Diagnosis of electrical faults in capacitive sensors

Abstract

Capacitive sensor comprising: a first guiding structure (12); a second conductive structure (13) opposite the first conductive structure (12), the second conductive structure (13) being movable relative to the first conductive structure (12) in response to an external force acting thereon, the second conductive structure (13) being capacitively coupled to the first conductive structure (12) to form a first capacitor (C top ) with a first capacitance which changes with a change in a distance between the first conductive structure (12) and the second conductive structure (13), wherein the first capacitance is representative of the external force and the first capacitor (C top ) comprises a first MEMS output configured to output a first sense signal representative of the first capacitance; a second capacitor (C ac-top), comprising a first terminal and a second terminal, wherein the first terminal is connected to the first MEMS output of the first capacitor (C top ) is coupled to receive the first detection signal, and the second terminal is configured to output a second detection signal based on the first detection signal; an amplifier (21) comprising a first amplifier input connected to the second terminal of the second capacitor (C ac-top ) and is configured to output a first amplified signal based on the second detection signal; and a diagnostic circuit (30) configured to receive one of the first detection signal, the second detection signal, or the first amplified signal as a first measurement signal, to receive another of the first detection signal, the second detection signal, or the first amplified signal as a second measurement signal, to generate a first offset measurement based on the first measurement signal and the second measurement signal, the first offset measurement being representative of a degree of pattern similarity between the first measurement signal and the second measurement signal, to compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and to detect a first error under a condition that the first offset measurement is outside the first threshold range.

Description

background

[0001] Capacitive sensors are versatile and can be used as pressure sensors, acoustic sensors, microphone sensors, and the like. A capacitive sensor can be a capacitive MEMS (micro-electromechanical system) sensor in any of the above-mentioned applications.

[0002] Leakage is a well-known failure mode in capacitive sensors. It can occur as an inherent leakage of the device itself, with expected drift during operation over its lifetime, or, more critically, it can occur as a result of contamination by conductive particles.

[0003] For example, a common failure mode is a conductive particle between the conductive membrane and a conductive backplate, which are typically electrically isolated from each other. The conductive particle can cause a short circuit between the conductive membrane and the conductive backplate, resulting in leakage current and an erroneous measurement. The result is leakage current and / or a degradation in sensitivity. The leakage current can also increase noise in the sensor.

[0004] Therefore, an improved device for detecting and diagnosing electrical faults in capacitive sensors due to the presence of leakage current may be desirable.

[0005] The document US 2020 / 0 373 931 A1 relates to an inverter-based capacitance-to-digital converter with successive approximation. The document US 2022 / 0 170 958 A1 relates to a sensor package with interference reduction and a corresponding operating method. The document DE 10 2015 217 666 A1 relates to a system and method for a converter. The document US 2023 / 0 064 937 A1 relates to the detection of sensitivity errors in capacitive sensors by utilizing pull-in functionality. The document DE 10 2022 100 125 A1 relates to the diagnosis of electrical faults in capacitive sensors. The document EP 1 106 981 A2 relates to a capacitive converter. JP S54-139453 A relates to a capacitance-to-digital converter. US 2004 / 0107775 A1 relates to a method and apparatus for standardizing the output signal levels of capacitive sensors with microelectromechanical systems.The document US 9 983 032 B1 relates to a sensor device and a method for continuous fault monitoring of a sensor device. Brief description

[0006] Embodiments provide a capacitive sensor comprising a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance;a second capacitor comprising a first terminal and a second terminal, the first terminal coupled to the first MEMS output of the first capacitor to receive the first sense signal, and the second terminal configured to output a second sense signal based on the first sense signal; an amplifier comprising a first amplifier input coupled to the second terminal of the second capacitor and configured to output a first amplified signal based on the second sense signal;and a diagnostic circuit configured to receive one of the first detection signal, the second detection signal, or the first amplified signal as a first measurement signal, receive another of the first detection signal, the second detection signal, or the first amplified signal as a second measurement signal, generate a first offset measurement based on the first measurement signal and the second measurement signal, the first offset measurement being representative of a degree of pattern similarity between the first measurement signal and the second measurement signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.;

[0007] Embodiments provide a capacitive sensor comprising a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance;a second capacitor comprising a first terminal and a second terminal, wherein the first terminal is coupled to the first MEMS output of the first capacitor to receive the first sense signal, and the second terminal is configured to output a second sense signal based on the first sense signal; an amplifier comprising a first amplifier input coupled to the second terminal of the second capacitor and configured to output a first amplified signal and a second amplified signal based on the second sense signal, wherein the first amplified signal is in phase with the second sense signal and the second amplified signal is 180° out of phase with the second sense signal;and a diagnostic circuit configured to receive a first pair of signals including the first amplified signal and the second amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement representative of a degree of pattern similarity between the first amplified signal and the second amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.;

[0008] Embodiments provide a capacitive sensor comprising a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure being movable relative to the first conductive structure in response to an external force acting thereon, the second conductive structure being capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance; an amplifier comprising a first amplifier input coupled to the first MEMS output,to receive the first detection signal and configured to output a first amplified signal and a second amplified signal based on the first detection signal, wherein the first amplified signal is in phase with the first detection signal and the second amplified signal is 180° out of phase with the first detection signal; and a diagnostic circuit configured to receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, wherein the first offset measurement is representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition,that the first offset measurement lies outside the first threshold range, or receive a second pair of signals including the first detection signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first detection signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement lies outside the second threshold range.

[0009] Embodiments provide a capacitive sensor comprising a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance;a third conductive structure opposite the first conductive structure, the third conductive structure being movable relative to the first conductive structure, the third conductive structure being capacitively coupled to the first conductive structure to form a second capacitor having a second capacitance that changes with a change in a distance between the first conductive structure and the third conductive structure, the second capacitance being representative of the external force, the second capacitor comprising a second MEMS output configured to output a second sense signal representative of the second capacitance;an amplifier comprising a first amplifier input coupled to the first MEMS output to receive the first sense signal and configured to output a first amplified signal based on the first sense signal, and comprising a second amplifier input coupled to the second MEMS output and configured to output a second amplified signal based on the second sense signal;and a diagnostic circuit configured to receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.; Short description of the drawings

[0010] Embodiments are described herein with reference to the accompanying drawings. Fig. 1 shows a cross-sectional view of a MEMS element of a capacitive sensor according to one or more embodiments; Fig. 2 is a block diagram of a capacitive sensor according to one or more embodiments; Fig. 3A and Fig. 3B are schematic block diagrams of readout circuits for capacitive sensors according to one or more embodiments; Fig. 4A is a schematic block diagram of a first type of evaluation circuit of a diagnostic circuit according to one or more embodiments; Fig. 4B is a schematic block diagram of a second type of evaluation circuit of a diagnostic circuit according to one or more embodiments; Fig. 4C is a schematic block diagram of a third type of evaluation circuit of a diagnostic circuit according to one or more embodiments; Fig. 5 is a schematic block diagram of a capacitive sensor readout circuit according to one or more embodiments; Fig. 6 is a schematic block diagram of a capacitive sensor readout circuit according to one or more embodiments; Fig. 7 is a schematic block diagram of a capacitive sensor readout circuit according to one or more embodiments; Fig. 8 is a schematic block diagram of a capacitive sensor readout circuit according to one or more embodiments; and Fig. 9 is a schematic block diagram of an error processing circuit of a capacitive sensor readout circuit according to one or more embodiments. Detailed description

[0011] Details are provided below to further explain the exemplary embodiments. However, it will be apparent to those skilled in the art that the embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram or schematic form rather than in detail so as not to obscure the embodiments. Furthermore, features of the various embodiments described below may be combined with one another unless expressly stated otherwise.

[0012] Furthermore, identical or similar elements, or elements with identical or similar functionality, are designated by identical or similar reference symbols in the following description. Since identical or functionally equivalent elements are provided with the same reference symbols in the figures, a repeated description for elements with the same reference symbols is unnecessary. Therefore, the descriptions for elements with identical or similar reference symbols are interchangeable.

[0013] It is understood that an element described as "connected" or "coupled" to another element may be directly connected or coupled to the other element, or there may be intervening elements. Conversely, when an element is described as "directly connected" or "directly coupled" to another element, no intervening elements are present. Other words used to describe the relationship between elements should be interpreted in the same way (e.g., "between" as opposed to "directly between," "adjacent" as opposed to "directly adjacent," etc.).

[0014] In the embodiments described herein or illustrated in the drawings, any direct electrical connection or coupling, i.e., any connection or coupling without additional intermediate elements, may also be realized by an indirect connection or coupling, i.e., a connection or coupling with one or more additional intermediate elements, or vice versa, as long as the general purpose of the connection or coupling, for example, the transmission of a specific type of signal or a specific type of information, is substantially retained. Features of different embodiments may be combined to form further embodiments. For example, variations or modifications described with respect to one of the embodiments may also be applicable to other embodiments, unless otherwise noted.

