Mode coupling detection and damping method for electrostatic MEMS mirrors and use thereof

Abstract

Various embodiments of the present disclosure relate to mode coupling detection and damping methods and uses for electrostatic MEMS mirrors. A scanning system includes: a microelectromechanical system (MEMS) scanning structure configured with a desired rotational motion mode based on a drive signal; a plurality of comb drives configured to drive the MEMS scanning structure according to the desired rotational motion mode based on the drive signal, each comb drive including a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element depending on the deflection angle of the MEMS scanning structure; a driver configured to generate at least one drive signal; a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sensing signals from the subset, wherein each sensing signal represents the capacitance of the corresponding comb drive; and a processing circuit configured to determine a scanning direction of the MEMS scanning structure in the desired rotational motion mode based on the sensing signals.

Description

Technical Field

[0001] Various embodiments of the present disclosure relate to mode coupling detection and damping methods and uses for electrostatic MEMS mirrors. Background Art

[0002] Light Detection and Ranging (LIDAR) is a remote sensing method that uses light in the form of pulsed lasers to measure the distance to one or more objects in a field of view (at a variable distance). In particular, microelectromechanical system (MEMS) mirrors are used to scan the light within the field of view. A photodetector array receives reflections from the objects illuminated by the light, and the time required for the reflections to reach the individual sensors in the photodetector array is determined. This is also known as measuring time of flight (ToF). LIDAR systems form depth measurements and perform distance measurements by mapping the distance to the object based on a time of flight calculation. Thus, the time of flight calculation can create a distance and depth map that can be used to generate an image.

[0003] To improve the scanning performance of MEMS mirrors by achieving high scanning frequencies, the goal is to design the MEMS mirrors to be lightweight. By selecting a thinner mirror plate thickness, the mirror's moment of inertia can be reduced. However, for a fixed frequency or trajectory (equal to a set frequency), a lighter mirror plate with a smaller thickness results in increased dynamic deformation at the mirror. This deformation can distort the transmitted and / or received light beams. Therefore, the mirror plate is supported by a stiffening structure that helps suppress dynamic deformation. However, the inclusion of a stiffening structure can result in coupling of the desired rotational mode Rx about the mirror's scanning axis to the unwanted in-plane translational mode Ty. The operating point at which Ty resonance occurs varies from device to device and is therefore difficult to predict or avoid through design. Another unwanted parasitic mode, the yaw mode Rz, also depends on the ambient temperature. For example, because Young's modulus is generally temperature-dependent, parasitic modes such as the yaw mode Rz can shift in resonant frequency. Furthermore, such parasitic modes can excite higher-order harmonic components of the actuation signal or the primary oscillatory motion, which coincide with other rigid-body modes. The detection and avoidance of such operating points, which exhibit strong coupling to unwanted parasitic modes, is crucial to ensure the correct operation of the MEMS mirror. In order to ensure high position accuracy and corresponding image resolution while emitting the laser pulses, an accurate position estimation of the mirror is required.

[0004] Therefore, an improved control structure for detecting, measuring, and / or canceling parasitic modes may be desirable. Summary of the Invention

[0005] One or more embodiments provide a scanning system, the scanning system comprising:

[0006] a microelectromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0007] a plurality of comb drives configured to drive the MEMS scanning structure about an axis according to a desired rotational motion pattern based on at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0008] a driver configured to generate at least one driving signal;

[0009] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0010] The processing circuit is configured to determine a scanning direction of the MEMS scanning structure in a desired rotational motion pattern based on the sensing signal.

[0011] One or more embodiments provide a scanning system, the scanning system comprising:

[0012] a microelectromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0013] a plurality of comb drives configured to drive the MEMS scanning structure about an axis according to a desired rotational motion pattern based on at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0014] a driver configured to generate at least one driving signal;

[0015] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0016] The processing circuit is configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensed signal.

[0017] One or more embodiments provide a scanning system, the scanning system comprising:

[0018] a microelectromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0019] a plurality of comb drives configured to drive the MEMS scanning structure about an axis according to a desired rotational motion pattern based on at least one drive signal, wherein each comb drive includes a rotor-driven comb electrode and a stator-driven comb electrode;

[0020] a driver configured to generate at least one driving signal;

[0021] a plurality of sensing combs, wherein each sensing comb comprises a rotor sensing comb electrode and a stator sensing comb electrode, the rotor sensing comb electrode and the stator sensing comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0022] a sensing circuit selectively coupled to at least a subset of the plurality of sensing combs to receive sensing signals from the subset, wherein each sensing signal represents a capacitance of a corresponding sensing comb; and

[0023] The processing circuit is configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensed signal.

[0024] One or more embodiments provide a scanning system, the scanning system comprising:

[0025] a microelectromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0026] a plurality of comb drives configured to drive the MEMS scanning structure about an axis according to a desired rotational motion pattern based on at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0027] a driver configured to generate at least one driving signal;

[0028] a system controller configured to shift a drive frequency of at least one drive signal to induce parasitic mode coupling between a desired rotational motion mode and a parasitic motion mode of the MEMS scanning structure;

[0029] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0030] processing circuitry configured to determine a frequency range of the drive frequency in which parasitic mode coupling occurs,

[0031] The system controller controls at least one driving signal to avoid parasitic modes.

[0032] One or more embodiments provide a scanning system, the scanning system comprising:

[0033] a microelectromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0034] a plurality of comb drives configured to drive the MEMS scanning structure about an axis according to a desired rotational motion pattern based on at least one drive signal, wherein each comb drive includes a rotor-driven comb electrode and a stator-driven comb electrode;

[0035] a driver configured to generate at least one driving signal;

[0036] a plurality of sensing combs, wherein each sensing comb comprises a rotor sensing comb electrode and a stator sensing comb electrode, the rotor sensing comb electrode and the stator sensing comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0037] a system controller configured to shift a drive frequency of at least one drive signal to induce parasitic mode coupling between a desired rotational motion mode and a parasitic motion mode of the MEMS scanning structure;

[0038] a sensing circuit selectively coupled to at least a subset of the plurality of sensing combs to receive sensing signals from the subset, wherein each sensing signal represents a capacitance of a corresponding sensing comb; and

[0039] processing circuitry configured to determine a frequency range of the drive frequency in which parasitic mode coupling occurs,

[0040] The system controller controls at least one driving signal to avoid parasitic modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Embodiments are described herein with reference to the accompanying drawings.

[0042] Figure 1A is a schematic diagram of a LIDAR scanning system according to one or more embodiments;

[0043] Figure 1B shows a schematic top view of an example of a mirror apparatus according to one or more embodiments;

[0044] Figure 1C shows a method according to one or more embodiments Figure 1B A schematic bottom view of an example of a mirror apparatus is shown;

[0045] Figure 1D illustrates a cross-sectional view of a MEMS mirror and actuator electrodes according to one or more embodiments;

[0046] Figure 2 is a schematic block diagram of a LIDAR scanning system according to one or more embodiments;

[0047] Figure 3 illustrates a signal diagram of various signals generated by a MEMS actuator based on a mirror angle θ and / or position according to one or more embodiments;

[0048] 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;

[0049] Figure 4B is a schematic diagram of a translation mode Ty measurement and mode damping system according to one or more embodiments;

[0050] Figure 4C is a schematic diagram of a parasitic mode measurement and mode damping system according to one or more embodiments;

[0051] Figure 4D illustrates a top view of a MEMS mirror compensated with a damping voltage in response to detecting a translational motion Ty according to one or more embodiments;

[0052] Figure 4E shows a timing diagram for implementing a first damping method (Method 1) for utilizing Ty damping parasitic modes according to one or more embodiments;

[0053] Figure 4F shows a timing diagram for implementing a second damping method (Method 2) for damping parasitic modes using Tz according to one or more embodiments;

[0054] Figure 5A illustrates a top view of a MEMS mirror arranged in a nominal centered position (left) and a yaw offset position (right) according to one or more embodiments;

[0055] Figure 5B is a schematic diagram of a yaw mode Rz measurement and compensation system according to one or more embodiments;

[0056] Figure 5C illustrates a top view of a MEMS mirror compensated with a damping voltage in response to detecting a yaw motion Rz according to one or more embodiments;

[0057] Figure 6A and Figure 6B illustrates a cross-sectional view of a MEMS mirror and actuator electrodes according to one or more embodiments;

[0058] Figure 6Cis a schematic diagram of a Tz mode measurement and compensation system according to one or more embodiments;

[0059] Figure 6D illustrates a cross-sectional view of a MEMS mirror compensated with a damping voltage in response to detecting Tz motion according to one or more embodiments;

[0060] Figure 6E depicts 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;

[0061] Figure 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;

[0062] Figure 7B is a schematic diagram of a Ty mode measurement and compensation system for a QS MEMS mirror according to one or more embodiments;

[0063] Figure 7C illustrates a top view of a QS MEMS mirror compensated with a damping voltage in response to detecting a translational motion Ty according to one or more embodiments;

[0064] Figure 7D illustrates a cross-sectional view of a QS MEMS mirror compensated with a damping voltage in response to detecting a translational motion Ty according to one or more embodiments;

[0065] Figure 7E illustrates a top view of a QS MEMS mirror compensated using an alternative approach to detecting translational motion Ty using a dedicated sensing comb in accordance with one or more embodiments; and

[0066] Figure 8 A flow chart illustrating a parasitic mode coupling avoidance method according to one or more embodiments is shown. DETAILED DESCRIPTION

[0067] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. It should be noted that these embodiments are for illustrative purposes only and should not be construed as limiting. For example, although an embodiment may be described as including a plurality of features or elements, this should not be construed as indicating that all of these features or elements are necessary for implementing the embodiment. On the contrary, in other embodiments, some features or elements may be omitted or may be replaced with alternative features or elements. Furthermore, in addition to the features or elements explicitly shown and described, other features or elements may also be provided, such as conventional components of a sensor device.

[0068] Unless otherwise specifically noted, features from different embodiments may be combined to form additional embodiments. Variations or modifications described with respect to one of the embodiments 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 confusing the embodiments.

[0069] In addition, equivalent or similar elements or elements having equivalent or similar functions are denoted by equivalent or similar reference numerals in the following description. Since identical or functionally equivalent elements are given the same reference numerals in the figures, repeated descriptions of elements having the same reference numerals may be omitted. Therefore, the descriptions provided for elements having the same or similar reference numerals are interchangeable.

[0070] Unless otherwise specified, the connections or couplings between elements shown in the drawings or described herein may be based on wired connections or wireless connections. In addition, such connections or couplings may be direct connections or couplings without additional intermediate elements, or indirect connections or couplings with one or more additional intermediate elements, as long as the general purpose of the connection or coupling (for example, transmitting a certain signal or transmitting a certain information) is essentially maintained.

[0071] The term "substantially" may be used herein to illustrate smaller manufacturing tolerances (eg, within 5%) that are considered acceptable in the industry without departing from aspects of the embodiments described herein.

[0072] Directional terms such as "top," "bottom," "left," "right," "above," "below," "front," "back," "rear," "front," "trailing," "above," "below," etc., may be used with reference to the orientation of the figures and / or elements being described. Because embodiments can be positioned in a variety of different orientations, the directional terms are used for illustrative purposes and are in no way limiting. In some cases, directional terms can be interchanged with equivalent directional terms based on the orientation of the embodiment, as long as the general directional relationship between the elements and their general purpose is maintained.

[0073] In the present disclosure, expressions including ordinal numbers such as "first" and "second" can modify various elements. However, such elements are not limited by the above expressions. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used to distinguish one element from other elements. For example, a first box and a second box represent different boxes, although they are both boxes. For another example, without departing from the scope of the present disclosure, a first element can be referred to as a second element, and similarly, a second element can also be referred to as a first element.

[0074] Embodiments relate to optical sensors and optical sensor systems, and to obtaining information about optical sensors and optical sensor systems. A sensor may refer to a component that converts a physical quantity to be measured into an electrical signal (e.g., a current signal or a voltage signal). The physical quantity may include, for example, but is not limited to, electromagnetic radiation such as visible light, infrared (IR) radiation, or other types of illumination signals, current, or voltage. For example, an image sensor may be a silicon chip within a camera that converts photons of light from a lens into a voltage. The larger the active area of ​​the sensor, the more light that can be collected to create an image.

[0075] As used herein, a sensor device may refer to a device that includes a sensor and additional components (e.g., bias circuitry, an analog-to-digital converter, or a filter). The sensor device may be integrated on a single chip, but in other embodiments, the sensor device may be implemented using multiple chips or components external to the chip.

[0076] In a light detection and ranging (LIDAR) system, a light source transmits a light pulse into the field of view, and the light is reflected from one or more objects by backscattering. Specifically, LIDAR is a direct time-of-flight (ToF) system in which a light pulse (e.g., a laser beam of infrared light) is transmitted into the field of view, and an array of pixels detects and measures the reflected light beam. For example, an array of photodetectors receives reflections from objects illuminated by the light.

[0077] The difference in the return time of each light pulse across multiple pixels of the pixel array can then be used to create a digital 3D representation of the environment or generate other sensor data. For example, a 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 (corresponding to a start signal) to the time the reflected light pulse is received at a receiver (i.e., at the pixel array) (corresponding to a stop signal). The "time of flight" of the light pulse is then converted to distance.

[0078] In another example, an analog-to-digital converter (ADC) can be electrically coupled to the pixel array (e.g., indirectly coupled with an intervening intermediate element) for pulse detection and ToF measurement. For example, the ADC can be used to estimate the time interval between the start / stop signals using an appropriate algorithm. For example, the ADC can be used to detect analog electrical signals from one or more photodiodes to estimate the time interval between the start signal (i.e., corresponding to the timing of the emitted light pulse) and the stop signal (i.e., corresponding to the timing of the analog electrical signal being received at the ADC) using an appropriate algorithm.

[0079] Scans such as oscillating horizontal scans (e.g., from the left side of the field of view to the right side and vice versa) or oscillating vertical scans (e.g., from the bottom to the top of the field of view and vice versa) can illuminate the scene in a continuous scanning manner. Each shot of the laser beam by the light source produces a scan line in the "field of view". By emitting continuous light pulses in different scan directions, an area called the field of view can be scanned, and objects within this area can be detected and imaged. The field of view thus represents a scan plane with a center of projection. Raster scanning can also be used.

[0080] Figure 1A FIG1 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 that includes a transmitter including an illumination unit 10, a transmitter optical device 11, and a one-dimensional (1D) micro-electromechanical system (MEMS) mirror 12, and a receiver including a second optical component 14 and a photodetector array 15.

[0081] The irradiation unit 10 includes a plurality of light sources (e.g., laser diodes or light emitting diodes) that are linearly arranged in a single strip and configured to transmit light for scanning an object. The light emitted by the light source is typically infrared light, but light of other wavelengths may also be used. Figure 1A As can be seen in the embodiment of FIG, the shape of the light emitted by the light source expands in a direction perpendicular to the transmission direction to form a beam having an elliptical shape perpendicular to the transmission direction. The illumination light emitted from the light source is directed to the emitter optical device 11, which is configured to focus each laser onto the one-dimensional MEMS mirror 12. The emitter optical device 11 can be, for example, a lens or a prism.

[0082] When reflected by the MEMS mirror 12, the light from the light source is vertically aligned to form a one-dimensional vertical infrared light scan line SL or a vertical infrared light strip for each emitted laser light. Each light source of the illumination unit 10 contributes to a different vertical region of the vertical scan line SL. Therefore, the light sources can be activated and deactivated simultaneously to obtain a light pulse having multiple segments, where each segment corresponds to a respective light source. However, each vertical region or segment of the vertical scan line SL can also be individually activated or deactivated by turning on or off the corresponding light source in the light sources of the illumination unit 10. Therefore, part or all of the vertical scan line SL of light can be output from the system 100 into the field of view.

[0083] Thus, the transmitter of the system 100 is an optical arrangement configured to generate a laser beam based on laser pulses, the laser beam having a rectangular shape extending in a direction perpendicular to the transmission direction of the laser beam.

[0084] In addition, although three laser sources are shown, it should be understood that the number of laser sources is not limited thereto. For example, the vertical scan line SL can be generated by a single laser source, two laser sources, or more than three laser sources.

