US-12620935-B2 - Circuit and method to detect faults of a MEMS device including an oscillating mass

US12620935B2US 12620935 B2US12620935 B2US 12620935B2US-12620935-B2

Abstract

Faults in a periodically oscillating MEMS mass are detected by processing a position signal, having an amplitude and oscillation frequency, generated as a function of mass position. First and second reference signals formed by samples of quadrature sinusoids at the oscillation frequency are generated. First and second multipliers generate a first product signal and a second product signal, respectively, via multiplication of the position signal by the first and second reference signals. The first and second product signals are low pass filtered to generate first and second filtered signals, respectively. An estimator circuit determines estimates of the amplitude as a function of the first and second filtered signals. A decision circuit detects the presence of faults on the basis of a comparison of the estimates with a range of values.

Inventors

Raffaele Enrico FURCERI
Marco Zamprogno

Assignees

STMICROELECTRONICS INTERNATIONAL N.V.

Dates

Publication Date: 20260505
Application Date: 20240624
Priority Date: 20230630

Claims (13)

1 . A circuit for detecting faults in a MicroElectroMechanical System (MEMS) device that includes a periodically oscillating mass, comprising: an input configured to receive a position signal formed by a succession of samples of an analog signal that is a function of a position of the periodically oscillating mass, said position signal having an amplitude and an oscillation frequency, said amplitude being directly proportional to an oscillation amplitude of the periodically oscillating mass of the MEMS device; a reference circuit configured to generate a first reference signal formed by successions of samples of a first sinusoidal signal and generate a second reference signal formed by successions of samples of a second sinusoidal signal, wherein the first and second sinusoidal signals having a frequency equal to the oscillation frequency and are phase-shifted with respect to one another by 90°; a first multiplier configured to multiply the position signal by the first reference signal to generate a first product signal; a second multiplier configured to multiply the position signal by the second reference signal to generate a second product signal; a first lowpass filter configured to filter the first product signal and generate a first filtered signal; a second lowpass filter configured to filter the second product signal and generate a second filtered signal; an estimator circuit configured to generate estimates of said amplitude as a function of the first and second filtered signals; and a decision circuit configured to perform a comparison of the estimates of said amplitude with a range of values to detect the presence of faults in the periodic oscillation of the mass of the MEMS device.
2 . The circuit according to claim 1 , wherein the first and second lowpass filters are configured to extract DC components of the first and second product signals, respectively.
3 . The circuit according to claim 1 , wherein the estimator circuit is configured to store a succession of a number Ntheta of angles θj indexed by an index j and such that: tan(θ j )=2− j , with j= 0,1,2, . . . ,Ntheta−1; and wherein, for each pair of samples of the first and second filtered signals, the estimator circuit is configured to: encode a first co-ordinate and a second co-ordinate of a first point on corresponding bit strings so that each of the first and second co-ordinates of the first point is, respectively, equal to a corresponding sample of the pair of samples; and then when the first co-ordinate of the first point is negative, invert signs of the first and second co-ordinates of the first point; and then starting from the first point, encode, for each angle θj of the succession of angles, the first and second co-ordinates of a corresponding point on corresponding bit strings so as to determine a succession of points including the first point; and wherein the estimator circuit is further configured to encode, for each angle θj of the succession of angles, the first and second co-ordinates of the corresponding point in such a way that: when the second co-ordinate of the previous point is greater than zero, the first co-ordinate of the point is equal to the sum of the first co-ordinate of the previous point and of a first quantity, and the second co-ordinate of the point is equal to the difference between the second co-ordinate of the previous point and a second quantity; and when the second co-ordinate of the previous point is less than or equal to zero, the first co-ordinate of the point is equal to the difference between the first co-ordinate of the previous point and the first quantity, and the second co-ordinate of the point is equal to the sum of the second co-ordinate of the previous point and of the second quantity; and wherein the estimator circuit is further configured to determine said first and second quantities by a translation, in the direction of the least significant bit and by a number of bits equal to the index j of the corresponding angle θj, of the bits of the strings that encode, respectively, the second co-ordinate of the previous point and the first co-ordinate of the previous point; and wherein the estimator circuit is further configured to determine, for each pair of samples of the first and second filtered signals, a corresponding estimate of said amplitude, on the basis of the first co-ordinate of the last point of the corresponding succession of points.
4 . The circuit according to claim 1 , wherein the first and second lowpass filters are moving-average filters.
