Method for detecting and attenuating mode coupling and use for electrostatic MEMS mirrors

Abstract

Scanning system, including: a MEMS (microelectromechanical system) scanning structure (12) designed to rotate about an axis (13) with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives (40) designed to drive the MEMS scanning structure (12) about the axis (13) according to the desired mode of rotation based on the at least one drive signal, each comb drive (40) comprising a rotor comb electrode and a stator comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure (12); a driver (25) designed to generate the at least one drive signal; a detection circuit (50) that is selectively coupled to at least one subset of the plurality of comb drives (40) to receive detection signals from them, each detection signal being representative of the capacity of a corresponding comb drive (40); and a processing circuit designed to detect and identify a parasitic motion mode of the MEMS scanning structure (12) based on the sensing signals, wherein the parasitic motion mode does not represent a rotational movement about the axis (13).

Description

background

[0001] LiDAR (Light Detection and Ranging) is a long-range sensing technique that uses light in the form of a pulsed laser to measure distances (variable distances) to one or more objects within a field of view. Specifically, a MEMS (microelectromechanical system) mirror is used to guide the light across the field of view. Arrays of photodetectors receive reflections from objects illuminated by the light, and the time it takes for these reflections to reach different sensors in the photodetector array is determined. This is also known as measuring the time-of-flight (ToF). LiDAR systems perform depth and distance measurements by mapping the distance to objects based on these time-of-flight calculations. Thus, the time-of-flight calculations can create distance and depth maps that can be used to generate images.

[0002] To improve the MEMS mirror scanning performance by achieving high scanning frequencies, one goal is to design the MEMS mirror to be lightweight. The mirror's moment of inertia can be reduced by choosing a thinner mirror plate. However, lighter, thinner mirror plates lead to increased dynamic deformation of the mirror for a given frequency or trajectory (corresponding to a range of frequencies). This deformation results in distortions of the emitted and / or received light beams. For this reason, the mirror plate is supported by reinforcement structures that help suppress the dynamic deformation. However, these reinforcement structures couple the desired rotation mode Rx around the mirror's scanning axis with an undesired translation mode Ty in the plane.The operating point at which the Ty resonance occurs is different for each device and is therefore difficult to predict or avoid through design. Another undesirable parasitic mode, a yaw mode Rz, also depends on the ambient temperature. Since, for example, the Young's modulus is generally temperature-dependent, parasitic modes such as the yaw mode Rz can shift in their resonant frequency. Furthermore, such parasitic modes can be excited by the high-order harmonic components of the drive signal or the main oscillatory motion, which coincide with other rigid-body modes. Detecting and avoiding such operating points, which exhibit strong coupling with undesirable parasitic modes, can be crucial to ensuring the proper operation of the MEMS mirror.To ensure high positional accuracy and corresponding image resolution during the recording of a laser pulse, precise position determination of the mirror is required.

[0003] German patent application DE 10 2018 211 755 A1 relates to an amplitude detection, amplitude control, and direction detection system for the oscillation of a vibrating body. German patent application DE 10 2021 201 585 A1 relates to a capacitive charge-based self-sensing and position monitoring device for electrostatic MEMS mirrors. German patent application US 2011 / 0 109 951 A1 relates to a method and device for monitoring the movement of mirrors in a MEMS device. German patent application US 2022 / 0 269 069 A1 relates to a technique for detecting the direction of rotation of resonant MEMS mirrors with parametric excitation.

[0004] Therefore, an improved control structure for detecting, measuring, and / or counteracting parasitic modes may be desirable. Brief description

[0005] One or more embodiments provide a scanning system comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate about an axis in a desired mode of rotation based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure about the axis in the desired mode of rotation based on the at least one drive signal, each comb drive comprising a rotor comb electrode and a stator comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a driver designed to generate the at least one drive signal;a detection circuit selectively coupled to at least one subset of the plurality of comb drives to receive detection signals from them, each detection signal being representative of the capacity of a corresponding comb drive; and a processing circuit designed to detect and identify a parasitic motion mode of the MEMS scanning structure based on the detection signals, the parasitic motion mode not representing rotation about the axis. Brief description of the drawings

[0006] The embodiments are described herein with reference to the accompanying drawings. Fig. Figure 1A is a schematic diagram of a LIDAR scanning system according to one or more embodiments; Fig. Figure 1B shows a schematic top view of an example of a mirror device according to one or more embodiments; Fig. Figure 1C shows a schematic bottom view of an example of the [unclear text] in the Fig. 1B mirror device shown according to one or more embodiments; Fig. Figure 1D illustrates a cross-sectional view of a MEMS mirror and drive electrodes according to one or more embodiments; Fig. Figure 2 is a schematic block diagram of the LIDAR scanning system according to one or more embodiments; Fig. Figure 3 illustrates a signal diagram of various signals generated by a MEMS driver based on a mirror angle θ and / or a position according to one or more embodiments; Fig. Figure 4A illustrates a top view of a MEMS mirror arranged in a nominal centered position (left) and a translationally displaced position (right) according to one or more embodiments; Fig. 4B is a schematic diagram of a system for measuring and damping a translation mode Ty according to one or more embodiments; Fig. Figure 4C is a schematic diagram of a system for measuring and attenuating a parasitic mode according to one or more embodiments; Fig. Figure 4D illustrates a top view of a MEMS mirror that is compensated with a damping voltage in response to the detection of a translational motion Ty according to one or more embodiments; Fig. Figure 4E shows a time diagram for implementing the first damping method (Method 1) for damping the parasitic mode with Ty according to one or more embodiments; Fig. Figure 4F shows a timing diagram for implementing the second damping method (Method 2) for damping the parasitic mode Tz according to one or more embodiments; Fig. Figure 5A illustrates a top view of a MEMS mirror arranged in a nominal centered position (left) and a yaw-shifted position (right) according to one or more embodiments; Fig. Figure 5B is a schematic diagram of a system for measuring and compensating a yaw mode Rz according to one or more embodiments; Fig. Figure 5C illustrates a top view of a MEMS mirror that is compensated with a damping voltage in response to the detection of a yaw motion Rz according to one or more embodiments; Fig. 6A and Fig. Figure 6B illustrates cross-sectional views of a MEMS mirror and drive electrodes according to one or more embodiments; Fig. Figure 6C is a schematic diagram of a system for measuring and compensating a Tz mode according to one or more embodiments; Fig. Figure 6D illustrates a cross-sectional view of a MEMS mirror that is compensated with a damping voltage in response to a detection of a Tz motion according to one or more embodiments. Fig. Figure 6E shows four capacitor currents DL1R, DL2R, DL1L, and DL2L in an excitation frequency sweep over a wide range from 4 kHz to 45 kHz for a MEMS mirror according to one or more embodiments. Fig. 7A illustrates a top view of a quasi-static (QS) MEMS mirror arranged in a nominally centered position (left) and a translationally displaced position (right) according to one or more embodiments; Fig. Figure 7B is a schematic diagram of a system for measuring and compensating for a QS-MEMS mirror according to one or more embodiments. Fig. Figure 7C illustrates a top view of a QS-MEMS mirror which is compensated with a damping voltage in response to a detection of a translational motion Ty according to one or more embodiments; Fig. Figure 7D illustrates a cross-sectional view of a QS-MEMS mirror that is compensated with a damping voltage in response to a detection of a translational motion Ty according to one or more embodiments; Fig. Figure 7E illustrates a top view of a QS-MEMS mirror that is compensated by an alternative method using dedicated sensing combs to detect a translational motion Ty according to one or more embodiments; and Fig. Figure 8 illustrates a flowchart of a method for avoiding parasitic coupling according to one or more embodiments. Detailed description

[0007] The following section describes various embodiments in detail with reference to the accompanying drawings. It should be noted that these embodiments serve only illustrative purposes and are not to be understood as limiting. While, for example, embodiments may be described that include a multitude of features or elements, this does not mean that all of these features or elements are required for the implementation of the embodiments. Instead, in other embodiments, some of the features or elements may be omitted or replaced by alternative features or elements. In addition to the features or elements explicitly shown and described, further features or elements may be provided, such as conventional sensor device components.

[0008] Features from different embodiments can be combined to form further embodiments, unless expressly stated otherwise. Variations or modifications described in relation to one embodiment may also be applicable to other embodiments. In some cases, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the embodiments.

[0009] Furthermore, equivalent or similar elements, or elements with equivalent or similar functionality, are designated by equivalent or similar reference symbols in the following description. Since identical or functionally equivalent elements in the figures are provided with the same reference symbols, repeated descriptions for elements with the same reference symbols are unnecessary. Therefore, the descriptions for elements with the same or similar reference symbols are interchangeable.

[0010] Connections or couplings between elements shown in the drawings or described herein may be wired or wireless unless otherwise specified. Furthermore, such connections or couplings may be direct connections or couplings without any additional intermediate elements, or indirect connections or couplings with one or more additional intermediate elements, provided that the general purpose of the connection or coupling, for example, to transmit a certain type of signal or information, is substantially maintained.

[0011] The term “essentially” may be used herein to account for small manufacturing tolerances (e.g. within 5%) which are considered acceptable in the industry without deviating from the aspects of the embodiments described herein.

[0012] Directional terms such as "above," "below," "left," "right," "above," "below," "front," "back," "behind," "anterior," "rear," "over," "under," etc., may be used in reference to the orientation of the described figures and / or elements. Since the embodiments can be positioned in a number of different orientations, the directional terminology serves for illustration and is in no way restrictive. In some cases, the directional terminology may be replaced by equivalent directional terminology based on the orientation of an embodiment, provided that the general directional relationships between elements and their overall purpose are maintained.

[0013] In the present disclosure, expressions containing ordinal numbers, such as "first," "second," and / or the like, may modify various elements. However, such elements are not restricted by the above expressions. For example, the above expressions do not restrict the order and / or meaning of the elements. The above expressions are used merely to distinguish one element from the other elements. For example, a first box and a second box denote different boxes, although both are boxes. Another example is that a first element may be called a second element, and similarly, a second element may also be called a first element, without deviating from the scope of the present disclosure.

[0014] Embodiments relate to optical sensors and optical sensor systems, and to the acquisition of information via optical sensors and optical sensor systems. A sensor can refer to a component that converts a physical quantity to be measured into an electrical signal, such as a current signal or a voltage signal. The physical quantity can include, for example, electromagnetic radiation such as visible light, infrared (IR) radiation, or another type of illumination signal, a current, or a voltage, but is not limited to these. An image sensor, for example, can be a silicon chip in a camera that converts light photons coming from a lens into voltages. The larger the active area of ​​the sensor, the more light can be collected to create an image.

[0015] A sensor device, as used herein, may refer to a device comprising a sensor and other components, for example, a bias circuit, an analog-to-digital converter, or a filter. A sensor device may be integrated on a single chip, although in other embodiments a plurality of chips or even off-chip components may be used to implement a sensor device.

[0016] In LiDAR (Light Detection and Ranging) systems, a light source emits light pulses into a field of view, and the light is reflected by one or more objects through backscattering. Specifically, LiDAR is a direct time-of-flight (ToF) system where the light pulses (e.g., laser beams of infrared light) are emitted into the field of view, and a pixel array detects and measures the reflected beams. For example, an array of photodetectors receives reflections from objects illuminated by the light.

[0017] Differences in the return times for each light pulse across multiple pixels of the pixel array can then be used to create digital 3D representations of an environment or to generate other sensor data. For example, the light source can emit a single light pulse, and a time-to-digital converter (TDC), electrically coupled to the pixel array, can count from the time the light pulse is emitted, which corresponds to a start signal, until the time the reflected light pulse is received at the receiver (i.e., the pixel array), which corresponds to a stop signal. The "travel time" of the light pulse is then translated into a distance measurement.

[0018] In another example, an analog-to-digital converter (ADC) can be electrically coupled to the pixel array (e.g., indirectly via intervening elements) to perform pulse detection and time-of-flight (ToF) measurement. An ADC can be used, for instance, to estimate the time interval between start and stop signals using a suitable algorithm. For example, an ADC can be used to detect an analog electrical signal from one or more photodiodes to estimate the time interval between a start signal (i.e., corresponding to the time of a transmitted light pulse) and a stop signal (i.e., corresponding to the time of reception of an analog electrical signal by the ADC) using a suitable algorithm.

[0019] A scan, such as an oscillating horizontal scan (e.g., from left to right and from right to left of a field of view) or an oscillating vertical scan (e.g., from bottom to top and from top to bottom of a field of view), can illuminate a scene in a continuous scanning manner. Each firing of the laser beam by the light sources can result in a scan line within the "field of view." By emitting successive light pulses in different scanning directions, an area, the so-called field of view, can be scanned, and objects within this area can be detected and imaged. The field of view thus represents a scanning plane with a projection center. A raster scan could also be used.

[0020] Fig. Figure 1A is a schematic diagram of a LIDAR scanning system 100 according to one or more embodiments. The LIDAR scanning system 100 is an optical scanning device comprising a transmitter with an illumination unit 10, a transmitter optic 11, and a one-dimensional (1D) microelectromechanical system (MEMS) mirror 12, and a receiver with a second optical component 14 and a photodetector array 15.

[0021] The illumination unit 10 contains several light sources (e.g., laser diodes or light-emitting diodes) arranged linearly in the form of a single bar and designed to emit light for scanning an object. The light emitted by the light sources is typically infrared light, although light with a different wavelength can also be used. As in the embodiment of the Fig. As can be seen in Figure 1A, the shape of the light emitted by the light sources is spread in a direction perpendicular to the transmission direction to form a light beam with an elongated shape perpendicular to the transmission. The illumination light emitted by the light sources is directed onto the transmitting optics 11, which is designed to focus each laser onto a one-dimensional MEMS mirror 12. The transmitting optics 11 can be, for example, a lens or a prism.

[0022] Upon reflection by the MEMS mirror 12, the light from the light sources is vertically aligned to form a one-dimensional vertical scanning line SL of infrared light or a vertical bar of infrared light for each emitted laser pulse. Each light source of the illumination unit 10 contributes to a different vertical section of the vertical scanning line SL. Thus, the light sources can be activated and deactivated simultaneously to obtain a multi-segmented light pulse, with each segment corresponding to a specific light source. However, each vertical section or segment of the vertical scanning line SL can also be activated or deactivated independently by switching a corresponding light source of the illumination unit 10 on or off. In this way, a partial or complete vertical scanning line SL of light from the system 100 can be projected into the field of view.

[0023] Accordingly, the transmitter of system 100 is an optical arrangement designed to generate laser beams based on the laser pulses, wherein the laser beams have an elongated shape extending in a direction perpendicular to a transmission direction of the laser beams.

[0024] Furthermore, although three laser sources are depicted, it is acknowledged that the number of laser sources is not limited to this. For example, the vertical scanning line SL can be generated by a single laser source, two laser sources, or more than three laser sources.

[0025] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) formed in a semiconductor substrate. According to this embodiment, the MEMS mirror 12 is suspended by mechanical springs (e.g., leaf springs, sometimes also referred to as cantilever beams) or bending elements and is designed to rotate about a single axis. It can be said to have only one desired degree of freedom for movement (i.e., one desired rotation mode about the single axis). While other degrees of freedom may exist, e.g., movements associated with other degrees of freedom of the rigid body, these modes are undesirable and are referred to as unwanted parasitic modes. One objective of the disclosed embodiments is to suppress the parasitic modes associated with these other, unwanted degrees of freedom.

[0026] The parasitic / undesired vibrations are described as the excitation of at least one of the rigid-body modes of the MEMS mirror 12 that differs from the desired operating mode (i.e., the desired rotation mode about the single axis). The parasitic / undesired vibrations can occur due to direct excitation of parasitic modes via the actuators (e.g., electrostatic comb drives, electromagnetic drives, etc.) or high-order harmonic motions of the main mode through nonlinear vibration, or due to indirect excitation of parasitic modes via mode-locking mechanisms.

[0027] Direct excitation of parasitic modes via the actuators can occur because, in resonant mirrors, a higher harmonic content of the periodic drive signal fulfills a condition for parametric resonance of a parasitic mode. Alternatively, in quasi-static mirrors, switching the drive voltage to change the scanning angle can trigger the parasitic mode, as the comb drive not only produces the intended rotation but also generates other forces, such as a y-force. Thus, changing the angle of a quasi-static MEMS mirror leads to transients of all modes, including both desired and undesired modes.