[0085] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) formed in a semiconductor substrate. The MEMS mirror 12 according to this embodiment is suspended by a mechanical spring (e.g., a leaf spring, sometimes referred to as a cantilever beam) or a flexure and is configured to rotate about a single axis. It can be said that it has only one desired degree of freedom of motion (i.e., a desired rotational mode about a single axis). Although other degrees of freedom may exist, such as motion associated with other rigid body degrees of freedom, these modes are undesirable and are referred to as unwanted parasitic modes. One object of the disclosed embodiments is to suppress parasitic modes associated with these other unwanted degrees of freedom.

[0086] Parasitic / unwanted oscillations are described as the excitation of at least one rigid body mode of the MEMS mirror 12 that is different from the desired operating mode (i.e., the desired rotational mode about a single axis). Parasitic / unwanted oscillations may occur due to direct excitation of the parasitic mode via an actuator (e.g., an electrostatic comb drive, an electromagnetic drive, etc.) or by inducing higher harmonic motion of the primary mode through nonlinear oscillations, or due to indirect excitation of the parasitic mode via a mode coupling mechanism.

[0087] Direct excitation of parasitic modes via actuators can be caused by the high-harmonic content of the periodic drive signal satisfying the parasitic mode's parametric resonance conditions in resonant mirrors, or in quasi-static mirrors, by switching the drive voltage to change the scan angle, which can excite ringing in parasitic modes because the comb drive not only induces the desired rotation but also transmits other forces, such as the y-force. Therefore, switching the angle of a quasi-state MEMS mirror will result in transients in all modes, both desired and undesired.

[0088] The indirect excitation of parasitic modes via the mode coupling mechanism may be caused by the Euler force coupling the desired Rx mode to the parasitic mode Ty. The Euler force may be caused by the offset of the center of mass and the rotation axis 13. The indirect excitation of parasitic modes via the mode coupling mechanism may be caused by the centrifugal force coupling the desired Rx mode to the parasitic mode Tz. The centrifugal force may be caused by the offset of the center of mass and the rotation axis 13. The indirect excitation of parasitic modes via the mode coupling mechanism may be caused by the coupling of all rotation modes Rx, Ry, and Rz through the Euler equation. The nonlinearity of the oscillation (for example, through geometric hardening) may contain specific frequency components of other parasitic modes, causing excitation. It may also be so-called self-parametric excitation and / or three-wave hybrid coupling, which are both the result of geometric nonlinearity caused by large deflections.

[0089] In order to make a MEMS scanning mirror robust to vibration, the mirror should have low inertia, that is, a lightweight mirror body, but be stiff enough to maintain acceptable dynamic deformation. In addition, the mirror should have a high-stiffness suspension 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 expected operating frequency.

[0090] In order to achieve a lightweight and rigid mirror body, the mirror body may include a relatively thin reflector and a thicker reinforcement structure for the reflector. The mirror body may be rotatably arranged in the mirror frame around a rotation axis (i.e., a scanning axis) extending in a plane defined by the mirror frame (e.g., in the xy plane). In the following examples, it will be assumed that the rotation axis extends parallel to the x dimension of the xy plane. The rotation axis may extend to first and second ends of the mirror body that are opposite to each other. The z-axis position of the rotation axis is mainly defined by the z-axis extension of the spring and the flexure. The reflector may have a reflecting plane on a first main surface, and a reinforcement structure may be provided on a second main surface opposite to the first main surface, the reinforcement structure typically having a greater thickness extending in the z direction than the flexure and the spring. Therefore, the reinforcement structure is displaced from both the first main surface and the rotation axis of the mirror body in the z dimension. For this reason, the center of mass of the entire rotating body is also typically displaced from the rotation axis in the z direction.

[0091] In order to achieve a high stiffness suspension, a support beam extending along the rotation axis and an additional cantilever beam or leaf spring assembly can be used to support the mirror body in the mirror frame, such as Figure 1B Generally, as defined herein, a leaf spring assembly may be referred to as a cantilever beam assembly, and vice versa. Similarly, leaf spring and cantilever beam may be used interchangeably.

[0092] The cantilever beam assembly may have a longitudinal orientation and extend within a plane defined by the frame. A support beam may be connected between the mirror body and the frame at two opposing ends of the mirror body along the rotational axis. The cantilever beam assembly may include a cantilever beam coupled to the mirror frame via a relief structure at a first end and secured to the mirror body at a second end. The cantilever beam may have a thickness perpendicular to the plane of the frame that is less than its width in the plane of the frame.

[0093] The low inertia of the mirror and the high suspension stiffness result in a high resonant frequency and good dynamic performance. These properties also enable very fast devices operating at the resonant frequency around the main rotation axis. In normal operation, that is, at resonance, the acceleration at the mirror tip can typically reach 10,000G.

[0094] The MEMS mirror 12 can be assembled in Figure 2The chip package 27 shown is used to protect the mirror. For example, the MEMS mirror 12 can be tightly sealed in the chip package at low pressure (ie, at a pressure below atmospheric pressure). The low pressure can provide a low damping environment in which the MEMS mirror 12 operates.

[0095] Conceivable packages may include or vary from one or more of the following: different substrates (e.g., metal (lead frame), ceramic, organic (similar to printed circuit board (PCB) material)), and different optical covers or lids (e.g., optical materials such as glass, silicon, sapphire, etc.). In addition, the optical cover or lid may be a cavity-forming cap, integrated into a frame (e.g., a metal frame), or assembled onto a pre-formed cavity or ceramic cavity.

[0096] One or more elements may be bonded together (e.g., to bond a cap or lid to a substrate) using one or more methods (e.g., adhesive bonding, gluing, soldering, welding, etc.) or one or more different materials (e.g., silicone, glass solder, AuSn, etc.). It should be understood that the bonding methods may be interchangeable in the various embodiments disclosed herein.

[0097] Alternatively, a wafer-level approach can be used whereby the cavity-shaped cover can be mounted directly onto the MEMS die (or even mounted at the wafer level before singulation). Here, if the cover attachment leaves the electrical pads exposed, the submounted die / cover can be further processed into a package using a molding or casting process.

[0098] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) integrated on a semiconductor chip (not shown). The MEMS mirror 12 according to this embodiment is configured to rotate about a single scanning axis and can be said to have only one scanning degree of freedom because other degrees of freedom (e.g., motion associated with other rigid body degrees of freedom) are significantly suppressed compared to the aforementioned rotation about a single axis. This is reflected in significantly higher characteristic frequencies of vibrations associated with other degrees of freedom compared to the aforementioned rotational motion about a single axis. Unlike 2D-MEMS mirrors (2D MEMS scanners), in 1D MEMS mirrors, the single scanning axis is fixed to a non-rotating substrate and thus maintains its spatial orientation during the oscillation of the MEMS mirror. Therefore, compared to 2D MEMS mirror solutions, 1D oscillating MEMS mirrors are designed to be more resistant to vibration and shock. Due to this single scanning rotation axis, the MEMS mirror 12 is referred to as a 1D MEMS mirror or a 1D MEMS scanner. Although the embodiments described herein use 1D oscillating MEMS mirrors, the methods described herein can also be extended to 2D MEMS mirrors. In this case, the two axes of a single 2D MEMS mirror are controlled by different controllers (in the case of a resonant MEMS with a phase-locked loop (PLL)), such that a first scanning direction of the 2D MEMS mirror according to the first axis is synchronized according to any synchronization technique described herein, and a second scanning direction of the 2D MEMS mirror according to the second axis is synchronized according to any synchronization technique described herein. Different controllers (e.g., PLLs) can also be provided in separate MEMS actuators, or different controllers (e.g., PLLs) can be integrated into a single MEMS actuator for the two axes of the 2D MEMS mirror.

[0099] The MEMS mirror 12 itself can be a static tiltable mover or oscillator (quasi-static MEMS mirror or resonator) that moves or oscillates "side to side" about a single scan axis 13 to follow a static position, trajectory, or resonant oscillation. For example, the MEMS mirror 12 can be a resonant mirror or a quasi-static (QS) mirror. The MEMS mirror 12 is configured to move or oscillate "side to side" about a single scan axis 13 so that light reflected from the MEMS mirror 12 (i.e., a vertical scan line of light) moves in a horizontal scan direction.

[0100] As a resonant mirror, MEMS mirror 12 can be a nonlinear resonator, characterized by nonlinear characteristics due to the increased stiffness of the suspension. In particular, because the torsional stiffness provided by leaf spring assembly 30 about scan axis 13 is not constant but increases with increasing angle, MEMS mirror 12 can exhibit nonlinear behavior. The result of this so-called geometric stiffening is that the oscillation frequency of the mirror increases with increasing oscillation amplitude (i.e., deflection angle amplitude θ). Therefore, the stiffening of the suspension causes MEMS mirror 12 to exhibit nonlinear characteristics.

[0101] Note that the deflection angle θ of the MEMS mirror 12 around the scanning axis 13 can be referred to as the tilt angle, rotation angle, scanning angle, or mirror angle θ. mirror or θ m etc., and these terms are used interchangeably throughout this disclosure.

[0102] As a QS MEMS mirror, the MEMS mirror 12 can be statically tilted, follow a trajectory (e.g., a stepped, triangular, and sawtooth trajectory), or resonate at its resonant frequency (i.e., its characteristic frequency). QS MEMS typically have weak to no nonlinear frequency-amplitude dependence because the torsional stiffness is more linear.

[0103] A scanning period or oscillation period is defined, for example, by one complete oscillation from a first edge of the field of view (eg, left) to a second edge of the field of view (eg, right) and then back to the first edge again. The mirror period of the MEMS mirror 12 corresponds to the scanning period.

[0104] Thus, by changing the angle θ of the MEMS mirror 12 on its scan axis 13, the field of view is scanned in the horizontal direction with a vertical light bar. For example, the MEMS mirror 12 can be configured to oscillate between + / - 15 degrees at a resonant frequency of 2 kHz to guide light within + / - 30 degrees to constitute the scanning range of the field of view. Thus, the field of view can be scanned line by line by rotating the MEMS mirror 12 around its axis through its degrees of motion. Such a sequence of degrees of motion (e.g., from -15 degrees to +15 degrees) is called a single scan or scan cycle. The processing unit can use multiple scans to generate distance and depth maps and 3D images.

[0105] While the transmission mirror is described in the context of a MEMS mirror, it should be understood that other 1D mirrors may also be used. Furthermore, the resonant frequency or degree of rotation is not limited to 2 kHz and + / - 15 degrees, respectively, and both the resonant frequency and the field of view may be increased or decreased depending on the application. Thus, the one-dimensional scanning mirror is configured to oscillate about a single scan axis and direct laser beams in different directions into the field of view. Thus, the transmission technique includes transmitting a light beam from the transmission mirror oscillating about the single scan axis into the field of view, such that the light beam is projected into the field of view as a vertical scan line SL, and the light beam moves horizontally across the field of view as the transmission mirror oscillates about the single scan axis.

[0106] Upon impacting one or more objects, the transmitted vertical light strips are reflected by backscattering as reflected vertical lines toward the LIDAR scanning system 100, where the reflected light is received by a second optical component 14 (e.g., a lens or prism). The second optical component 14 directs the reflected light onto a photodetector array 15, which receives the reflected light as receive lines RL and is configured to generate electrical measurement signals. The 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 calculation and processing).

[0107] The receiving line is shown as a vertical optical column extending along one of the pixel columns in the longitudinal direction of the pixel column. Figure 1A 15. As shown in FIG. 15 , the vertical scanning line SL corresponds to three regions. As 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. As the receiving direction of the reflected light beam RL changes, the reflected light beam RL moves from a first edge of the photodetector array 15 to a second edge of the photodetector array 15. The receiving direction of the reflected light beam RL corresponds to the transmission direction of the scanning line SL.

[0108] The photodetector array 15 can be any of a variety of photodetector types; including avalanche photodiodes (APDs), silicon photomultiplier (SiPM) phototubes, and / or other photodiode devices. Imaging sensors such as charge coupled devices (CCDs) can be 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 the light pulses emitted by the illumination unit 10. Alternatively, a single photodetector cell / pixel can be used instead of an array. For example, in the case of a 2x1D scanning emitter in a coaxial LIDAR architecture, a single photodetector cell / pixel can be used.

[0109] The photodetector array 15 receives the reflected light pulses as receive lines RL and generates an electrical signal in response thereto. Since the transit time of each light pulse from the illumination unit 10 is known, and since light travels at a known speed, the distance of an object from the photodetector array 15 can be determined using the time-of-flight calculation of the electrical signal. This distance information can be plotted in a depth map.

[0110] In one example, for each distance sample, the microcontroller triggers a laser pulse from each light source of the illumination unit 10 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 field, and is captured by the APDs of the APD array 15. The APDs emit short electrical pulses, which are then amplified by an electrical signal amplifier. The comparator IC recognizes 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 serial data of the time difference between the start and stop digital signals to the microcontroller, which filters out any erroneous readings, averages multiple time measurements, and calculates the distance to the target at that particular field position. By continuously emitting light pulses in different directions established by the MEMS mirrors, an area (i.e., field of view) can be scanned, a three-dimensional image generated, and objects within the area detected.

[0111] Alternatively, instead of using the TDC method, an ADC can be used for signal detection and ToF measurement. For example, each ADC can be used to detect analog electrical signals from one or more photodiodes to estimate the time interval between the start signal (i.e., the timing corresponding to the emission of the light pulse) and the stop signal (i.e., the timing corresponding to the receipt of the analog electrical signal at the ADC) using an appropriate algorithm.

[0112] It should be understood that the horizontal scanning system 100 described above can also be used for vertical scanning. In this case, the scanning arrangement is arranged so that the scanning direction is rotated 90°, so that the scan line SL and the receive line RL move in the vertical direction (i.e., from top to bottom or from bottom to top). In this way, the scan line is a horizontal scan line SL, which is projected into the field of view and moves vertically across the field of view as the transmission mirror oscillates about a single scan axis. In addition, as the horizontal scan line SL moves vertically across the field of view, the horizontal column light RL incident on the 2D photodetector array 15 also moves vertically across the 2D photodetector array 15.

[0113] It should also be understood that the 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 in the vehicle and are configured to scan both dimensions (horizontally and vertically) of a common field of view.

[0114] Figure 1B A schematic top view of an example of a mirror device according to one or more embodiments is shown. Figure 1B Now, an example of a reflector device such as a MEMS scanning micro-mirror is explained. The reflector device includes a mirror body 8. The mirror body 8 includes a reflector 12 and a reflector support 16. The reflector device also includes a frame 17. The mirror body 8 is set in the frame 17. The frame 17 defines a plane, that is, Figure 1B The plane defined by the frame 17 may be parallel to a plane defined by the major surfaces of the layer or layers in which the frame 17 is formed.

[0115] The mirror body 8 is rotatable about a scan axis 13, which extends in a plane defined by a frame 17. A support beam 18 (also referred to as a torsion beam) is connected between the mirror body 8 and the frame 17 along the scan axis 13. More specifically, 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, wherein the second end of the mirror body 8 is opposite to the first end in the direction of the scan axis 13. An enlarged view of one of the support beams 18 is shown in FIG. Figure 1B 1. It can be seen in the enlarged portion C of the right-hand side of the mirror that the support beam 18 connects part of the mirror support 16 to part of the frame 17 and allows the mirror body 8 to rotate about the scan axis 13. The support beam 18 can be colinear with the scan axis 13.

[0116] Those skilled in the art will appreciate that the shape of the reflector 12 may be any shape required for a particular application, such as circular, elliptical, square, rectangular, or other desired shape.

[0117] The mirror frame 17 defines a mirror groove 20 in which the mirror body 8 is disposed. The mirror groove 20 is defined by a recessed perimeter 28 of the mirror frame 17. The mirror frame 17 may also be configured to define additional recesses in which other components such as actuators, sensors, and leaf spring assemblies may be disposed.

[0118] The mirror device can include a leaf spring assembly 30. In the example shown, the mirror device includes two pairs of leaf spring assemblies 30, with 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 scan axis 13. However, for QS MEMS mirrors, leaf springs are not used. Instead, torsion bars (or equivalent structures with multiple torsion bars, such as V-shaped or PI-shaped structures) support the MEMS mirror.