5 . The circuit according to claim 1 , wherein the reference circuit is configured to generate each sample of each pair of samples of the first and second reference signals on the basis of a linear combination of the samples of the previous pair of samples of the first and second reference signals.
6 . An electronic circuit, comprising: the fault-detection circuit according to claim 1 ; and an analog-to-digital conversion circuit configured to be coupled to the MEMS device and generate the position signal.
7 . The electronic circuit according to claim 6 , further comprising: a control circuit configured to generate, on the basis of the position signal, a timing signal phase-locked with said analog signal and having a frequency that is a multiple of the oscillation frequency; and a driving circuit configured to be controlled by the control circuit so as to generate a driving signal for application to the MEMS device so as to cause oscillation of the periodically oscillating mass, the driving signal having a frequency equal to the oscillation frequency and a respective amplitude; and wherein the control circuit and the driving circuit are further configured to control the amplitude of the driving signal so as to form a closed control loop for control of said amplitude of the analog signal.
8 . An electronic system, comprising: the electronic circuit according to claim 7 ; and the MEMS device.
9 . A method for detecting faults in a MicroElectroMechanical System (MEMS) device that includes a periodically oscillating mass, said method comprising: receiving a position signal formed by a succession of samples of an analog signal that is a function of a position of the periodically oscillating mass and has an amplitude and an oscillation frequency, said amplitude being directly proportional to an oscillation amplitude of the periodically oscillating mass of the MEMS device; generating a first reference signal formed by successions of samples of a first sinusoidal signal; generating a second reference signal formed by successions of samples of a second sinusoidal signal; wherein the first and second sinusoidal signals have a frequency equal to the oscillation frequency and are phase-shifted with respect to one another by 90°; multiplying the position signal by the first reference signal to generate a first product signal; multiply the position signal by the second reference signal to generate a second product signal via; lowpass filtering the first product signal to generate a first filtered signal; lowpass filtering the second product signal to generate a second filtered signal; generating estimates of said amplitude as a function of the first and second filtered signals; and comparing the estimates of said amplitude with a range of values to detect the presence of faults in the periodic oscillation of the mass of the MEMS device.
10 . The method according to claim 9 , wherein lowpass filtering comprises extracting DC components of the first and second product signals.
11 . The method according to claim 9 , further comprising: storing a succession of a number Ntheta of angles θj indexed by an index j and such that tan(θj)=2−j, with j=0, 1, 2, . . . , Ntheta−1; for each pair of samples of the first and second filtered: encoding a first co-ordinate and a second co-ordinate of a first point on corresponding bit strings so that each of the first and second co-ordinates of the first point are, respectively, equal to a corresponding sample of the pair; and then when the first co-ordinate of the first point is negative, inverting the signs of the first and second co-ordinates of the first point; and then starting from the first point, encoding, for each angle θj of the succession of angles, the first and second co-ordinates of a corresponding point on corresponding bit strings so as to determine a succession of points including the first point; encoding, for each angle θj of the succession of angles, the first and second co-ordinates of the corresponding point in such a way that: when the second co-ordinate of the previous point is greater than zero, the first co-ordinate of the point is equal to the sum of the first co-ordinate of the previous point and of a first quantity, and the second co-ordinate of the point is equal to the difference between the second co-ordinate of the previous point and a second quantity; and when the second co-ordinate of the previous point is less than or equal to zero, the first co-ordinate of the point is equal to the difference between the first co-ordinate of the previous point and the first quantity, and the second co-ordinate of the point is equal to the sum of the second co-ordinate of the previous point and of the second quantity; determining said first and second quantities via a translation, in the direction of the least significant bit and by a number of bits equal to the index j of the corresponding angle θj, of the bits of the strings that encode, respectively, the second co-ordinate of the previous point and the first co-ordinate of the previous point; and determining, for each pair of samples of the first and second filtered signals, a corresponding estimate of said amplitude, on the basis of the first co-ordinate of the last point of the corresponding succession of points.
12 . The method according to claim 9 , wherein lowpass filtering comprises performing a moving average filtering of the first and second product signals.
13 . The method according to claim 9 , comprising generating each sample of each pair of samples of the first and second reference signals on the basis of a linear combination of the samples of the previous pair of samples of the first and second reference signals.

