby incorporated by reference. TECHNICAL FIELD The present invention relates to the field of capacitive sensors and in particular concerns a capacitive proximity sensor and a method for detecting presence using such a sensor. PRIOR ART In a motor vehicle, it is known to use capacitive sensors to detect a human presence and trigger functions of the vehicle. For example, it is known to install a capacitive sensor in the handles of the opening elements in order to detect the presence of the hand of a user of the vehicle and thus unlock the opening elements or else under the trunk of the vehicle in order to detect the passing of a foot so as to open it. Such a detection is possible due to the fact that the proximity of a part of the human body increases the capacitance value of a capacitor. Thus, in a known solution called “DCVD” (Differential Capacitive Voltage Divider), the capacitive sensor comprises an electrode, which is connected to a detection circuit comprising capacitors and switches, and a microcontroller making it possible to control the switches so as to carry out measurements based on instructions stored in its memory area. A measurement is divided into a series of successive analog-to-digital conversions, for example 8. The measurements are performed by the microcontroller as soon as it is available, that is to say when the microcontroller is not in the process of processing instructions, the time between two measurements therefore not being predefined. For each measurement, the microcontroller controls the switches to open and close periodically so as to fill a detection capacitor then to empty it into a storage capacitor before measuring the voltage across the terminals of the storage capacitor to determine the value therefrom. In the absence of human presence in proximity to the sensor, the value of the detection capacitor remains below a certain threshold for a predetermined number of consecutive measurements, for example three. In the event of human presence, the value of the detection capacitor exceeds the threshold for the predetermined number of consecutive measurements. In a motor vehicle, the capacitive proximity sensors may be subjected to external factors which may disrupt the measurements, such as, in particular, other signals, water, sunlight, etc. It is therefore necessary to use means that make it possible to counteract these electromagnetic compatibility effects. One known solution consists in adding an RC low-pass filter which prevents high-frequency noises from disrupting the measurements. This type of filter works effectively so long as the frequency of the disrupter is high in relation to the measurement frequency, but this is no longer the case when the frequency of the disrupter becomes lower. In this case, the filter becomes more and more ineffective as the measurement frequency decreases, thus allowing the noise to disrupt the measurements, in particular between 1 and 100 kHz. FIG. 1 shows an example of noise frequency response between 1 and 100 kHz by a sensor of the prior art. The frequency f of the noise is shown on the x-axis and the amplitude A of the noise after digital conversion by the sensor on the y-axis. It can be seen that the noise peaks are random over the frequency range studied. Thus, since the noise peaks are random, a human presence may be detected by mistake over the course of several consecutive measurements, leading to a false detection owing only to the noise present during these consecutive measurements. It will therefore prove useful to eliminate these disadvantages at least partly. DISCLOSURE OF THE INVENTION The invention therefore aims to provide an effective solution that makes it possible to limit the impact of the noise on the measurements. In particular, one of the aims of the invention is to provide a sensor which has an increased immunity to low-frequency noise. For this purpose, the invention first of all relates to a capacitive proximity sensor comprising a detection circuit, comprising a detection capacitor, a storage capacitor and switches, and a microcontroller which is configured to control the switches of the detection circuit in order to perform measurements for detecting whether or not a human is present in proximity to the sensor, each measurement comprising the alternation of a first acquisition phase and of a second acquisition phase over a constant period, said first acquisition phase comprising the charging of the detection capacitor then the discharging of the detection capacitor into the storage capacitor in order to obtain a voltage value across the terminals of the storage capacitor by analog-to-digital conversion, said second acquisition phase comprising the charging of the storage capa