[0119] At least one leaf spring assembly 30 includes a leaf spring 32 and a release link 34. The release link 34 may have one or more release springs 35. The leaf spring 32 includes 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 fixed to the mirror support (not shown), and the second end 32b is coupled to the frame 17 via the release link 34. In an example, the first ends 32a of two leaf springs 32 extending from the same portion of the mirror body 8 in different directions can be connected to each other (for example, a leaf spring on the left side of the mirror 12 or a leaf spring on the right side of the mirror 12), and reinforced only near the scan axis 13 by a reinforcement structure (not shown) so that the two leaf springs 32 can apply torque to the mirror body 8.

[0120] In some examples, the shape of mirror 12 can include a recess in the area of ​​scan axis 13, with portions of leaf spring 32 extending into the recess of mirror 12. In some examples, leaf spring 32 and mirror 12 can be formed from the same layer of material and can be connected to each other near scan axis 13.

[0121] In some examples, the leaf spring 32 can be implemented in a single crystal silicon layer having a direction of lower material stiffness, wherein the longitudinal direction of the leaf spring is aligned with the direction of lower material stiffness. <100> The shaft is realized in a silicon layer and the longitudinal direction of the leaf spring is in the same direction as the material with lower stiffness in this case. <100> Direction alignment.

[0122] The torsional stiffness about the scan axis 13 can be set using a leaf spring assembly 30. The pair of support beams 18 support the mirror body 8 vertically (i.e., perpendicular to the major surfaces of the frame 17) at the scan axis 13. However, the effect of the support beams 18 on the torsional stiffness is negligible, so the natural frequency of the mirror body can be substantially determined by the leaf spring assembly 30. The natural frequency can be substantially independent of the support beams 18. The natural frequency defined herein is the undamped frequency of the eigenmode of the mirror body 8 (i.e., the reflector 12) at a relatively small angle about its scan axis 13. The support beams 18 can define the out-of-plane rocking and vertical translation mode stiffnesses and the corresponding eigenfrequencies for the corresponding rigid body modes. The torsional stiffness can be separated from the out-of-plane rocking and vertical translation mode stiffnesses so that the out-of-plane rocking and vertical translation mode frequencies can be set to desired values, such as higher values, without affecting the torsional mode stiffness and the resonant frequency.

[0123] As defined herein, the X-axis is along the scan axis 13, the Y-axis is perpendicular to the X-axis in the mirror plane when the mirror 12 is stationary, and the Z-axis is perpendicular to and out of the mirror plane when the mirror 12 is stationary. The X, Y, and Z axes are axes of a three-dimensional Cartesian coordinate system.

[0124] exist Figure 1B In the example shown, one end of at least one leaf spring 32 is connected to the mirror body 8 at a position close to the scan axis 13. The other end 32b is connected to an associated release link 34 at a position away from the scan axis 13. The leaf spring assembly 30 can provide torsional stiffness to the mirror body 8 about the scan axis 13. The release link 34 can provide a compliant or flexible coupling from the leaf spring 32 to the frame 17. The release link 34 can be rotatable relative to the longitudinal direction of the leaf spring 32 (i.e., in the longitudinal direction). Figure 1B The release link 34 has a relatively low stiffness in the Y direction (in the Y direction in FIG), which allows one end of the leaf spring 32 to move in its longitudinal direction when the mirror body 8 rotates around the scanning axis 13. Figure 1B It has relatively high rigidity in the Z and X directions.

[0125] The resonant frequency of the mirror 12 rotating about the scan axis 13 can be primarily determined by the inertia of the mirror body 8 and the stiffness of the leaf spring assembly 30. The stiffness of the leaf spring assembly 30 can be determined by the bending stiffness of the leaf spring 32 and the torsional and translational stiffness of the release link 34. The bending stiffness of the leaf spring 32 can be determined by the length, width, and particularly the thickness of the leaf spring 32. The combined stiffness of the support beam 18 and the release link 34 in the Y direction can prevent the mirror body 8 from moving perpendicular to the scan axis 13 (in the X direction) during operation. More details about the release link are provided below.

[0126] The support beam 18 is connected between the frame 17 and the mirror body 8 along the scan axis 13 to support the mirror body 8 in the frame 17. In one example, the support beam 18 has a narrow rectangular cross-section perpendicular to the scan axis 13, with the major axis of the rectangle perpendicular to the face of the reflector 12 and the mirror body 8, and the minor axis of the rectangle parallel to the face of the reflector 12. The torsional stiffness corresponding to the rotation of the mirror body 8 about the scan axis 13 can be provided by the leaf spring assembly 30. The support beam 18 can be used only to support the mirror body 8 and its effect on the torsional stiffness can be negligible. The size of the support beam 18 can be designed so that the stiffness against the vertical translation displacement of the mirror body 8 (in the Z direction) and against its in-plane translation perpendicular to the scan axis 13 (i.e., along the Y axis) can be as high as possible.

[0127] The mirror device may also include at least one actuator to provide torque to drive the mirror body 8 around the scan axis 13. In one example, the actuator may be a comb drive comprising a mirror comb attached to the mirror body 8 and interleaved with a frame comb attached to the frame 17. Applying a potential difference between the interleaved mirror combs and the frame combs generates a driving force between the mirror combs and the frame combs, which generates a torque on the mirror body 8 around the scan axis 13. An oscillating potential may be applied to resonantly excite the mirror device close to its natural frequency. In this example, four comb drives 40TL (upper left), 40BL (lower left), 40TR (upper right), and 40BR (lower right) are provided. The left side is arranged on the left side of the scan axis 13, while the right side is arranged on the right side of the scan axis 13. Each comb drive includes a stator comb drive electrode fixed to the frame 17 and a rotor comb drive electrode that is movable as the mirror body 8 rotates around the scan axis 13.

[0128] In other examples, actuation methods may include electromagnetic actuation and piezoelectric actuators. In electromagnetic actuation, the micromirror can be "immersed" in a magnetic field, and alternating current through a conductive path on the mirror body can generate an oscillating torque about the scan axis 13. The piezoelectric actuator can be integrated into the leaf spring or the leaf spring can be made of piezoelectric material to generate an alternating beam bending force and generate an oscillating torque in response to an electrical signal.

[0129] The desired rotation pattern Rx of the MEMS mirror 12 around the scanning axis 13 is Figure 1B . The double-headed arrow corresponding to the rotation mode Rx indicates that the MEMS mirror 12 is configured to oscillate around the scanning axis 13 to perform a scanning operation. Unwanted parasitic modes are also shown. For example, an in-plane translation mode Ty representing the translational motion of the mirror body 8 in the Y direction is shown. In particular, there is a resonant coupling from the desired rotation mode Rx to the translation mode Ty in the Y direction. The coupling of mode Rx to the translation mode Ty is mainly caused by the reinforcement structure. In addition, nonlinear coupling from the desired rotation mode Rx to the unwanted parasitic yaw mode Rz may occur. Therefore, the false yaw mode Rz causes the mirror body 8 to move around the Z axis. In addition, mode Rx can be coupled to the translation mode Tz in the Z direction. This coupling of Rx to Tz is mainly caused by the reinforcement structure. The coupling of Rx to Ty and Tz, respectively, originates from inertial forces, which are caused by rotational imbalance because the center of mass is displaced along the Z axis relative to the rotation axis due to the mass of the reinforcement structure.

[0130] Figure 1C shows a method according to one or more embodiments Figure 1BSchematic bottom view of an example of a mirror device shown. 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. Here, the reinforcement structure 9 supporting the mirror body 8 can be seen.

[0131] Figure 1D FIG2 illustrates a cross-sectional view of a MEMS mirror and actuator 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 page. The MEMS mirror 12 includes mirror comb electrodes 41 and 42, a drive voltage v drive is applied to the mirror comb electrodes 41 and 42. As described above, the MEMS mirror 12 is supported by the mirror frame 17 (not shown). The mirror frame 17 includes static comb electrodes 43 and 44. The mirror comb electrodes 41 and 42 coupled to opposite ends of the mirror body 8 move with the oscillation of the MEMS mirror 12. The driving voltage v drive A driving force is induced between the crossed mirror comb electrodes 41, 42 and the static comb electrodes 43, 44. In particular, the MEMS mirror 12 is driven in parametric resonance by a square wave voltage with a 50% (or different) duty cycle.

[0132] The first driving capacitor C A (Also known as C A (θ)) is formed by the overlap of the electrodes 41 and 44. The overlap of the two electrodes 41 and 44 increases with the rotation angle θ of the MEMS mirror 12 around the rotation axis 13. mirror As the overlap increases, the first drive capacitor C A Conversely, as the overlap decreases, the first drive capacitor C A The capacitance also decreases.

[0133] Similarly, the second drive capacitor C B (Also known as C B (θ)) is formed by the overlap of the electrodes 42 and 43. The overlap of the two electrodes 42 and 43 increases with the rotation angle θ of the MEMS mirror 12 around the rotation axis 13. mirror As the overlap increases, the second drive capacitor C B Conversely, as the overlap decreases, the capacitance of the second drive capacitor C B The capacitance also decreases.

[0134] Therefore, the first driving capacitor C A is a function of the rotation angle θ, and stores the rotation angle θ based on the MEMS mirror 12. mirrorThe first charge of the second drive capacitor C leads to a first displacement current, which also depends on the rotation angle θ of the MEMS mirror 12. B Also the rotation angle θ mirror and 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 .

[0135] For QS MEMS, actuation is unipolar, meaning that for positive deflection angles, one capacitor increases (immersed comb) while the other capacitance is approximately zero (non-immersed comb). The reverse is true for negative deflections. For resonant MEMS, the two drive capacitors each have symmetrical capacitance characteristics depending on the deflection direction (e.g., tilt direction) of the MEMS mirror 12. However, bipolar actuation can also be used, where the third capacitor is formed with an intermediate electrode (e.g., a resonant electrode).

[0136] More specifically, this means that the comb C is perfectly aligned. A (-θ mirror )=C A (θ mirror ) and C B (-θ mirror )=C B (θ mirror ), that is, both capacitors are even functions with symmetric capacitance dependence, and the value of the capacitor does not change if the angle of the mirror is reversed. Due to the symmetry of the design, C A (θ mirrorr )=C B (θ mirrorr It should also be noted that although two drive capacitors C are shown in the cross-sectional view A and C B , but there are four driving capacitors, such as Figure 1B and 1C Therefore, based on the rotation angle θ mirror Four displacement currents are generated. Due to the symmetry of the capacitance θ→-θ, for ideal and pure Rx rotational motion, the scanning direction (e.g., clockwise or counterclockwise) cannot be detected.

[0137] Figure 1D It further shows the mode coupling between the Rx mode and the Ty mode caused by the displacement L between the center of mass M and the rotation axis (scan axis 13) due to the reinforcement structure 9. According to equation 1, the coupling force is derived from the Euler force:

[0138]

[0139] The mass of the mirror is m, and the rotational acceleration is Therefore, the Ty mode is composed of an inertial force f having the same frequency component as the Rx trajectory θ(t) Y (t) excitation, which depends on the rotational acceleration, which is the second derivative of the trajectory. In addition, the Rx and Ty eigenmodes are not perfectly pure rotational and translational modes, respectively, which means that the non-zero amplitude of the Ty mode also has a small rotational mixture, that is, a rotation about the X axis.

[0140] One or more embodiments use the changes in sense signals (e.g., current signals) of a subset of comb drive electrodes caused by excited parasitic modes to detect the scanning direction (e.g., clockwise or counterclockwise) and the amplitude and phase of the parasitic mode's motion, i.e., Ty, Tz, and Rz. The comb drive electrode subset can include any combination of left / right, top / bottom, front / back electrodes.

[0141] The Euler force caused by the finite displacement L between the center of mass M and the rotation axis 13 results in a small excitation of Ty superimposed on the motion of Rx. This superimposed motion eliminates the symmetry of the displacement currents of θ and -θ, making it possible to detect the sign of the angle, i.e., the scanning direction.

[0142] The comb drive electrode subset can be a subset of the stator or rotor electrodes, or in the case of a 2D MEMS mirror, a subset of the rotor, inner frame and / or outer frame (i.e., the actual stator). For example, different cases are shown where two current signals are subtracted (e.g., the left current signal is subtracted from the right current signal) to obtain the highest efficiency. However, it is also possible to detect the mode by only one side of the current or even by only the current of one comb drive, but with lower efficiency. Furthermore, the sensing does not have to be current-based. It can be any method that provides a sense signal that is related to the capacitance or capacitance change of one or more drive capacitors (e.g., charge sensing, current sensing, or sensing based on frequency modulation).

[0143] After detection, the parasitic modes Ty, Tz, Ry, and Rz can be actively damped. In particular, the system controller 23 can apply a resistive force / torque by appropriately selecting any combination of comb electrodes (combs typically used for actuation / sensing / damping, or even individual combs used only for damping). The appropriate selection of comb electrodes means that the selection will have a force / torque corresponding to the identified parasitic mode and can offset the mirror motion in the identified parasitic mode. Therefore, the selection of comb electrodes to which a reaction force (e.g., a damping voltage) is applied is based on the parasitic modes Ty, Tz, Ry, Rz, etc., which the system controller 23 targets for damping based on its detection by the system controller. The system controller 23 can use a switching network to apply a reaction force to the selected comb electrodes corresponding to the target parasitic mode at a timing effective for damping the target parasitic mode. This parasitic mode detection, identification, and target damping will be described in detail below.

[0144] Figure 2 is a schematic block diagram of a LIDAR scanning system 200 according to one or more embodiments. In particular, Figure 2 Additional features of LIDAR scanning system 200 are shown, including example processing and control system components, such as MEMS actuators, receiver circuitry, and a system controller.

[0145] The LIDAR scanning system 200 includes a transmitter unit 21 responsible for the transmitter path of the system 200 and a receiver unit 22 responsible for the receiver path of the system 200. The system also includes a system controller 23, which is configured to control the components of the transmitter unit 21 and the receiver unit 22, and receives raw data from the receiver unit 22 and processes it (e.g., via digital signal processing) to generate object data (e.g., point cloud data). Therefore, the system controller 23 includes at least one processor and / or processor circuit system for processing data, and control circuit system, such as a microcontroller, configured to generate control signals. The LIDAR scanning system 200 may also include a temperature sensor 26.

[0146] The receiver unit 22 includes a photodetector array 15 and a receiver circuit 24. The receiver circuit 24 may include one or more circuits or subcircuits for receiving and / or processing information. The receiver circuit 24 may receive analog electrical signals from the APD diodes of the photodetector array 15 and transmit the electrical signals as raw analog data or raw digital data to the system controller 23. In order to transmit the raw data as digital data, the receiver circuit 24 may include an ADC and a field programmable gate array (FPGA). The receiver circuit 24 may also receive a trigger control signal from the system controller 23 that triggers activation of one or more APD diodes. The receiver circuit 24 may also receive a gain setting control signal for controlling the gain of one or more APD diodes.

[0147] Emitter unit 21 includes an illumination unit 10, a MEMS mirror 12, and a MEMS actuator 25 configured to drive the MEMS mirror 12. Specifically, MEMS actuator 25 actuates and senses the rotational position of the mirror and provides position information of the mirror (e.g., tilt angle or rotation degrees around the rotation axis) to system controller 23. Based on this position information, the laser source of illumination unit 10 is triggered by system controller 23 and a photodiode (e.g., an APD diode) is activated to sense and thereby measure the reflected light signal. Thus, the higher accuracy of the position sensing of the MEMS mirror results in more accurate and precise control of other components of the LIDAR system.

[0148] The MEMS actuator 25 may also measure and record the mirror frequency and current using capacitance changes in the comb drive rotor and stator of the actuator structure used to drive the MEMS mirror 12. The MEMS mirror 12 also includes the suspension structure discussed above. Accordingly, the MEMS actuator 25 may also include measurement circuitry configured to measure one or more characteristics of the MEMS mirror 12 described herein. The MEMS actuator 25 may also include processing circuitry including at least one processor (e.g., analog signal processing circuitry and / or digital signal processing circuitry) configured to process measurement information from the measurement circuitry to assess the mechanical health of the MEMS mirror 12 and / or the status of the chip package.