[0015] The term "substantially" may be used herein to account for small manufacturing tolerances (e.g., within 5%) that are considered acceptable in the industry without departing from the aspects of the embodiments described herein.

[0016] In the present disclosure, terms containing ordinal numbers such as "first," "second," and / or the like may modify various elements. However, these elements are not limited by the above terms. For example, the above terms do not limit the order and / or meaning of the elements. The above terms are used merely to distinguish one element from the other elements. For example, a first box and a second box refer to different boxes even though both are boxes. As another example, a first element could be referred to as a second element, and similarly, a second element could also be referred to as a first element, without departing from the scope of the present disclosure.

[0017] One or more aspects of the present disclosure may be implemented as a non-transitory computer-readable recording medium having recorded thereon a program embodying methods / algorithms for instructing the processor to perform the methods / algorithms. Thus, a non-transitory computer-readable recording medium may store electronically readable control signals that cooperate (or are capable of cooperating) with a programmable computer system to execute the respective methods / algorithms. The non-transitory computer-readable recording medium may be, for example, a CD-ROM, DVD, Blu-ray Disc, RAM, ROM, PROM, EPROM, EEPROM, FLASH memory, or an electronic storage device.

[0018] Each of the elements of the present disclosure may be configured by implementing dedicated hardware or a software program on memory that controls a processor to perform the functions of the individual components or combinations thereof. Each of the components may be implemented as a central processing unit (CPU) or other processor that reads and executes a software program from a recording medium such as a hard disk or a semiconductor memory device. The instructions may be executed, for example, by one or more processors, such as one or more CPUs, digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), programmable logic controllers (PLCs), or other equivalent integrated or discrete logic circuits.

[0019] Accordingly, the term "processor" as used herein refers to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. The techniques described in this disclosure may thus be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented in one or more processors, including one or more microprocessors, DSPs, ASICs, or other equivalent integrated or discrete logic circuits, as well as any combinations of such components.

[0020] A controller including hardware may also perform one or more of the techniques of this disclosure. A controller, including one or more processors, may use electrical signals and digital algorithms to perform its receiving, analyzing, and controlling functions, which may also further include correction functions. Such hardware, software, and firmware may be implemented in the same device or in separate devices to support the various techniques described in this disclosure. Software may be stored on a non-transitory, computer-readable medium such that the non-transitory, computer-readable medium includes program code or a program algorithm stored thereon that, when executed, causes the controller, via a computer program, to perform the steps of a method.

[0021] A signal processing circuit and / or signal conditioning circuit may receive one or more signals from one or more components and perform signal conditioning or processing thereon. As used herein, signal conditioning refers to the manipulation of a signal in such a way that the signal meets the requirements of a next stage of further processing. Signal conditioning may include analog-to-digital conversion (e.g., via an analog-to-digital converter), amplification, filtering, conversion, biasing, range adjustment, isolation, and any other processes necessary to make a signal suitable for post-conditioning processing.

[0022] Thus, a signal processing circuit may include an analog-to-digital converter (ADC) that converts the analog signal from the one or more sensor elements into a digital signal. The signal processing circuit may also include a digital signal processor (DSP) that processes the digital signal.

[0023] Embodiments are directed to the diagnosis of electrical faults in capacitive sensors, more specifically, to the diagnosis of leakage currents in capacitive MEMS (micro-electromechanical system) sensors, one of the critical failure modes of these devices. The diagnosis can be applied to any capacitive sensor, including single capacitive sensors or those that use two capacitors (e.g., an upper capacitor C Top and a lower capacitor C Bot) to acquire and generate measurement signals representative of the physical quantity measured by the capacitive sensor (e.g. pressure, acoustic waves, vibrations, or any other external AC force).

[0024] The diagnostic circuit performs its diagnosis by measuring some selected electrical parameters of the capacitive MEMS sensor, such as direct current (DC) voltages extracted from two different nodes within the circuit, and then, after some preprocessing, provides this information as output diagnostics. Depending on the readout solution used (e.g., constant charge), a leakage current or other fault, if present, will result in a DC voltage shift at the output of the capacitive MEMS sensor, at an input of a sense amplifier, or at an output of a sense amplifier that unexpectedly differs from another comparable node within the circuit. The diagnostic circuit is designed to detect the deviation between two sense signals (e.g., between two DC voltages) and report an error when the deviation is detected.

[0025] Fig. 1 shows cross-sectional views of a MEMS element of a capacitive sensor according to one or more embodiments. In particular, Fig. 1 shows a MEMS element 11 of a dual-backplate capacitive sensor, which may be implemented as a MEMS microphone, but the embodiments are not limited thereto. Capacitive MEMS sensors may also be used, for example, as pressure sensors.

[0026] The MEMS element 11 of the dual-backplate capacitive sensor includes three electrodes, including a conductive membrane 12 and two conductive backplates 13 and 14. The membrane 12 is movable, and the two conductive backplates 13 and 14 can be movably mounted in a stationary position. In other embodiments, one or more of the backplates 13 and 14 can also be movable.

[0027] An upper capacitor CTop is formed between the upper backplate 13 and the diaphragm 12, and a lower capacitor CBot is formed between the lower backplate 14 and the diaphragm 12. As the distance (i.e., the thickness of the gap g1 or g2) between the respective electrodes changes in response to an external force (e.g., pressure or acoustic waves (sound)) acting on the movable conductive structure (e.g., the diaphragm 12), the capacitance of each capacitor CTop and CBot changes. The capacitance is calculated, for example, using the formula Q=CV, where Q is the charge in coulombs, C is the capacitance in farads, and V is the potential difference between the electrodes of the capacitor in volts.

[0028] A readout circuit can be used to measure the change in capacitance. For example, a readout circuit can use a constant readout during which the voltage V is measured while the charge Q is kept constant. The change in capacitance caused by the change in the thickness of the gaps g1 and g2 results in a change in the voltages Vtop and Vbot applied to the capacitors, and a measurement circuit can measure these voltages as sensor signals. In particular, the voltage across each capacitor CTop and CBot represents a sensor signal that can be measured by a readout circuit and correlated to a physical quantity such as pressure or acoustic waves (sound). The voltage is thus the quantity to be measured.

[0029] In the present example, the diaphragm 12 may move closer to one backplate as it moves farther from the other backplate, changing the capacitance of each capacitor CTop and CBot. As a result, the voltages Vtop and Vbot change inversely, or 180° out of phase with each other, because the conductive diaphragm 12 moves closer to one of the backplates 13 or 14 as it moves farther from the other of the backplates 13 or 14. The movement of the diaphragm 12 is caused by an external force (e.g., pressure, acoustic waves (sound), or vibration) acting on the diaphragm 12. These external forces are oscillating or external AC forces whose polarity or direction changes over time.

[0030] It will also be appreciated that the embodiments are not limited to dual-backplate capacitive sensors, but may also apply to single-capacitor sensors consisting of two electrodes or capacitive sensors with two or more capacitors, including dual capacitive sensors where the two outer electrodes are movable and the middle electrode is movably mounted. For example, the MEMS element 11 may be a single-backplate capacitive sensor that includes only one of the conductive backplates 13 or 14 to form a single capacitor. Regardless of the type of capacitive sensor, at least two electrodes are used to form at least one capacitor. Each capacitor thus consists of two electrodes, at least one of which is movable relative to the other when subjected to an external force.One electrode of a capacitor can be called the reference electrode, while the other electrode of a capacitor can be called the counter electrode.

[0031] An insulating material 15 is also provided to provide electrical insulation between the conductive elements 12, 13 and 14.

[0032] Conductive materials such as metal particles or water droplets can penetrate the MEMS element 11 and form a conductive path (e.g., a short circuit) between otherwise electrically isolated parts of the MEMS element 11. This can result in an undesirable leakage current that negatively impacts the performance of the MEMS element 11. Leakage current can also be caused by internal defects in the integrated circuit itself that can develop over the lifetime of the device. The following embodiments provide additional readout circuits that can detect leakage current and potentially compensate for the leakage current to restore or otherwise enhance the functionality of the capacitive sensor.

[0033] Fig. 2 is a block diagram of a capacitive sensor 200 according to one or more embodiments. The capacitive sensor 200 includes a MEMS element (e.g., MEMS element 1 or 11) and a signal processing circuit 20 configured to receive sensor signals Ssense (e.g., voltages Vtop and Vbot) from the MEMS element 11, perform signal processing thereon, and output the processed sensor signals as measurement signals Smeas at the signal output. A readout circuit is provided between the MEMS element 11 and the signal processing circuit 20. The readout circuit receives signals from the MEMS element 11 and may include a bias circuit (e.g., a resistor bias circuit) to provide signals to the signal processing circuit 20.The capacitive sensor 200 also includes an electrical fault diagnostic circuit 30 configured to receive the sensor signals Ssense and / or the measurement signals Smeas and, based thereon, to detect a leakage current or other fault. In response to the detection of an electrical fault, such as a leakage current, the electrical fault diagnostic circuit 30 is configured to generate a fault signal Serr and output the fault signal Serr at the fault output.