Description

PRIORITY CLAIM This application claims the priority benefit of Italian Application for Patent No. 102023000013692, filed on Jun. 30, 2023, the content of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law. TECHNICAL FIELD The present invention relates to a circuit and to a method to detect faults in a MicroElectroMechanical System (MEMS) device including an oscillating mass. BACKGROUND As is known, there are today available MEMS devices that envisage the presence of a mobile mass, which, in use, oscillates, for example, linearly or angularly. For instance, MEMS mirrors are known, in which the mobile mass is formed by a so-called micromirror, which oscillates angularly. Generally, MEMS mirrors are driven at a desired frequency, which typically is approximately equal to the resonance frequency, so as to maximize the angle of aperture, i.e., the amplitude of the (angular) oscillation of the micromirror, and reduce consumption levels. Further available are malfunction-detection circuits, also known as “fault-detection circuits”, which, when coupled, for example, to a MEMS mirror, continuously detect whether a reduction of the angle of aperture of the micromirror occurs, for example, because the micromirror is driven at a frequency higher or lower than the desired frequency. Further, fault-detection circuits are able to detect possible situations of failure of the micromirror, i.e., situations in which the micromirror is no longer able to move. Fault-detection circuits are designed so as to detect possible faults in times as short as possible and in a reliable way, i.e., so as to detect any possible malfunctioning, without giving rise to so-called false positives. Further, fault-detection circuits must ideally be simple from a circuit standpoint in order to reduce the consumption levels and the overall dimensions and facilitate the corresponding calibration procedures. An example of circuit to detect faults in a micromirror is illustrated in United States Patent Application Publication No. 2018/0129036 A1 (incorporated herein by reference). This solution envisages providing a differentiator circuit downstream of an analog-to-digital converter so as to have a shorter response time. However, it has been noted how, on account of the frequency response of a highpass type that characterizes the differentiator, this solution is extremely subject to the phenomenon of high-frequency noise, with consequent degradation of the performance. There is a need in the art to provide a fault-detection circuit that will overcome at least in part the drawbacks of the prior art. SUMMARY Embodiments herein concern a circuit and a method to detect faults. In an embodiment, a circuit is provided to detect faults in a MEMS device including a mass that oscillates periodically. The circuit is configured to receive a position signal formed by a succession of samples of an analog signal that is a function of the position of the mass and has an amplitude and an oscillation frequency. The fault-detection circuit comprises: a reference circuit configured to generate a first reference signal and a second reference signal formed by successions of samples of a first sinusoidal signal and, respectively, a second sinusoidal signal, the first and second sinusoidal signals having a frequency equal to the oscillation frequency and being phase-shifted with respect to one another by 90°; a first multiplier configured to generate a first product signal by multiplication of the position signal and the first reference signal; a second multiplier configured to generate a second product signal by multiplication of the position signal and the second reference signal; a first filter and a second filter of a lowpass type configured to filter, respectively, the first and second product signals and generating, respectively, a first filtered signal and a second filtered signal; an estimator circuit configured to determine estimates of said amplitude as a function of the first and second filtered signals; and a decision circuit configured to compare the estimates of said amplitude with a range of values and to detect the presence of faults on the basis of the outcomes of the comparisons. In an embodiment, a method is presented to detect faults in a MEMS device including a mass that oscillates periodically on the basis of a position signal formed by a succession of samples of an analog signal that is a function of the position of the mass and has an amplitude and an oscillation frequency. The method comprises: generating a first reference signal and a second reference signal formed by successions of samples of a first sinusoidal signal and a second sinusoidal signal, respectively, the first and second sinusoidal signals having a frequency equal to the oscillation frequency and being phase-shifted with respect to one another by 90°; generating a first product signal via multiplication of the position signal and the first