Drift suppression method, proximity sensor and wireless device

Patent metadata

Field	Value
Publication number	US-2025277681-A1
Application number	US-202519213563-A
Country	US
Kind code	A1
Filing date	May 20, 2025
Priority date	Apr 27, 2022
Publication date	Sep 4, 2025
Grant date	—

Abstract

A portable device including a capacitive proximity sensor can suppress a drift superimposed to the capacitive proximity signal and the corresponding method. A processor generates a baseline value by integrating a series of values that are derived from the slope of the proximity signal, when the slope is within stated limits, or a fixed value outside of the stated limits.

First claim

1 . A method of suppressing a drift superimposed to a signal generated by a sensor, including:
receiving a series of samples of an output of the sensor comprising the proximity signal with the superimposed drift, estimating repeatedly a variation of the samples testing whether the variation is within a predetermined region of acceptation updating a baseline value by adding either
a value derived from the samples when the variation is in the region of acceptation, or
a fixed value when the variation is not in the region of acceptation,
obtain a drift-suppressed signal by subtracting the baseline value from the samples.

2 . The method of claim 1 , wherein the region of acceptation is an interval between an upper threshold and with a lower threshold, and, the added value is a first fixed value when the average slope is below the lower threshold, and a second fixed value when the average slope is above the upper threshold.

3 . The method of claim 1 , wherein the variation is a difference between a sample and a preceding sample, or a running average of differences between consecutive samples in a window.

4 . The method of claim 2 , comprising generating a flag from the drift-suppressed signal, wherein the upper and lower thresholds are altered when the flag has a first value and set back to a previous value when the flag has a second value.

5 . The method of claim 1 , comprising resetting a value of the baseline to a value of the samples from time to time.

6 . The method of claim 1 , wherein the value derived from the samples is related to a derivative of the samples such that successive updates of the baseline follow the samples.

7 . The method of claim 6 , wherein the value derived from the samples is an instantaneous slope of the samples or an average slope of the samples.

8 . The method of claim 1 , comprising a step of limiting the variation when it transiently exceeds a set value or transiently crosses zero.

9 . A capacitive proximity sensor for a portable device, comprising a sense electrode and a readout circuit configured to read a self-capacitance of the sense electrode and provide a proximity signal including a series of capacitance values, the capacitive proximity sensor comprising an A/D converter providing a series of samples of the capacity signal and a drift suppression unit configured for:
estimating repeatedly a variation of the samples testing whether the variation is within a predetermined region of acceptation updating a baseline value by adding either
a value derived from the samples when the variation is in the region of acceptation, or
a fixed value when the variation is not in the region of acceptation,
obtain a drift-suppressed proximity signal by subtracting the baseline value from the samples, deriving a proximity output signal from the drift-suppressed proximity signal.

10 . The proximity sensor of claim 9 , comprising an analogue processor configured to subtract a programmable offset from the capacity signal.

11 . The proximity sensor of claim 9 , wherein the region of acceptation is an interval between an upper threshold and with a lower threshold, and, the added value is a first fixed value when the average slope is below the lower threshold, and a second fixed value when the average slope is above the upper threshold.

12 . The proximity sensor of claim 9 , wherein the variation is a difference between a sample and a preceding sample, or a running average of differences between consecutive samples in a window.

13 . The proximity sensor of claim 9 , wherein the value derived from the samples is related to a derivative of the samples such that successive updates of the baseline follow the samples.

14 . The proximity sensor of claim 13 , wherein the value derived from the samples is an instantaneous slope of the samples or an average slope of the samples.

15 . The proximity sensor of claim 11 , wherein the upper and lower thresholds are altered when the proximity output signal has a first value and set back to a previous value when the proximity output signal has a second value.

16 . A portable wireless device comprising the proximity sensor of claim 9 .

17 . The portable wireless device of claim 16 , configured to take a programmed action when the proximity output signal has a predetermined value.

18 . The portable wireless device of claim 17 , the programmed action being one of:
switching off a display, inhibiting a tactile input, or adapting a radio transmission power.

19 . The portable wireless device of claim 16 , the sense electrode being:
a RF antenna, or a part of a metallic chassis of the device, or a copper area on a printed circuit board.

Assignees

• Semtech Corp

Inventors

• Rouaissia Chaouki

Classifications

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• H03K2217/94031

  Calibration involving digital processing · CPC title

• H03K2217/94026

  Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input · CPC title

• H03H2017/0081

  of FIR filters · CPC title

• G01V3/00

  Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation · CPC title