[0034] To detect an electrical fault, the electrical fault diagnostic circuit 30 is configured to measure one of the electrical parameters affected by the MEMS leakage current, compare the electrical parameter to a predetermined fault threshold, and generate the fault signal Serr in response to the electrical parameter exceeding (e.g., exceeding) the predetermined fault threshold. An electrical parameter affected by the MEMS leakage current may include a DC voltage. In particular, a leakage current, if present, may result in a DC voltage shift at the output of the MEMS element 11, at the input of a sense amplifier, or at an output of the sense amplifier. The electrical fault diagnostic circuit 30 may be configured to monitor and detect the DC voltage shift that exceeds a predetermined fault threshold at one or more of these circuit nodes.

[0035] The error signal Serr can be forwarded to another diagnostic circuit (not shown) configured to perform further analysis of the capacitive sensor 200 to determine the cause or source of the electrical error. The electrical error diagnostic circuit 30 can also be configured to compensate for the detected leakage current by regulating the affected electrical parameter and restore appropriate performance. The electrical error diagnostic circuit 30 is configured to generate a compensation signal Scomp and transmit it to the signal processing circuit 20 or to a readout circuit, where the compensation information contained in the compensation signal Scomp is used to compensate for the affected electrical parameter.

[0036] Fig. 3A and Fig. 3B are schematic block diagrams of readout circuits of capacitive sensors according to one or more embodiments. In particular, Fig. 3A shows a single-ended capacitive MEMS sensor 300A that includes only one conductive backplate to form a single capacitor CMEMS, and the Fig. Figure 3B illustrates a differential capacitive MEMS sensor 300B that includes two conductive backplates to form two capacitors CTop and CBot. Both capacitive sensors 300A and 300B include constant charge (CC) readout circuits for reading the signals of a capacitive MEMS element (e.g., MEMS element 11). Thus, the charge of each capacitor CMEMS, CTop, and CBot is kept constant, while the voltage across the capacitors is varied based on the change in capacitance.

[0037] A DC bias supply Vcp, which supplies a DC bias voltage (common potential) to the conductive structures (i.e., the backplate(s) and membrane(s)) of the MEMS device. External AC forces are applied and act on the conductive structures, causing a capacitance change across the capacitors CMEMS, CTop, and / or CBot.

[0038] An amplifier 21, such as a programmable gain amplifier (single or differential) or a buffer amplifier, is configured to receive the voltages Vtop and Vbot from the MEMS element as sensor signals. The amplifier 21 is part of the signal processing circuit 20 and may be the beginning of a signal processing chain. For example, the amplifier 21 may be configured to receive the sensor signals (i.e., the voltages VMEMS, Vtop, and / or Vbot) and provide amplified sensor signals to a discrete-time ADC (not shown) arranged downstream of the signal processing circuit 20 along the signal processing chain.

[0039] A leakage current can be modeled as a leakage component Zleak (e.g., a leakage resistor or a leakage current source) coupled in parallel with the MEMS equivalent capacitance CMEMS, CTop, or CBot, respectively. Leakage can occur between the two upper conductive structures of the MEMS element 11 (e.g., conductive structures 12 and 13) or between the two lower conductive structures of the MEMS element 11 (e.g., conductive structures 12 and 14). Thus, for each leakage current, a leakage component Zleak can be modeled, as specified by the leakage components Zleak, Zleak1, and Zleak2.

[0040] In the Fig. 3A, the output voltage VMEMS of the MEMS capacitor CMEMS is adjusted via a high-impedance bias resistor Rbias1 and a bias voltage Vbias1. The output voltage VMEMS is transmitted to an input node of the sense amplifier 21 via an AC capacitor Cac. The AC capacitor Cac includes a first terminal and a second terminal, the first terminal coupled to the output of the MEMS capacitor CMEMS to receive the output voltage VMEMS as a first sense signal, and the second terminal configured to output an amplifier input voltage Vpga as a second sense signal based on the first sense signal. The input node of the sense amplifier at Vpga is adjusted via a high-impedance bias resistor Rbias2 and a bias voltage Vbias2. The AC capacitor Cac and the input node at Vpga may be integrated into the sense amplifier or implemented externally.

[0041] The bias resistors Rbias1 and Rbias2 are set to a very high value to reduce the noise present at the output of the MEMS element 11 and at the input of the amplifier 21. For example, the bias resistors Rbias1 and Rbias2 can initially be set to a value between 1Gohm and 500Gohms, depending on the noise rejection requirements and the bandwidth of the readout circuit. The higher the resistance, the higher the noise rejection, providing a higher SNR. However, it is conceivable that other resistors could be used. In this example, the bias resistors Rbias1 and Rbias2 are kept the same or essentially the same and can be adjustable to compensate for a detected leakage current or other error.

[0042] The first detection signal (VMEMS) comprises a first AC component and a first DC component, and the second detection signal (Vpga) comprises a second AC component and a second DC component. The first AC component and the second AC component are in phase with each other (e.g., maintained by the AC capacitor Cac). This in-phase relationship makes it possible to compare the two voltages or detection signals, and in particular, to compare the DC components of the two voltages or detection signals.

[0043] The output voltage VMEMS and the amplifier input voltage Vpga should have similar DC and AC values ​​when the 300A capacitive sensor is operating normally. If both the DC and AC components are the same, no fault is detected. On the other hand, if the AC components for VMEMS and Vpga remain the same and one of the DC voltage values ​​changes, a DC offset or difference between the two sense signals can be detected to detect a fault. A DC shift in VMEMS can signal a fault at the MEMS element 11, such as a leakage current, and a DC shift in Vpga can signal a fault at the sense amplifier. This principle can enable a diagnostic circuit to distinguish the origin of a detected fault for further evaluation and / or compensation.

[0044] The sense amplifier 21 includes a first amplifier input at Vpga connected to the second terminal of the AC capacitor Cac and is configured to output an amplified signal Vamp based on the amplifier input voltage Vpga. The sense amplifier 21 may apply a predetermined gain to the amplifier input voltage Vpga to generate the amplified signal Vamp. Additionally, the output of the sense amplifier may be an inverting or non-inverting output such that the amplified signal Vamp is either 180° out of phase or in phase with the amplifier input voltage Vpga.

[0045] Fig. Figure 3B shows that the differential capacitive MEMS sensor 300B includes similar components as described for the single-ended capacitive MEMS sensor 300A, but in duplicate for each MEMS capacitor CTop and CBot. Leakage current is modeled for each MEMS capacitor CTop and CBot by the leakage current components Zleak1 and Zleak2, respectively. The output voltages VTop and VBot correspond to the output voltage VMEMS for the respective MEMS capacitors CTop and CBot. Each readout channel includes a corresponding AC capacitor, Cac_top and Cac_bot, connected to a corresponding input of the read simplifier, where a corresponding amplifier input voltage Vpga_top or Vpga_bot is generated similarly as described above.

[0046] The outputs of the MEMS capacitors CTop and CBot are biased by a bias circuit including two bias resistors Rbias1 and a bias voltage Vbias1 coupled to a common node to reduce noise present at the MEMS outputs. The inputs of the sense amplifier 21 are biased by a bias circuit including two bias resistors Rbias2 and a bias voltage Vbias2 coupled to a common node to reduce noise at the amplifier inputs.

[0047] The output voltage VTop and the amplifier input voltage Vpga_top should have similar DC and AC values ​​when the capacitive sensor 300B is operating normally. If the DC and AC components are the same, no error is detected. On the other hand, if the AC components for VTop and Vpga_top remain the same and one of the DC values ​​changes, a DC offset or DC voltage difference between the two sense signals can be detected to detect an error. A DC shift at VTop can signal an error at Ctop, such as a leakage current, and a DC shift at Vpga_top can signal an error at the sense amplifier 21. This principle can allow a diagnostic circuit to distinguish the origin of a detected error for further evaluation and / or compensation.

[0048] Likewise, the output voltage VBot and the amplifier input voltage Vpga_bot should have similar DC and AC values ​​when the capacitive sensor 300B is operating normally. If the DC and AC components are the same, no fault is detected. On the other hand, if the AC components for VBot and Vpga_bot remain the same and one of the DC voltage values ​​changes, a DC offset or difference between the two sense signals can be detected to detect a fault. A DC shift in VBot can signal a fault in Cbot, such as a leakage current, and a DC shift in Vpga_bot can signal a fault in the sense amplifier 21. This principle can allow a diagnostic circuit to distinguish the origin of a detected fault for further evaluation and / or compensation.