[0028] Indirect excitation of parasitic modes via mode-locking mechanisms can be caused by an Euler force that couples the desired Rx mode with the parasitic mode Ty. This Euler force can be caused by an offset between a center of mass and the axis of rotation 13. Indirect excitation of parasitic modes via mode-locking mechanisms can also be caused by a centrifugal force that couples the desired Rx mode with the parasitic mode Tz. This centrifugal force can be due to an offset between a center of mass and the axis of rotation 13. Furthermore, indirect excitation of parasitic modes via mode-locking mechanisms can be caused by coupling all rotational modes Rx, Ry, and Rz via Euler's equations. The nonlinearity of the oscillation, e.g., due to geometric hardening, can contain specific frequency components of other parasitic modes that cause excitation.Also possible is so-called autoparametric excitation and / or three-wave mixed coupling, both a consequence of geometric nonlinearities caused by large displacements.

[0029] To make a MEMS scanning mirror robust against vibrations, the mirror should have low inertia, i.e., a lightweight mirror body, but stiff enough to keep dynamic deformations within acceptable limits. Furthermore, the mirror should exhibit high stiffness in its mounting for all parasitic degrees of freedom (DOF) of the mirror body. The stiffness associated with rotation about the operating axis should be designed to match the desired operating frequency.

[0030] To achieve a lightweight and rigid mirror body, the mirror body can comprise a relatively thin mirror and a thicker reinforcing structure. The mirror body can be rotatably mounted within a mirror frame around an axis of rotation (i.e., a scanning axis) that extends in a plane defined by the mirror frame (e.g., an xy-plane). In the following examples, the axis of rotation is assumed to extend parallel to the x-dimension of the xy-plane. The axis of rotation can extend to the first and second, opposite end sections of the mirror body. The z-axis position of the axis of rotation is primarily determined by the z-axis extension of the springs and bends.The mirror can have a reflective surface on a first primary surface and, opposite the first primary surface, a second primary surface provided by the reinforcement structure, which generally has a greater thickness extending in the z-direction than the bends and springs. Thus, the reinforcement structure is offset in the z-dimension from both the first primary surface of the mirror body and the axis of rotation. For this reason, the center of mass of the entire rotating body is also generally offset in the z-dimension from the axis of rotation.

[0031] To achieve a highly rigid suspension, the mirror body can be supported within the mirror frame using support beams extending along the axis of rotation and additional cantilever beams or leaf spring arrangements, as shown in the Fig. Figure 1B illustrates this. In general, as defined herein, leaf spring assemblies may also be referred to as cantilever beam assemblies, and vice versa. Similarly, leaf springs and cantilever beams may be used interchangeably.

[0032] A cantilever beam assembly can be longitudinal and extend within the plane defined by the frame. The support beams can be connected between the mirror body and the frame at two opposite ends of the mirror body along the axis of rotation. The cantilever beam assembly can include a cantilever beam that is connected to the mirror frame at one end via a relief structure and attached to the mirror body at the other end. The cantilever beam can have a thickness perpendicular to a plane of the frame that is less than its width in the plane of the frame.

[0033] The low inertia and high spring stiffness of the mirror body result in high resonant frequencies and good dynamic performance. These properties can make the device, when operated at the resonant frequency around the main axis of rotation, very fast. In normal operation, i.e., at resonance, accelerations of typically 10,000 G can be achieved at the mirror tips.

[0034] The MEMS mirror 12 can be placed in a housing to protect the mirror. Fig. The chip package 27 shown in the illustration can be installed. For example, the MEMS mirror 12 can be hermetically sealed in a chip package at a low pressure (i.e., at a pressure lower than atmospheric pressure). This low pressure can provide a low-attenuation environment in which the MEMS mirror 12 operates.

[0035] Possible housings can include or differ in one or more of the following: different substrates (e.g., metal (leadframe), ceramic, organic material (similar to printed circuit board (PCB) material)), and different optical covers or lids (e.g., optical material made of glass, silicon, sapphire, etc.). Furthermore, the optical covers or lids can be cavity-forming caps, integrated into a frame (e.g., a metal frame), or mounted on a pre-molded cavity or a ceramic cavity.

[0036] One or more methods (e.g., adhesive bonding, gluing, soldering, welding, and the like) or one or more different materials (e.g., silicone, glass solder, AuSn, and the like) can be used to join one or more elements together (e.g., to join the cap or lid to the substrate). It is acknowledged that the bonding methods are interchangeable in the various embodiments disclosed herein.

[0037] Alternatively, a wafer-level approach can be used, where a cavity-shaped lid is mounted directly onto the MEMS chip (or even at the wafer level before singulation). If the lid attachment leaves the electrical pads exposed, the submount chip / lid can be further processed into a package using molding or casting processes.

[0038] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) integrated onto a semiconductor chip (not shown). In this embodiment, the MEMS mirror 12 is designed to rotate about a single scanning axis and can be said to have only one degree of freedom for scanning, since other degrees of freedom, e.g., movements associated with other degrees of freedom of rigid bodies, are significantly suppressed compared to the aforementioned rotation about the single axis. This is reflected in significantly higher natural frequencies of the vibrations associated with the other degrees of freedom compared to the said rotation about the single axis. Unlike 2D MEMS mirrors (2D MEMS scanners), in the 1D MEMS mirror, the single scanning axis is fixed to a non-rotating substrate and therefore maintains its spatial orientation during the vibration of the MEMS mirror.Therefore, a 1D oscillating MEMS mirror is inherently more robust to vibrations and shocks than 2D MEMS mirror solutions. Because of this single axis of rotation, the MEMS mirror 12 is also referred to as a 1D MEMS mirror or 1D MEMS scanner. While the embodiments described herein use 1D oscillating MEMS mirrors, the methods described herein can also be extended to 2D MEMS mirrors. In this case, both axes of a single 2D MEMS mirror are controlled by different controllers (in the case of resonant MEMS, with phase-locked loops (PLLs)), such that a first scanning direction of the 2D MEMS mirrors along a first axis is synchronized according to one of the synchronization techniques described herein, and a second scanning direction of the 2D MEMS mirrors along a second axis is synchronized according to one of the synchronization techniques described herein. It is further possible that the different controllers (e.g.,PLLs) are provided in separate MEMS drivers or are integrated into a single MEMS driver for both axes of the 2D MEMS mirror.

[0039] The MEMS mirror 12 itself can be a statically tiltable mover or oscillator (quasi-static MEMS mirror or resonator) that moves or oscillates "side-to-side" about a single scanning axis 13, following a static position, a trajectory, or a resonant oscillation. For example, the MEMS mirror 12 can be either a resonant mirror or a quasi-static (QS) mirror. The MEMS mirror 12 is designed to move or oscillate "side-to-side" about the single scanning axis 13, such that the light reflected by the MEMS mirror 12 (i.e., the vertical scanning line of the light) moves in a horizontal scanning direction.

[0040] As a resonant mirror, the MEMS mirror 12 can be a nonlinear resonator exhibiting nonlinear properties due to the increasing stiffness of its suspension. In particular, the MEMS mirror 12 can exhibit nonlinear behavior due to the torsional stiffness about the scanning axis 13 provided by the leaf spring arrangements 30, which is not constant but increases with increasing angle. This so-called geometric stiffening results in the mirror's vibration frequency increasing with increasing vibration amplitude (i.e., displacement angle amplitude θ). Thus, the stiffening of the suspension causes the MEMS mirror 12 to exhibit nonlinear properties.

[0041] It is noted that the deflection angle θ of the MEMS mirror 12 about the scanning axis 13 can be referred to as tilt angle, rotation angle, scanning angle, mirror angle θ. mirror or θ m, or similar, and that these terms are used interchangeably throughout the entire revelation.

[0042] As a QS-MEMS mirror, the MEMS mirror 12 can tilt statically, follow trajectories (e.g., step, triangular, and sawtooth trajectories), or oscillate at its resonant frequency (i.e., its natural frequency). The QS-MEMS typically exhibits a weak to no nonlinear frequency-amplitude dependence, as its torsional stiffness is more linear.

[0043] A sampling period or oscillation period is defined, for example, by one complete oscillation from a first edge of the field of view (e.g., left side) to a second edge of the field of view (e.g., right side) and then back to the first edge. One mirror period of the MEMS mirror 12 corresponds to one sampling period.

[0044] Thus, the field of view is scanned horizontally by the vertical light bar by changing the angle θ of the MEMS mirror 12 on its scanning axis 13. For example, the MEMS mirror 12 can be designed to oscillate at a resonant frequency of 2 kHz between + / -15 degrees to deflect the light over + / -30 degrees, which defines the scanning area of ​​the field of view. The field of view can then be scanned line by line by rotating the MEMS mirror 12 around the axis of its degree of movement. Such a sequence through the degree of movement (e.g., from -15 degrees to +15 degrees) is called a single scan or scan cycle. Multiple scans can be used to generate distance and depth maps, as well as 3D images, by a processing unit.

[0045] While the transmission mirror is described in the context of a MEMS mirror, other 1D mirrors can, of course, also be used. Furthermore, the resonant frequency or degree of rotation is not limited to 2 kHz or ±15 degrees, and both the resonant frequency and the field of view can be increased or decreased depending on the application. A one-dimensional scanning mirror is thus designed to oscillate around a single scanning axis and direct the laser beams into a field of view from various directions. A transmission technique therefore involves transferring the light beams into the field of view from a transmission mirror oscillating around a single scanning axis, so that the light beams are projected into the field of view as a vertical scanning line SL, which moves horizontally across the field of view as the transmission mirror oscillates around the single scanning axis.

[0046] Upon striking one or more objects, the transmitted vertical light beam is reflected back towards the LIDAR scanning system 100 as a reflected vertical line, where the second optical component 14 (e.g., a lens or prism) receives the reflected light. The second optical component 14 directs the reflected light onto the photodetector array 15, which receives the reflected light as a receive line RL and is designed to generate electrical measurement signals. These electrical measurement signals can be used to generate a 3D map of the environment and / or other object data based on the reflected light (e.g., via ToF calculations and processing).

[0047] The receiving line is represented as a vertical column of light extending along one of the pixel columns in a longitudinal direction. The receiving line has three areas, which are described in the Fig. The vertical scanning line SL shown in Figure 1A corresponds to the vertical scanning line SL. While the vertical scanning line SL moves horizontally across the field of view, the vertical light column RL incident on the 2D photodetector array 15 also moves horizontally across the 2D photodetector array 15. The reflected light beam RL moves from a first edge of the photodetector array 15 to a second edge of the photodetector array 15 when the receiving direction of the reflected light beam RL changes. The receiving direction of the reflected light beam RL corresponds to a transmission direction of the scanning line SL.

[0048] The photodetector array 15 can consist of any number of photodetector types, including avalanche photodiodes (APDs), silicon photomultiplier (SiPMs) photocells, and / or other photodiode devices. Imaging sensors, such as charge-coupled devices (CCDs), can be the photodetectors. In the examples provided herein, the photodetector array 15 is a two-dimensional (2D) APD array comprising an array of APD pixels. In other embodiments, the photodetector array 15 can be a 1D array comprising a single column of photodiodes. The activation of the photodiodes can be synchronized with light pulses emitted by the illumination unit 10. Alternatively, a single photodetector cell / pixel, as opposed to an array, can be used. For example, a single photodetector cell / pixel can be used in the case of a 2x1D Abast transmitter in a coaxial LIDAR architecture.

[0049] The photodetector array 15 receives reflected light pulses as the receive line RL and generates electrical signals in response. Since the transmission time of each light pulse from the illumination unit 10 is known, and since light propagates at a known speed, a time-of-flight calculation using the electrical signals can determine the distance of objects from the photodetector array 15. A depth map can then display this distance information.

[0050] In one example, a microcontroller triggers a laser pulse from each of the light sources of the illumination unit 10 for each distance scan and also starts a timer in a time-to-digital converter (TDC) integrated circuit (IC). The laser pulse propagates through the transmission optics, is reflected by the target array, and is detected by an APD of the APD array 15. The APD emits a short electrical pulse, which is then amplified by an electrical signal amplifier. A comparator IC detects the pulse and sends a digital signal to the TDC to stop the timer. The TDC uses a clock frequency to calibrate each measurement. The TDC sends the serial data of the time difference between the start and stop digital signals to the microcontroller, which filters out any read errors, averages multiple time measurements, and calculates the distance to the target at the respective array position.By emitting successive light pulses in different directions, determined by the MEMS mirror, an area (i.e., a field of view) can be scanned, a three-dimensional image can be generated, and objects within the area can be detected.

[0051] Alternatively, instead of using the TDC approach, ADCs can be used for signal detection and ToF measurement. For example, any ADC can be used to detect an analog electrical signal from one or more photodiodes in order to estimate a time interval between a start signal (i.e., corresponding to the time of a transmitted light pulse) and a stop signal (i.e., corresponding to the time of reception of an analog electrical signal at an ADC) using a suitable algorithm.

[0052] It is acknowledged that the horizontal scanning system 100 described above can also be used for vertical scanning. In this case, the scanning arrangement is positioned such that the scanning direction is rotated by 90°, so that the scanning line SL and the receiving line RL move in a vertical direction (i.e., from top to bottom or from bottom to top). The scanning line is thus a horizontal scanning line SL projected into the field of view and moves vertically across the field of view as the transmission mirror oscillates around the single scanning axis. Furthermore, since the horizontal scanning line SL moves vertically across the field of view, the horizontal column of light RL incident on the 2D photodetector array 15 also moves vertically across the 2D photodetector array 15.

[0053] It is further acknowledged that a LIDAR scanning system can include synchronized MEMS mirrors used in a 2x1D system, such as a Lissajous scanning system. In this case, the MEMS mirrors are mounted in the same location on the vehicle and designed to scan the two dimensions (horizontal and vertical) of a common field of view.

[0054] Fig. Figure 1B shows a schematic top view of an example of a mirror device according to one or more embodiments. With reference to the Fig. Section 1B now describes an example of a mirror device, such as a MEMS scanning micromirror. The mirror device comprises a mirror body 8. The mirror body 8 comprises a mirror 12 and a mirror support 16. The mirror device further includes a frame 17. The mirror body 8 is arranged in the frame 17. The frame 17 defines a plane, i.e., the (x, y)-plane in the Fig. 1B. The plane defined by the frame 17 can run parallel to planes defined by principal surfaces of a layer or a plurality of layers in which the frame 17 is formed.

[0055] The mirror body 8 is rotatable about a scanning axis 13, which lies in the plane defined by the frame 17. Support beams 18, which can also be called torsion beams, are connected between the mirror body 8 and the frame 17 along the scanning axis 13. More precisely, a first support beam 18 is connected between a first end of the mirror body 8 and the frame 17, and a second support beam 18 is connected between a second end of the mirror body 8 and the frame 17, with the second end of the mirror body 8 being opposite the first end in the direction of the scanning axis 13. An enlarged view of one of the support beams 18 is shown in the enlarged section C on the right side of the Fig. Figure 1B shows that the support beams 18 connect parts of the mirror support 16 to parts of the frame 17 and allow the mirror body 8 to rotate about the scanning axis 13. The support beams 18 can be collinear with the scanning axis 13.

[0056] The expert will appreciate that the shape of the mirror 12 can be any shape desired for a particular application, e.g. a circle, an ellipse, a square, a rectangle or any other desired shape.

[0057] The mirror frame 17 defines a mirror recess 20 in which the mirror body 8 is arranged. The mirror recess 20 is defined by a recess periphery 28 of the mirror frame 17. The mirror frame 17 can also be designed to define further recesses in which other components, such as actuators, sensors, and leaf spring assemblies, can be arranged.

[0058] The mirror device can include a leaf spring assembly 30. In the example shown, the mirror device contains two pairs of leaf spring assemblies 30, with the leaf spring assembly in each pair extending from the mirror body 8 in opposite directions. In the example shown, the leaf spring assemblies 30 are arranged symmetrically about the scanning axis 13. However, leaf springs are not used in QS-MEMS mirrors. Instead, torsion beams (or equivalent structures with multiple torsion beams, e.g., V-shape, PI-shape) support the MEMS mirror.