[0149] Additionally or alternatively, system controller 23 may receive and process measurement information from the measurement circuitry of MEMS actuator 25. Thus, system controller 23 may also include processing circuitry including at least one processor (e.g., analog signal processing circuitry and / or digital signal processing circuitry) configured to process the measurement information from the measurement circuitry to assess the mechanical health of MEMS mirror 12 and / or the status of the chip package.

[0150] For QS MEMS, the rotational position is continuously measured (and controlled) using sensing circuitry (at the rotor).

[0151] For resonant MEMS: By sensing the rotational position of the MEMS mirror 12 around its rotational axis (scan axis), the MEMS driver 25 can sense the zero-crossing event of the MEMS mirror 12. A zero-crossing event is, for example, when the MEMS mirror 12 has a rotation angle of 0° around its rotational axis (scan axis). Specifically, this is 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 a static position (for example, when the MEMS mirror 12 stops after the driving force is turned off). Since the MEMS mirror 12 oscillates back and forth between two rotational directions (for example, clockwise and counterclockwise), two zero-crossing events occur within a scanning cycle - one when the mirror oscillates in the first rotational direction and one when the mirror oscillates in the second rotational direction. It should also be understood that an angle crossing event at another predefined angle can also be used instead of a zero-crossing event.

[0152] In some embodiments, the event time may correspond to a non-zero-crossing event. For example, the sensed rotation angle may be an angle other than 0°. However, for purposes of explanation, the examples herein will be described in the context of sensing a zero-crossing event.

[0153] The MEMS actuator 25 is configured to detect each zero-crossing event and record the timing of each event. This timing information (i.e., the measured zero-crossing time) can then be transmitted to the system controller 23 as position information. Specifically, the MEMS actuator 25 triggers a change in the output of the position signal (position_L) at each zero-crossing event or angle crossing event.

[0154] Figure 3 The figure illustrates a signal diagram of various signals generated by the MEMS actuator 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 pulse signal during which, as the mirror oscillates in a first rotational direction (e.g., from left to right), a first pulse transition (e.g., a falling edge transition) is triggered at a zero crossing, and as the mirror oscillates in a second rotational direction (e.g., from right to left), a second pulse transition (e.g., a rising edge transition) is triggered at a zero crossing. Furthermore, the signal is "high" when the mirror is pointing in one direction (e.g., to the left) and "low" when the mirror is pointing in a second direction (e.g., to the right). Thus, the position signal not only indicates zero crossing events by triggering pulse transitions, but also indicates absolute phase information by indicating the directional tilt of the mirror. As the interval between zero crossing events increases, the frequency of the position signal decreases. Based on the position signal, the phase and / or frequency of two or more position signals can be compared.

[0155] Alternatively, the MEMS actuator 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. That is, the signal remains low (or high) between zero-crossing pulses. In this case, absolute phase information indicating the direction of movement of the mirror will not exist because a low level (high level) of the position signal (position_L) does not indicate whether the mirror is pointing to the left or right. Based on this position signal, the phase and / or frequency of two or more position signals can be compared.

[0156] The MEMS actuator 25 can send position information to the system controller 23 so that the system controller 23 can use the position 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 information so that the system controller 23 can maintain stable operation of the MEMS mirror 12 via the control signal provided to the MEMS actuator 25 and also maintain synchronization with other MEMS mirrors.

[0157] The MEMS mirror 12 includes an actuator structure for driving the mirror. The actuator structure includes interdigitated electrodes made of crossed mirror combs and frame combs, to which the MEMS actuator 25 applies a drive voltage v drive (i.e., an actuation or drive signal). The drive voltage may be referred to as a high voltage (HV). The frame comb fingers and the mirror comb fingers form electrodes of a capacitor. The drive voltage across the finger-like structure generates a driving force between the cross-mirror comb electrodes and the frame comb electrodes, which generates a torque on the mirror body 8 about the axis of rotation. The drive voltage may be switched on or off, thereby generating an oscillating drive force. The drive waveform of the drive voltage may be any waveform, including a sine wave, a triangular wave, a rectangular wave, etc. The oscillating drive force causes the mirror to oscillate back and forth between two extreme values ​​about its axis of rotation. Depending on the configuration, the actuation may be adjusted or regulated by adjusting the drive voltage off time, the voltage level of the drive voltage, or the duty cycle.

[0158] 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 an oscillating drive force. Therefore, it should be understood that drive / drive voltage and drive / drive current can be used interchangeably herein to refer to an actuation signal or a drive signal, and both can generally be referred to as a drive force.

[0159] As the mirror oscillates, the capacitance or charge between the interdigitated electrodes changes depending on the rotational position of the mirror. The MEMS actuator 25 is configured to measure the capacitance or charge between the interdigitated electrodes via, for example, a four-quadrant comb drive displacement current, and thereby determine the rotational position or angular position of the MEMS mirror 12. More specifically, the displacement current is the time derivative of the corresponding capacitance times the voltage, i.e., the derivative is measured rather than the capacitance or charge. By monitoring the displacement current, the MEMS actuator 25 can detect zero-crossing events and other non-zero angle events and their timing, and can determine the deflection or tilt angle of the MEMS mirror 12 at any given moment. The MEMS actuator 25 can also use the measured displacement current to determine the mirror frequency and record the information in a memory at the MEMS actuator 25 or the system controller 23.

[0160] Sensing of the position of the MEMS mirror 12 is performed based on a detector configured to measure capacitance via displacement current or displacement charge (i.e., integrating current). Capacitance or charge sensing can be performed indirectly by measuring a derived quantity (such as displacement current). For example, as the MEMS mirror moves, the geometry of the finger-like structure changes, causing the geometry of the capacitor to change. As the geometry of the capacitor changes, the capacitance of the capacitor also changes. Therefore, a specific capacitance directly corresponds to a specific deflection position (e.g., tilt angle) of the MEMS mirror. By sensing the capacitance of the finger-like structure, the MEMS driver 25 can monitor and track the oscillations of the mirror and determine a specific position of the MEMS mirror, including zero crossings.

[0161] One way to measure capacitance is to measure the current flowing through the finger-like electrode structure, convert the measured current to a voltage, and then further relate the voltage to the capacitance and / or the rotation angle θ. However, any method of measuring capacitance may be used.

[0162] The sign of the current (i.e., positive or negative capacitance change over time) only indicates whether the MEMS mirror is moving towards the rest position (positive current → capacitor charging) or away from the rest position (negative current → capacitor discharging). If the MEMS mirror is moving towards the rest position (near zero), this can be seen as either a clockwise or counterclockwise swing. For comb drives with symmetric capacitance dependence, the direction of rotation and the sign of the current cannot be distinguished, and C A (-θ mirror )=C A (θ mirror ) and C B (-θ mirror )=C B (θ mirror ).

[0163] Because the mirror is driven at an oscillating frequency (e.g., 2 kHz), when the mirror rotates in a first rotational direction (e.g., from left to right or clockwise), it passes through a zero position (i.e., 0°) at a certain point in time. Similarly, when the mirror rotates in a second rotational direction (e.g., from right to left or counterclockwise), it can be said that the mirror passes through a zero position at a certain point in time. These instances of zero crossings can be referred to as zero crossing events occurring at zero crossing times.

[0164] As described above, one or more embodiments use changes in the sensed signals (e.g., current signals) of a subset of comb drive electrodes caused by an excited parasitic mode to detect the scanning direction (e.g., clockwise or counterclockwise) and the amplitude and phase of the motion of the parasitic mode, i.e., Ty, Tz, and Rz. Here, the difference in capacitance of each comb drive, the difference in displacement current of each of the four quadrant comb drive displacement currents, or the difference in displacement current of a specific combination of quadrants can be used. After detection, any of the parasitic modes Ty, Rz, Ry, and / or Tz can be avoided or actively damped.

[0165] Figure 4A A top view of a MEMS mirror arranged in a nominal center position (left) and a translationally shifted position (right) according to one or more embodiments is shown. On the left, the MEMS mirror 12 (mirror body 8) operates in a pure rotational mode Rx about the scan axis 13, and the torsion bar 18 is not bent. The four comb drives 40TL, 40BL, 40TR, and 40BR are symmetrically located within the frame 17. Conversely, on the right, the MEMS mirror 12 (mirror body 8) moves to the right in the translational Y direction and oscillates back and forth in the Y direction due to mode coupling from the Rx mode to the Ty mode. Here, the torsion bar 18 bends back and forth in the Y direction. The stator electrodes of the comb drives are mechanically coupled to the frame 17, while the rotor electrodes of the comb drives are mechanically coupled to the mirror body 8. The stator comb drive electrodes are divided into a left pair (stators of comb drives 40TL and 40BL) and a right pair (stators of comb drives 40TR and 40BR) to detect Rx-Ty mode coupling.

[0166] Embodiments also include sensing circuitry electrically coupled to the stator comb drive electrodes of each comb drive 40TL, 40BL, 40TR, and 40BR to receive its corresponding displacement current therefrom. The stator comb drive electrodes are electrically coupled to the sensing circuitry to detect modes of interest, such as Ty mode, Rz mode, or Tz mode. It is also possible to isolate the rotor comb drive electrodes and sense those electrodes instead of the stator electrodes. Furthermore, it is not necessary to measure displacement current or use all comb drives for sensing. Any signal related to capacitance or capacitance change can be used.

[0167] Figure 4B Schematic diagram of a translational mode Ty measurement and mode damping system 400A according to one or more embodiments. The translational mode Ty measurement system 400A includes a MEMS actuator 25, a MEMS mirror 12 having four comb drives 40TL, 40BL, 40TR, and 40BR, a sensing circuit 50, and a system controller 23.

[0168] The MEMS driver 25 receives the digital control signal D HVactAnd according to the digital control signal D HVact The MEMS driver 25 may include a digital control signal DHVact, which generates a driving voltage v based on the digital value of the digital control signal DHVact. drive The MEMS actuator 25 may also add or superimpose the value of the damping signal Vdmp onto the value of the digital control signal DHVact to generate a drive voltage with a damping voltage or only a damping voltage (e.g., if the drive voltage is zero), as described below. In this manner, DHVact is a digital input to the DAC, which can generate a voltage in the range of 0V to 200V. The drive voltage Vdrive can then have any waveform.

[0169] The MEMS driver 25 generates a driving voltage v with an appropriate duty cycle drive And the driving voltage v drive As a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitances C of the four comb drives 40TL, 40BL, 40TR, and 40BR are TL 、C BL 、C TR , and C BR Change and displacement current i TL 、i BL 、i TR and, and i BR The sensing circuit 50 is coupled to the stator comb electrodes of the four comb drivers 40TL, 40BL, 40TR, and 40BR and extracts the displacement current i TL 、i BL 、i TR , and i BR .

[0170] To measure the translation mode Ty, the two left displacement currents i TL and i BLis provided to the input of a transimpedance amplifier (TIA) 51 of the sensing circuit 50. Although a TIA is used in this example, it will be appreciated that other sensing elements for capacitive sensing may be used. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation based sensing may be used to generate the sensing signal. The TIA 51 may be coupled to the MEMS mirror 12 and, in particular, to the stator of the assigned comb drive via the switch SW1. The switch SW1 may be controlled by the system controller 23 (via the switch control signal SWCTRL) to perform a pattern measurement when the switch SW1 is in position "m" or to perform a damping operation when the switch SW1 is in position "d", where "m" represents the measurement position of the switch for measuring the corresponding comb drive and "d" represents the damping position of the switch for applying the damping voltage Vdmp,left to the corresponding left comb drive. As the TIA 51 receives the displacement current i TL and i BL As a result, the two left displacement currents i TL and i BL The sum of the two voltages is converted by TIA 51 into the left voltage V L .

[0171] Similarly, the two right displacement currents i TR and i BR is provided to the input of the TIA 52 of the sensing circuit 50. Again, although a TIA is used in this example, it will be appreciated that other sensing elements for capacitive sensing may be used. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation based sensing may be used to generate the sensing signal. The TIA 52 may be coupled to the MEMS mirror 12 and, in particular, to the stator of the assigned comb drive via the switch SW2. The switch SW2 may be controlled by the system controller 23 (via the switch control signal SW CTRL) to perform a pattern measurement when the switch SW2 is in position "m" or to perform a damping operation when the switch SW1 is in position "d", where "m" represents the measurement position of the switch for measuring the corresponding comb drive and "d" represents the damping position of the switch for applying the damping voltage Vdmp,right to the corresponding right comb drive. As the TIA 51 receives the displacement current i TR and i BR As a result, the two right displacement currents i TR and i BR The sum of the values ​​is converted by TIA 52 into the right voltage V R .

[0172] Alternatively, each comb driver electrode can be coupled to a separate TIA, and the individual voltage signals can then be added and / or subtracted, enabling the sensing circuit 50 to detect each pattern simultaneously. In other words, four TIAs can be used, each individually connected to a corresponding driver electrode (i.e., capacitor C ) of the four comb drivers 40TL, 40BL, 40TR, and 40BR. TL 、C BL 、C TR , and C BR ).

[0173] Figure 4C FIG2 is a schematic diagram of a parasitic mode measurement and mode damping system 400B according to one or more embodiments. The parasitic mode measurement system 400B is similar to the system 400A, except that the sensing circuit 50 includes a switching network 55 that switches the driver electrodes (i.e., capacitors C ) of the four comb drivers 40TL, 40BL, 40TR, and 40BR in any combination. TL 、C BL 、C TR , and C BR ) are switchably coupled to TIAs 51 and 52. Switch network 55 may be a network of eight switches—two switches for each driver electrode—that switchably connect their respective driver electrodes to TIAs 51 and 52. Such a switch network allows the input configurations of TIAs 51 and 52 to be fully configurable for receiving displacement currents i in any combination. TL 、i BL 、i TR , and i BR , to allow the sensing circuit 50 to measure individual parasitic modes or to detect each mode simultaneously (for example, if individual TIAs are also provided). A switch control signal SW CTRL representing one or more control signals can control the switches of the switch network 55. A multiplexer network can also be used.

[0174] As an example, two pairs of switches corresponding to two driver electrodes of comb drivers 40TL and 40BR are shown, wherein one switch in each pair is coupled to TIA 51 and the other switch in each pair is coupled to TIA 52. Although not shown, other switch pairs are provided for the remaining comb drivers in a similar manner so that their corresponding displacement currents are switchably provided to TIA 51 or TIA 52.

[0175] Back to Figure 4B , the sensing circuit 50 further includes an adder 53 and a subtractor 54. The adder 53 receives the left voltage V L and the right voltage V R , and add them together to generate the total voltage V I, the total voltage V I Represents all displacement currents i TL 、i BL 、i TR , and i BR Conversely, the subtractor 54 receives the left voltage V L and the right voltage V R , and the voltage from the left side V L Subtract the voltage on the right from V R To generate the current i on the left TL 、i BL With the current i on the right TR 、i BR The difference between the voltage ΔV I Total voltage V I (ie, the total current signal or measurement signal) allows the system controller 23 to use accurate phase and amplitude measurements of the Rx mode for proper MEMS mirror control. However, the total voltage V I does not provide any information about the scanning direction, since the four comb drives are symmetrical. On the other hand, the difference voltage ΔV I (i.e., the differential current signal or differential measurement signal) provides a signal for the Rx mode that depends on the scanning direction. It also provides the amplitude of the Ty mode and the phase of the Ty mode relative to the Rx mode. Therefore, the system controller 23 can be based on the differential voltage ΔV I The system controller 23 can generate a digital control signal D based on the phase, amplitude (θ0) and scanning direction. HVact For example, the voltage difference ΔV I The symbol indicates the scanning direction.

[0176] In implementation, the system controller 23 may use an additional memory to record the scanning direction, even if the differential voltage ΔV at certain operating points I Memory or filters can be used to confirm direction based on weak signals, or to reduce noise in the measurement, for example via averaging.

[0177] Another use of the proposed method is to evaluate the differential voltage ΔV by the system controller 23 I (ie, the differential current signal) to detect the Ty mode amplitude. This can be used for safety issues such as the possibility of material failure or electrostatic attraction.