[0049] It should also be noted that the output voltages VTop and VBot should be 180° out of phase with each other. As a result, the amplifier input voltages Vpga_top and Vpga_bot should also be 180° out of phase with each other.

[0050] The sense amplifier 21 may be a differential amplifier with programmable gain or a differential buffer amplifier and is configured to receive the amplifier input voltages Vpga_top and Vpga_bot as sensor signals and output a differential signal representative of the difference between the voltages Vtop and Vbot. The differential amplifier 21 is part of the signal processing circuit 20 and may be the beginning of a signal processing chain. For example, the differential amplifier 21 may be configured to receive the sensor signals (i.e., the voltages Vpga_top and Vpga_bot) and provide amplified sensor signals to a discrete-time ADC arranged downstream of the signal processing circuit 20 along the signal processing chain.

[0051] In particular, the sense amplifier 21 includes a first amplifier input at Vpga_top connected to the second terminal of the AC capacitor Cac_top and is configured to output a first amplified signal Vamp_top based on the amplifier input voltage Vpga_top. The sense amplifier 21 may apply a predetermined gain to the amplifier input voltage Vpga_top to generate the first amplified signal Vamp_top. Additionally, the first output of the sense amplifier may be an inverting or non-inverting output such that the first amplified signal Vamp_top is either 180° out of phase or in phase with the first amplifier input voltage Vpga_top.The sense amplifier 21 also includes a second amplifier input at Vpga_bot, connected to the second terminal of the AC capacitor Cac_bot, and is configured to output a second amplified signal Vamp_bot based on the amplifier input voltage Vpga_bot. The sense amplifier 21 may apply a predetermined gain to the amplifier input voltage Vpga_bot to generate the second amplified signal Vamp_bot. Additionally, the second output of the sense amplifier may be an inverting or non-inverting output such that the second amplified signal Vamp_bot is either 180° out of phase or in phase with the second amplifier input voltage Vpga_bot.

[0052] As described in more detail below, the capacitive sensors 300A and 300B each include a diagnostic circuit that includes one or more evaluation circuits. Each evaluation circuit evaluates an offset measurement (e.g., a DC offset) of a different pair of measurement signals by comparing the DC offset to a predetermined threshold range. The offset measurement is representative of a degree of pattern similarity between a first measurement signal and a second measurement signal. The measurement signals can be selected from any combination of the signals present at the MEMS outputs, the sense amplifier inputs, or the sense amplifier outputs. The pattern similarity of two in-phase signals can consist of the DC components following the same sine wave as their corresponding AC components.Thus, the DC components should be essentially the same at any given time as the signals oscillate. The pattern similarity of two out-of-phase signals can be that the mean value of a DC component is essentially the same as the mean value of a DC component over time. Thus, the extrema of the two signals should remain essentially the same over time as the signals oscillate.

[0053] For example, if two in-phase signals are being compared, the DC components of these two signals should remain in lockstep, while the two AC components oscillate. In other words, the two signals should be essentially equal. In this case, the offset measurement can represent a difference between the two measurement signals. If there is a DC shift in one of the measurement signals, the difference will be driven up or down and may be outside the specified threshold range.

[0054] However, if two phase-shifted signals are compared, the DC components of these two signals should be offset from each other according to the phase offset. In this case, one or more phase shifters can be used to align the phases of the two signals so that the two signals should be essentially the same. Again, the offset measurement can represent a difference between the two measurement signals if the phases of the two signals are aligned. If there is a DC shift in one of the measurement signals, the difference will be driven up or down and may be outside the specified threshold range.

[0055] Alternatively, an averaging circuit can be used to generate the offset measurement of the two phase-shifted signals, with the offset measurement representing an average of the two signals. If there is a DC offset in one of the measurement signals, the average value will be driven up or down and may be outside the specified threshold range.

[0056] Each evaluation circuit is configured to compare an offset measurement to a corresponding threshold range defined by a corresponding first threshold and a corresponding second threshold, and to detect an error if the offset measurement is determined to be outside the corresponding threshold range. If the offset measurement is determined to be within the predetermined threshold range, no error is detected. However, if the offset measurement is determined to be outside the predetermined threshold range, an error may be detected. In some cases, an error is detected if the offset measurement is outside the predetermined threshold range. In other cases, the error is passed through an error processing circuit that checks for the presence of an error.

[0057] Fig. 4A is a schematic block diagram of a first type of evaluation circuit 400A of a diagnostic circuit according to one or more embodiments. The evaluation circuit 400A is configured to evaluate two in-phase measurement signals S1 and S2.

[0058] The evaluation circuit 400A may include two optional DC shift circuits 401 and 402. The DC shift circuits 401 and 402 are used to primarily shift the DC component of its measurement signal to a centered output value (e.g., a center supply value). In this way, the evaluation circuit can provide a reliable error output that maximizes the AC current superimposed at the block's input. In other words, the DC shift circuits 401 and 402 help prevent the measurement signals from being clipped. The DC shift blocks may have a simple structure, such as source followers, implementing a DC shift from their input to their output.

[0059] The measurement signals S1 and S2 are provided to another circuit 403 (e.g., a subtractor), which generates a measurement offset signal S3 as the difference between the two measurement signals S1 and S2. Ideally, the value of the measurement offset signal S3 should be 0V or substantially 0V, since the two measurement signals S1 and S2 should be equal or substantially equal under normal conditions. A window comparator circuit comprises two comparators 404 and 405 connected in parallel to determine whether the measurement offset signal S3 lies between two reference voltages Vref1 and Vref2. The reference voltage Vref1 can be a positive voltage (e.g., 0.5V, 1V, etc.) and the reference voltage Vref2 can be a negative voltage (e.g., -0.5V, -1V, etc.). The two reference voltages Vref1 and Vref2 should be symmetrical around a 0V center point.When using a window comparator, the circuit can tolerate a small difference between the AC and DC components of S1 and S2 if the comparator thresholds are chosen accordingly. If the measurement offset signal S3 is within the window (i.e., within the specified threshold range), the output of an OR gate 406 is low, signaling no error at the error output. If the measurement offset signal S3 is outside the window (i.e., greater than Vref1 or less than Vref2 and thus outside the specified threshold range), the output of the OR gate 406 is high, signaling an error or potential error at the error output.

[0060] From the Fig. 5-8 it can be seen that any two pairs of in-phase measurement signals can be input to the evaluation circuit 400A and that the measurement signals S1 and S2 are used only as an example.

[0061] Fig. 4B is a schematic block diagram of a second type of evaluation circuit 400B of a diagnostic circuit according to one or more embodiments. The evaluation circuit 400A is configured to evaluate two phase-shifted measurement signals S1 and S2.

[0062] The evaluation circuit 400A may include two optional DC shift circuits 401 and 402, similarly described above. The measurement signals S1 and S2 are provided to an averaging circuit, which generates a measurement offset signal S3 as the average of the two measurement signals S1 and S2. Ideally, the value of the measurement offset signal S3 should be 0V or substantially 0V, since the average of the two measurement signals S1 and S2 over time should be the same or substantially the same under normal conditions. A window comparator circuit includes two comparators 404 and 405 connected in parallel to determine whether the measurement offset signal S3 lies between two reference voltages Vref1 and Vref2. The reference voltage Vref1 may be a positive voltage (e.g., 0.5V, 1V, etc.) and the reference voltage Vref2 may be a negative voltage (e.g., -0.5V, -1V, etc.).The two reference voltages Vref1 and Vref2 should be symmetrical around a 0V center point. If the measurement offset signal S3 is within the window (i.e., within the specified threshold range), the output of an OR gate 406 is low, thus indicating no error. If the measurement offset signal S3 is outside the window (i.e., greater than Vref1 or less than Vref2 and thus outside the specified threshold range), the output of the OR gate 406 is high, indicating an error or a potential error.

[0063] From the Fig. 5-8 it can be seen that any two pairs of phase-shifted measurement signals can be input to the evaluation circuit 400B and that the measurement signals S1 and S2 are used merely as an example.

[0064] It will be appreciated that an optional phase shifter 410 may be included in the evaluation circuit 400A to evaluate out-of-phase signals. For example, the phase shifter 410 may be used to shift a measurement signal by 180° so that it is in-phase with its paired measurement signal. In this way, the two measurement signals are expected to be equal or substantially equal, and their difference is expected to be zero or substantially zero. The phase setting of the phase shifter 410 may be considered 0° for in-phase signals and 180° (or a different phase setting) for out-of-phase signals, and may be adjustable depending on the design.

[0065] Fig. 4C is a schematic block diagram of a third type of evaluation circuit 400C of a diagnostic circuit according to one or more embodiments. The evaluation circuit 400A is configured to evaluate two in-phase measurement signals S1 and S2 and can be used interchangeably with the evaluation circuit 400C.