[0059] The at least one leaf spring assembly 30 comprises a leaf spring 32 and a relief member 34. The relief member 34 may have one or more relief springs 35. The leaf spring 32 comprises a first end 32a and a second end 32b. The first end 32a is connected to the mirror body 8 and the second end is connected to the frame 17. Each leaf spring 32 has a longitudinal direction or extension between the first end 32a and the second end 32b. The first end 32a is attached to the mirror support (not illustrated) and the second end 32b is connected to the frame 17 via the relief member 34. In the examples, the first ends 32a of two leaf springs 32 extending from the same section of the mirror body 8 in different directions may be connected to each other (e.g.,, the leaf springs on the left side of the mirror 12 or the leaf springs on the right side of the mirror 12) and only near the scanning axis 13 are stiffened by a reinforcing structure (not illustrated) so that the two leaf springs 32 can exert a torque on the mirror body 8.

[0060] In some examples, the shape of the mirror 12 can have concave sections in the region of the scanning axis 13, with parts of the leaf springs 32 extending into the concave sections of the mirror 12. In some examples, the leaf springs 32 and the mirror 12 can be formed in the same material layer and can be connected to each other near the scanning axis 13.

[0061] In some examples, the leaf springs 32 can be implemented in a single-crystal silicon layer with a direction of lower material stiffness, wherein the longitudinal direction of the leaf springs is aligned with the direction of lower material stiffness. In some examples, the leaf springs 32 can be implemented in a silicon layer with a <100> -axis implemented, and the longitudinal direction of the leaf springs is aligned with the <100> -direction which in this case has the lower material stiffness.

[0062] The torsional stiffness about the scanning axis 13 can be adjusted using the leaf spring arrangements 30. The support beam pair 18 supports the mirror body 8 vertically, i.e., perpendicular to a major surface of the frame 17, at the scanning axis 13. However, the support beams 18 can have a negligible effect on the torsional stiffness, so that the natural frequency of the mirror body can be essentially determined by the leaf spring arrangements 30. The natural frequency can be essentially independent of the support beams 18. The natural frequency defined herein is the undamped frequency of the natural mode of the mirror body 8 (i.e., the mirror 12) about its scanning axis 13 at small angles. The support beams 18 can determine the out-of-plane tilt and the vertical translation mode stiffness for the corresponding rigid body modes, as well as the corresponding natural frequencies.The torsional stiffness can be decoupled from the out-of-plane tilt and the vertical translation mode stiffness, so that the out-of-plane tilt and vertical translation mode frequencies can be set to desired values, such as higher values, without affecting the torsional mode stiffness and resonance frequency.

[0063] As defined herein, the X-axis runs along the scanning axis 13, the Y-axis is perpendicular to the X-axis in the mirror plane when the mirror 12 is at rest, and the Z-axis is perpendicular to and from the mirror plane when the mirror 12 is at rest. The X-, Y-, and Z-axes are axes of a three-dimensional Cartesian coordinate system.

[0064] In the Fig. In the example shown in Figure 1B, one end of the at least one leaf spring 32 is connected to the mirror body 8 at a location near the scanning axis 13. The other end 32b is connected to the associated load-bearing element 34 at a location further away from the scanning axis 13. The leaf spring arrangements 30 can provide torsional stiffness to the mirror body 8 about the scanning axis 13. The load-bearing elements 34 can provide a compliant or flexible connection from the leaf springs 32 to the frame 17. The load-bearing elements 34 can have relatively low stiffness in the longitudinal direction of the leaf springs 32, i.e., in the Y-direction. Fig. 1B, which allows one end of the leaf springs 32 to move in their longitudinal direction as the mirror body 8 rotates about the scanning axis 13. The relief elements 34 can have a relatively high stiffness in the transverse direction, i.e., in the Z-direction and in the X-direction. Fig. 1B.

[0065] The resonant frequency for the rotation of the mirror 12 about the scanning axis 13 can be determined primarily by the inertia of the mirror body 8 and the stiffness of the leaf spring assemblies 30, which can be defined by the bending stiffness of the leaf springs 32 and by the torsional and translational stiffness of the stabilizing elements 34. The bending stiffness of the leaf springs 32 can be determined by their length, width, and, in particular, their thickness. The combined stiffness in the Y-direction of the support beams 18 and the stabilizing elements 34 can prevent movement of the mirror body 8 perpendicular to the scanning axis 13 (in the X-direction) during operation. Further details regarding the stabilizing elements are provided below.

[0066] The support beams 18 are connected between the frame 17 and the mirror body 8 along the scanning axis 13 to support the mirror body 8 within the frame 17. In one example, the support beams 18 have a narrow rectangular cross-section perpendicular to the scanning axis 13, with the long axis of the rectangle being perpendicular to the surface of the mirror 12 and the mirror body 8, and the short axis of the rectangle being parallel to the surface of the mirror 12. The torsional stiffness corresponding to a rotation of the mirror body 8 about the scanning axis 13 can be provided by the leaf spring arrangements 30. The support beams 18 can serve only to support the mirror body 8 and have a negligible effect on the torsional stiffness. The support beams 18 can be dimensioned such that the stiffness against a vertical displacement (in the Z-direction) of the mirror body 8 and against its displacement in the plane perpendicular to the scanning axis 13 (i.e.,, along the Y-axis) as high as possible.

[0067] The mirror device can also include at least one actuator to provide a torque for driving the mirror body 8 about the scanning axis 13. In one example, the actuator can be a comb drive having mirror combs attached to the mirror body 8, which are nested with frame combs attached to the frame 17. Applying a difference in electrical potential between the nested mirror combs and frame combs generates a driving force between the mirror combs and the frame combs, which produces a torque on the mirror body 8 about the scanning axis 13. An oscillating electrical potential can be applied to resonate the mirror device near its natural frequency. In this example, four comb drives 40TL (top left), 40BL (bottom left), 40TR (top right), and 40BR (bottom right) are provided.The left side is located to the left of the scanning axis 13, while the right side is located to the right of the scanning axis 13. Each comb drive comprises a stator comb drive electrode, which is attached to the frame 17, and a rotor comb drive electrode, which is movable with the mirror body 8 as it rotates around the scanning axis 13.

[0068] In other examples, the actuation methods can include electromagnetic and piezoelectric actuation. With electromagnetic actuation, the micromirror can be immersed in a magnetic field, and an alternating electric current through conductive paths on the mirror body can generate the oscillating torque about the scanning axis 13. Piezoelectric actuators can be integrated into the leaf springs, or the leaf springs can be made of piezoelectric material to generate alternating beam bending forces in response to an electrical signal and thus produce the oscillating torque.

[0069] The desired rotation mode Rx of the MEMS mirror 12 about the scanning axis 13 is in the Fig. Figure 1B illustrates this. The bidirectional arrow, corresponding to the rotation mode Rx, indicates that the MEMS mirror 12 is designed to oscillate around the scanning axis 13 to perform a scanning operation. Undesired parasitic modes are also shown. For example, a translation mode Ty lying in the plane is depicted, representing a translational movement of the mirror body 8 in the Y direction. In particular, there is a resonant coupling from the desired rotation mode Rx to a translation mode in the Y direction, Ty. The coupling of mode Rx to the translation mode Ty is primarily caused by the gain structures. Furthermore, a nonlinear coupling from the desired rotation mode Rx to an undesired false yaw mode Rz can occur. Thus, the false yaw mode Rz causes the mirror body 8 to move around the Z-axis. Additionally, mode Rx can couple with the translation mode in the Z direction, Tz.This coupling of Rx to Tz is primarily caused by the reinforcement structures. The coupling of Rx to Ty or Tz arises from inertial forces caused by a rotational imbalance, since the center of mass is offset along the Z-axis relative to the axis of rotation due to the mass of the reinforcement structures.

[0070] Fig. Figure 1C shows a schematic bottom view of an example of the [unclear text] in the Fig. Figure 1B shows the mirror device according to one or more embodiments. In particular, the underside of the mirror body 8 and the frame 17 are shown. The four comb drives 40TL, 40BL, 40TR, and 40BR are also visible. The reinforcing structure 9, which supports the mirror body 8, is also visible.

[0071] Fig. Figure 1D illustrates a cross-sectional view of a MEMS mirror and drive electrodes according to one or more embodiments. In particular, the MEMS mirror 12 is shown, rotating about a rotation axis 13 extending orthogonally to the side. The MEMS mirror 12 includes mirror comb electrodes 41 and 42 to which a drive voltage v is applied. drive is applied. As described above, the MEMS mirror 12 is supported by a mirror frame 17 (not illustrated). The mirror frame 17 includes static comb electrodes 43 and 44. The mirror comb electrodes 41 and 42, which are connected to opposite ends of the mirror body 8, move with the oscillation of the MEMS mirror 12. The drive voltage v driveinduces a driving force between the interlocking mirror comb electrodes 41, 42 and the static comb electrodes 43, 44. In particular, the MEMS mirror 12 is driven into parametric resonance by a square wave voltage with a duty cycle of 50% (or otherwise).

[0072] A first drive capacitor C A (also known as C) A (θ) is formed by an overlap of electrodes 41 and 44. The overlap of the two electrodes 41 and 44 varies with the rotation angle θ. mirror of the MEMS mirror 12 around the axis of rotation 13. With increasing overlap, the capacitance of the first drive capacitor C also increases. A Conversely, the capacitance of the first drive capacitor C increases. A off when the overlap decreases.

[0073] Similarly, a second drive capacitor C is used. B (also known as C) B(θ) is formed by an overlap of electrodes 42 and 43. The overlap of the two electrodes 42 and 43 varies with the rotation angle θ. mirror of the MEMS mirror 12 around the axis of rotation 13. With increasing overlap, the capacitance of the second drive capacitor C also increases. B Conversely, the capacitance of the second drive capacitor C increases. B off when the overlap decreases.

[0074] Thus, the first drive capacitor is C A a function of the rotation angle θ, which defines a first charge based on the rotation angle θ mirror of the MEMS mirror 12, which leads to a first displacement current that also depends on the rotation angle θ of the MEMS mirror 12. Similarly, the second drive capacitor C B also a function of the rotation angle θ mirror, which stores a second charge based on the rotation angle of the MEMS mirror 12, resulting in a second displacement current that also depends on the rotation angle of the MEMS mirror 12.

[0075] For the QS-MEMS, the actuation is unipolar, meaning that at a positive deflection angle, one capacitor (submerged combs) increases in capacitance, while the other capacitance is zero (unsubmerged combs). The opposite occurs at a negative deflection. For resonant MEMS, the two drive capacitors each have a symmetrical capacitance characteristic corresponding to the deflection direction (e.g., the tilting direction) of the MEMS mirror 12. However, bipolar actuation can also be used, in which a third capacitor is formed with the central electrode (like the resonant electrode).

[0076] More precisely, this means that with perfectly aligned combs C A (-θ mirror ) - C A (θ mirror ) and CB (-θ mirror ) - C B (θ mirror ), i.e., both capacitances are even functions with symmetric capacitance dependence, which do not change their value when the angle of the mirror is reversed. Due to the symmetry of the construction, C also holds. A (θ mirror ) - C B (θ mirror It should also be noted that in the cross-sectional view, although two drive capacitors C are shown... A and C B are shown, but four drive capacitors are present, as in the Fig. 1B and Fig. Figure 1C shows four displacement currents as a function of the rotation angle θ. mirror generated. Due to the symmetry of the capacitances for θ → -θ, the scanning direction (e.g., clockwise or counterclockwise) could not be detected for an ideal and pure Rx rotary motion.

[0077] Fig. Figure 1D further shows the mode coupling between the Rx mode and the Ty mode, which is caused by a displacement L of the center of mass M from the axis of rotation (scanning axis 13) due to the amplification structure 9. The coupling force results from the Euler force according to equation 1: fY(t)=−m L θ¨m(t) with the mirror mass m and the rotational acceleration θ̈ mirror (t). Thus, the Ty mode is determined by the inertial force f. Y (t) excited, which, due to its dependence on the rotational acceleration (the second derivative of the trajectory), has the same frequency content as the Rx trajectory θ(t). Furthermore, the Rx and Ty eigenmodes are not perfectly pure rotational or translational modes, respectively, meaning that a non-zero amplitude of the Ty mode also exhibits a small rotational component, i.e., a rotation about the x-axis.

[0078] One or more embodiments use the change in the detection signal (e.g., a current signal) of a subset of comb drive electrodes, caused by an excited parasitic mode, to detect the scanning direction (e.g., clockwise or counterclockwise) as well as the amplitude and phase of the parasitic modes, i.e., Ty, Tz, and Rz. A subset of comb drive electrodes can comprise any combination of left / right, top / bottom, front / back electrodes.

[0079] The Euler force, caused by the finite displacement L between the center of mass M and the axis of rotation 13, leads to a small excitation of Ty, which is superimposed on the Rx motion. This superimposed motion removes the symmetry of the displacement currents for θ and -θ, so that the sign of the angle, i.e., the scanning direction, can be detected.

[0080] The subset of comb drive electrodes can be a subset of the stator or rotor electrodes, or, in the case of the 2D MEMS mirror, a subset of the rotor, inner frame, and / or outer frame (i.e., the stator itself). Various cases are shown as examples where two current signals are subtracted (e.g., a left current signal from a right current signal) to achieve the highest efficiency. However, it would also be possible to detect the modes using only a side current or even just the current of a comb drive, albeit with lower efficiency. Furthermore, the detection does not have to be current-based. Any method that provides a detection signal related to the capacitance or capacitance change of one or more drive capacitors can be used (e.g., charge detection, current detection, or frequency modulation-based detection).

[0081] After detection, the parasitic modes Ty, Tz, Ry, and Rz can be actively damped. Specifically, a system controller 23 can apply a counterforce / countertorque by appropriately selecting comb electrodes in any combination (either combs for shared actuation / detection / damping or even individual combs solely for damping). An appropriate selection of comb electrodes means that the selection has a force / torque that corresponds to the identified parasitic mode and can counteract the mirror motion in that identified parasitic mode. The selection of the comb electrodes to which a counterforce (e.g., a damping voltage) is to be applied is therefore based on the parasitic mode Ty, Tz, Ry, Rz, etc., which is targeted for damping by the system controller 23 based on its detection.A switching network can be used by the system controller 23 to apply the counterforce to selected comb electrodes corresponding to the target parasitic mode at a time effective for attenuating the target parasitic mode. This parasitic mode detection, identification, and targeted attenuation is described in detail below.

[0082] Fig. Figure 2 is a schematic block diagram of the LIDAR scanning system 200 according to one or more embodiments. Fig. Figure 2 shows in particular additional features of the LIDAR scanning system 200, including exemplary processing and control system components such as a MEMS driver, a receiver circuit, and a system controller.

[0083] The LiDAR scanning system 200 comprises a transmitter unit 21, responsible for one transmission path of the system 200, and a receiver unit 22, responsible for one reception path of the system 200. The system also includes a system controller 23, designed to control components of the transmitter unit 21 and the receiver unit 22, and to receive raw data from the receiver unit 22 and process it (e.g., via digital signal processing) to generate object data (e.g., point cloud data). The system controller 23 therefore includes at least one processor and / or a processor circuit for data processing, as well as a control circuit, such as a microcontroller, designed to generate control signals. The LiDAR scanning system 200 may also include a temperature sensor 26.

[0084] The receiver unit 22 includes the photodetector array 15 and a receiver circuit 24. The receiver circuit 24 can contain one or more circuits or sub-circuits for receiving and / or processing information. The receiver circuit 24 can receive the analog electrical signals from the APD diodes of the photodetector array 15 and transmit the electrical signals as raw analog or raw digital data to the system controller 23. To transmit the raw data as digital data, the receiver circuit 24 can include an ADC and an FPGA (Field Programmable Gate Array). The receiver circuit 24 can also receive trigger control signals from the system controller 23, which trigger the activation of one or more APD diodes. The receiver circuit 24 can also receive gain setting control signals for controlling the gain of one or more APD diodes.

[0085] The transmitter unit 21 contains the illumination unit 10, the MEMS mirror 12, and a MEMS driver 25, which is designed to drive the MEMS mirror 12. Specifically, the MEMS driver 25 actuates and detects the rotational position of the mirror and provides position information (e.g., tilt angle or degree of rotation about the axis of rotation) of the mirror to the system controller 23. Based on this position information, the laser sources of the illumination unit 10 are triggered by the system controller 23, and the photodiodes (e.g., APD diodes) are activated to detect and thus measure a reflected light signal. Therefore, higher accuracy in the position detection of the MEMS mirror leads to more accurate and precise control of other components of the LiDAR system.