[0178] In the case where the Rx trace is not a single sine wave but consists of multiple harmonics, one harmonic may reach the Ty mode resonance frequency. Experiments have shown that for a MEMS mirror 12, the fifth harmonic of the Rx trace can cause a Ty mode resonance when scanning the MEMS mirror response curve. However, depending on the design of the MEMS mirror 12, the separation factor between the Rx and Ty modes can vary, so that different harmonics of the Rx trace may cause a Ty mode resonance.

[0179] If the Rx-Ty coupling via the Euler force satisfies this resonant condition, the Ty mode is excited to a much higher amplitude than in the case of non-resonant coupling. Due to the large motion amplitude of the Ty mode, the mirror's rotational motion may be distorted by a strong fifth (or other) harmonic. This is a result of the Ty mode not being a purely translational mode. Instead, it contains a small rotational component, which leads to a distortion of the overall rotation due to the overall effect of the Rx rotation and the small rotational contribution of the Ty mode.

[0180] The fifth (5th) harmonic content of the overall rotational motion, obtained by scanning a portion of the MEMS mirror response curve for different drive voltages, shows that the Ty response curve has an upper branch with a larger Ty mode amplitude (top response curve) and a lower branch with a lower Ty mode amplitude (bottom response curve).

[0181] The system controller 23 may be configured to monitor the voltage difference ΔV at different operating points (eg, at the Ty mode resonance peak and at non-resonance). I Based on the differential voltage ΔV I The signal shape of the two operating points can be clearly distinguished. Therefore, 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 5th harmonic of the overall rotation response curve without the need for trajectory measurement. Based on this information, the system controller 23 can adjust the digital control signal D HVact To force the jump from the upper branch of the 5th harmonic to the lower branch. This can be achieved by increasing the digital control signal D HVact The driving frequency is set to exceed the back-off frequency of the upper response curve of the Ty mode resonance, so that the Ty mode excitation collapses. In addition, the proposed mode damping can be applied by the damping signal Vdmp to force the jump to the lower branch.

[0182] In other words, the system controller 23 can I The Ty mode amplitude is determined, and based on the determined Ty mode amplitude, it is determined whether the MEMS mirror 12 is on the upper branch or the lower branch of the 5th harmonic. If the Ty mode amplitude exceeds a predetermined amplitude threshold, the system controller 23 determines that the MEMS mirror 12 is on the upper branch of the 5th harmonic of the Rx mode and adjusts the digital control signal D HVactTake countermeasures.

[0183] After the unwanted parasitic oscillations (e.g., mode Ty, mode Rz, mode Ry, or mode Tz) are detected, they can be actively damped. Because smaller Ty mode amplitudes typically occur during normal operation, a threshold should be defined for stronger unwanted excitations of the Ty mode caused by resonant coupling. That is, active damping is applied when a non-zero threshold is exceeded, with the threshold being set to allow some smaller Ty mode amplitudes to normally occur. The threshold can be determined for a specific design through experiments and numerical simulations, and the non-resonant amplitudes of the Ty mode may reach 1-3 μm. Resonant coupling via harmonics of the Rx trajectory or by direct excitation of the comb drive may result in higher amplitudes. Therefore, a threshold can be selected based on a dynamic model of the coupling to determine that the magnitude of Ty amplitudes greater than 3 μm is considered to be caused by resonant coupling. This threshold of the mechanical amplitude of the Ty mode can be converted into a differential voltage ΔV I The corresponding threshold of the amplitude.

[0184] Alternatively, the differential voltage ΔV I The frequency content of can be monitored by the system controller 23. Resonant out-coupling will result in a motion of Ty at the same frequency as Rx. Conversely, resonant on-coupling, for example via the fifth harmonic content of a specially designed mirror track, will result in a differential voltage ΔV I The fifth harmonic content in the voltmeter increases sharply. It can be determined that if the difference voltage ΔV corresponding to the fifth harmonic I Increasing the spectral component of φ by a predetermined factor, for example a factor of 5, is considered as a detection of on-resonance coupling. This can be done via the system controller 23 during normal operation of the MEMS mirror 12.

[0185] During the observation phase, when the driving voltage v drive When connected (for example, corresponding to D HVact =1 and v drive The type of parasitic oscillation, its frequency, and its phase are controlled by the system controller 23 according to the corresponding differential voltage ΔV I Therefore, the system controller 23 evaluates the difference voltage ΔV I And based on the difference voltage ΔV I The amplitude and difference voltage ΔV I A predetermined threshold of the relative intensity of the harmonic content is used to detect translational Ty modes.

[0186] At the driving voltage v drive The turn-off phase (e.g., corresponding to D HVact =0 and v driveDuring the off-time (off time of 0 V), the TIAs 51 and 52 are disconnected from the stator electrodes (eg, via the switches SW1 and SW2 being turned on), and a damping voltage Vdmp is applied to the stator electrodes to counteract the parasitic translation motion Ty.

[0187] In particular, Figure 4D A top view of a MEMS mirror is illustrated that is compensated with a damping voltage in a first damping method (Method 1) in response to detection of a translational motion Ty according to one or more embodiments. In order to damp and reduce the translational motion Ty, a damping voltage Vdmp is applied to two stator electrodes located on the same side of the mirror body 8 (i.e., on the same lateral side of the scan axis 13). Therefore, the damping voltage Vdmp can be applied to the two stator electrodes of the comb drives 40TL and 40BL or to the two stator electrodes of the comb drives 40TR and 40BR. Another pair of stator electrodes on the opposite side of the mirror body 8 (i.e., on the opposite lateral side of the scan axis 13) is grounded to 0V. As a result, the detected Ty mode is damped by applying the damping voltage Vdmp to offset the translational motion.

[0188] 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 absent), and the damping voltage Vdmp is superimposed on the drive voltage Vdrive. Thus, the dashed lines for the damping voltage Vdmp illustrate two options for applying the damping voltage Vdmp depending on the damping method used. As an alternative to applying the damping voltage Vdmp directly to the signal line of the drive voltage Vdrive, the system controller 23 can transmit a damping control signal Ddmp to the MEMS actuator 25, and the MEMS actuator 25 can generate the damping voltage Vdmp, which is superimposed on the drive voltage Vdrive.

[0189] In principle, both damping methods are applicable to any mode and rely on the specific capacitance dependence of the total capacitance of all four stator quadrants on the corresponding degrees of freedom (DOF). Due to symmetry, the total capacitance will always form a local extremum for any DOF. For the Rx and Tz modes, the local extremum is a maximum, while for the Rz mode, the local extremum is a minimum.

[0190] For the Ty mode, the situation is more complicated. In pure translation, the total capacitance as a function of DOF Ty is essentially constant, because the increase in capacitance on one side is exactly balanced by the decrease in capacitance on the other side. This is a consequence of the fact that the fingers of the rotor and stator are already in a stationary position (for truly planar drives, such as in gyroscopes, where the tips of the rotor and stator are designed to end up in the same position, this is not the case). If the rotational component of the Ty mode is added, the capacitance of the Ty mode also has a local maximum, but the correlation is still weak.

[0191] The forces (for translational motions Ty and Tz) and torques (for rotational motions Rz) that can be applied by an actuator relative to a particular DOF depend on the strength of the capacitance dependence of the capacitor configuration used to enforce that DOF. More specifically, the force or torque at position q (where q is the degree of freedom under consideration) can be expressed as F(q) or Here, C includes the stator comb for damping operation. In the first damping method, C includes the stator to which Vdmp is applied. Since in the first damping method, C(q) is essentially linear for the Ty case, the derivative is essentially constant, resulting in a constant factor multiplied by the square of the applied damping voltage. In the second damping method, C includes all four stator quadrants, which results in a parabolic dependence of C around q=0. Therefore, the force or torque has a linear dependence on q through the derivative, where the slope of the linear dependence is proportional to the curvature of the local extreme value, the capacitance formed at q=0. Driving or damping using the second damping method is very similar to the parametric excitation of the Rx mode in normal operation.

[0192] Because the curvature of the local maximum of Ty is very low, method 1 may be preferred for Ty, as it uses the linear capacitance dependence of only the left or only the right stator pair in an alternating manner resulting in a much higher force.

[0193] For other DOFs, such as Tz, Rz, and Ry, Method 2 can be chosen because each quadrant individually already has an inherently parabolic capacitance dependency. Therefore, Method 2 doubles the drive force / torque. It also does not require switches or differential biasing, but the damping voltage can be directly superimposed on the regular drive signal, Vdrive.

[0194] Furthermore, method 2 may generally be preferred because the damping signal for parasitic motion can be applied continuously during both the on-time and the off-time of the drive voltage (and not only during the off-time). Therefore, the damping signal contains only the higher harmonics of the drive signal and does not affect the Rx motion averaged over one Rx cycle. In contrast, if the damping signal is applied only during the off-time of the drive signal, it does in fact affect the Rx motion due to the capacitive dependence of the angle θ of the stator pair for the damping operation. The Rx motion is decelerated by , where θ is the mirror angle and dC / dθ is the derivative of the capacitance with respect to the mirror angle. Therefore, damping method 1 has an effect on the Rx mode amplitude. Figure 4E A timing diagram for implementing a first damping method (Method 1) for utilizing the Ty damping parasitic mode in accordance with one or more embodiments is shown. Here, the translational motion of the MEMS mirror 12 in the Ty mode is shown as Ymirror, while θmirror is the mirror angle about the scan axis 13 (i.e., Rx mode). Two damping signals (voltages) Vdmp,left and Vdmp,right are applied to the left or right stator electrode, respectively, to apply damping during the off-time of the drive voltage Vdrive to damp the Ty oscillations.

[0195] Figure 4F A timing diagram for implementing a second damping method (Method 2) for damping parasitic modes utilizing Tz, according to one or more embodiments, is shown. Here, the translational motion of the MEMS mirror 12 in Tz mode is shown as Zmirror, while θmirror is the mirror angle about the scan axis 13 (i.e., Rx mode). Based on the detection of the Tz mode, a damping signal (voltage) Vdmp is superimposed on the drive voltage Vdrive during the on-time and off-time to damp the Tz oscillations. To account for nonlinear driving forces or torques, Vdmp can be locally adjusted during the on-time and off-time of Vdrive, for example, with the amplitude of Vdmp being lower during the on-time of Vdrive.

[0196] During the observation phase, the system controller 23 generates a voltage difference ΔV I The sign of determines the phase relationship of the Ty mode motion relative to the observation phase, which is the actuation phase of the Rx mode. This means that it determines during which time intervals of the observation phase the mirror body 8 moves from left to right, and during which time intervals it moves from right to left in the translational Y direction. Because the frequency of the Ty mode motion is typically an integer multiple of the Rx mode motion in the case of resonant coupling (e.g., the Ty mode can be resonantly excited by the fifth harmonic content of the Rx trajectory), the observation phase can include phases during which the mirror body 8 moves from left to right and phases during which the mirror body 8 moves from right to left.

[0197] During the off phase, a damping voltage Vdmp (Vdmp,left and Vdmp,right) must be applied alternately to the pair formed by the two left stator electrodes 40TL and 40BL or the pair formed by the two right stator electrodes 40TR and 40BR, while the other pair can be set to 0V or another absolute value smaller than that of the other comb drive side. This AC signal must have a timing or phase relationship, that is, when Ty moves from left to right, the damping voltage Vdmp is applied to the left pair, and when Ty moves from right to left, the damping voltage Vdmp is applied to the right pair. For this signal configuration, the system controller 23 uses the phase information about the Ty pattern derived during the observation phase.

[0198] Another aspect of mode coupling in comb-drive-actuated MEMS mirrors is the coupling of the rotational mode Rx into the yaw mode Rz. In particular, coupling can occur from the desired rotational mode Rx to the undesired yaw mode Rz. The yaw mode Rz is susceptible to direct parametric excitation by the comb drive. Direct parametric excitation is possible because the capacitive dependence of this degree of freedom is very strong when the higher harmonics of the rectangular drive signal Vdrive for the Rx mode meet the parametric resonance criteria for the Rz mode. More specifically, parametric excitation of the Rz mode can occur if an odd multiple of the drive frequency equals twice the eigenfrequency of the Rz mode. However, parametric resonance requires a threshold excitation intensity for this to occur. Therefore, if the odd integer (i.e., the higher harmonic order that meets the resonance criteria) is too high, parametric resonance of the Rz mode will not occur. The exact threshold depends on the curvature of the capacitive dependence of the Rz mode and the applied voltage. Once the yaw mode Rz is excited, i.e., when there is an initial Rz motion, the inertial coupling term according to the Euler rotation equation leads to coupling of the Rz and Rx modes. The yaw mode Rz can be detected and measured by subtracting the diagonal displacement current signal.

[0199] Figure 5A A top view of a MEMS mirror arranged in a nominally centered position (left) and a yaw offset position (right) according to one or more embodiments is shown. On the left, the MEMS mirror 12 (mirror body 8) operates in a pure rotational mode Rx about the scan axis 13 and the torsion bar 18 is not bent. The four comb drives 40TL, 40BL, 40TR, and 40BR are symmetrically located within the frame 17. In contrast, on the right, the MEMS mirror 12 (mirror body 8) moves about the Z direction (i.e., rotates about the Z axis) and oscillates back and forth about the Z axis via mode coupling to the Rz mode. Here, the torsion bar 18 bends back and forth in the Y direction. The stator comb drive electrodes are divided into a diagonal pair across the first diagonal of the MEMS chip (the stators of comb drives 40TL and 40BR) and a diagonal pair across the second diagonal of the MEMS chip (the stators of comb drives 40BL and 40TR) to detect RxRz mode coupling.

[0200] The embodiment also includes a sensing circuit coupled to the stator comb drive electrodes of each comb drive 40TL, 40BL, 40TR, and 40BR to receive the corresponding displacement current therefrom. The stator comb drive electrodes are coupled to the sensing circuit to detect a mode of interest such as a Ty mode or an Rz mode.

[0201] Figure 5B is a schematic diagram of a yaw mode Rz measurement and compensation system 500 according to one or more embodiments. The yaw mode Rz measurement and compensation system 500 includes a MEMS actuator 25, a MEMS mirror 12 having four comb drives 40TL, 40BL, 40TR, and 40BR, a sensing circuit 60, and a system controller 23. It should be further understood that the sensing circuits 50 and 60 can be combined to sense both the Ty mode and the Rz mode.

[0202] The MEMS driver 25 receives the digital control signal D HVact And according to the digital control signal D HVact Drive the MEMS mirror 12. The MEMS driver 25 generates a driving voltage v with an appropriate duty cycle drive And the driving voltage v drive As a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitances C of the four comb drives 40TL, 40BL, 40TR, and 40BR are TL 、C BL 、C TR , and C BR Change and displacement current i TL 、i BL 、i TR , and i BR The sensing circuit 60 is coupled to the stator comb electrodes of the four comb drivers 40TL, 40BL, 40TR, and 40BR and extracts the displacement current i TL 、i BL 、i TR , and i BR .

[0203] To measure the yaw mode Rz, the two diagonal or angular displacement currents i TL and i BRis provided to the input of the TIA 61 of the sensing circuit 60. Although a TIA is used in this example, it should be understood that other sensing elements for capacitive sensing can be used. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation-based sensing can be used to generate the sense signal. The TIA 61 can be coupled to the MEMS mirror 12 and, in particular, to the stator of a given comb drive. The diagonal displacement current i TL and i BR The currents are extracted from the stator comb electrodes of the comb drives 40TL and 40BR arranged diagonally across the mirror body 8. As a result, two diagonally displaced currents i TL and i BR The sum of the two diagonal voltages is converted into a first diagonal voltage V by TIA 61. D1 .

[0204] Similarly, the other two diagonal or angular displacement currents i TR and i BL is provided to the input of the TIA 62 of the sensing circuit 60. Again, while a TIA is used in this example, it should be understood that other sensing elements for capacitive sensing may be used. For example, any sensing circuit that performs charge sensing, current sensing, or frequency modulation-based sensing may be used to generate the sense signal. The TIA 62 may be coupled to the MEMS mirror 12, and specifically to the stator of a given comb drive. The diagonal displacement current i TR and i BL Extracted from the stator comb electrodes of the comb drives 40TR and 40BL arranged diagonally to each other across the mirror body 8. As a result, the other two diagonal displacement currents i TR and i BL The sum of the two diagonal voltages is converted by TIA 62 into a second diagonal voltage V D2 .