[0066] The evaluation circuit 400A may include two voltage-to-current converters 407 and 408, which convert the measurement signals S1 and S2 into current signals I1 and I2. The current signal I1 is connected to a common input node of the two comparators 404 and 405. The current signal I2 is connected to a 1:1 current mirror 409.

[0067] If signals S1 and S2 are two signals with the same DC and AC values ​​that overlap, then the outputs of voltage-to-current converters 407 and 408 have the same current value, and the resulting current injected into node S3 would be zero, since the output current of current mirror 409 is I2=I1. In this case, node S3 would receive the DC value specified by the VDD / 2 source, resulting in a voltage of VDD / 2 at node S3 (S3=VDD / 2). If node S3=VDD / 2 and Vref1 and Vref2 are symmetrical with respect to VDD / 2 (e.g., VDD=1.5V, S3=1.5V / 2=0.75V, and Vref1=1V and Vref2=0.5V), then error_high and error_low are low.

[0068] If signals S1 and S2 have different DC or AC values, this results in a differential current being injected into node S3 and resistor R. This current difference (delta I=I1-I2) would be injected into node S3, creating a voltage shift from the normal VDD / 2 voltage of node S3. This shift is deltaV=deltaI*R=(I1-I2)*R. If S3=VDD / 2-deltaV is outside the threshold range set by Vref1 and Vref2, the error_high or error_low signal goes high (not both at the same time), depending on whether the voltage at node S3 is greater than Vref1 or less than Vref2.

[0069] Thus, the two currents I1 and I2 result in a measurement offset signal S3 that is equal to or corresponds to the difference between the two currents. A window comparator circuit comprises two parallel-connected comparators 404 and 405 to determine whether the measurement offset signal S3 lies between two reference voltages Vref1 and Vref2. If either of the two error outputs, error_high or error_low, is high, an error is signaled.

[0070] From the Fig. 5-8 it can be seen that any two pairs of in-phase measurement signals can be input into the evaluation circuit 400C and that the measurement signals S1 and S2 are used only as an example.

[0071] Fig. 5 is a schematic block diagram of a capacitive sensor readout circuit 500 according to one or more embodiments. The capacitive sensor readout circuit 500 is similar to 300A except that the sense amplifier 21 is a differential amplifier with two outputs, including a non-inverting output and an inverting output. In particular, the sense amplifier 21 generates the amplified signals Vamp1 and Vamp2 based on Vpga, where Vamp1 is in-phase with Vpga and Vamp2 is 180° out of phase with Vpga.

[0072] The capacitive sensor readout circuit 500 shows a diagnostic circuit with three evaluation circuits 404A, 404B and 404B'. The evaluation circuit 404A receives VMEMS and Vpga as measurement signals S1 and S2, respectively, and operates as described above with respect to the Fig. 4A. The evaluation circuit 404B receives Vamp1 and Vamp2 as measurement signals S4 and S5, respectively, and operates as described above with respect to the Fig. 4B. The evaluation circuit 404B' receives Vamp2 and Vpga as measurement signals S5 and S6, respectively, and operates as described above with respect to the Fig. 4B.

[0073] Each of the three evaluation circuits 404A, 404B and 404B' calculates a corresponding offset measurement representative of a degree of pattern similarity of its measurement signal pair and generates an error at error_out1, error_out2 or error_out3 if the corresponding offset measurement exceeds its threshold range.

[0074] Fig. 6 is a schematic block diagram of a capacitive sensor readout circuit 600 according to one or more embodiments. The capacitive sensor readout circuit 600 is similar to 300A, except that the sense amplifier 21 is a differential amplifier with two outputs, including a non-inverting output and an inverting output, and the output voltage VMEMS of the MEMS capacitor CMEMS is coupled to the amplifier input of the sense amplifier 21 without an AC capacitor in between. Thus, the sense amplifier 21 generates amplified signals Vamp1 and Vamp2 based on VMEMS, where Vamp1 is in phase with VMEMS and Vamp2 is 180° out of phase with VMEMS.

[0075] The capacitive sensor readout circuit 600 shows a diagnostic circuit with two evaluation circuits 404A and 404B. The evaluation circuit 404A receives VMEMS and Vamp1 as measurement signals S1 and S2, respectively, and operates as described above with respect to the Fig. 4A. The evaluation circuit 404B receives VMEMS and Vamp2 as measurement signals S1 and S4, respectively, and operates as described above with respect to the Fig. 4B.

[0076] Each of the two evaluation circuits 404A and 404B calculates a corresponding offset measurement value representative of a degree of pattern similarity for its measurement signal pair and generates an error at error_out1 or error_out2 if the corresponding offset measurement value exceeds its threshold range.

[0077] Fig. 7 is a schematic block diagram of a capacitive sensor readout circuit 700 according to one or more embodiments. The readout circuit for capacitive sensor 700 is similar to 300B except that the outputs of sense amplifier 21 are both inverting outputs. In particular, sense amplifier 21 generates the amplified signal Vamp1 as an inversion of Vpga_top and generates the amplified signal Vamp2 as an inversion of Vpga_bot. As before, Vamp1 and Vamp2 are 180° out of phase with each other.

[0078] The capacitive sensor readout circuit 700 shows a diagnostic circuit with four evaluation circuits 404A, 404A', 404B and 404B'. The evaluation circuit 404A receives VTop and Vpga_top as measurement signals S1 and S2, respectively, and operates as described above with respect to the Fig. 4A. The evaluation circuit 404A' receives VBot and Vpga_bot as measurement signals S6 and S7, respectively, and operates as described above with respect to the Fig. 4A. The evaluation circuit 404B receives Vpga_top and Vamp1 as measurement signals S2 and S4, respectively, and operates as described above with respect to the Fig. 4B. The evaluation circuit 404B' receives Vpga_bot and Vamp2 as measurement signals S7 and S5, respectively, and operates as described above with respect to the Fig. 4B.

[0079] Each of the four evaluation circuits 404A, 404A', 404B and 404B' calculates a corresponding offset measurement representative of a degree of pattern similarity of its measurement signal pair and generates an error at error_out1, error_out2, error_out3 or error_out4 if the corresponding offset measurement exceeds its threshold range.

[0080] Fig. 8 is a schematic block diagram of a capacitive sensor readout circuit 800 according to one or more embodiments. The capacitive sensor readout circuit 800 is similar to FIG. 300B, except that the outputs of sense amplifier 21 are both inverting outputs, and the output voltages VTop and VBot of the MEMS capacitors CTop and CBot are coupled to the amplifier inputs of sense amplifier 21 without an intervening AC capacitor. Thus, sense amplifier 21 generates the amplified signal Vamp1 as an inversion of VTop and generates the amplified signal Vamp2 as an inversion of Vbot. As before, Vamp1 and Vamp2 are 180° out of phase with each other.

[0081] The capacitive sensor readout circuit 800 shows a diagnostic circuit with two evaluation circuits 404B and 404B'. The evaluation circuit 404B receives VTop and Vamp1 as measurement signals S1 and S2, respectively, and operates as described above with respect to the Fig. 4B. The evaluation circuit 404B' receives VBot and Vamp2 as measurement signals S4 and S5, respectively, and operates as described above with respect to the Fig. 4B.

[0082] Each of the two evaluation circuits 404B and 404B' calculates a corresponding offset measurement value representative of a degree of pattern similarity of its measurement signal pair and generates an error at error_out1 or error_out2 if the corresponding offset measurement value exceeds its threshold range.

[0083] The Fig. The diagnostic circuits shown in Figures 5-8 provide the advantage of not requiring a low-pass filter, which is typically very large due to the required low cutoff frequency of approximately 5 Hz. The diagnostic circuits are also capable of diagnosing faults other than leakage current faults, including faults in the bias circuits and the sense amplifier. The diagnostic circuit also provides evaluation circuitry with relatively low complexity and reasonable area requirements, which reduces manufacturing costs and meets size requirements. The diagnostic circuits can be used for differential signal paths by duplicating the circuitry for both negative / positive paths, again saving chip area.

[0084] Fig.9 is a schematic block diagram of an error processing circuit 900 of a capacitive sensor readout circuit according to one or more embodiments. The error processing circuit 900 is configured to receive an error signal (e.g., error_out1, error_out2, error_out3, or error_out4) from an evaluation circuit 404A, 404B, or 404C to verify whether an error has actually occurred and is not the result of jitter or another type of signaling error. In other words, the error processing circuit 900 may be a type of deglitch filter that filters out noise from the error signal to filter out false error signals.

[0085] In general, the error processing circuit 900 is configured to receive the first error signal (error_out) from one of the evaluation circuits 404A, 404B, or 404C and generate a second error signal (error_out final) in response to the first error signal being continuously asserted for a predetermined time interval, wherein the second error signal indicates confirmation of the first error. In other words, the error processing circuit 900 generates the second error signal (error_out final) in response to the offset measurement signal S3 remaining outside a threshold range for the predetermined time interval.