[0086] The MEMS driver 25 can also measure and record the mirror frequency and currents by using a change in capacitance in a comb drive rotor and stator of an actuator structure to drive the MEMS mirror 12. The MEMS mirror 12 further incorporates the suspension structure described above. Therefore, the MEMS driver 25 can also include a measurement circuit designed to measure one or more of the properties of the MEMS mirror 12 described herein. The MEMS driver 25 can further include a processing circuit comprising at least one processor (e.g., an analog signal processing circuit and / or a digital signal processing circuit) designed to process measurement information from the acquisition circuit to evaluate the mechanical condition of the MEMS mirror 12 and / or the condition of the chip package.

[0087] Additionally, or alternatively, the system controller 23 can receive measurement information from the measurement circuit of the MEMS driver 25 and process it. Thus, the system controller 23 can also include a processing circuit comprising at least one processor (e.g., an analog signal processing circuit and / or a digital signal processing circuit) designed to process measurement information from the acquisition circuit in order to assess the mechanical condition of the MEMS mirror 12 and / or the condition of the chip package.

[0088] For the QS-MEMS, the rotational position is continuously measured (and controlled) using the sensing circuit (at the rotor).

[0089] For a resonant MEMS: By detecting the rotational position of the MEMS mirror 12 about its axis of rotation (scanning axis), the MEMS driver 25 can detect zero-crossing events of the MEMS mirror 12. A zero-crossing event occurs when the MEMS mirror 12 has a rotation angle of 0° about its axis of rotation (scanning axis). This is specifically the moment when the MEMS mirror 12 is parallel to the frame or in a neutral position. The neutral position can also be referred to as the rest position (e.g., when the MEMS mirror 12 comes to a standstill after the drive force is switched off). Since the MEMS mirror 12 oscillates back and forth between two directions of rotation (e.g., clockwise and counterclockwise), a zero crossing occurs twice during a scanning period—once when the mirror oscillates in the first direction of rotation and once when the mirror oscillates in the second direction.It is also acknowledged that, instead of a zero-crossing event, angle-crossing events at a different predefined angle can also be used.

[0090] In some embodiments, an event time may correspond to a non-zero-crossing event. For example, the detected rotation angle may be an angle other than 0°. However, for illustrative purposes, the examples described here are in the context of zero-crossing event detection.

[0091] The MEMS driver 25 is designed to detect each zero-crossing event and record a time for each event. This time information (i.e., the measured zero-crossing time) can then be transmitted as position information to the system controller 23. Specifically, the MEMS driver 25 triggers a change in the output of a position signal (position_L) at each zero-crossing or angle-crossing event.

[0092] Fig. Figure 3 illustrates a signal diagram of various signals generated by a MEMS driver 25 based on the mirror angle θ and / or position, including a position signal (position_L). For example, the position signal (position_L) can be a pulsed signal during which a first pulse transition (e.g., a falling-edge transition) is triggered at a zero crossing when the mirror oscillates in a first direction of rotation (e.g., from left to right), and a second pulse transition (e.g., a rising-edge transition) is triggered at a zero crossing when the mirror oscillates in a second direction of rotation (e.g., from right to left). Furthermore, the signal is "high" when the mirror points in one direction (e.g., to the left), and the signal is "low" when the mirror points in a second direction (e.g., to the right).Thus, the position signal not only indicates a zero-crossing event by triggering a pulse transition, but also provides absolute phase information by showing the mirror's directional tilt. As the interval between zero-crossing events increases, the frequency of the position signal decreases. Based on this position signal, both the phase and / or frequency of two or more position signals can be compared.

[0093] Alternatively, the MEMS driver 25 can generate a short pulse at each zero-crossing event, so that a pulsed position signal (position_L) is output to the system controller 23. This means that the signal remains low (or high) between zero-crossing pulses. In this case, the absolute phase information indicating the direction of mirror movement would be missing, since the low (high) level of the position signal (position_L) does not indicate whether the mirror is pointing left or right. Based on this position signal, the phase and / or frequency of two or more position signals can be compared.

[0094] The MEMS driver 25 can send the position information to the system controller 23, which can then use this information to control the triggering of the laser pulses of the illumination unit 10 and the activation of the photodiodes of the photodetector array 15. The system controller can also use the position information as feedback, enabling it to maintain stable operation of the MEMS mirror 12 via control signals provided to the MEMS driver 25 and to maintain synchronization with other MEMS mirrors.

[0095] The MEMS mirror 12 contains an actuator structure used to drive the mirror. The actuator structure includes interlocking finger electrodes consisting of interlocking mirror combs and frame combs, to which the MEMS driver 25 applies a drive voltage v. drive(i.e., an actuation or drive signal) is applied. The drive voltage can be referred to as high voltage (HV, High Voltage). The frame comb fingers and the mirror comb fingers form the electrodes of a capacitor. The drive voltage across the finger structure generates a driving force between interlocking mirror comb electrodes and the frame comb electrodes, which produces a torque on the mirror body 8 about the axis of rotation. The drive voltage can be switched on and off, resulting in an oscillating drive force. The driving waveform of the drive voltage can be any waveform, including sinusoidal, triangular, rectangular, etc. The oscillating drive force causes the mirror to oscillate back and forth about its axis of rotation between two extrema.Depending on the configuration, this actuation can be regulated or adjusted by setting the switch-off time of the drive voltage, a voltage level of the drive voltage, or a duty cycle.

[0096] In other embodiments, an electromagnetic actuator can be used to drive the MEMS mirror 12. For an electromagnetic actuator, a drive current (i.e., an actuation or drive signal) can be used to generate the oscillating drive force. It is therefore acknowledged that driver / drive voltage and driver / drive current may be used interchangeably herein to denote an actuation signal or a drive signal, and both may be generally referred to as the drive force.

[0097] When the mirror oscillates, the capacitance or charge between the finger electrodes changes according to the mirror's rotational position. The MEMS driver 25 is designed to measure the capacitance or charge between the interlocking finger electrodes, for example, via the four quadrant comb drive displacement currents, and from this determine a rotational or angular position of the MEMS mirror 12. More precisely, the displacement currents are the time derivatives of the respective capacitances multiplied by the voltage; that is, derived quantities are measured instead of the capacitance or charge itself. By monitoring the displacement currents, the MEMS driver 25 can detect zero-crossing events and other non-zero-angle events and their times, and can determine the deflection or tilt angle of the MEMS mirror 12 at any given time.The MEMS driver 25 can also use the measured displacement currents to determine a mirror frequency and store the information in a memory of the MEMS driver 25 or at the system controller 23.

[0098] The position of the MEMS mirror 12 is determined using a detector designed to measure capacitance through the displacement current or displacement charge (i.e., the integrated current). Capacitance or charge measurement can be performed indirectly by measuring derived quantities, such as the displacement currents. For example, when the MEMS mirror moves, the geometry of the finger structure changes, resulting in a change in the capacitor geometry. As the capacitor geometry changes, the capacitor's capacitance changes. Thus, a specific capacitance directly corresponds to a specific displacement position (e.g., a tilt angle) of the MEMS mirror. By sensing the capacitance of the finger structure, the MEMS driver 25 can monitor and track the mirror's oscillations and determine a specific position of the MEMS mirror, including its zero crossing.

[0099] One way to measure capacitance is to measure the current flowing through the finger electrode structure, convert the measured current into a voltage, and then correlate the voltage with a capacitance and / or a rotation angle θ. However, any method can be used to measure capacitance.

[0100] The sign of the currents (i.e., positive or negative change in capacitance over time) only indicates whether the MEMS mirror is moving towards its rest position (positive currents → charging the capacitor) or away from it (negative currents → discharging the capacitor). When the MEMS mirror moves towards its rest position (approaching zero), this can occur either clockwise or counterclockwise. For comb drives with symmetrical capacitance dependence, C A (-θ mirror ) - C A (θ mirror ) and C B (θ mirror ) - C B (θ mirror), the direction of rotation cannot be distinguished by the sign of the currents.

[0101] Since the mirror is driven at an oscillation frequency (e.g., 2 kHz), when it rotates in a first direction (e.g., left-to-right or clockwise), it passes through a zero position (i.e., 0°) at a specific time. The same applies when the mirror rotates in a second direction (e.g., right-to-left or counterclockwise); the mirror will cross the zero position at a specific time. These crossings of the zero position can be referred to as zero-crossing events, which occur at zero-crossing times.

[0102] As mentioned above, in one or more embodiments, the change in a detection signal (e.g., a current signal) of a subset of the comb drive electrodes, caused by an excited parasitic mode, is used to detect the scanning direction (e.g., clockwise or counterclockwise) as well as the amplitude and phase of the parasitic modes, i.e., Ty, Tz, and Rz. This can be achieved by using the difference in the capacitance of each comb drive, the difference in each of the four quadrant comb drive displacement currents, or the difference in the displacement currents of specific combinations of quadrants. After detection, each of the parasitic modes Ty, Rz, Ry, and / or Tz can be avoided or actively attenuated.

[0103] Fig. Figure 4A illustrates a top view of a MEMS mirror arranged in a nominally centered position (left) and a translationally displaced position (right) according to one or more embodiments. On the left side, the MEMS mirror 12 (mirror body 8) operates in a pure rotational mode Rx about the scanning axis 13, and the torsion bars 18 do not bend. The four comb drives 40TL, 40BL, 40TR, and 40BR are arranged symmetrically within the frame 17. On the right side, however, the MEMS mirror 12 (mirror body 8) is displaced to the right in the translational Y-direction and oscillates back and forth in the Y-direction due to mode coupling between the Rx mode and the Ty mode. During this oscillation, the torsion bars 18 bend back and forth in the Y-direction. A stator electrode of a comb drive is mechanically connected to the frame 17, while the rotor electrode of a comb drive is mechanically connected to the mirror body 8.The stator comb drive electrodes are divided into left pairs (stators of comb drives 40TL and 40BL) and right pairs (stators of comb drives 40TR and 40BR) to detect the Rx-Ty mode coupling.

[0104] Embodiments further include a sensing circuit electrically coupled to the stator comb drive electrodes of each comb drive 40TL, 40BL, 40TR, and 40BR to receive their respective displacement currents. The stator comb drive electrodes are electrically coupled to the sensing circuit to detect the mode of interest, such as the Ty mode, the Rz mode, or the Tz mode. It is also possible to disconnect the rotor comb drive electrodes and sensing these electrodes instead of those of the stator. Furthermore, it is not necessary to measure the displacement current or to use all comb drives for sensing. Any signal associated with capacitance or capacitance change can be used.

[0105] Fig. Figure 4B is a schematic diagram of a system 400A for measuring and attenuating a translation mode Ty according to one or more embodiments. The system 400A for measuring the translation mode Ty includes the MEMS driver 25, the MEMS mirror 12 with four comb drives 40TL, 40BL, 40TR, and 40BR, a detection circuit 50, and the system controller 23.

[0106] The MEMS driver 25 receives a digital control signal D HVact and drives the Rx mode of the MEMS mirror 12 (i.e., the rotation about the scanning axis 13) in accordance with the digital control signal D HVact The digital control signal DHVact can be a single-bit digital signal (i.e., 0 for off and 1 for on) or a multi-bit digital signal capable of indicating different levels (e.g., different voltage levels). The MEMS driver 25 can include a digital-to-analog converter (DAC) that converts the drive voltage vdrive The MEMS driver 25 is generated based on the digital value of the digital control signal DHVact. As explained below, the MEMS driver 25 can also add or superimpose a damping signal value Vdmp onto the value of the digital control signal DHVact to generate a drive voltage with a damping voltage or just a damping voltage (e.g., when the drive voltage is zero). In this way, DHVact is a digital input for a DAC that generates voltages in the range of 0V–200V. The drive voltage Vdrive can then be any waveform.

[0107] The MEMS driver 25 generates the drive voltage v drive with the appropriate duty cycle and sets the drive voltage v drive to the mirror comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR. As a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitances C change. TL , C BL , C TR , and C BRthe four comb drives 40TL, 40BL, 40TR, and 40BR and displacement currents i TL , i BL , i TR , and i BR generated by their respective drive capacities. The detection circuit 50 is coupled to the stator comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR and extracts the displacement currents i from them. TL , i BL , i TR , and i BR .

[0108] To measure the translation mode Ty, the two left displacement currents i are used. TL and i BLThe input of a transimpedance amplifier (TIA) 51 of the sensing circuit 50 is provided. Although a TIA is used in this example, other sensing elements can also be used for capacitive sensing. For example, any sensing circuit that performs charge sensing, current sensing, or frequency-modulated sensing can be used to generate sensing signals. The TIA 51 can be coupled to the MEMS mirror 12 and, in particular, to the stators of associated comb drives via a switch SW1.Switch SW1 can be controlled by the system controller 23 (via a switch control signal SW CTRL) to perform mode measurements when switch SW1 is in position "m", or to perform an attenuation operation when switch SW1 is in position "d", where "m" represents a measurement position of the switch for performing measurements of corresponding comb drives and "d" represents an attenuation position of the switch, which is used to apply an attenuation voltage Vdmp,left to the corresponding left-hand comb drives. After the TIA 51 has determined the displacement currents i. TL and i BL has been obtained, the sum of the two left displacement currents i TL and i BL through the TIA 51 into a left-hand voltage V L converted.

[0109] Similarly, the two right-hand displacement flows i TR and i BRThe input of a TIA 52 sensor is provided to the sensing circuit 50. Although a TIA is used again in this example, other sensing elements can also be used for capacitive sensing. For example, any sensing circuit that performs charge sensing, current sensing, or frequency-modulated sensing can be used to generate sensing signals. The TIA 52 can be coupled to the MEMS mirror 12 and, in particular, to the stators of associated comb drives via a switch SW2.Switch SW2 can be controlled by the system controller 23 (via a switch control signal SW CTRL) to perform mode measurements when switch SW2 is in position "m", or to perform an attenuation operation when switch SW1 is in position "d", where "m" represents a measurement position of the switch for performing measurements of the corresponding comb drives and "d" represents an attenuation position of the switch, which is used to apply an attenuation voltage Vdmp,right to the corresponding right-hand comb drives. After the TIA 51 has determined the displacement currents i. TR and i BR has received, the sum of the two right-hand displacement flows i TR and i BR through the TIA 52 into a right-hand voltage V R converted.

[0110] Alternatively, each comb drive electrode can be connected to a separate TIA, and then the individual voltage signals can be added and / or subtracted so that the detection circuit 50 is able to detect each mode simultaneously. In other words, four TIAs can be used, each individually connected to a corresponding drive electrode (i.e., the capacitors C). TL , C BL , C TR , and C BR ) the four comb drives 40TL, 40BL, 40TR and 40BR are connected.

[0111] Fig. Figure 4C is a schematic diagram of a system 400B for measuring and attenuating a parasitic mode according to one or more embodiments. The system 400B for measuring parasitic modes is similar to the system 400A, except that the sensing circuit 50 includes a switching network 55 that connects the drive electrode (i.e., the capacitors C). TL , C BL , C TR , and C BRThe switching network 55 couples the four comb drives 40TL, 40BL, 40TR, and 40BR in any combination with the TIAs 51 and 52. The switching network 55 can be a network of eight switches—two for each drive electrode—that switchably connect their respective drive electrode to the TIAs 51 and 52. With such a switching network, the input configuration for the TIAs 51 and 52 can be fully configured to control displacement currents. TL , is, i TR , and i BR to be received in any combination so that the detection circuit can measure 50 individual parasitic modes or detect each mode simultaneously (e.g., if individual TIAs are also provided). The switch control signal SW CTRL, which is representative of one or more control signals, can control the switches of the switching network 55. It is also possible to use a network of multiplexers.

[0112] As an example, two pairs of switches for two drive electrodes corresponding to the 40TL and 40BR comb drives are shown, with one switch of each pair connected to the TIA 51 and the other switch of each pair connected to the TIA 52. Other pairs of switches are provided similarly for the remaining comb drives, although not illustrated, so that their respective displacement currents are switchable to either the TIA 51 or the TIA 52.