[0205] The sensing circuit 60 further includes an adder 63 and a subtractor 64. The adder 63 receives the first diagonal voltage VD1 and the second diagonal voltage V D2 Both, and add them together to generate a representation of the total displacement current i TL 、i BL 、i TR , and i BR The total voltage V I In contrast, the subtractor 64 receives the first diagonal voltage V D1 and the second diagonal voltage V D2 , and from the first diagonal voltage V D1 Subtract the second diagonal voltage V D2 To generate a first pair of diagonal currents i TL 、i BR (i.e., their sum) and the second pair of diagonal currents iTR 、i BL The difference voltage ΔV between the sum of the I Total voltage V I (ie, the total current signal) allows the system controller 23 to make accurate phase and amplitude measurements of the Rx mode for proper MEMS mirror control. However, the total voltage V I does not provide any information about the scanning direction, since the four comb drives are symmetrical. On the other hand, the difference voltage ΔV I (ie, the differential current signal) provides information corresponding to the amplitude of the yaw pattern Rz and the phase of the yaw pattern Rz. For example, when the MEMS mirror 12 oscillates about the Z axis, the differential voltage ΔV I The system controller 23 can oscillate between positive and negative values. mirror ) to generate the digital control signal D HVact .

[0206] Furthermore, after detecting unwanted parasitic oscillations (eg, mode Ty, mode Rz, mode Ry, or mode Tz), they can be actively damped using the above-mentioned method 2, which superimposes a damping signal Vdmp on the driver signal Vdrive.

[0207] The differential voltage ΔV can be limited I The threshold value of yaw mode Rz is determined to be excited. The difference voltage ΔV I A threshold value of ΔV such that it is equivalent to the Rz rotation angle is considered critical. Since in the Rz mode the comb fingers of the rotor and stator are brought close to each other due to a considerable lateral displacement component, which can lead to potentially destructive effects of electrostatic pulling, a lower threshold angle for the critical Rz motion is usually chosen. In some embodiments, it can be chosen in the range of 0.015° to 0.15°. A suitable threshold angle can be determined for a specific design by experiments and numerical simulations and converted into a differential voltage ΔV taking into account the readout electronics. I In addition, the difference voltage ΔV can be analyzed I The spectral components of the yaw mode Rz are examined to determine whether an enhanced component is present at the expected frequency of the yaw mode Rz. The threshold criteria described above can be applied only to the spectral components at the expected frequency of the yaw mode Rz to make the detection more robust by excluding other spectral components that may indicate acceptable minor non-resonant motion in the yaw mode Rz, such as due to manufacturing-induced asymmetries. These procedures can be applied via system controller 23 during normal operation of MEMS mirror 12.

[0208] In the initial observation stage, when the driving voltage v driveWhen connected (for example, corresponding to D HVact =1 and v drive 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 according to the corresponding differential voltage ΔV I Therefore, the system controller 23 estimates the difference voltage ΔV I And based on the difference voltage ΔV I The predetermined threshold value or difference voltage ΔV of the magnitude I The rotational yaw pattern Rz is detected by a predetermined threshold value of the amplitude of the spectral component at the expected frequency of the yaw pattern Rz.

[0209] After the initial observation period, the damping voltage Vdmp is superimposed on the driving voltage v drive This means that it is applied to the rotor electrodes while the stator electrodes remain grounded. The damping voltage Vdmp is twice the parasitic yaw mode frequency and is proportional to v drive The phase of is selected based on the determination of the phase of the yaw mode Rz relative to the operating mode Rx so that the Rz mode motion is decelerated. drive Both the damping voltage Vdmp and the driving voltage Vdmp can be unipolar square waves, and the frequency of the damping voltage Vdmp is the driving voltage v under the condition of resonant parasitic excitation. drive In contrast to the method 1 described for the damping of the parasitic Ty mode, 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 used separately with the drive voltage v drive The same rotor and stator bias is applied to perform. In addition, no switches are required.

[0210] In particular, Figure 5C FIG2 illustrates a top view of a MEMS mirror that is compensated with a damping voltage in response to detecting a yaw motion Rz according to one or more embodiments. Here, the damping voltage Vdmp is superimposed on the drive voltage v applied to the rotor. drive The stator poles of 40TL, 40TR, 40BL, and 40BR are grounded. To account for nonlinear driving force or torque, Vdmp can be adjusted locally at the on-time and off-time of Vdrive.

[0211] In order to damp and reduce the yaw motion Rz, the damping voltage Vdmp is added to the driving voltage v drive The displacement current is monitored by applying the current to the rotor electrodes while the stator electrodes are kept grounded to 0 V. drive The detected Rz mode can be damped by applying a damping voltage Vdmp to counteract the unwanted rotational motion.

[0212] During a subsequent observation phase, the amplitude and phase of the yaw pattern Rz may be continuously monitored, and the damping voltage Vdmp may be adjusted in amplitude and phase based on the updated information about the amplitude and phase of the Rz pattern.

[0213] During the observation phase, the system controller 23 generates a voltage difference ΔV I The phase of the Rz motion is determined. More specifically, it is determined in relation to the Rz degree of freedom whether the mirror body 8 is approaching a rest position or moving away from a rest position. If the mirror is approaching an Rz-related rest position, the Rz-related capacitance is reduced, resulting in a discharge current. If the mirror is moving away from an Rz-related rest position, the Rz-related capacitance is increased, resulting in a charging current. The charging and discharging currents result in corresponding difference voltages with opposite signs. By this process, the phase of the Rz motion can be determined relative to the drive signal. In response to this phase detection of the movement about the Z axis, it is then possible to detect the phase of the Rz motion by superimposing it onto the drive signal v at the stage when the mirror is approaching an Rz-related rest (intermediate) position. drive The damping voltage Vdmp is applied to the mirror without superimposing an additional voltage during the phases when the mirror moves away from the Rz-related rest position. The Rz-related capacitance has its minimum value at the Rz-related rest position. Therefore, applying the voltage Vdmp between the rotor and stator pulls the mirror away from the Rz-related rest position. If the voltage is applied during the phase when the mirror approaches the Rz-related rest position, the Rz motion is decelerated, i.e., damped. The Rz motion is continuously monitored, and the application of the damping voltage Vdmp is adjusted based on updated phase and amplitude information about the yaw mode Rz motion.

[0214] 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, then the translational mode Tz in the Z direction (i.e., out-of-plane upward and downward translational motion) can be detected by the difference in the front and back layer currents, where "front" refers to the current with respect to the Figure 1B The coordinate system of the layer is located at a larger (i.e., more positive) z coordinate. In contrast, the "back" refers to the layer with respect to Figure 1B The coordinate system of layers is located at lower (ie, more negative) z-coordinates.

[0215] Figure 6A and 6B 1 shows a cross-sectional view of a MEMS mirror and actuator electrodes according to one or more embodiments. Figure 6A In FIG, the left stator comb driver electrode 43 includes two layers of equal thickness: a front layer 43a and a back layer 43b. Similarly, the right stator comb driver electrode 44 includes two layers of equal thickness: a front layer 44a and a back layer 44b. In contrast, in FIG. Figure 6B In the embodiment, the corresponding front and back layers have different thicknesses.

[0216] Due to the reinforcement structure 9, the mode coupling between the Rx mode and the Tz mode can be caused by the displacement L between the center of mass M and the rotation axis (scanning axis 13). According to equation 2, this inertial coupling is caused by the sum of the Euler force component and the centrifugal force component:

[0217]

[0218] M represents the quality of the reflector, θ m (t) represents the reflector angle, represents the angular velocity of the reflector, represents the mirror rotation acceleration. Therefore, due to its dependence on the mirror angle and its time derivative, the Tz mode consists of an inertial force f with a frequency component that is twice the harmonic frequency θ(t) of the Rx trajectory. Z (t) excitation. If f Z (t) has a frequency component at the resonant frequency of the Tz mode, then the resonant excitation of the Tz mode may occur. The different coupling mechanism between the Rx mode and the Tz mode is through the driving voltage v of the Rx mode. drive The high-order harmonic content of the Tz mode is directly parametrically excited.

[0219] Subtracting all rear layer displacement currents from all front layer displacement currents allows detection of Tz motion via the difference signal. Detection of Tz motion is also possible for layers of unequal thickness, but the acquired difference currents require further processing by the system controller 23, as it is expected that the Rx mode also results in a non-zero signal. Therefore, unequal thicknesses can result in differences in the front and rear currents for both Rx and Tz modes.

[0220] Figure 6C is a schematic diagram of a Tz mode measurement and compensation system 600 according to one or more embodiments. The Tz mode measurement and compensation system 600 includes a MEMS actuator 25, a MEMS mirror 12 having four comb drives 40TL, 40BL, 40TR, and 40BR (each comb drive consisting of a front layer and a back layer), a sensing circuit 70, and a system controller 23. It should be further understood that the sensing circuits 50, 60, and 70 can be combined to sense the Ty mode, the Rz mode, and the Tz mode.

[0221] The MEMS driver 25 receives the digital control signal D HVact And according to the digital control signal D HVact Drive the MEMS mirror 12. The MEMS driver 25 generates a driving voltage v with an appropriate duty cycle drive And the driving voltage v driveAs a result of the movement of the MEMS mirror 12 about its scanning axis 13, the drive capacitance C of the four comb drives 40TL, 40BL, 40TR, and 40BR is TL-FS 、C BL-FS 、C TR-FS 、C BR-FS 、C TL-BS 、C BL-BS 、C TR-BS and C BR-BS changes and its corresponding driving capacitance generates displacement current 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 The sensing circuit 70 is coupled to the stator comb electrodes of the four comb drivers 40TL, 40BL, 40TR, and 40BR and extracts the displacement current i therefrom. TL-FS 、i BL_FS 、i TR_FS 、i BR-FS 、i TL-BS 、i BL_BS 、i TR_BS and i BR-BS .

[0222] To measure the Tz mode, all the front displacement currents i TL-FS 、i BL_FS 、i TR_FS and i BR-FS is provided to the input of the TIA 71 of the sensing circuit 70. The TIA 71 may be coupled to the MEMS mirror 12 and in particular to the frontal layer of the stator of all comb drives. TL-FS 、i BL_FS 、i TR_FS and i BR-FS Extracted from the front layers of the stator comb electrodes of the comb drives 40TL, 40BL, 40TR, and 40BR. As a result, all the front displacement currents i TL-FS 、i BL_FS 、i TR_FS and i BR-FS The sum of the voltages is converted into a first voltage V by the TIA 71. FS .

[0223] Similarly, all rear displacement currents i TL-BS 、i BL_BS 、i TR_BS and iBR-BS is provided to the input of the TIA 72 of the sensing circuit 70. The TIA 72 may be coupled to the MEMS mirror 12 and in particular to the backside layers of the stators of all comb drives. TL-BS 、i BL_BS 、i TR_BS and i BR-BS Extracted from the back layer of the stator comb electrodes of the comb drivers 40TL, 40BL, 40TR, and 40BR. As a result, all back displacement currents i TL-BS 、i BL_BS 、i TR_BS and i BR-BS The sum of the voltages is converted by the TIA 72 into a second voltage V BS .

[0224] The sensing circuit 70 further includes an adder 73 and a subtractor 74. The adder 73 receives the first voltage V FS and the second voltage V BS Both and add them together to generate a representation of the total displacement current 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 The total voltage V I In contrast, the subtractor 74 receives the first voltage V FS and the second voltage V BS , and from the first voltage V FS Subtract the second voltage V BS To generate a total positive current i TL-FS 、i BL_FS 、i TR_FS and i BR-FS With all back current i TL-BS 、i BL_BS 、i TR_BS and i BR-BS The difference between the voltage ΔV I Total voltage V I (ie, the total current signal) allows the system controller 23 to measure the precise phase and amplitude of the Rx mode for proper MEMS mirror control. I (ie, the differential current signal) provides information corresponding to the amplitude of the Tz mode and the phase of the Tz mode relative to the Rx mode. For example, when the MEMS mirror 12 oscillates along the Z direction, the differential voltage ΔV I The system controller 23 can oscillate between positive and negative values. mirror) to generate the digital control signal D HVact .

[0225] In addition, after the unwanted parasitic oscillation of the Tz mode is detected, it can be actively damped. The differential voltage ΔV can be defined I The threshold value of the differential voltage can be determined to determine that the Tz mode is excited. The threshold value of the differential voltage can be determined so that it is equivalent to the Tz displacement, which is considered critical. Since in the Tz mode, additional mechanical stress is exerted on the mirror suspension, especially on the torsion bar, a lower threshold displacement of the critical Tz motion is usually chosen. In an embodiment, it can be chosen in the range of 1.5-10 μm. A suitable threshold displacement can be determined for a specific design by experiments and numerical simulations and converted into a differential voltage ΔV taking into account the readout electronics. I In addition, the differential voltage ΔV I The spectral components of the MEMS mirror 12 are then analyzed to determine whether an enhanced component is present at the expected frequency of the Tz mode. The threshold criteria described above can be applied only to the spectral components at the expected frequency of the Tz mode to make the detection more robust by excluding other spectral components that may indicate small, acceptable non-resonant motions in the Tz mode, such as those due to manufacturing asymmetries. These procedures can be applied by the system controller 23 during normal operation of the MEMS mirror 12.

[0226] In the initial observation stage, when the driving voltage v drive When connected (for example, corresponding to D HVact =1 and v drive The on-time of the predetermined voltage is set, for example, 0V to 200V), the type of parasitic oscillation, its frequency, its frequency and its phase relative to the operating mode Rx are determined by the system controller 23 according to the corresponding difference voltage ΔV I Therefore, the system controller 23 estimates the difference voltage ΔV I And based on the difference voltage ΔV I The predetermined threshold value or difference voltage ΔV of the magnitude I The translational Tz mode is detected by a predetermined threshold value of the amplitude of the spectral component at the expected frequency of the translational Tz mode.

[0227] After the initial observation period, the damping voltage Vdmp is superimposed on the driving voltage v drive This means that it is applied to the rotor while the stator electrodes remain grounded. The damping voltage Vdmp is twice the frequency of the parasitic translational Tz mode and is proportional to v drive The phase of is selected based on the determination of the phase of the translation Tz mode relative to the operating mode Rx so that the Tz mode motion is decelerated. For example, the drive voltage v driveBoth the damping voltage Vdmp and the driving voltage Vdmp can be unipolar square waves, and the frequency of the damping voltage Vdmp is the driving voltage v under the condition of resonant parasitic excitation. drive Different from the method described for the damping of parasitic Ty mode, the damping voltage of Tz mode is not only drive This is possible because it can be applied during the turn-off phase and during the turn-on phase respectively with the drive voltage v drive The same rotor and stator bias is applied to perform. In addition, no switches are required.

[0228] In particular, Figure 6D A cross-sectional view of a MEMS mirror is shown that compensates with a damping voltage in response to detecting Tz motion according to one or more embodiments. To damp and reduce Tz motion, the damping voltage Vdmp is superimposed on the drive voltage v drive The displacement current is monitored by applying the current to the rotor electrodes while the stator electrodes are kept grounded to 0 V. drive The detected Tz mode can be damped by applying a damping voltage Vdmp to counteract the unwanted translational motion.

[0229] During a subsequent observation phase, the amplitude and phase of the Tz mode may be continuously monitored, and the damping voltage Vdmp may be adjusted in amplitude and phase based on the updated information about the amplitude and phase of the Tz mode.

[0230] During the observation phase, the system controller 23 calculates the voltage difference ΔV I The phase of the Tz motion is determined. More specifically, it is determined whether the mirror 8 is approaching or moving away from the rest position in relation to the Tz degree of freedom. If the mirror is approaching the Tz-related rest position, the Tz-related capacitance increases, causing a current to charge the comb capacitors. If approaching from the negative Z side, mainly the capacitors associated with the front layer are charged, resulting in a non-zero current i TL-FS 、i BL-FS 、i TR-FS and i BR-FS If approached from the positive Z side, mainly the capacitors associated with the backside layers are charged, resulting in a non-zero current i TL-BS 、i BL-BS 、i TR-BS and i BR-BS If the mirror is moving away from the Tz-related rest position, it reduces the Tz-related capacitance, which generates a current that discharges the comb capacitors. If it is moving away on the negative Z side, mainly the capacitors associated with the front layers are discharged, resulting in a non-zero current i TL-FS 、i BL-FS 、i TR-FS and i BR-FSIf it is far away on the positive Z side, mainly the capacitor associated with the back layer is discharged, resulting in a non-zero current i TL-BS 、i BL-BS 、i TR-BS and i BR-BS These signals have relative signs compared to the approaching case. These signals result in a relative differential voltage. The loading and unloading of the back or front current also depends on the current rotation angle.