[0086] The error processing circuit 900 includes a counter 901 and a digital comparator 902. The counter 901 receives the first error signal (error_out) from one of the evaluation circuits 404A, 404B, or 404C and a clock signal CLK on which an incrementation rate is based. The counter 901 increments a counter value at each clock pulse for which the first error signal (error_out) is high and resets the counter value each time a clock pulse is received and the first error signal (error_out) is low. The counter 901 outputs a time value (e.g., a voltage or code representing the counter value), and the digital comparator 902 compares the time value with a reference threshold value Tref corresponding to a predetermined time interval. If the time value is less than the reference threshold value Tref, the output of the digital comparator 902 remains low, indicating that no error is present.If, however, the time value is equal to or greater than the reference threshold Tref, the output of digital comparator 902 is switched high, indicating a confirmed error. The first error signal (error_out) must therefore remain high for the entire duration of the specified time interval to trigger the second error signal (error_out final); otherwise, the output of digital comparator 902 remains low.

[0087] Further examples are provided below.

[0088] 1. A capacitive sensor comprising: a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure being movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure being capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance;a second capacitor comprising a first terminal and a second terminal, the first terminal coupled to the first MEMS output of the first capacitor to receive the first sense signal, and the second terminal configured to output a second sense signal based on the first sense signal;

[0089] an amplifier comprising a first amplifier input coupled to the second terminal of the second capacitor and configured to output a first amplified signal based on the second detection signal;and a diagnostic circuit configured to receive one of the first detection signal, the second detection signal, or the first amplified signal as a first measurement signal, receive another of the first detection signal, the second detection signal, or the first amplified signal as a second measurement signal, generate a first offset measurement based on the first measurement signal and the second measurement signal, the first offset measurement being representative of a degree of pattern similarity between the first measurement signal and the second measurement signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.;

[0090] 2. The capacitive sensor of embodiment 1, wherein: the first sensing signal is the first measurement signal and the second sensing signal is the second measurement signal, and the diagnostic circuit comprises a differential circuit configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal.

[0091] 3. The capacitive sensor of embodiment 2, wherein the first offset measurement is a difference between a DC value of the first measurement signal and a DC value of the second measurement signal.

[0092] 4. The capacitive sensor according to embodiment 2, wherein the first detection signal comprises a first AC component and a first DC component, the second detection signal comprises a second AC component and a second DC component, the first AC component and the second AC component being in phase with each other.

[0093] 5. The capacitive sensor of embodiment 2, wherein the diagnostic circuit comprises a first DC shifter configured to shift the first DC component to a middle supply value and a second DC shifter configured to shift the second DC component to the middle supply value.

[0094] 6. The capacitive sensor according to embodiment 2, wherein the diagnostic circuit comprises: a first voltage-to-current converter configured to generate the first measurement signal by converting the first detection signal into a first current; and a second voltage-to-current converter configured to generate the second measurement signal by converting the second detection signal into a second current.

[0095] 7. The capacitive sensor of embodiment 1, wherein: the first detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit comprises a differential circuit configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal.

[0096] 8. The capacitive sensor of embodiment 7, wherein: the first sense signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are in phase with each other, and the first offset measurement is a difference between the first DC component of the first sense signal and the second DC component of the second sense signal.

[0097] 9. The capacitive sensor of embodiment 1, wherein: the first detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit comprises an averaging circuit configured to generate the first offset measurement as an average of the first measurement signal and the second measurement signal.

[0098] 10. The capacitive sensor of embodiment 9, wherein: the first sense signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average of the first DC component of the first sense signal and the second DC component of the second sense signal.

[0099] 11. The capacitive sensor of embodiment 1, wherein: the second sense signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit comprises a differential circuit configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal.

[0100] 12. The capacitive sensor of embodiment 11, wherein: the second sense signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are in phase with each other, and the first offset measurement is a difference between the first DC component of the first sense signal and the second DC component of the second sense signal.

[0101] 13. The capacitive sensor of embodiment 1, wherein: the second sense signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit comprises an averaging circuit configured to generate the first offset measurement as an average of the first measurement signal and the second measurement signal.

[0102] 14. The capacitive sensor of embodiment 13, wherein: the second sense signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average of the first DC component of the first sense signal and the second DC component of the second sense signal.

[0103] 15. The capacitive sensor of embodiment 1, further comprising: a third conductive structure opposite the first conductive structure, the third conductive structure being movable relative to the first conductive structure, the third conductive structure being capacitively coupled to the first conductive structure to form a third capacitor having a third capacitance that changes with a change in a distance between the first conductive structure and the third conductive structure, the third capacitance being representative of the external force, the third capacitor comprising a second MEMS output configured to output a third sensing signal representative of the third capacitance; and a fourth capacitor comprising a third terminal and a fourth terminal, the third terminal being coupled to the second MEMS output of the third capacitor.to receive the third detection signal, and the fourth terminal is configured to output a fourth detection signal based on the third detection signal, wherein the amplifier further comprises a second amplifier input coupled to the fourth terminal of the fourth capacitor and configured to output a second amplified signal based on the fourth detection signal, and wherein the diagnostic circuit is further configured to receive the third detection signal, the fourth detection signal, or the second amplified signal as a third measurement signal, receive another one of the third detection signal, the fourth detection signal, or the second amplified signal as a fourth measurement signal, generate a second offset measurement based on the third measurement signal and the fourth measurement signal,wherein the second offset measurement is representative of a degree of pattern similarity between the third measurement signal and the fourth measurement signal, comparing the second offset measurement with a second threshold range defined by a third threshold and a fourth threshold, and detecting a second error under a condition that the second offset measurement lies outside the second threshold range.

[0104] 16. The capacitive sensor of embodiment 1, wherein the detected first fault indicates a leakage current in the capacitive sensor.

[0105] 17. The capacitive sensor according to embodiment 1, wherein the external force is an external AC force.

[0106] 18. The capacitive sensor of embodiment 1, wherein the diagnostic circuit comprises: a comparator circuit configured to compare the first offset measurement to the first threshold range and assert a first error signal under the condition that the first offset measurement is outside the first threshold range; and an error processing circuit configured to receive the first error signal and generate a second error signal in response to the first error signal being continuously asserted for a predetermined time interval, the second error signal indicating confirmation of the first error.

[0107] 19. The capacitive sensor of embodiment 1, wherein the diagnostic circuit comprises: a deglitch filter configured to generate a first error signal in response to the first offset measurement remaining outside the first threshold range for a predetermined time interval.

[0108] 20. A capacitive sensor comprising: a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance;a second capacitor comprising a first terminal and a second terminal, wherein the first terminal is coupled to the first MEMS output of the first capacitor to receive the first sense signal, and the second terminal is configured to output a second sense signal based on the first sense signal; an amplifier comprising a first amplifier input coupled to the second terminal of the second capacitor and configured to output a first amplified signal and a second amplified signal based on the second sense signal, wherein the first amplified signal is in phase with the second sense signal and the second amplified signal is 180° out of phase with the second sense signal;and a diagnostic circuit configured to receive a first pair of signals including the first amplified signal and the second amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement representative of a degree of pattern similarity between the first amplified signal and the second amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.;

[0109] 21. The capacitive sensor of embodiment 20, wherein the diagnostic circuit comprises an averaging circuit configured to generate the first offset measurement as an average of the first amplified signal and the second amplified signal.

[0110] 22. The capacitive sensor of embodiment 21, wherein: the first amplified signal comprises a first AC component and a first DC component, and the second amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average of the first DC component of the first amplified signal and the second DC component of the second amplified signal.

[0111] 23. The capacitive sensor of embodiment 20, wherein the diagnostic circuit comprises: at least one phase shifter configured to align a phase of the first amplified signal with a phase of the second amplified signal; and a differential circuit connected downstream of the at least one phase shifter and configured to generate the first offset measurement as a difference between the first amplified signal and the second amplified signal.

[0112] 24. The capacitive sensor of embodiment 20, wherein the diagnostic circuit is further configured to receive a second pair of signals including the second sense signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the second sense signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second fault under a condition that the second offset measurement is outside the second threshold range.

[0113] 25. The capacitive sensor of embodiment 20, wherein the diagnostic circuit is further configured to receive a second pair of signals including the first sense signal and the second sense signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first sense signal and the second sense signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second fault under a condition that the second offset measurement is outside the second threshold range.

[0114] 26. A capacitive sensor comprising: a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure being movable relative to the first conductive structure in response to an external force acting thereon, the second conductive structure being capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, the first capacitor comprising a first MEMS output configured to output a first sensing signal representative of the first capacitance; an amplifier comprising a first amplifier input coupled to the first MEMS output to receive the first sensing signal and configured tooutput a first amplified signal and a second amplified signal based on the first detection signal, wherein the first amplified signal is in phase with the first detection signal and the second amplified signal is 180° out of phase with the first detection signal; and a diagnostic circuit configured to: receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first fault under a condition,that the first offset measurement lies outside the first threshold range, or receive a second pair of signals including the first detection signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first detection signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement lies outside the second threshold range.