[0113] Returning to the Fig. 4B contains the detection circuit 50, a summing amplifier 53, and a subtracting amplifier 54. The summing amplifier 53 receives both the left-hand voltage V. L as well as the right-side voltage V R and sums them together to obtain a total voltage V I to generate which is the sum of all displacement flows i TL , i BL , i TR , and i BRrepresents. Conversely, the subtractor 54 receives the voltage V on the left side. L as well as the right-side voltage V R and subtracts the right-hand voltage V R from the left-hand voltage V L , to create a differential voltage ΔV I to generate which the difference between the left-hand currents i TL , i BL and the right-hand currents i TR , i BR represents the total voltage V. I (i.e., the summed current signal or measurement signal) enables precise phase and amplitude measurements of the Rx mode, which the system controller 23 uses for suitable MEMS mirror control. The summed voltage V I However, it provides no information about the scanning direction, since the four comb drives are symmetrical. On the other hand, the differential voltage ΔV I(i.e., the differential current signal or differential measurement signal) provides scanning direction-dependent signals for the Rx mode. It also provides the amplitude of the Ty mode and the phase of the Ty mode relative to the Rx mode. Thus, the system controller 23 can determine the scanning direction (clockwise or counterclockwise) of the MEMS mirror 12 based on the differential voltage ΔV I determine. The system controller 23 can determine the digital control signal D Hvact based on the phase, the amplitude (θ0), and the sampling direction. For example, the sign of the differential voltage ΔV I Specify the scanning direction.

[0114] In the implementation, additional memory can be used by the system controller 23 to record the sampling direction, even if the differential voltage ΔV IThe signal is weak at certain operating points. The memory or filter can be used to confirm the direction based on a weak signal or to reduce noise in the measurements, e.g., by averaging.

[0115] Another application of the proposed method is to determine the Ty mode amplitude by evaluating the differential voltage ΔV I (i.e., the differential current signal) is detected by the system controller 23. This can be used for safety aspects such as material failure or the possibility of electrostatic ingress.

[0116] If the Rx trajectory is not a single sine wave but consists of several harmonics, one harmonic can coincide with the Ty mode resonance frequency. Experiments have shown that for the MEMS mirror 12, the 5 teA harmonic of the Rx trajectory can lead to a Ty mode resonance if it sweeps through the response curve of the MEMS mirror. However, depending on the design of the MEMS mirror 12, the separation factors between the Rx and Ty modes can differ, so that a different harmonic of the Rx trajectory can lead to the Ty mode resonance.

[0117] If the Rx-Ty coupling via the Euler force fulfills such a resonance condition, the Ty mode is excited to significantly higher amplitudes than in the non-resonant coupling case. The rotational movement of the mirror can be caused by a strong 5 te (or other) harmonics are distorted due to the large amplitude of motion of the Ty mode. This is a consequence of the fact that the Ty mode is not a pure translation mode. Rather, it contains a small rotational component, which leads to a distortion of the overall rotation resulting from the total effect of the Rx rotation and the small rotational contribution of the Ty mode.

[0118] The fifth 5 te The harmonic content of the overall rotational motion, obtained by sweeping through a portion of the MEMS mirror response curve for various drive voltages, shows that the Ty response curve has an upper branch (upper response curve) with a high Ty mode amplitude and a lower branch (lower response curve) with a low Ty mode amplitude.

[0119] The system controller 23 can be designed to measure the differential voltage ΔV I to monitor at various operating points (e.g., at the Ty mode resonance peak and outside the resonance). Based on the waveform of the differential voltage ΔV I Both operating points can be clearly distinguished. Thus, the system controller 23 can determine whether the current operating point of the MEMS mirror is on the upper branch or the lower branch of the 5. tenHarmonics of the response curve of the total rotation are located without the need for a trajectory measurement. Based on this information, the system controller 23 can generate the digital control signal D. Hvact adjust to make a jump from the upper branch to the lower branch of the 5 ten To force harmonics. This can be achieved by increasing the drive frequency of the digital control signal D. Hvact This can be achieved beyond the fallback frequency of the upper response curve of the Ty mode resonance, causing the Ty mode excitation to collapse. Furthermore, the proposed mode damping can also be applied via the damping signal Vdmp to force a jump to the lower branch.

[0120] In other words, the system controller 23 can determine the Ty mode amplitude from the differential voltage ΔV I determine and, based on the determined Ty mode amplitude, determine whether the MEMS mirror 12 is located on the upper or lower branch of the 5 tenharmonics. If the Ty mode amplitude exceeds a predetermined amplitude threshold, the system controller 23 determines that the MEMS mirror 12 is located on the upper branch of the 5 ten The harmonics of the Rx mode are present, and a countermeasure is taken by adjusting the digital control signal D. Hvact adapts.

[0121] Once an unwanted parasitic oscillation (e.g., mode Ty, mode Rz, mode Ry, or mode Tz) has been detected, it can be actively damped. Since a small Ty mode amplitude is typically present during normal operation, a threshold for stronger unwanted excitation of the Ty mode through resonant coupling should be defined. This means that active damping occurs when a non-zero threshold is exceeded, with the threshold being set to allow the small Ty mode amplitude that normally occurs. The threshold can be determined for a specific design through experimentation and numerical simulations such that off-resonance Ty mode amplitudes of up to 1–3 µm can occur. On-resonance coupling via a harmonic of the Rx trajectory or by direct excitation of the comb drive can lead to higher amplitudes.Therefore, based on a dynamic coupling model, a threshold can be chosen that specifies that Ty amplitudes greater than 3 µm are considered to be caused by on-resonance coupling. This threshold for the mechanical amplitude of the Ty mode can be converted into a corresponding threshold for the magnitude of the differential voltage ΔV. I be converted.

[0122] Alternatively, the frequency content of the differential voltage ΔV can be used. I The system controller 23 monitors the system. Off-resonance coupling will result in Ty movement at the same frequency as Rx. In contrast, on-resonance coupling, e.g., via the fifth harmonic component of the mirror trajectory in a given design, will lead to a sharp increase in the fifth harmonic component of the differential voltage ΔV. I This can lead to an increase in the spectral component of the differential voltage ΔV. IThe frequency corresponding to the fifth harmonic is adjusted by a specific factor, e.g., by a factor of 5, to detect on-resonance coupling. This can be done during normal operation of the MEMS mirror 12 via the system controller 23.

[0123] During an observation phase, while the drive voltage V drive is switched on (e.g., according to an on-time in which D Hvact = 1 is and V drive (set to a value between 0-200 V), the type of parasitic oscillation, its frequency, and its phase are determined by the system controller 23 from the corresponding differential voltage ΔV. I determined. Thus, the system controller 23 evaluates the differential voltage ΔV. I It detects the translational Ty mode based on predefined threshold values ​​of the magnitude of the differential voltage ΔV. I and the relative strength of the harmonic content of the differential voltage ΔV I .

[0124] During the off-phase of the drive voltage v drive (e.g., corresponding to a time off, during which the D HVact = 0 and V drive (0V is) the TIAs 51 and 52 are disconnected from the stator electrodes (e.g., via an open switch SW1 and SW2), and a damping voltage Vdmp is applied to the stator electrodes to counteract the parasitic translational motion Ty.

[0125] In particular, the Fig. Figure 4D shows a top view of a MEMS mirror that is compensated in a first damping method (Method 1) with a damping voltage in response to the detection of a translational motion Ty according to one or more embodiments. To dampen and reduce the translational motion Ty, the damping voltage Vdmp is applied to the two stator electrodes located on the same side of the mirror body 8 (i.e., on the same lateral side of the scanning axis 13). The damping voltage Vdmp can therefore be applied either to both stator electrodes of the comb drives 40TL and 40BL or to both stator electrodes of the comb drives 40TR and 40BR. The other pair of stator electrodes on the opposite side of the mirror body 8 (i.e., on the opposite side of the scanning axis 13) is grounded to 0 V. As a result, the detected Ty mode is damped by applying the damping voltage Vdmp to counteract the translational motion.

[0126] Alternatively, in a second damping method (Method 2), the TIAs 51 and 52 can remain connected to the stator electrodes during damping (e.g., switches SW1 and SW2 are closed or not present), and the damping voltage Vdmp is superimposed on the drive voltage Vdrive. The dashed lines representing the damping voltage Vdmp thus illustrate the two ways in which the damping voltage Vdmp can be applied, depending on the damping method. As an alternative to directly applying the damping voltage Vdmp to the signal line of the drive voltage Vdrive, the system controller 23 can transmit a damping control signal Ddmp to the MEMS driver 25, and the MEMS driver 25 can generate the damping voltage Vdmp, superimposing it on the drive voltage Vdrive.

[0127] Both damping methods work in principle for any mode and depend on the specific capacitance dependence of the total capacitance of all four stator quadrants on the respective degree of freedom (DOF). Due to the symmetry, the total capacitance will always form a local extremum for each degree of freedom. For the Rx and Tz modes, the local extremum is a maximum, while for Rz, the local extremum is a minimum.

[0128] For the Ty mode, the situation is more complex. In pure translation, the total capacitance as a function of the DOF Ty is essentially constant, since the increase in capacitance on one side is exactly balanced by the decrease in capacitance on the other. This is a consequence of the fact that the rotor and stator fingers already interlock in the rest position (in a true plane drive, such as a gyroscope, the tips of the rotor and stator would be designed to end in the same position, and then the situation is different). When the rotational component of the Ty mode is added, the capacitance for the Ty mode also has a local maximum, but the dependence is still quite weak.

[0129] The force (for translational motion, Ty and Tz) and the torque (for rotational motion, Rz) that can be exerted by the drive on a given DOF depend on the strength of the capacitance dependence of the capacitor configuration used to enforce that DOF. More precisely, the force or torque at position q, where q is the DOF under consideration, can be expressed by F(q) or τ(q)=12∂C∂qV2 can be expressed as follows. Here, C contains the stator combs used for damping operation. In the first damping method, C contains the stators to which Vdmp is applied. Since C(q) is essentially linear for the Ty case in the first damping method, the derivative is essentially constant, resulting in a constant factor that squares the applied damping voltage. In the second damping method, C contains all four stator quadrants, resulting in a parabolic dependence of C around q = 0. Consequently, due to the derivative, the force or torque has a linear dependence on q, with the slope of the linear dependence being proportional to the curvature of the local extremum formed by the capacitance at q = 0. Driving or damping with the second damping method is in perfect analogy to the parametric excitation of the Rx mode in normal operation.

[0130] Since the curvature of the local maximum for Ty is very small, method 1 can be preferred for Ty because it leads to a much higher force by alternately using the linear capacitance dependence of only the left or only the right stator pair.

[0131] For the other DOFs, e.g., Tz, Rz, Ry, method 2 can be selected, since each quadrant already exhibits an essentially parabolic capacitance dependency. Method 2 thus doubles the driving force / torque. It also requires no switches or other bias voltages; the damping voltage can simply be superimposed on the regular drive signal Vdrive.

[0132] Furthermore, method 2 is generally preferable because the damping signal for the parasitic motion can be applied continuously during both the on and off times of the drive voltage (and not just during the off times). Therefore, the damping signal contains only higher harmonics of the drive signal and does not affect the Rx motion averaged over an Rx period. If, on the other hand, the damping signal is applied only during the off times of the drive signal, it slows down the Rx motion due to the capacitance dependence on the angle θ. dCdθ', of the stator pair used for the damping process, where θ is the mirror angle and dC / dθ is the capacitance derivative with respect to the mirror angle. For this reason, damping method 1 has an influence on the Rx mode amplitude. Fig. Figure 4E shows a timing diagram for the implementation of the first damping method (Method 1) for damping the parasitic mode Ty according to one or more embodiments. Here, the translational motion of the MEMS mirror 12 for the Ty mode is represented as Ymirror, while θmirror is the mirror angle about the scanning axis 13 (i.e., the Rx mode). Two damping signals (voltages) Vdmp,left and Vdmp,right are applied to the left stator electrodes and the right stator electrodes, respectively, to apply damping during the off-times of the drive voltage Vdrive to dampen the Ty oscillation.

[0133] Fig. Figure 4F shows a timing diagram for the implementation of the second damping method (Method 2) for damping the parasitic mode Tz according to one or more embodiments. Here, the translational motion of the MEMS mirror 12 for the Tz mode is represented as Zmirror, while θmirror is the mirror angle about the scanning axis 13 (i.e., the Rx mode). A damping signal (voltage) Vdmp is superimposed on the drive voltage Vdrive during both the on and off times, based on the detection of the Tz mode, to dampen the Tz oscillation. Taking into account the nonlinear actuation force or torque, Vdmp can be adjusted locally during the on and off times of Vdrive, e.g., a lower amplitude of Vdmp during the on time of Vdrive.

[0134] During the observation phase, the system controller 23 determines the sign of the differential voltage ΔV. IThe phase relation of the Ty mode motion relative to the observation phase, which is the activation phase of the Rx mode, determines the time intervals within the observation phase in which the mirror body 8 moves from left to right and from right to left in the translational Y direction. Since, in the case of on-resonance coupling, the frequency of the Ty mode motion is generally an integer multiple of the Rx mode motion (e.g., the Ty mode could be resonantly excited by the content of the fifth harmonic of the Rx trajectory), the observation phase can contain phases in which the mirror body 8 moves from left to right as well as phases in which it moves from right to left.

[0135] During the off-phase, the damping voltage Vdmp (Vdmp,left and Vdmp,right) must be applied alternately to either the pair formed by the two left stator electrodes 40TL and 40BL or to the pair formed by the two right stator electrodes 40TR and 40BR, while the other pair can be set to 0V or a different absolute value smaller than the other comb drive side. This alternating signal must be constructed with a time or phase relationship such that the damping voltage Vdmp is applied to the left pair during time intervals when the Ty movement is from left to right, and to the right pair during time intervals when the Ty movement is from right to left. For this signal construction, the system controller 23 uses the phase information about the Ty mode derived during the observation phase.

[0136] Another aspect of mode-locking for a comb-driven MEMS mirror is the coupling of the rotation mode Rx with the yaw mode Rz. Specifically, coupling can occur from the desired rotation mode Rx to an undesired yaw mode Rz. The yaw mode Rz is susceptible to direct parametric excitation by the comb drives. Direct parametric excitation is possible due to the very strong capacitance dependence for this degree of freedom if higher harmonics of the square-wave drive signal Vdrive for the Rx mode satisfy the criterion for parametric resonance of the Rz mode. More precisely, if an odd integer multiple of the drive frequency equals twice the natural frequency of the Rz mode, parametric excitation of the Rz mode can occur. However, a threshold excitation strength is required for parametric resonance. For this reason, parametric resonance of the Rz mode does not occur if the odd integer, i.e.,The order of the higher harmonics, which fulfills the resonance condition, is too high. The exact threshold depends on the curvature of the capacitance dependence for the Rz mode and the applied voltage. As soon as the yaw mode Rz is excited, i.e., when there is an initial Rz movement, inert coupling terms according to Euler's rotation equation lead to a coupling of the Rz and Rx modes. The yaw mode Rz can be detected and measured by subtracting diagonal displacement current signals.

[0137] Fig. Figure 5A illustrates a top view of a MEMS mirror arranged in a nominal centered position (left) and a yaw-shifted position (right) according to one or more embodiments. On the left, the MEMS mirror 12 (mirror body 8) operates in a pure rotational mode Rx about the scanning axis 13, and the torsion bars 18 are not bent. The four comb drives 40TL, 40BL, 40TR, and 40BR are arranged symmetrically within the frame 17. In contrast, on the right, the MEMS mirror 12 (mirror body 8) is shifted about the Z-direction (i.e., rotated about a Z-axis) and oscillates back and forth about the Z-axis via mode-locking with the Rz mode. During this oscillation, the torsion bars 18 bend back and forth in the Y-direction.The stator comb drive electrodes are divided into diagonal pairs of a first diagonal perpendicular to the MEMS chip (stators of comb drives 40TL and 40BR) and into diagonal pairs of a second diagonal perpendicular to the MEMS chip (stators of comb drives 40BL and 40TR) to detect the RxRz mode coupling.