[0231] By appropriate analysis of the differential voltage, the phase of the Tz motion can be established relative to the drive signal. This phase detection in response to the movement along the Z axis can then be used to detect the phase of the mirror moving away from its Tz-related rest (intermediate) position by superimposing it on the drive signal v drive The damping voltage Vdmp is applied without superimposing an additional voltage during the phase when the mirror approaches the Tz-related rest position. The Tz-related capacitance reaches its maximum value at the Tz-related rest position. Therefore, applying the voltage Vdmp between the rotor and stator pulls the mirror toward the Tz-related rest position. If the voltage is applied during the phase when the mirror moves away from the Tz-related rest position, the Tz motion is decelerated, i.e., damped. The Tz motion 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 motion.

[0232] Tz mode coupling can be detected by monitoring the difference signal between the front and back stator layers. The frequency position of the mode coupling to the Tz mode can be recorded and stored in memory to avoid excitation of the Tz mode in the future, for example by restarting the mirror while sweeping the drive voltage frequency in open loop to initiate Rx oscillation for initial signal acquisition. The system controller 23 can detect a failure of the mirror 12 using a large change in the mirror position in the translational Z direction, for example, if the difference signal exceeds a predetermined amplitude threshold.

[0233] Figure 6E The four capacitor currents DL1R, DL2R, DL1L, and DL2L are depicted in a wide range of excitation frequency sweeps from 4 kHz to 45 kHz for a MEMS mirror according to one or more embodiments. Figure 6B and 6C DL1R represents the sum of the currents of the front layer (DL1... device layer 1 = front layer) on the right. DL2L represents the sum of the currents of the back layer on the left, etc. The capacitor currents DL1R, DL2R, DL1L, and DL2L can be summarized as the displacement current i xL -FS=DL1L、i xR -FS=DL1R、i xL -BS=DL2L、ixR -BS = DL2R, where the "bottom" and "top" currents are not differentiated here (they are summed by the joint contact), so "x" can apply to either the bottom or the top current. Direct excitation of the operating mode Rx as well as the parasitic modes Tz and Rz at twice their respective resonance frequencies is observed. This means that they are excited in the first-order parametric resonance. However, mode Rz is also excited at one-third of its parametric resonance frequency. This can be achieved by drive This can be explained by a square-wave drive with higher odd harmonics at 3, 5, and 7 times the fundamental frequency. Therefore, the third harmonic content of the square-wave drive meets the resonance criterion for the first-order parametric resonance of the yaw mode Rz. This behavior is stimulated by sweeping the excitation frequency. However, this unwanted excitation can also occur in normal operation, that is, when the drive frequency is twice the Rx frequency, if the parasitic mode meets the criterion Rx·(2n+1)=Rp, where Rp is the frequency of the parasitic mode and n=0, 1, 2, .... Such parasitic excitation can be detected and identified using the methods described above.

[0234] After detecting an unwanted parasitic oscillation (eg, mode Ty, mode Rz, mode Ry, or mode Tz), it can be actively damped. This can be done via the system controller 23 during normal operation of the MEMS mirror 12.

[0235] During the observation phase, when the driving voltage v drive When connected (for example, when D HVact =1 and v drive is set to a value between 0V and 200V), the type of parasitic oscillation, its frequency and its phase are determined by the system controller 23 according to the corresponding differential voltage ΔV I to confirm.

[0236] In particular, the Tz mode can be actively damped in response to its detection. When the rotor moves up or down from the center, a voltage V is applied between the rotor and stator electrodes. damp When the rotor moves back to the center, no voltage (0V) is applied.

[0237] Figure 7A A top view of a quasi-static (QS) MEMS mirror is shown, arranged in a nominal center position (left) and a translationally shifted position (right), according to one or more embodiments. For the QS MEMS mirror 12, a stator comb is used to drive the MEMS mirror 12 about a rotation axis 13, and a rotor is used for sensing via a sensing circuit. For the QS mirror, two individual drive voltages are applied to the stator comb electrodes (typically either the left or right side, with the other set to zero voltage), while the rotor comb electrodes are assigned to ground.

[0238] Figure 7Bis a schematic diagram of a Ty mode measurement and damping system 700 for a QS MEMS mirror according to one or more embodiments. The Ty mode measurement system 700 includes a MEMS driver 25, which includes two high voltage (HV) drivers 25a and 25b, each of which applies an individual drive voltage to a corresponding set of stator comb electrodes. In particular, the HV driver 25a applies a drive voltage to the stator comb electrodes of the comb drivers 40TL and 40BL (i.e., on the left side), and the HV driver 25b applies a drive voltage to the stator comb electrodes of the comb drivers 40TR and 40BR (i.e., on the right side). For the QS mirror, two individual drive voltages are applied so that the QS MEMS mirror 12 tilts in the positive direction or the negative direction. It is generally avoided to apply two drive voltages simultaneously to avoid exciting the Tz mode. When using the digital control signal D HVact When each HV driver 25a and 25b receives a corresponding digital control signal D HVleft Or digital control signal D HVright And the MEMS mirror 12 is driven in a similar manner as described above according to its corresponding digital control signal.

[0239] For QS mirror sensing in Rx nominal mode and Ty parasitic mode, a sensing circuit 80 (eg, a TIA) is connected to the rotor comb to measure capacitance via displacement charge or displacement current received from the rotor (ie, rotor comb electrodes).

[0240] For QS mirror sensing, a high frequency modulation voltage can be added to the nominal drive voltage to allow mirror position sensing (Rx) and parasitic mode sensing (Ty) independent of the applied drive voltage.

[0241] For QS mirror sensing, the system controller 23 distinguishes the Ty parasitic mode from the Rx nominal mode by its frequency component. Once the system controller 23 detects the Ty mode and determines that its value is above a predetermined threshold, the system controller 23 can actively damp the Ty mode by adding a counter voltage Vdmp to the drive comb electrodes on one side or the other, or in an alternative manner when applying the drive voltage respectively. That is, when the drive voltage is applied to the right stator comb electrodes to the left stator comb electrodes, the counter voltage Vdmp is superimposed on the drive voltage. Adders 81 and 82 can be used to add or combine the counter voltage (damping voltage) Vdmp to the digital control signal D HVleft and D HVright The counter voltage Vdmp is thus superimposed on the drive voltage Vdrive via the corresponding HV drivers 25a, 25b. When not driven / damped, the stator comb electrodes on the opposite side are grounded. Taking into account the nonlinear drive force and torque, Vdmp can be scaled by Vdrive.

[0242] Figure 7C A top view of a QS MEMS mirror is shown that compensates with a damping voltage in response to detecting a translational motion Ty according to one or more embodiments. drive According to the digital control signal D HVleft and D HVright When applied alternately, the damping voltage for counteracting the Ty mode is applied alternately to the left stator comb electrodes and the right stator comb electrodes to be superimposed on the drive voltage Vdrive. As shown in the figure, ground and Vdrive / Vdmp are alternated.

[0243] Figure 7D A cross-sectional view of a QS MEMS mirror is shown that compensates with a damping voltage in response to detecting a translational motion Ty according to one or more embodiments. Here, when the stator comb drive electrodes 43 and 44 have two layers (a front top layer 43a, 44a and a back bottom layer 43b, 44b), the drive voltage Vdrive and the damping voltage Vdmp can be applied side-to-side to alternately ground. Here, the stator electrodes ( Figure 7D 44a at the top and Figure 7D The bottom portion 43a) may be applied with a damping voltage Vdmp so that the nominal Rx drive and Ty compensation are applied separately from each other.

[0244] Figure 7E A top view of a QS MEMS mirror compensated using an alternative approach of using a dedicated sensing comb to detect translational motion Ty, according to one or more embodiments, is shown. It should be understood that resonant MEMS mirrors can also use dedicated sensing combs. Thus, dedicated sensing combs are not limited to QS MEMS mirrors, but can be applied to any MEMS mirror, including those described herein.

[0245] Here, the QS MEMS mirror 12 includes four dedicated sensing combs 45TL, 45BL, 45TR, and 45BR, each of which is fixed to the mirror frame 17 and is used to measure the capacitance caused by the displacement charge or displacement current received from the stator comb electrode, as described above with respect to e.g. Figure 4B and 4C The dedicated sensing combs 45TL, 45BL, 45TR, and 45BR also have corresponding rotor comb electrodes that are grounded.

[0246] Once the system controller 23 detects the Ty mode and determines that its value is above a predetermined threshold, the system controller 23 can actively damp the Ty mode by adding a counter voltage Vdmp to the driving stator comb electrodes when the corresponding drive voltage Vdrive is applied to the electrode. The application of Vdrive / Vdmp is based on the digital control signal DHVleft and D HVright Alternate left and right.

[0247] It should also be noted that the sensing combs 45TL, 45BL, 45TR, and 45BR can be used with Figure 4B 、 Figure 4C 、 Figure 5B 、 Figure 6C ,as well as Figure 7B A similar arrangement as shown is electrically coupled to the sensing circuitry (TIA, adder, and subtractor) (e.g., as done by drive rods 40TL, 405BL, 40TR, and 40BR) for not only detecting and identifying one or more parasitic modes, but also for determining the phase, amplitude, and scanning 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 as described above, for example, by analyzing the differential measurement signal. Thus, the sense comb is used to sense and generate the measurement signal, and the drive comb is used to drive the MEMS mirror 12 and to damp the identified parasitic modes.

[0248] After detection, not only can any parasitic modes Ty, Rz, Ry, and / or Tz be actively damped, but they can also be avoided in advance. The parasitic modes of Ty and Tz each have a high Q factor of their Rx mode parasitic dynamics. The high Q factor results in large coupling with the Rx mode, which may cause inaccurate scanning angles due to distortion of the scanning trajectory and failure of the mirror control system. In the worst case, the parasitic mode can damage the MEMS mirror through large displacement of the comb drive and fatigue in the weak structure of the MEMS mirror. However, due to the inherent high Q factor, the large coupling occurs in a very small frequency region and also varies with operating conditions, such as peak input voltage, duty cycle, and excitation waveform shape. If the parasitic mode contains a nonlinear spring constant, such as hardening or softening, the parasitic mode will exhibit hysteresis behavior. Those large parasitic mode couplings should not be used as the operating point of LIDAR operation or should be avoided during the startup operation of the MEMS mirror 12 to avoid potential damage or fatigue.

[0249] Figure 8A flow chart of a parasitic mode coupling avoidance method according to one or more embodiments is illustrated. When a parasitic coupling mode is detected during operation of the MEMS mirror 12 (operation 805), the mode coupling impact is evaluated (operation 810), such as the condition and frequency region of the parasitic mode, the strength of the mode coupling, and whether it is a disaster point, which is detected as having a serious impact or potentially destructive to the MEMS mirror. Specifically, the frequency location of the Rx mode coupling to the parasitic mode and the amplitude of the parasitic mode can be determined, and the amplitude and frequency location (region) of the parasitic mode coupling are recorded in a memory (operation 820). If the amplitude and frequency location (region) of the parasitic mode coupling are determined to be an operating point in the Rx mode in operation 825 and are determined to have a serious impact or destructive to the MEMS mirror, the system controller 23 prevents or avoids the operating point in operation 830 by modifying the operating conditions of the MEMS mirror 12 by applying a frequency shift or duty cycle change to drive the Rx mode. That is, if the harmonic number of the parasitic mode coupling is critical according to its frequency position relative to the operating point of the Rx mode and / or according to the amplitude of the parasitic mode coupling, the operating point driving the Rx mode is avoided to prevent the excitation of the corresponding parasitic mode.

[0250] If the system controller 23 determines that the harmonics (frequency locations) of the spurious mode are not located at the operating point of the Rx mode, but only at some activation points of the MEMS mirror and may cause damage to the MEMS mirror 12 based on, for example, that their amplitude exceeds a predetermined threshold (operation 835), the system controller 23 may modify the activation of the MEMS mirror 12 to avoid such peak coupling frequency or a frequency near it in operation 840. In operation 840, the system controller 23 may also modify operating conditions during activation, such as the peak input voltage, duty cycle, and input waveform of the drive voltage Vdrive.

[0251] When it is at the operating point of the desired operating frequency and amplitude for mode Rx, the operating frequency and amplitude of the drive voltage Vdrive can be moved to another value, for example, to a slightly higher operating frequency with lower parasitic coupling, in operation 830. The system controller 23 can adjust the amplitude for the target operating condition of Rx by adjusting the duty cycle or voltage scaling of the drive voltage Vdrive.

[0252] If the system controller 23 does not determine in operation 825 that the parasitic mode is at the operating point of the Rx mode or does not determine in operation 835 that the parasitic mode is destructive to the MEMS mirror, the system controller 23 continues to record the parasitic coupling behavior to the Rx mode in operation 845 and returns to operation 825 for continuous monitoring until the entire frequency of the parasitic mode region is fully analyzed.

[0253] In the case of coupled-mode Duffing oscillations, their hysteretic behavior can be exploited, such as by slightly increasing the frequency of the coupled-mode backoff and sweeping it slightly downward under the same operating conditions. This can significantly reduce the coupling effects of the hysteretic behavior while maintaining the desired operating conditions. For example, the system controller 23 can evaluate the differences in the Rx trajectory when the Ty mode is excited at high and low amplitudes. This is due to the hysteretic (Duffing) behavior of the Ty mode. For example, the fifth harmonic content of the Rx trajectory of the MEMS mirror 12 caused by the high Ty mode amplitude can be evaluated. When sweeping the drive signal from low frequency to high frequency (activating the MEMS mirror to reach the desired operating point), the upper branch of the MEMS mirror 12's response curve is followed until a backoff point occurs at a high Ty amplitude in the lower branch of the response curve. If a high Ty mode amplitude is detected (i.e., via capacitive readout), the system controller 23 can initiate a jump from the upper branch to the lower branch to avoid large parasitic Ty mode coupling. Similar evaluations can be applied to other parasitic modes.

[0254] Additional embodiments are provided below:

[0255] 1. A scanning system comprising:

[0256] a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0257] a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0258] a driver configured to generate the at least one drive signal;

[0259] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0260] The processing circuit is configured to determine a scanning direction of the MEMS scanning structure in the desired rotational motion mode based on the sensing signal.

[0261] 2. The scanning system of embodiment 1, wherein:

[0262] the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives,

[0263] The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and

[0264] The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

[0265] 3. The scanning system of embodiment 2, wherein the sign of the differential measurement signal indicates the scanning direction.

[0266] 4. The scanning system according to embodiment 2, further comprising:

[0267] A system controller is configured to modify the at least one drive signal based on the determined scan direction.

[0268] 5. The scanning system of embodiment 2, wherein:

[0269] The sensing circuit is configured to sum the at least one sensing signal provided by the first subset of comb drivers and the at least one sensing signal provided by the second subset of comb drivers to generate a total measurement signal, and

[0270] The processing circuit is configured to determine at least one of a phase or an amplitude of the desired rotational motion pattern based on the total measurement signal.

[0271] 6. The scanning system according to embodiment 5, further comprising:

[0272] A system controller is configured to modify the at least one drive signal based on at least one of the determined phase of the desired rotational motion pattern or the determined amplitude of the desired rotational motion pattern.

[0273] 7. The scanning system of embodiment 1, wherein the processing circuit is configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensed signal.

[0274] 8. The scanning system of embodiment 7, wherein:

[0275] the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives,

[0276] The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and

[0277] The processing circuit is configured to identify the parasitic motion pattern, determine a magnitude of the parasitic motion pattern, and determine a phase of the parasitic motion pattern relative to the at least one drive signal based on the differential measurement signal.