[0115] 27. The capacitive sensor of embodiment 26, wherein the diagnostic circuit is configured to: receive a first pair of signals including the first detection signal and the first amplified signal; generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first detection signal and the first amplified signal; compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold; and detect a first error under a condition that the first offset measurement is outside the first threshold range; and receive a second pair of signals including the first detection signal and the second amplified signal; generate a second offset measurement based on the second pair of signals.wherein the second offset measurement is representative of a degree of pattern similarity between the first detection signal and the second amplified signal, comparing the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detecting a second error under a condition that the second offset measurement is outside the second threshold range.

[0116] 28. The capacitive sensor of embodiment 27, wherein the diagnostic circuit comprises: a difference circuit configured to generate the first offset measurement as a difference between the first sense signal and the first amplified signal; and an averaging circuit configured to generate the second offset measurement as an average of the first sense signal and the second amplified signal.

[0117] 29. The capacitive sensor of embodiment 27, wherein the diagnostic circuit comprises: at least one phase shifter configured to align a phase of the first sense signal with a phase of the second amplified signal; a first differential circuit configured to generate the first offset measurement as a difference between the first sense signal and the first amplified signal; and a second differential circuit downstream of the at least one phase shifter and configured to generate the second offset measurement as a difference between the first sense signal and the second amplified signal.

[0118] 30. A capacitive sensor comprising: a first conductive structure; a second conductive structure opposite the first conductive structure, the second conductive structure movable relative to the first conductive structure in response to an external force applied thereto, the second conductive structure capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and the second conductive structure, the first capacitance being representative of the external force, and the first capacitor comprising a first MEMS output configured to output a first sense signal representative of the first capacitance;a third conductive structure opposite the first conductive structure, the third conductive structure being movable relative to the first conductive structure, the third conductive structure being capacitively coupled to the first conductive structure to form a second capacitor having a second capacitance that changes with a change in a distance between the first conductive structure and the third conductive structure, the second capacitance being representative of the external force, the second capacitor comprising a second MEMS output configured to output a second sense signal representative of the second capacitance;an amplifier comprising a first amplifier input coupled to the first MEMS output to receive the first sense signal and configured to output a first amplified signal based on the first sense signal, and comprising a second amplifier input coupled to the second MEMS output and configured to output a second amplified signal based on the second sense signal;and a diagnostic circuit configured to receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range.;

[0119] 31. The capacitive sensor of embodiment 30, wherein the diagnostic circuit is further configured to receive a second pair of signals including the second sense signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the second sense signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second fault under a condition that the second offset measurement is outside the second threshold range.

[0120] While various embodiments have been described, it will be apparent to those skilled in the art that many other embodiments and implementations are possible within the scope of the disclosure. Accordingly, the invention is not to be limited except in light of the appended claims and their equivalents.

[0121] With regard to the various functions performed by the components or structures (assemblies, devices, circuits, systems, etc.) described above, the terms (including reference to a "means") used to describe such components, unless otherwise specified, are intended to correspond to any component or structure that performs the stated function of the described component (i.e., that is functionally equivalent), even if it is not structurally equivalent to the disclosed structure that performs the function in the exemplary embodiments of the invention presented herein.

[0122] In addition, the following claims are incorporated into the detailed description, each claim being capable of standing on its own as a separate embodiment. While each claim being capable of standing on its own as a separate embodiment, it should be noted that although a dependent claim in the claims may refer to a specific combination with one or more other claims, other embodiments may also include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are suggested herein unless it is stated that a particular combination is not intended. Furthermore, it is intended to include features of one claim in another independent claim even if that claim is not directly made dependent on the independent claim.

[0123] It should further be noted that the methods disclosed in the description or in the claims may be implemented by an apparatus having means for performing each of the respective acts of those methods.

[0124] It should further be understood that the disclosure of multiple acts or functions disclosed in the description or claims cannot be construed as occurring in any particular order. Therefore, the disclosure of multiple acts or functions does not limit them to any particular order unless such acts or functions are not interchangeable for technical reasons. Moreover, in some embodiments, a single act may comprise or be divided into multiple subacts. Such subacts may be included in the disclosure of the single act unless expressly excluded.

[0125] In summary, although various exemplary embodiments have been disclosed, it will be apparent to those skilled in the art that various changes and modifications may be made to achieve some of the advantages of the concepts disclosed herein without departing from the spirit and scope of the invention. It will be apparent to those skilled in the art that other components that perform the same functions may be suitably substituted. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. It should be noted that features explained with reference to a particular figure may be combined with features of other figures, even if not expressly mentioned.Such modifications of the general inventive concept are intended to be covered by the appended claims and their legal equivalents.