[0138] Embodiments further include a detection circuit coupled to the stator comb drive electrodes of each comb drive 40TL, 40BL, 40TR, and 40BR to receive their respective displacement currents. The stator comb drive electrodes are coupled to the detection circuit such that the mode of interest, such as the Ty mode or the Rz mode, is detected.

[0139] Fig. Figure 5B is a schematic diagram of a system 500 for measuring and compensating a yaw mode Rz according to one or more embodiments. The system 500 for measuring and compensating the yaw mode Rz includes the MEMS driver 25, the MEMS mirror 12 with four comb drives 40TL, 40BL, 40TR, and 40BR, a sensing circuit 60, and the system controller 23. It is further noted that the sensing circuits 50 and 60 can be combined to detect both the Ty mode and the Rz mode.

[0140] The MEMS driver 25 receives a digital control signal D Hvact and drives the MEMS mirror 12 in accordance with the digital control signal D HVact The MEMS driver 25 generates the drive voltage V. drive with the appropriate duty cycle and sets the drive voltage V driveto the mirror comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR. As a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitances C change. TL , C BL , C TR , and C BR the four comb drives 40TL, 40BL, 40TR, and 40BR and displacement currents i TL , is, i TR , and i BR generated by their respective drive capacities. The detection circuit 60 is coupled to the stator comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR and extracts the displacement currents i from them. TL , i BL , i TR , and i BR .

[0141] To measure the yaw mode Rz, the two diagonally or transversely opposite displacement currents i are measured. TL and i BRan input of a TIA 61 of the sensing circuit 60 is provided. While a TIA is used in this example, other sensor elements can also be used for capacitive sensing. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation-based sensing can be used to generate sensing signals. The TIA 61 can be coupled to the MEMS mirror 12 and, in particular, to the stators of the associated comb drives. The diagonal displacement currents i TL and i BR are taken from the stator comb electrodes of the comb drives 40TL and 40BR, which are arranged diagonally to each other across the mirror body 8. Consequently, the sum of the two diagonal displacement currents i TL and i BR through the TIA 61 into a first diagonal voltage V D1 converted.

[0142] Similarly, the two other diagonal or transversely opposed displacement flows are i TR and i BL a signal is provided to an input of a TIA 62 of the sensing circuit 60. Although a TIA is used in this example, other sensor elements can also be used for capacitive sensing. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation-based sensing can be used to generate measurement signals. The TIA 62 can be coupled to the MEMS mirror 12 and, in particular, to the stators of the associated comb drives. The diagonal displacement currents i TR and i BL are taken from the stator comb electrodes of the comb drives 40TR and 40BL, which are arranged diagonally to each other across the mirror body 8. Consequently, the sum of the two other diagonal displacement currents i TR and i BLthrough the TIA 62 into a second diagonal voltage V D2 converted.

[0143] The detection circuit 60 further includes a summing amplifier 63 and a subtracting amplifier 64. The summing amplifier 63 receives both the first diagonal voltage V D1 as well as the second diagonal voltage V D2 and sums them together to obtain a total voltage V I to generate which is the sum of all displacement flows i TL , i BL , i TR , and i BR represents. Conversely, the subtractor 64 receives both the first diagonal voltage V. D1 as well as the second diagonal voltage V D2 and subtracts the second diagonal voltage V D2 from the first diagonal tension V D1 , to create a differential voltage ΔV I to generate which the difference between the first pair of diagonal currents i TL , i BR (i.e., a sum thereof) and the second pair of diagonal currents i TR , iBL (i.e., a sum thereof). The summed voltage V I (i.e., the summed current signal) enables precise phase and amplitude measurements of the Rx mode, which the system controller 23 uses for correct MEMS mirror control. However, the summed voltage V I It provides no information about the scanning direction, since the four comb drives are symmetrical. On the other hand, the differential voltage ΔV I (i.e., the differential current signal) provides information about the amplitude of the yaw mode Rz and the phase of the yaw mode Rz relative to the Rx mode. For example, the differential voltage ΔV I oscillate between positive and negative values ​​when the MEMS mirror 12 oscillates around the Z-axis. The system controller 23 can process the digital control signal D. HVact based on the phase and amplitude of the Rx mode (rotation angle θ) mirror ) generate.

[0144] Additionally, after an unwanted parasitic oscillation has been detected (e.g., Mode Ty, Mode Rz, Mode Ry, or Mode Tz), it can be actively damped using the method 2 described above, where a damping signal Vdmp is superimposed on the drive signal Vdrive.

[0145] A threshold value in the differential voltage ΔV I can be defined to determine that the yaw mode Rz is excited. The threshold of the differential voltage ΔV IThe threshold angle can be determined to correspond to an Rz rotation angle considered critical. Since, in Rz mode, the rotor and stator comb fingers approach each other due to a significant transverse displacement component, which can lead to the potentially destructive effect of electrostatic pull-in, the threshold angle for critical Rz movement is typically chosen to be very low. In some embodiments, it can be selected in the range of 0.015° to 0.15°. A suitable threshold angle for a given design can be determined through experimentation and numerical simulations and translated into a corresponding threshold value for the magnitude of the differential voltage ΔV. I taking into account the readout electronics, the spectral components of the differential voltage ΔV can also be calculated. IThe data must be analyzed to determine whether an amplified component is present at the expected frequency of the yaw mode Rz. The threshold criterion described above can be applied only to the spectral component at the expected frequency of the yaw mode Rz to make the detection more robust by excluding other spectral components that might indicate small, acceptable non-resonant movements in the yaw mode Rz, e.g., caused by manufacturing asymmetries. These procedures can be applied during normal operation of the MEMS mirror 12 via the system controller 23.

[0146] During an initial observation phase, while the drive voltage V drive is switched on (e.g., according to an on-time during which the D Hvact = 1 and V drive(set to a predetermined voltage, e.g. 0-200V), the type of parasitic oscillation, its amplitude, its frequency, and its phase relative to the operating mode Rx are determined by the system controller 23 from the corresponding differential voltage ΔV I determined. The system controller 23 therefore evaluates the differential voltage ΔV I It detects the yaw mode Rz based on certain threshold values ​​of the differential voltage ΔV. I or the magnitude of the spectral component of the differential voltage ΔV I at the expected frequency of the yaw mode Rz.

[0147] After an initial observation phase, the drive voltage v drive A damping voltage Vdmp is superimposed. This means it is applied to the rotor electrodes, while the stator electrodes remain grounded. The damping voltage Vdmp has twice the frequency of the parasitic yaw mode and its phase relative to V. driveThe phase of the yaw mode Rz relative to the operating mode Rx is chosen based on the determination of such a factor that the movement of the Rz mode is slowed down. For example, both the drive voltage V and the operating voltage V can be used. drive as well as the damping voltage Vdmp being unipolar square waves, and the frequency of the damping voltage Vdmp is an integer multiple of the frequency of the driving voltage V drive In the case of resonant parasitic excitation, unlike the method described for damping the parasitic Ty mode (1), the damping voltage for the Rz mode is applied not only during the off-phase of the drive voltage but also during the on-phase. This is possible because it can be performed with the same rotor or stator bias voltage as the application of the drive voltage v. dri-ve Furthermore, no switches are required.

[0148] In particular, the Fig. 5C is a top view of a MEMS mirror that is compensated with a damping voltage in response to the detection of a yaw motion Rz according to one or more embodiments. The drive voltage V applied to the rotor is used in this process. drive A damping voltage Vdmp is superimposed. The stator electrodes of 40TL, 40TR, 40BL, and 40BR are grounded. Vdmp can be locally adjusted during the on and off times of Vdrive, taking into account the nonlinear actuation force or torque.

[0149] To dampen and reduce the yaw motion Rz, the damping voltage Vdmp is superimposed on the drive voltage V. drive The voltage is applied to the rotor electrode, while the stator electrodes remain grounded at 0 V to monitor the displacement currents. As a result, the detected Rz mode is superimposed on the drive voltage V by applying the damping voltage Vdmp. drivedampened to counteract the unwanted rotational movement.

[0150] In subsequent observation phases, the amplitude and phase of the yaw mode Rz can be continuously monitored and the damping voltage Vdmp can be adjusted in amplitude and phase to the updated information about the amplitude and phase of the Rz mode.

[0151] During the observation phase, the system controller 23 determines from the differential voltage ΔV IThe phase of the Rz movement. More precisely, it determines whether the mirror body 8, relative to the Rz degree of freedom, is approaching or moving away from its rest position. If the mirror approaches the Rz-related rest position, it decreases the Rz-related capacitance, resulting in discharge currents. If the mirror moves away from the Rz-related rest position, it increases the Rz-related capacitance, resulting in charging currents. The charging and discharging currents lead to corresponding differential voltages with opposite signs. Through this process, the phase of the Rz movement relative to the drive signal can be determined. In response to this phase detection of the movement around the Z-axis, it can then be superimposed onto the drive signal V. driveDuring the phases in which the mirror approaches the Rz-related rest (mean) position, the damping voltage Vdmp is applied, while no additional voltage is superimposed during the phases in which the mirror moves away from the Rz-related rest position. The Rz-related capacitance has a minimum at the Rz-related rest position. For this reason, applying a voltage Vdmp between the rotor and stators pulls the mirror away from the Rz-related rest position. If a voltage is applied during the phases in which the mirror approaches the Rz-related rest position, the Rz movement is slowed down, i.e., damped. The Rz movement is continuously monitored, and the application of the damping voltage Vdmp is adjusted based on updated phase and amplitude information about the movement of the yaw mode Rz.

[0152] Furthermore, if the stator comb drive electrodes of each of the four comb drives 40TL, 40BL, 40TR, and 40BR are divided into two layers of equal thickness, a translational mode Tz in the Z-direction (i.e., a translational motion out of the plane upwards and downwards) can be detected by the difference in the layer currents of the front and back sides, where "front side" refers to the layer that has a larger (i.e., more positive) z-coordinate with respect to the coordinate system of the Fig. 1B. Conversely, "back side" refers to the layer that is located at a lower (i.e., more negative) z-coordinate with respect to the coordinate system of the Fig. 1B is located.

[0153] Fig. 6A and Fig. Figure 6B illustrates cross-sectional views of a MEMS mirror and drive electrodes according to one or more embodiments. In particular, in the Fig. 6A contains the left stator comb drive electrode 43, which has two layers: a front layer 43a and a back layer 43b, both of equal thickness. Similarly, the right stator comb drive electrode 44 contains two layers: a front layer 44a and a back layer 44b, both of equal thickness. In contrast, in the Fig. 6B the respective front and back layers have different thicknesses.

[0154] Mode coupling between the Rx mode and the Tz mode can be caused by a displacement L of the center of mass M from the axis of rotation (scanning axis 13) due to the amplification structure 9. This inertial coupling results from the sum of an Euler force component and a centrifugal component according to equation 2: fZ(t)=−m L θm(t)θ¨m(t)−mL(θ˙m(t))2 with the mirror mass m, the mirror angle θ m (t), the mirror angular velocity θ m(t) and the mirror rotation acceleration θ̈ m (t). The Tz mode is thus determined by the inertial force f. z (t) excited, whose frequency content, due to its dependence on the mirror angle and its time derivatives, is twice as high as the harmonic frequencies of the Rx trajectory θ(t). If f z If (t) has a frequency content at the resonant frequency of the Tz mode, resonant excitation of the Tz mode can occur. Another coupling mechanism between the Rx mode and the Tz mode is the direct parametric excitation of the Tz mode by a higher harmonic content of the drive voltage V. drive the Rx mode.

[0155] Subtracting all back-side layer displacement currents from all front-side displacement currents enables the detection of Tz movement via a differential signal. Detection of Tz movement is also possible with layers of unequal thickness, but the resulting differential current must be further processed by the system controller 23, since the desired Rx mode also generates a non-zero signal. Thus, layers of unequal thickness cause a difference in the front and back-side currents for both the Rx and Tz modes.

[0156] Fig. Figure 6C is a schematic diagram of a system 600 for measuring and compensating a Tz mode according to one or more embodiments. The system 600 for measuring and compensating the Tz mode includes the MEMS driver 25, the MEMS mirror 12 with four comb drives 40TL, 40BL, 40TR, and 40BR, each consisting of a front layer and a back layer, a sensing circuit 70, and the system controller 23. It is further noted that the sensing circuits 50, 60, and 70 can be combined to sensing the Ty mode, the Rz mode, and the Tz mode.

[0157] The MEMS driver 25 receives a digital control signal D Hvact and drives the MEMS mirror 12 in accordance with the digital control signal D Hvact The MEMS driver 25 generates the drive voltage V. drive with the appropriate duty cycle and sets the drive voltage V driveto both layers of the mirror comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR. As a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitances C change. TL-FS , C BL-FS , C TR-FS , C BR-FS , C TL-BS , C BL-BS , C TR-BS and C BR-BS the four comb drives 40TL, 40BL, 40TR, and 40BR and displacement currents I TL-FS , i BL_FS , i TR_FS , i BR-FS , i TL-BS , i BL_BS , i TR_BS and i BR _ BS are generated by their respective drive capacities. The detection circuit 70 is coupled to the stator comb electrodes of the four comb drives 40TL, 40BL, 40TR, and 40BR and extracts the displacement currents i from them. TL-FS , i BL_FS , i TR_FS , i BR-FS , 1 TL-BS , 1 BL_BS , i TR_BS and i BR-BS ,

[0158] To measure the Tz mode, all front-side displacement currents i TL-FS , i BL_FS , i TR_FS and i BR-FS An input of a TIA 71 of the sensing circuit 70 is provided. The TIA 71 can be coupled to the MEMS mirror 12, and in particular to the front-facing layers of the stators of all comb drives. The front-facing displacement currents i TL-FS , i BL_FS , i TR_FS and i BR-FS are derived from the front layers of the stator comb electrodes of the comb drives 40TL, 40BL, 40TR, and 40BR. The result is the sum of all front-side displacement currents i TL-FS , i BL_FS , i TR_FS and i BR-FS from the TIA 71 into a first voltage V FS converted.

[0159] Similarly, all backside displacement currents i TL-BS , i BL_BS , i TR_BS , and i BR-BSAn input of a TIA 72 of the sensing circuit 70 is provided. The TIA 72 can be connected to the MEMS mirror 12 and, in particular, to the rear layers of the stators of all comb drives. The rear displacement currents I TL-BS , i BL_BS , i TR_BS and i BR-BS are derived from the back-side layers of the stator comb electrodes of the comb drives 40TL, 40BL, 40TR, and 40BR. The result is the sum of all back-side displacement currents I. TL-BS , i BL_BS , i TR_BS and i BR-BS through the TIA 72 into a second voltage V BS converted.

[0160] The detection circuit 70 further includes a summing amplifier 73 and a subtracting amplifier 74. The summing amplifier 73 receives both the first voltage V FS as well as the second voltage V BS and sums them together to obtain a total voltage V I to generate which is the sum of all displacement flows i TL-FS , iBL_FS , i TR_FS , I BR-FS , i TL-BS , i BL_BS , i TR_BS and i BR-BS represents. Conversely, the subtractor 74 receives both the first voltage V FS as well as the second voltage V BS and subtracts the second voltage V BS from the first voltage V FS , to create a differential voltage ΔV I to generate which is the difference between all front currents i TL-FS , i BL_FS , i TR_FS and i BR-FS and all back currents I TL-BS , i BL_BS , i TR_BS and i BR-BS represents the total voltage V. I (i.e., the sum current signal) enables precise phase and amplitude measurements of the Rx mode, which the system controller 23 uses for proper MEMS mirror control. The differential voltage ΔV I(i.e., the differential current signal) provides information according to the amplitude of the Tz mode and the phase of the Tz mode relative to the Rx mode. For example, the differential voltage ΔV I oscillate between positive and negative values ​​when the MEMS mirror 12 oscillates along the Z-direction. The system controller 23 can process the digital control signal D. Hvact based on the phase and amplitude of the Rx mode (rotation angle θ) mirror ) generate.

[0161] Additionally, once an unwanted parasitic oscillation of the Tz mode has been detected, it can be actively damped. A threshold value can be set in the differential voltage ΔV. IA threshold of differential stress must be set to determine whether the Tz mode is excited. This threshold can be determined to correspond to a Tz displacement considered critical. Since an additional mechanical load is exerted on the mirror suspensions, particularly the torsion beams, in Tz mode, the threshold displacement for the critical Tz movement is typically chosen to be low. In some embodiments, it can be in the range of 1.5–10 µm. A suitable threshold displacement for a given design can be determined through experimentation and numerical simulations and translated into a corresponding threshold for the magnitude of the differential stress ΔV. I taking into account the readout electronics, the spectral components of the differential voltage ΔV can also be determined. IThe spectral components are analyzed to determine whether an amplified component is present at the expected frequency of the Tz mode. The threshold criterion described above can be applied only to the spectral component at the expected frequency of the Tz mode to make the detection more robust by excluding other spectral components that might indicate a small, acceptable non-resonant motion in the Tz mode, e.g., caused by manufacturing asymmetries. These procedures can be applied during normal operation of the MEMS mirror 12 via the system controller 23.

[0162] During an initial observation phase, while the drive voltage v drive is (e.g., corresponding to an on-time during which the D Hvact = 1 and v drive(set to a predetermined voltage, e.g. 0-200V), the type of parasitic oscillation, its frequency, and its phase relative to the operating mode Rx are determined by the system controller 23 from the corresponding differential voltage ΔV I determined. Thus, the system controller 23 evaluates the differential voltage ΔV. I It detects the translational Tz mode based on predefined threshold values ​​of the differential voltage ΔV. I or the magnitude of the spectral component of the differential voltage ΔV I at the expected frequency of the translational Tz mode.

[0163] After an initial observation phase, the drive voltage v drive A damping voltage Vdmp is superimposed. That is, it is applied to the rotor while the stator electrodes remain grounded. The damping voltage Vdmp has twice the frequency of the parasitic translational Tz mode and its phase relative to v. driveThe phase of the translational Tz mode relative to the operating mode Rx is chosen based on the determination of that phase, thus slowing down the Tz mode motion. For example, both the drive voltage v and the operating mode Rx can be used to determine the Tz mode motion. drive as well as the damping voltage Vdmp being unipolar square waves, and the frequency of the damping voltage Vdmp is an integer multiple of the frequency of the driving voltage v drive In the case of resonant parasitic excitation. Unlike the method described for damping the parasitic Ty mode, the damping voltage for the Tz mode is not only applied during the off-phase of the driving voltage v. drive , but also during the start-up phase. This is possible because it can be done with the same preload on the rotor or stators as the application of the drive voltage v. drive Furthermore, no switches are needed.

[0164] In particular, the Fig. Figure 6D shows a cross-sectional view of a MEMS mirror that is compensated with a damping voltage in response to the detection of a Tz motion, according to one or more embodiments. To dampen and reduce the Tz motion, the damping voltage Vdmp is applied to the rotor electrode by superimposing it on the drive voltage v. drive The damping voltage Vdmp is applied while the stator electrodes remain grounded at 0 V to monitor the displacement currents. As a result, the detected Tz mode is superimposed on the drive voltage v by applying the damping voltage Vdmp. drive dampened to counteract the unwanted translational movement.

[0165] In the subsequent observation phases, the amplitude and phase of the Tz mode can be continuously monitored, and the damping voltage Vdmp can be adjusted in amplitude and phase according to the updated information about the amplitude and phase of the Tz mode.

[0166] During the observation phase, the system controller 23 determines from the differential voltage ΔV I the phase of the Tz movement. More precisely, it determines whether the mirror body 8, relative to the Tz degree of freedom, is approaching or moving away from its equilibrium position. If the mirror approaches the Tz-related equilibrium position, it increases the Tz-related capacitance, leading to currents that charge the comb capacitors. If it approaches from the negative Z-side, mainly the capacitors of the front layers are charged, resulting in non-zero currents. TL-FS, i BL-FS , i TR-FS and i BR-FS This leads to a situation where, as it approaches from the positive Z-side, mainly the capacitors of the back layers are charged, resulting in non-zero currents: I TL-BS , i BL-BS , i TR-BS and i BR_BSIf the mirror moves away from its Tz-related rest position, the Tz-related capacitance decreases, leading to currents that discharge the comb capacitors. With a change in distance on the negative Z-side, primarily the capacitors of the front layers discharge, resulting in non-zero currents. TL-FS , i BL-FS , i TR-FS and i BR-FS with the opposite sign compared to the approach case. When a distance is drawn on the positive Z-side, primarily the capacitors of the back layers are discharged, resulting in non-zero currents. TL-BS , i BL-BS , i TR-BS and i BR-BS with the opposite sign compared to the approach case. These signals lead to corresponding differential voltages. The charging and discharging of the rear or front currents also depends on the instantaneous angle of rotation.

[0167] By appropriately evaluating the differential voltage, the phase of the Tz movement relative to the drive signal can be determined. In response to this phase detection of the movement along the Z-axis, the damping voltage Vdmp can then be applied to the drive signal v during the phases in which the mirror moves away from its Tz-related rest (center) position. driveThe voltage is superimposed during phases in which the mirror approaches its Tz-related equilibrium position, while no additional voltage is superimposed during phases in which the mirror approaches its Tz-related equilibrium position. The Tz-related capacitance has a maximum at the Tz-related equilibrium position. For this reason, applying a voltage Vdmp between the rotor and stators pulls the mirror towards its Tz-related equilibrium position. If a voltage is applied during phases in which the mirror moves away from its Tz-related equilibrium position, the Tz movement is therefore slowed down, i.e., damped. The Tz movement is continuously monitored, and the application of the damping voltage Vdmp is adjusted based on updated phase and amplitude information about the translational Tz mode movement.

[0168] Tz mode-locking can be detected by monitoring the differential signal of the front and rear layers of the stator. The frequency locus of the mode-locking with the Tz mode can be recorded and stored in memory to prevent future excitation of the Tz mode, for example, during a mirror restart when the drive voltage frequency is driven in an open-loop system to initiate the Rx oscillations for capturing the initial signals. A large change in the mirror position in the translational Z direction can be used by the system controller 23 to detect a malfunction of the mirror 12, for example, if the differential signal exceeds a predefined amplitude threshold.

[0169] Fig. Figure 6E shows four capacitor currents DL1R, DL2R, DL1L, and DL2L in an excitation frequency sweep over a wide range from 4 kHz to 45 kHz for a MEMS mirror according to one or more embodiments. The capacitor currents DL1R, DL2R, DL1L, and DL2L refer to the Fig. 6B and Fig. 6C. DL1R, for example, represents the sum of the front-side layer currents (DL1 ... Device Layer 1 = front side) on the right side. DL2L represents the sum of the back-side layer currents on the left side, and so on. The capacitor currents DL1R, DL2R, DL1L, and DL2L can be generalized as displacement currents ixL-FS = DL1L, ixR-FS = DL1R, ixL-BS = DL2L, ixR-BS = DL2R, where "lower" and "upper" layer currents are not distinguished (summed by common contacting), so that "x" can represent a lower or upper layer current. Direct excitation of the operating mode Rx and the parasitic modes Tz and Rz is observed at twice their respective resonant frequencies. This means they are excited in first-order parametric resonance. However, the Rz mode is also excited at one-third of its parametric resonant frequency. This can be explained by the rectangular wave that travels over v driveThe drive is driven by a parasitic mode and exhibits higher, odd harmonics at 3, 5, 7, ... times the fundamental frequency. Thus, the third harmonic component of the square wave drive satisfies the resonance criterion for the first-order parametric resonance of the yaw mode Rz. This behavior is provoked by the excitation frequency sweep. However, such unwanted excitations can also occur during normal operation, i.e., when the drive frequency is twice the Rx frequency, if a parasitic mode satisfies the criterion Rx · (2n+1) = Rp, where Rp is the frequency of the parasitic mode and n = 0, 1, 2, ... Such parasitic excitations can be detected and identified using the methods described above.

[0170] Once an unwanted parasitic oscillation (e.g., Mode Ty, Mode Rz, Mode Ry, or Mode Tz) has been detected, it can be actively dampened. This can be done during the normal operation of the MEMS mirror 12 via the system controller 23.

[0171] During an observation phase, while the control voltage v drive is (e.g. during D Hvact = 1 and v drive (set to a value between 0-200V), the type of parasitic oscillation, its frequency, and its phase are determined by the system controller 23 from the corresponding differential voltage ΔV. I certainly.

[0172] In particular, the Tz mode can be actively damped in response to its detection. When the rotor moves from the center up or down, a voltage Vdamp is applied between the rotor and stator electrodes. When the rotor moves back to the center, no voltage (0 V) is applied.

[0173] Fig. Figure 7A illustrates a top view of a quasi-static (QS) MEMS mirror arranged in a nominal, centered position (left) and a translationally displaced position (right) according to one or more embodiments. In the QS MEMS mirror 12, the stator combs are used to drive the MEMS mirror 12 about the axis of rotation 13, and the rotor is used for sensing via a sensing circuit. For QS mirrors, the stator comb electrodes (typically either the left or the right, with the other set to zero voltage) are supplied with two individual drive voltages, while the rotor comb electrodes are connected to ground.

[0174] Fig. Figure 7B is a schematic diagram of a system 700 for measuring and damping a Ty mode for a QS-MEMS mirror according to one or more embodiments. The system 700 for measuring the Ty mode includes a MEMS driver 25 having two high-voltage (HV) drivers 25a and 25b, each applying an individual drive voltage to a corresponding set of stator comb electrodes. Specifically, HV driver 25a applies a drive voltage to the stator comb electrodes of comb drives 40TL and 40BL (i.e., the left side), and HV driver 25b applies a drive voltage to the stator comb electrodes of comb drives 40TR and 40BR (i.e., the right side). For QS mirrors, the two individual drive voltages are applied such that the QS-MEMS mirror 12 tilts either in the positive or negative direction. Applying both control voltages at the same time is normally avoided to prevent exciting the Tz mode.Each HV driver 25a and 25b receives a corresponding digital control signal D. HVleft or a digital control signal D HVright and drives the MEMS mirror 12 in accordance with its respective digital control signal in a similar manner to how described above when using the digital control signal D. Hvact described.

[0175] For QS mirror detection of the Rx nominal mode and the Ty parasitic mode, a detection circuit 80 (e.g., a TIA) is connected to the rotor combs to measure the capacitance through the displacement charge or displacement current received by the rotor (i.e., the rotor comb electrodes).

[0176] For QS mirror detection, a high-frequency modulation voltage can be added to the nominal drive voltage to enable mirror position detection (Rx) and parasitic mode detection (Ty) that are independent of the applied drive voltage.

[0177] For QS mirror detection, the Ty parasitic mode is distinguished from the Rx nominal mode by its frequency component by the system controller 23. Once the system controller 23 detects the Ty mode and determines that its value is above a certain predetermined threshold, the system controller 23 can actively attenuate the Ty mode by adding a counter-voltage Vdmp to the drive comb electrodes on one side or the other, or alternatively, when the drive voltages are applied. That is, a counter-voltage Vdmp is superimposed on a drive voltage when the drive voltage is applied to the right-side stator comb electrodes, and vice versa. The summing circuits 81 and 82 can be used to apply the counter-voltage (attenuation voltage) Vdmp to the digital control signals D. HVleft and D HVrightto add or combine so that the back EMF Vdmp is superimposed on the drive EMF Vdrive by the respective HV driver 25a, 25b. The stator comb electrodes on the opposite side are grounded when not driven / damped. Vdmp can be scaled by Vdrive taking into account the non-linear actuation force and torque.

[0178] Fig. Figure 7C illustrates a top view of a QS MEMS mirror that is compensated with a damping voltage in response to the detection of a translational motion Ty according to one or more embodiments. The damping voltage applied to counteract the Ty mode is alternately applied to the left-hand stator comb electrodes and the right-hand stator comb electrodes to be superimposed on the drive voltage Vdrive when alternately driven according to the digital control signals D HVleft and D HVrightis created. The mass alternates with Vdrive / Vdmp as shown.

[0179] Fig. Figure 7D illustrates a cross-sectional view of a QS-MEMS mirror that is compensated with a damping voltage in response to the detection of a translational motion Ty according to one or more embodiments. In this embodiment, if the stator comb drive electrodes 43 and 44 have two layers (the upper layer 43a, 44a on the front and the lower layer 43b, 44b on the back), the drive voltage Vdrive and the damping voltage Vdmp can be applied alternately with ground from side to side. Here, the stator electrode (44a in the Fig. 7D above and 43a in the Fig. 7D below) are subjected to the damping voltage Vdmp, so that nominal Rx drive and Ty compensation are applied separately.

[0180] Fig. Figure 7E illustrates a top view of a QS-MEMS mirror compensated by an alternative method using dedicated sensing combs to detect a translational motion Ty according to one or more embodiments. It is acknowledged that a resonant MEMS mirror can also use dedicated sensing combs. Therefore, dedicated sensing combs are not limited to QS-MEMS mirrors but can be applied to any MEMS mirror, including those described herein.

[0181] The QS-MEMS mirror 12 contains four dedicated measuring combs 45TL, 45BL, 45TR, and 45BR, each of which is attached to the mirror frame 17 by a stator comb electrode and is used to measure the capacitance by the displacement charge or displacement current received by the stator comb electrodes, similarly to above with respect to, for example, the Fig. 4B and Fig. 4C described. The dedicated measuring combs 45TL, 45BL, 45TR, and 45BR also have a corresponding rotor comb electrode that is grounded.

[0182] Once the system controller 23 detects the Ty-Mode and determines that its value exceeds a certain predetermined threshold, the system controller 23 can actively dampen the Ty-Mode by adding a counter-voltage Vdmp to the driving stator comb electrodes when a corresponding drive voltage Vdrive is applied to these electrodes. The application of Vdrive / Vdmp alternates from side to side based on the digital control signals D HVleft and D HVright .

[0183] It is also noted that the 45TL, 45BL, 45TR, and 45BR detection combs can be electrically coupled to a detection circuit (e.g., TIAs, adders, and subtractors) in a similar manner to that shown in 4B, 4C, 5B, 6C, and 7B (e.g., as with the 40TL, 405BL, 40TR, and 40BR comb drives), not only for detecting and identifying one or more parasitic modes, but also for determining the phase, amplitude, and sampling direction of the rotating Rx mode. Furthermore, the type of parasitic oscillation (i.e., whether it is a Ty, Rz, Ry, or Tz mode), its frequency, and its phase can be determined in a similar manner to that described above, for example, by analyzing a differential measurement signal. Thus, the sensing combs are used to scan and generate measurement signals, and the drive combs are used to drive the MEMS mirror 12 and to dampen identified parasitic modes.

[0184] After detection, each of the parasitic modes Ty, Rz, Ry, and / or Tz can not only be actively attenuated but also preventively avoided. The parasitic modes Ty and Tz each have a high Q factor in their parasitic dynamics of the Rx mode. This high Q factor causes strong coupling with the Rx mode, which can lead to inaccuracies in the scanning angle due to distortion of the scanning trajectories and to malfunction of the mirror control system. In the worst case, a parasitic mode can destroy the MEMS mirror by causing large displacement of the comb drives and fatigue in a weak MEMS mirror structure. However, due to the high Q factor, strong coupling only occurs over a very small frequency range and also varies depending on the operating conditions, such as the peak input voltage, the duty cycle, and the shape of the excitation waveform.A parasitic mode can exhibit hysterical behavior if it contains a nonlinear spring constant, e.g., stiffening or softening. These large parasitic mode couplings should not be used as operating points for LIDAR operation or should be avoided during the start-up of the MEMS mirror 12 to prevent potential damage or fatigue.

[0185] Fig.Figure 8 illustrates a flowchart of a method for avoiding parasitic mode-locking according to one or more embodiments. If a parasitic coupling mode is detected during operation of the MEMS mirror 12 (Process 805), the influence of the mode-locking is evaluated (Process 810), e.g., the conditions and frequency range of the parasitic mode, the intensity of the mode-locking, and whether it is the critical point detected as having a critical impact or could be destructive to the MEMS mirror. In particular, the frequency locus of the Rx mode-locking with the parasitic mode, together with the amplitude of the parasitic mode, can be determined, and the amplitude and frequency locus (range) of the parasitic mode-locking are recorded in the memory (Process 820).If, in process 825, the amplitude and frequency location (range) of the parasitic mode-locking are determined to be at an operating point of the Rx mode, and are determined to critically affect or destroy the MEMS mirror, then the system controller 23 blocks or avoids this operating point in process 830 by modifying the operating state of the MEMS mirror 12 through applying a frequency shift or a change in the duty cycle for driving the Rx mode. That is, if the harmonics of the parasitic mode-locking are critical according to their frequency relative to the operating point of the Rx mode and / or according to the amplitude of the parasitic mode-locking, this operating point for driving the Rx mode is avoided in order not to excite the corresponding parasitic mode.