Claims

[1] Capacitive sensor comprising: a first guiding structure (12); a second conductive structure (13) opposite the first conductive structure (12), the second conductive structure (13) being movable relative to the first conductive structure (12) in response to an external force acting thereon, the second conductive structure (13) being capacitively coupled to the first conductive structure (12) to form a first capacitor (C top ) with a first capacitance which changes with a change in a distance between the first conductive structure (12) and the second conductive structure (13), wherein the first capacitance is representative of the external force and the first capacitor (C top ) comprises a first MEMS output configured to output a first sense signal representative of the first capacitance; a second capacitor (C ac-top), comprising a first terminal and a second terminal, wherein the first terminal is connected to the first MEMS output of the first capacitor (C top ) is coupled to receive the first detection signal, and the second terminal is configured to output a second detection signal based on the first detection signal; an amplifier (21) comprising a first amplifier input connected to the second terminal of the second capacitor (C ac-top ) and is configured to output a first amplified signal based on the second detection signal; and a diagnostic circuit (30) configured to receive one of the first detection signal, the second detection signal, or the first amplified signal as a first measurement signal, to receive another of the first detection signal, the second detection signal, or the first amplified signal as a second measurement signal, to generate a first offset measurement based on the first measurement signal and the second measurement signal, the first offset measurement being representative of a degree of pattern similarity between the first measurement signal and the second measurement signal, to compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and to detect a first error under a condition that the first offset measurement is outside the first threshold range. [2] Capacitive sensor according to claim 1, wherein: the first detection signal is the first measurement signal and the second detection signal is the second measurement signal, and the diagnostic circuit (30) comprises a differential circuit (403a) configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal. [3] The capacitive sensor of claim 2, wherein the first offset measurement is a difference between a DC value of the first measurement signal and a DC value of the second measurement signal. [4] A capacitive sensor according to claim 2 or 3, wherein the first detection signal comprises a first AC component and a first DC component, the second detection signal comprises a second AC component and a second DC component, the first AC component and the second AC component being in phase with each other. [5] A capacitive sensor according to claim 4, wherein the diagnostic circuit (30) comprises a first DC shifter (401) configured to shift the first DC component to a mean supply value and a second DC shifter (402) configured to shift the second DC component to the mean supply value. [6] Capacitive sensor according to one of claims 2 to 5, wherein the diagnostic circuit (30) comprises: a first voltage-to-current converter (407) configured to generate the first detection signal by converting the first measurement signal into a first current; and a second voltage-to-current converter (408) configured to generate the second measurement signal by converting the second detection signal into a second current. [7] Capacitive sensor according to claim 1, wherein: the first detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit (30) comprises a differential circuit (403a) configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal. [8] Capacitive sensor according to claim 7, wherein: the first detection signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are in phase with each other, and the first offset measurement is a difference between the first DC component of the first measurement signal and the second DC component of the second measurement signal. [9] Capacitive sensor according to claim 7 or 8, wherein: the first detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit (30) comprises an averaging circuit (403b) configured to generate the first offset measurement as an average of the first measurement signal and the second measurement signal. [10] Capacitive sensor according to claim 9, wherein: the first detection signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average value of the first DC component of the first measurement signal and the second DC component of the second measurement signal. [11] Capacitive sensor according to claim 1, wherein: the second detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit (30) comprises a differential circuit (403a) configured to generate the first offset measurement as a difference between the first measurement signal and the second measurement signal. [12] Capacitive sensor according to claim 11, wherein: the second detection signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are in phase with each other, and the first offset measurement is a difference between the first DC component of the first measurement signal and the second DC component of the second measurement signal. [13] Capacitive sensor according to claim 11 or 12, wherein: the second detection signal is the first measurement signal and the first amplified signal is the second measurement signal, and the diagnostic circuit (30) comprises an averaging circuit (403b) configured to generate the first offset measurement as an average of the first measurement signal and the second measurement signal. [14] Capacitive sensor according to claim 13, wherein: the second detection signal comprises a first AC component and a first DC component, and the first amplified signal comprises a second AC component and a second DC component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average value of the first DC component of the first measurement signal and the second DC component of the second measurement signal. [15] Capacitive sensor according to one of the preceding claims, further comprising: a third conductive structure (14) opposite the first conductive structure (12), the third conductive structure (14) being movable relative to the first conductive structure (12), the third conductive structure (14) being capacitively coupled to the first conductive structure (12) to form a third capacitor (C bot ) having a third capacitance which changes with a change in a distance between the first conductive structure (12) and the third conductive structure (14), wherein the third capacitance is representative of the external force and the third capacitor (C bot) comprises a second MEMS output configured to output a third sense signal representative of the third capacitance; and a fourth capacitor (C ac-bot ), comprising a third terminal and a fourth terminal, wherein the third terminal is connected to the second MEMS output of the third capacitor (C bot ) is coupled to receive the third detection signal, and the fourth terminal is configured to output a fourth detection signal based on the third detection signal, wherein the amplifier (21) further comprises a second amplifier input connected to the fourth terminal of the fourth capacitor (C ac-bot ) and is adapted to output a second amplified signal based on the fourth detection signal, and wherein the diagnostic circuit (30) is further configured to receive one of the third detection signal, the fourth detection signal, or the second amplified signal as a third measurement signal, receive another of the third detection signal, the fourth detection signal, or the second amplified signal as a fourth measurement signal, generate a second offset measurement based on the third measurement signal and the fourth measurement signal, the second offset measurement being representative of a degree of pattern similarity between the third measurement signal and the fourth measurement signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range. [16] A capacitive sensor according to any one of the preceding claims, wherein the detected first fault indicates a leakage current in the capacitive sensor. [17] A capacitive sensor according to any one of the preceding claims, wherein the external force is an external AC force. [18] Capacitive sensor according to one of the preceding claims, wherein the diagnostic circuit (30) comprises: a comparator circuit configured to compare the first offset measurement with the first threshold range and to activate a first error signal under the condition that the first offset measurement is outside the first threshold range; and an error processing circuit (900) configured to receive the first error signal and generate a second error signal in response to the first error signal being continuously activated for a predetermined time interval, the second error signal indicating acknowledgment of the first error. [19] Capacitive sensor according to one of the preceding claims, wherein the diagnostic circuit (30) comprises: a deglitch filter configured to generate a first error signal in response to the first offset measurement remaining outside the first threshold range for a predetermined time interval. [20] Capacitive sensor comprising: a first guiding structure (12); a second conductive structure (13) opposite the first conductive structure (12), the second conductive structure (13) being movable relative to the first conductive structure (12) in response to an external force acting thereon, the second conductive structure (13) being capacitively coupled to the first conductive structure (12) to form a first capacitor (C MEMS ) with a first capacitance which changes with a change in a distance between the first conductive structure (12) and the second conductive structure (13), wherein the first capacitance is representative of the external force and the first capacitor (C MEMS ) comprises a first MEMS output configured to output a first sense signal representative of the first capacitance; a second capacitor (C ac) comprising a first terminal and a second terminal, wherein the first terminal is connected to the first MEMS output of the first capacitor (C MEMS ) is coupled to receive the first detection signal, and the second terminal is configured to output a second detection signal based on the first detection signal; an amplifier (21) comprising a first amplifier input connected to the second terminal of the second capacitor (C ac ) and is configured to output a first amplified signal and a second amplified signal based on the second detection signal, wherein the first amplified signal is in phase with the second detection signal and the second amplified signal is 180° out of phase with the second detection signal; and a diagnostic circuit (30) configured to receive a first pair of signals including the first amplified signal and the second amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first amplified signal and the second amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range. [21] The capacitive sensor of claim 20, wherein the diagnostic circuit (30) comprises an averaging circuit (403b) configured to generate the first offset measurement as an average of the first amplified signal and the second amplified signal. [22] Capacitive sensor according to claim 21, wherein: the first amplified signal comprises a first alternating current component and a first direct current component and the second amplified signal comprises a second alternating current component and a second direct current component, the first AC component and the second AC component are 180° out of phase with each other, and the first offset measurement is an average of the first DC component of the first amplified signal and the second DC component of the second amplified signal. [23] Capacitive sensor according to one of claims 20 to 22, wherein the diagnostic circuit (30) comprises: at least one phase shifter (410) configured to match a phase of the first amplified signal with a phase of the second amplified signal; and a differential circuit (403a) connected downstream of the at least one phase shifter (410) and configured to generate the first offset measurement as a difference between the first amplified signal and the second amplified signal. [24] The capacitive sensor of any one of claims 20 to 23, wherein the diagnostic circuit (30) is further configured to receive a second pair of signals including the second sense signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the second sense signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range. [25] The capacitive sensor of any one of claims 20 to 24, wherein the diagnostic circuit (30) is further configured to receive a second pair of signals including the first sense signal and the second sense signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first sense signal and the second sense signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range. [26] Capacitive sensor comprising: a first guiding structure (12); a second conductive structure (13) opposite the first conductive structure (12), the second conductive structure (13) being movable relative to the first conductive structure (12) in response to an external force acting thereon, the second conductive structure (13) being capacitively coupled to the first conductive structure (12) to form a first capacitor (C MEMS ) with a first capacitance which changes with a change in a distance between the first conductive structure (12) and the second conductive structure (13), wherein the first capacitance is representative of the external force and the first capacitor (C MEMS ) comprises a first MEMS output configured to output a first sense signal representative of the first capacitance; an amplifier (21) comprising a first amplifier input coupled to the first MEMS output to receive the first detection signal and configured to output a first amplified signal and a second amplified signal based on the first detection signal, wherein the first amplified signal is in phase with the first detection signal and the second amplified signal is 180° out of phase with the first detection signal; and a diagnostic circuit (30) designed to: receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range, or receive a second pair of signals including the first detection signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first detection signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range. [27] Capacitive sensor according to claim 26, wherein the diagnostic circuit (30) is designed to: receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range, and receive a second pair of signals including the first detection signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the first detection signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range. [28] Capacitive sensor according to claim 27, wherein the diagnostic circuit (30) comprises: a differential circuit (403a) configured to generate the first offset measurement as the difference between the first detection signal and the first amplified signal; and an averaging circuit (403b) configured to generate the second offset measurement as an average of the first detection signal and the second amplified signal. [29] Capacitive sensor according to claim 27 or 28, wherein the diagnostic circuit (30) comprises: at least one phase shifter (410) configured to match a phase of the first detection signal with a phase of the second amplified signal; a first differential circuit (403a) configured to generate the first offset measurement as a difference between the first detection signal and the first amplified signal; and a second differential circuit (403a) connected downstream of the at least one phase shifter (410) and configured to generate the second offset measurement as a difference between the first detection signal and the second amplified signal. [30] Capacitive sensor comprising: a first guiding structure (12); a second conductive structure (13) opposite the first conductive structure (12), the second conductive structure (13) being movable relative to the first conductive structure (12) in response to an external force acting thereon, the second conductive structure (13) being capacitively coupled to the first conductive structure (12) to form a first capacitor (C top ) with a first capacitance which changes with a change in a distance between the first conductive structure (12) and the second conductive structure (13), wherein the first capacitance is representative of the external force and the first capacitor (C top ) comprises a first MEMS output configured to output a first sense signal representative of the first capacitance; a third conductive structure (14) opposite the first conductive structure (12), the third conductive structure (14) being movable relative to the first conductive structure (12), the third conductive structure (14) being capacitively coupled to the first conductive structure (12) to form a second capacitor (C bot ) with a second capacitance which changes with a change in a distance between the first conductive structure (12) and the third conductive structure (14), wherein the second capacitance is representative of the external force and the second capacitor (C bot ) comprises a second MEMS output configured to output a second sense signal representative of the second capacitance; an amplifier (21) comprising a first amplifier input coupled to the first MEMS output to receive the first detection signal and configured to output a first amplified signal based on the first detection signal, and comprising a second amplifier input coupled to the second MEMS output and configured to output a second amplified signal based on the second detection signal; and a diagnostic circuit (30) configured to receive a first pair of signals including the first detection signal and the first amplified signal, generate a first offset measurement based on the first pair of signals, the first offset measurement being representative of a degree of pattern similarity between the first detection signal and the first amplified signal, compare the first offset measurement to a first threshold range defined by a first threshold and a second threshold, and detect a first error under a condition that the first offset measurement is outside the first threshold range. [31] The capacitive sensor of claim 30, wherein the diagnostic circuit (30) is further configured to receive a second pair of signals including the second sense signal and the second amplified signal, generate a second offset measurement based on the second pair of signals, the second offset measurement being representative of a degree of pattern similarity between the second sense signal and the second amplified signal, compare the second offset measurement to a second threshold range defined by a third threshold and a fourth threshold, and detect a second error under a condition that the second offset measurement is outside the second threshold range.

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