[0186] If the system controller 23 determines that the harmonics (frequency position) of the parasitic mode are not at the operating point of the Rx mode, but only at some of the start-up points of the MEMS mirror and may potentially damage the MEMS mirror 12, for example, based on their amplitude exceeding a predetermined threshold (operation 835), then the system controller 23 can modify the start-up of the MEMS mirror 12 in operation 840 to avoid such peak coupling frequencies or their near frequencies. The system controller 23 can also modify the operating conditions during start-up, e.g., peak input voltages, duty cycles, and the input waveform of the drive voltage Vdrive in operation 840.

[0187] Once the operating point for a desired operating frequency and amplitude of mode Rx is reached, the operating frequency and amplitude of the drive voltage Vdrive can be shifted to the other value in operation 830, e.g., shifted to a slightly higher operating frequency that exhibits lower parasitic coupling. The amplitude for the target operating state of Rx can be set by the system controller 23 by adjusting either the duty cycle or the voltage scale of the drive voltage Vdrive.

[0188] If the system controller 23 does not determine that a parasitic mode is located at the operating point of the Rx mode in process 825 or is destructive to the MEMS mirror in process 835, the system controller 23 continues to record the parasitic coupling behavior to the Rx mode in process 845 and returns to process 825 for continuous monitoring until all frequencies for a range of a parasitic mode have been fully analyzed.

[0189] In the case of a coupling mode's muffling oscillation, its hysterical behavior can be utilized, e.g., a slight increase in frequency for the coupling mode's fallback and a slight downward sweep for operation under the same operating conditions. This can significantly reduce the coupling effect caused by the hysterical behavior while maintaining the desired operating conditions. For example, the system controller 23 can evaluate the difference in the Rx trajectory when the Ty mode is excited at high amplitude and at low amplitude. This is due to the Ty mode's hysteresis (duffing) behavior. For example, the proportion of the 5 tenHarmonics of the Rx trajectory of the MEMS mirror 12, caused by a high Ty mode amplitude, are evaluated. During the sweep of the drive signal from low to high frequencies (starting the MEMS mirror until the desired operating point), an upper branch of the response curve of the MEMS mirror 12 is tracked until a fallback point to the lower branch of the response curve occurs at a high Ty amplitude. If the high Ty mode amplitude is detected (e.g., by capacitive readout), the system controller 23 can initiate a jump from the upper branch to the lower branch to avoid a large parasitic Ty mode coupling. A similar evaluation can be applied to the other parasitic modes.

[0190] Further embodiments are provided below: 1. Scanning system, comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate around an axis with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure around the axis according to the desired rotary motion mode based on the at least one drive signal, each comb drive comprising a rotor comb electrode and a stator comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a driver designed to generate at least one drive signal; a detection circuit that is selectively coupled to at least one subset of the plurality of comb drives in order to receive detection signals from them, each detection signal being representative of the capacity of a corresponding comb drive; and a processing circuit designed to determine a scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the acquisition signals. 2. Scanning system according to embodiment 1, wherein: the multitude of comb drives comprises a first subgroup of comb drives and a second subgroup of comb drives, the detection circuit is designed to subtract at least one detection signal provided by the second subgroup of comb drives from at least one detection signal provided by the first subgroup of comb drives in order to generate a differential measurement signal, and The processing circuit is designed to determine the scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the differential measurement signal. 3. Scanning system according to embodiment 2, wherein the sign of the differential measurement signal indicates the scanning direction. 4. Scanning system according to embodiment 2, further comprising: a system controller designed to modify at least one drive signal based on the specified scanning direction. 5. Scanning system according to embodiment 2, wherein: the detection circuit is designed to add the at least one detection signal provided by the first subgroup of comb drives and the at least one detection signal provided by the second subgroup of comb drives to generate a summed measurement signal, and The processing circuit is designed to determine at least one of the phases or amplitudes of the desired rotary motion mode based on the summed measurement signal. 6. Scanning system according to embodiment 5, further comprising: a system controller designed to modify at least one drive signal based on at least one of the specified phase of the desired rotary motion mode or the specified amplitude of the desired rotary motion mode. 7. Sampling system according to embodiment 1, wherein the processing circuit is designed to detect and identify a parasitic motion mode of the MEMS scanning structure based on the acquisition signals. 8. Scanning system according to embodiment 7, wherein: the multitude of comb drives comprises a first subgroup of comb drives and a second subgroup of comb drives, the detection circuit is designed to subtract at least one detection signal provided by the second subgroup of comb drives from at least one detection signal provided by the first subgroup of comb drives in order to generate a differential measurement signal, and The processing circuit is designed to identify the parasitic motion mode, determine the amplitude of the parasitic motion mode, and determine the phase of the parasitic motion mode relative to the at least one drive signal based on the differential measurement signal. 9. Scanning system according to embodiment 8, further comprising: a system controller designed to attenuate the identified parasitic motion mode by applying at least one attenuation signal, wherein the system controller sets an amplitude and a phase of the at least one attenuation signal based on the amplitude and phase of the parasitic motion mode. 10. Scanning system according to embodiment 1, further comprising: a system controller wherein the processing circuit is designed to determine an amplitude and a phase of a parasitic motion mode of the MEMS scanning structure relative to the at least one drive signal based on the detection signals, and The system controller is designed to attenuate the identified parasitic motion mode by applying at least one attenuation signal, wherein the system controller sets an amplitude and a phase of the at least one attenuation signal based on the amplitude and phase of the parasitic motion mode. 11. Scanning system according to embodiment 7, further comprising: a system controller designed to attenuate the identified parasitic motion mode based on the identified parasitic motion mode by applying at least one attenuation signal directly to at least one subset of stator comb electrodes of the plurality of comb drives or directly to each rotor comb electrode of the plurality of comb drives. 12. Scanning system according to embodiment 7, further comprising: a system controller designed to attenuate the identified parasitic motion mode based on the identified parasitic motion mode by superimposing the at least one attenuation signal onto the at least one drive signal. 13. Scanning system according to embodiment 1, wherein: the multitude of comb drives comprises a first subgroup of comb drives and a second subgroup of comb drives, the detection circuit is designed to add the detection signals from the first subset of comb drives to generate a first summed detection signal, to add the detection signals from the second subset of comb drives to generate a second summed detection signal, and to subtract the second summed detection signal from the first summed detection signal to generate a differential measurement signal, and The processing circuit is designed to determine the scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the differential measurement signal. 14. Scanning system according to embodiment 1, wherein: the multitude of comb drives comprises a first subgroup of comb drives arranged laterally to the axis in a first direction, and a second subgroup of comb drives arranged laterally to the axis in a second direction opposite to the first direction, the detection circuit is designed to add the detection signals from the first subset of comb drives to generate a first summed detection signal, to add the detection signals from the second subset of comb drives to generate a second summed detection signal, and to subtract the second summed detection signal from the first summed detection signal to generate a differential measurement signal, and The processing circuit is designed to determine the scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the differential measurement signal. 15. Scanning system according to embodiment 1, wherein: the multitude of comb drives comprises a first subgroup of comb drives arranged diagonally to each other across the axis on a first diagonal, and a second subgroup of comb drives arranged diagonally to each other across the axis on a second diagonal that intersects the first diagonal, the detection circuit is designed to add the detection signals from the first subset of comb drives to generate a first summed detection signal, to add the detection signals from the second subset of comb drives to generate a second summed detection signal, and to subtract the second summed detection signal from the first summed detection signal to generate a differential measurement signal, and The processing circuit is designed to determine the scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the differential measurement signal. 16. Scanning system, comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate around an axis with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure around the axis according to the desired rotary motion mode based on the at least one drive signal, each comb drive comprising a rotor comb electrode and a stator comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a driver designed to generate at least one drive signal; a detection circuit that is selectively coupled to at least one subset of the plurality of comb drives in order to receive detection signals from them, each detection signal being representative of the capacity of a corresponding comb drive; and a processing circuit designed to detect and identify a parasitic motion mode of the MEMS scanning structure based on the acquisition signals. 17. Scanning system according to embodiment 16, further comprising: a system controller designed to attenuate the identified parasitic motion mode based on the identified parasitic motion mode by applying an attenuation signal to at least one subset of stator comb electrodes of the plurality of comb drives or to each rotor comb electrode of the plurality of comb drives. 18. Sampling system according to embodiment 17, wherein the system controller selectively determines the subset of stator comb electrodes to which the at least one attenuation signal based on the identified parasitic mode is applied. 19. Sampling system according to embodiment 17, wherein the system controller is designed to superimpose the at least one damping signal onto the at least one drive signal. 20. Scanning system according to embodiment 16, further comprising: a system controller designed to selectively couple the detection circuit with at least the subset of the plurality of comb drives so that the detection circuit receives detection signals from them, based on a type of evaluated parasitic motion mode. 21. Scanning system according to embodiment 16, wherein: the multitude of comb drives comprises a first subgroup of comb drives and a second subgroup of comb drives, the detection circuit is designed to subtract at least one detection signal provided by the second subgroup of comb drives from at least one detection signal provided by the first subgroup of comb drives in order to generate a differential measurement signal, and The processing circuit is designed to identify a parasitic motion mode of the MEMS scanning structure, to determine an amplitude of the parasitic motion mode, and to determine a phase of the parasitic motion mode relative to the at least one drive signal based on the differential measurement signal. 22. Scanning system according to embodiment 21, further comprising: a system controller designed to attenuate the identified parasitic motion mode by applying at least one attenuation signal, wherein the system controller sets an amplitude and a phase of the at least one attenuation signal based on the amplitude and phase of the parasitic motion mode. 23. Scanning system according to embodiment 16, further comprising: a system controller designed to dampen the identified parasitic motion mode by biasing a pair of stator comb electrodes during a drive voltage off-time of the drive signal to slow down the identified parasitic motion mode in accordance with the identified parasitic motion mode, wherein the MEMS scanning structure is a resonant MEMS scanning structure. 24. Scanning system according to embodiment 16, further comprising: a system controller designed to dampen the identified parasitic motion mode by superimposing a damping voltage onto the at least one drive signal applied to each of the rotor comb electrodes in order to slow down the identified parasitic motion mode, where the MEMS scanning structure is a resonant MEMS scanning structure. 25. Scanning system according to embodiment 16, further comprising: a system controller designed to dampen the identified parasitic motion mode by superimposing a damping voltage onto the at least one drive signal applied to a pair of stator comb electrodes, to slow down the identified parasitic movement pattern, where the MEMS scanning structure is a quasi-static MEMS scanning structure. 26. Scanning system, comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate around an axis with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure around the axis according to the desired rotary motion mode based on the at least one drive signal, each comb drive comprising a rotor drive comb electrode and a stator drive comb electrode; a driver designed to generate at least one drive signal; a plurality of sensing combs, each sensing comb comprising a rotor sensing comb electrode and a stator sensing comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a detection circuit that is selectively coupled to at least one subset of the multitude of detection combs, to receive detection signals from these, each detection signal being representative of the capacity of a corresponding detection comb; and a processing circuit designed to detect and identify a parasitic motion mode of the MEMS scanning structure based on the acquisition signals. 27. Scanning system according to embodiment 26, further comprising: a system controller designed to attenuate the identified parasitic motion mode according to the identified parasitic motion mode by applying at least one attenuation signal to at least one subset of stator drive comb electrodes of the plurality of comb drives or to each rotor drive comb electrode of the plurality of comb drives. 28. Sampling system according to embodiment 27, wherein the system controller selectively determines the subgroup of stator drive comb electrodes to which the at least one damping signal based on the identified parasitic mode is applied. 29. Sampling system according to embodiment 27, wherein the system controller is designed to superimpose the at least one damping signal onto the at least one drive signal. 30. Scanning system according to embodiment 26, wherein the processing circuit is designed to determine a scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the detection signals. 31. Scanning system according to embodiment 30, wherein: the multitude of recording combs has a first subgroup of recording combs and a second subgroup of recording combs, the detection circuit is designed to subtract at least one detection signal provided by the second subset of detection combs from at least one detection signal provided by the first subset of detection combs in order to generate a differential measurement signal, and The processing circuit is designed to determine the scanning direction of the MEMS scanning structure in the desired rotary motion mode based on the differential measurement signal. 32. Scanning system according to embodiment 31, wherein: the acquisition circuit is designed to add the acquisition signals from the first subgroup of acquisition combs and the second subgroup of acquisition combs to generate a summed measurement signal, and The processing circuit is designed to determine at least one of the phases or amplitudes of the desired rotary motion mode based on the summed measurement signal. 33. Scanning system according to embodiment 26, wherein: the multitude of recording combs has a first subgroup of recording combs and a second subgroup of recording combs, the detection circuit is designed to subtract at least one detection signal provided by the second subset of detection combs from at least one detection signal provided by the first subset of detection combs in order to generate a differential measurement signal, and The processing circuit is designed to identify the parasitic motion mode, determine an amplitude of the parasitic motion mode, and determine a phase of the parasitic motion mode relative to the at least one drive signal based on the differential measurement signal. 34. Scanning system according to embodiment 33, further comprising: a system controller designed to attenuate the identified parasitic motion mode by applying at least one attenuation signal, wherein the system controller sets an amplitude and a phase of the at least one attenuation signal based on the amplitude and phase of the parasitic motion mode. 35. Scanning system according to embodiment 26, further comprising: a system controller designed to attenuate the identified parasitic motion mode by superimposing a damping voltage onto the at least one drive signal applied to a pair of stator drive comb electrodes in order to slow down the identified parasitic motion mode. 36. Scanning system, comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate around an axis with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure around the axis according to the desired rotary motion mode based on the at least one drive signal, each comb drive comprising a rotor comb electrode and a stator comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a driver designed to generate at least one drive signal; a system controller designed to shift a drive frequency of the at least one drive signal in order to induce parasitic mode coupling between the desired rotary motion mode and a parasitic motion mode of the MEMS scanning structure; a detection circuit that is selectively coupled to at least one subset of the plurality of comb drives in order to receive detection signals from them, each detection signal being representative of the capacity of a corresponding comb drive; and a processing circuit designed to determine a frequency range of the drive frequency at which parasitic coupling occurs, where the system controller controls at least one drive signal to avoid parasitic mode. 37. Sampling system according to embodiment 36, wherein the system controller controls at least one of the drive frequency, a peak input voltage, a duty cycle, or a waveform of the at least one drive signal, so that the parasitic mode is avoided. 38. Scanning system, comprising: a MEMS (microelectromechanical system) scanning structure designed to rotate around an axis with a desired rotary motion mode based on at least one drive signal; a plurality of comb drives designed to drive the MEMS scanning structure around the axis according to the desired rotary motion mode based on the at least one drive signal, each comb drive comprising a rotor drive comb electrode and a stator drive comb electrode; a driver designed to generate at least one drive signal; a plurality of sensing combs, each sensing comb comprising a rotor sensing comb electrode and a stator sensing comb electrode forming a capacitive element having a capacitance that depends on the deflection angle of the MEMS scanning structure; a system controller designed to shift a drive frequency of the at least one drive signal in order to induce parasitic mode coupling between the desired rotary motion mode and a parasitic motion mode of the MEMS scanning structure; a detection circuit that is selectively coupled to at least one subset of the plurality of detection combs in order to receive detection signals from them, each detection signal being representative of the capacity of a corresponding detection comb; and a processing circuit designed to determine a frequency range of the drive frequency at which parasitic mode coupling occurs, where the system controller controls at least one drive signal to avoid parasitic mode. 39. Sampling system according to embodiment 38, wherein the system controller controls at least one of the drive frequency, a peak input voltage, a duty cycle, or a waveform of the at least one drive signal, so that the parasitic mode is avoided.

[0191] Although the embodiments described herein relate to a MEMS device with a mirror, it is understood that other implementations may incorporate optical devices other than MEMS mirror devices, including other oscillating structures, including those not associated with LIDAR.

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