[0278] 9. The scanning system according to embodiment 8, further comprising:

[0279] A system controller is configured to damp the identified parasitic motion pattern by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

[0280] 10. The scanning system according to embodiment 1, further comprising:

[0281] System Controller,

[0282] wherein the processing circuit is configured to determine the amplitude and phase of the parasitic motion mode of the MEMS scanning structure relative to the at least one drive signal based on the sensing signal, and

[0283] The system controller is configured to damp the identified parasitic motion pattern by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

[0284] 11. The scanning system according to embodiment 7, further comprising:

[0285] A system controller is configured to damp the identified parasitic motion mode based on the identified parasitic motion mode by applying at least one damping signal directly to at least a subset of stator comb electrodes of the plurality of comb drives or directly to each rotor comb electrode of the plurality of comb drives.

[0286] 12. The scanning system according to embodiment 7, further comprising:

[0287] A system controller is configured to damp the identified parasitic motion mode based on the identified parasitic motion mode by superimposing the at least one damping signal on the at least one drive signal.

[0288] 13. The scanning system of embodiment 1, wherein:

[0289] the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives,

[0290] The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and

[0291] The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

[0292] 14. The scanning system of embodiment 1, wherein:

[0293] the plurality of comb drives including a first subset of comb drives arranged transversely from the axis in a first direction and a second subset of comb drives arranged transversely from the axis in a second direction opposite the first direction,

[0294] The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and

[0295] The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

[0296] 15. The scanning system of embodiment 1, wherein:

[0297] the plurality of comb drives including a first subset of comb drives arranged diagonally across the axis from one another on a first diagonal line and a second subset of comb drives arranged diagonally across the axis from one another on a second diagonal line intersecting the first diagonal line,

[0298] The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and

[0299] The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

[0300] 16. A scanning system comprising:

[0301] a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0302] a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0303] a driver configured to generate the at least one drive signal;

[0304] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0305] A processing circuit is configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensed signal.

[0306] 17. The scanning system according to embodiment 16, further comprising:

[0307] A system controller is configured to damp the identified parasitic motion mode based on the identified parasitic motion mode by applying at least one damping signal to at least a subset of stator comb electrodes of the plurality of comb drives or to each rotor comb electrode of the plurality of comb drives.

[0308] 18. The scanning system of embodiment 17, wherein the system controller selectively determines the subset of stator comb electrodes to which the at least one damping signal is applied based on the identified parasitic modes.

[0309] 19. The scanning system of embodiment 17, wherein the system controller is configured to superimpose the at least one damping signal on the at least one drive signal.

[0310] 20. The scanning system of embodiment 16, further comprising:

[0311] A system controller is configured to selectively couple the sensing circuit to at least the subset of the plurality of comb drives so that the sensing circuit receives a sensing signal from the subset based on the type of the parasitic motion pattern being evaluated.

[0312] 21. The scanning system of embodiment 16, wherein:

[0313] the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives,

[0314] The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and

[0315] The processing circuit is configured to identify a parasitic motion pattern of the MEMS scanning structure, determine a magnitude of the parasitic motion pattern, and determine a phase of the parasitic motion pattern relative to the at least one drive signal based on the differential measurement signal.

[0316] 22. The scanning system according to embodiment 21, further comprising:

[0317] A system controller is configured to damp the identified parasitic motion pattern by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

[0318] 23. The scanning system according to embodiment 16, further comprising:

[0319] a system controller configured to damp the identified parasitic motion mode according to the identified parasitic motion mode by biasing a pair of stator comb electrodes during a drive voltage off time of the drive signal to decelerate the identified parasitic motion mode,

[0320] The MEMS scanning structure is a resonant MEMS scanning structure.

[0321] 24. The scanning system of embodiment 16, further comprising:

[0322] a system controller configured to damp the identified parasitic motion mode by superimposing a damping voltage on the at least one drive signal, the at least one drive signal being applied to each of the rotor comb electrodes to decelerate the identified parasitic motion mode,

[0323] The MEMS scanning structure is a resonant MEMS scanning structure.

[0324] 25. The scanning system of embodiment 16, further comprising:

[0325] a system controller configured to damp the identified parasitic motion mode by superimposing a damping voltage on the at least one drive signal applied to a pair of stator comb electrodes to decelerate the identified parasitic motion mode,

[0326] The MEMS scanning structure is a quasi-static MEMS scanning structure.

[0327] 26. A scanning system comprising:

[0328] a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0329] a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor-driven comb electrode and a stator-driven comb electrode;

[0330] a driver configured to generate the at least one drive signal;

[0331] a plurality of sensing combs, wherein each sensing comb comprises a rotor sensing comb electrode and a stator sensing comb electrode, the rotor sensing comb electrode and the stator sensing comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0332] a sensing circuit selectively coupled to at least a subset of the plurality of sensing combs to receive sensing signals from the subset, wherein each sensing signal represents a capacitance of a corresponding sensing comb; and

[0333] A processing circuit is configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensed signal.

[0334] 27. The scanning system of embodiment 26, further comprising:

[0335] A system controller is configured to damp the identified parasitic motion mode according to the identified parasitic motion mode by applying at least one damping signal to at least a 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.

[0336] 28. The scanning system of embodiment 27, wherein the system controller selectively determines the subset of stator drive comb electrodes to which the at least one damping signal is applied based on the identified parasitic modes.

[0337] 29. The scanning system of embodiment 27, wherein the system controller is configured to superimpose the at least one damping signal on the at least one drive signal.

[0338] 30. The scanning system of embodiment 26, wherein the processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the sensed signal.

[0339] 31. The scanning system of embodiment 30, wherein:

[0340] The plurality of sensing combs include a first set of sensing combs and a second set of sensing combs,

[0341] The sensing circuit is configured to subtract at least one sensing signal provided by the second set of sensing combs from at least one sensing signal provided by the first set of sensing combs to generate a differential measurement signal, and

[0342] The processing circuit is configured to determine the scanning direction of the MEMS scanning structure of the desired rotational motion pattern based on the differential measurement signal.

[0343] 32. The scanning system of embodiment 31, wherein:

[0344] The sensing circuit is configured to add the sensing signals from the first set of sensing combs and the second set of sensing combs to generate a total measurement signal, and

[0345] The processing circuit is configured to determine at least one of a phase or an amplitude in the desired rotational motion pattern based on the total measurement signal.

[0346] 33. The scanning system of embodiment 26, wherein:

[0347] The plurality of sensing combs include a first set of sensing combs and a second set of sensing combs,

[0348] The sensing circuit is configured to subtract at least one sensing signal provided by the second set of sensing combs from at least one sensing signal provided by the first set of sensing combs to generate a differential measurement signal, and

[0349] The processing circuit is configured to identify the parasitic motion pattern, determine a magnitude of the parasitic motion pattern, and determine a phase of the parasitic motion pattern relative to the at least one drive signal based on the differential measurement signal.

[0350] 34. The scanning system of embodiment 33, further comprising:

[0351] A system controller is configured to damp the identified parasitic motion pattern by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

[0352] 35. The scanning system of embodiment 26, further comprising:

[0353] A system controller is configured to damp the identified parasitic motion mode by superimposing a damping voltage on the at least one drive signal applied to a pair of stator drive comb electrodes to decelerate the identified parasitic motion mode.

[0354] 36. A scanning system comprising:

[0355] a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0356] a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitance applied to a pair of stator drive comb electrodes that depends on a deflection angle of the MEMS scanning structure;

[0357] a driver configured to generate the at least one drive signal;

[0358] a system controller configured to shift a drive frequency of the at least one drive signal to induce parasitic mode coupling between the desired rotational motion mode and a parasitic motion mode of the MEMS scanning structure;

[0359] a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; and

[0360] processing circuitry configured to determine a frequency range of the drive frequency in which the parasitic mode coupling occurs,

[0361] The system controller controls the at least one driving signal to avoid the parasitic mode.

[0362] 37. The scanning system of embodiment 36, wherein the system controller controls at least one of the drive frequency, peak input voltage, duty cycle, or waveform of the at least one drive signal such that the parasitic mode is avoided.

[0363] 38. A scanning system comprising:

[0364] a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal;

[0365] a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor-driven comb electrode and a stator-driven comb electrode;

[0366] a driver configured to generate the at least one drive signal;

[0367] a plurality of sensing combs, wherein each sensing comb comprises a rotor sensing comb electrode and a stator sensing comb electrode, the rotor sensing comb electrode and the stator sensing comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure;

[0368] a system controller configured to shift a drive frequency of the at least one drive signal to induce parasitic mode coupling between the desired rotational motion mode and a parasitic motion mode of the MEMS scanning structure;

[0369] a sensing circuit selectively coupled to at least a subset of the plurality of sensing combs to receive sensing signals from the subset, wherein each sensing signal represents a capacitance of a corresponding sensing comb; and

[0370] processing circuitry configured to determine a frequency range of the drive frequency in which the parasitic mode coupling occurs,

[0371] The system controller controls the at least one driving signal to avoid the parasitic mode.

[0372] 39. The scanning system of embodiment 38, wherein the system controller controls at least one of the drive frequency, peak input voltage, duty cycle, or waveform of the at least one drive signal such that the parasitic mode is avoided.

[0373] Although the embodiments described herein relate to MEMS devices having mirrors, it should be understood that other implementations may include other optical devices besides MEMS mirror devices, including other oscillating structures, including oscillating structures that are not related to LIDAR. In addition, although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of a corresponding method, where a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware device, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some of one or more method steps may be performed by such a device.

[0374] Although various embodiments have been described, it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the present disclosure. Accordingly, the present invention is limited only by the appended claims and their equivalents. With respect to the various functions performed by the aforementioned components or structures (assemblies, devices, circuits, systems, etc.), the terms used to describe such components (including references to "devices") are intended to correspond (unless otherwise indicated) to any component or structure that performs the designated function of the described component (i.e., is functionally equivalent), even if not structurally equivalent to the disclosed structures that perform the functions in the exemplary implementations of the invention shown herein.

[0375] In addition, the following claims are hereby incorporated into the detailed description, where each claim can stand on its own as a separate example embodiment. Although each claim can stand on its own as a separate example embodiment, it should be noted that although a dependent claim may refer to a specific combination with one or more other claims in a claim, other example embodiments may also include a combination of the dependent claim with the subject matter of each other's dependent or independent claims. Unless it is stated that a specific combination is not intended, such a combination is suggested herein. In addition, it is also intended to include features of a claim into any other independent claim, even if that claim is not directly dependent on the independent claim.

[0376] It should also be noted that the methods disclosed in the specification or claims may be implemented by a device having means for performing each of the corresponding acts of these methods.

[0377] Furthermore, it should be understood that the disclosure of multiple actions or functions disclosed in the specification or claims should not be interpreted as being in a specific order. Therefore, unless these actions or functions are not interchangeable for technical reasons, the disclosure of multiple actions or functions does not restrict them to a specific order. Furthermore, in some embodiments, a single action may include or be decomposed into multiple sub-actions. Unless explicitly excluded, such sub-actions may be included and are part of the disclosure of the single action.

[0378] Instructions may be executed by one or more processors, such as one or more central processing units (CPUs), digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuit systems. Thus, as used herein, the terms "processor" or "processing circuitry" refer to any of the foregoing structures or any other structure suitable for the implementation of the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules. Furthermore, these techniques may be implemented entirely in one or more circuits or logic elements.

[0379] Thus, the techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors, including one or more microprocessors, DSPs, ASICs, or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components.

[0380] A controller including hardware may also perform one or more of the techniques described in this disclosure. Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various techniques described in this disclosure. The software may be stored on a non-transitory computer-readable medium such that the non-transitory computer-readable medium includes program code or a program algorithm stored thereon that, when executed, causes the controller to perform the steps of the method via a computer program.

[0381] Although various exemplary embodiments have been disclosed, it will be apparent to those skilled in the art that various changes and modifications may be made to achieve some of the advantages of the concepts disclosed herein without departing from the spirit and scope of the present invention. It will be apparent to those skilled in the art that other components performing the same function may be appropriately replaced. It will be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. It should be noted that features explained with reference to specific figures may be combined with features of other figures, even in those figures not explicitly mentioned. Such modifications to the general inventive concept are intended to be covered by the appended claims and their legal equivalents.

Claims

1. A scanning system comprising: a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal; a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure; a driver configured to generate the at least one drive signal; a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; The processing circuit is configured to: determining a parasitic motion mode and a scanning direction of the MEMS scanning structure in the desired rotational motion mode based on the sensing signal; as well as System controller, configured to: At a timing effective for damping the parasitic motion mode, a reaction force is applied to one or more of the rotor comb electrodes corresponding to the parasitic motion mode or the stator comb electrodes corresponding to the parasitic motion mode.

2. The scanning system according to claim 1, wherein: the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives, The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal. The scanning system of claim 2 , wherein the sign of the differential measurement signal indicates the scanning direction.

4. The scanning system of claim 2 , wherein the system controller is configured to: The at least one drive signal is modified based on the determined scan direction.

5. The scanning system according to claim 2, wherein: The sensing circuit is configured to sum the at least one sensing signal provided by the first subset of comb drivers and the at least one sensing signal provided by the second subset of comb drivers to generate a total measurement signal, and The processing circuit is configured to determine at least one of a phase of the desired rotational motion pattern or an amplitude of the desired rotational motion pattern based on the total measurement signal.

6. The scanning system of claim 5, wherein the system controller is further configured to: The at least one drive signal is modified based on at least one of the phase of the desired rotational motion pattern or the amplitude of the desired rotational motion pattern.

7. The scanning system of claim 1 , wherein: the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives, The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and The processing circuit is configured to determine the parasitic motion pattern, determine a magnitude of the parasitic motion pattern, and determine a phase of the parasitic motion pattern relative to the at least one drive signal based on the differential measurement signal.

8. The scanning system of claim 7, wherein the system controller is further configured to: The parasitic motion pattern is damped by applying at least one damping signal corresponding to the reaction force, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude of the parasitic motion pattern and the phase of the parasitic motion pattern.

9. The scanning system of claim 1 , wherein the processing circuit is further configured to: determining an amplitude and a phase of the parasitic motion mode of the MEMS scanning structure relative to the at least one drive signal based on the sensed signal, and The system controller is further configured to: The parasitic motion pattern is damped by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

10. The scanning system of claim 1 , wherein the system controller is further configured to: The parasitic motion mode is damped by applying at least one damping signal directly to at least a subset of stator comb electrodes of the plurality of comb drives or directly to each rotor comb electrode of the plurality of comb drives.

11. The scanning system of claim 1 , wherein the system controller is further configured to: The parasitic motion mode is damped by superimposing at least one damping signal on the at least one drive signal.

12. The scanning system of claim 1 , wherein: the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives, The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

13. The scanning system of claim 1 , wherein: the plurality of comb drives including a first subset of comb drives arranged transversely from the axis in a first direction and a second subset of comb drives arranged transversely from the axis in a second direction opposite the first direction, The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

14. The scanning system of claim 1 , wherein: the plurality of comb drives including a first subset of comb drives arranged diagonally across the axis from one another on a first diagonal line and a second subset of comb drives arranged diagonally across the axis from one another on a second diagonal line intersecting the first diagonal line, The sensing circuit is configured to sum the sense signals from the first subset of comb drivers to generate a first total sense signal, sum the sense signals from the second subset of comb drivers to generate a second total sense signal, and subtract the second total sense signal from the first total sense signal to generate a differential measurement signal, and The processing circuit is configured to determine the scanning direction of the MEMS scanning structure in the desired rotational motion pattern based on the differential measurement signal.

15. A scanning system comprising: a micro-electromechanical system (MEMS) scanning structure configured to rotate about an axis in a desired rotational motion pattern based on at least one drive signal; a plurality of comb drives configured to drive the MEMS scanning structure about the axis according to the desired rotational motion pattern based on the at least one drive signal, wherein each comb drive includes a rotor comb electrode and a stator comb electrode, the rotor comb electrode and the stator comb electrode forming a capacitive element, the capacitance of the capacitive element being dependent on a deflection angle of the MEMS scanning structure; a driver configured to generate the at least one drive signal; a sensing circuit selectively coupled to at least a subset of the plurality of comb drives to receive sense signals from the subset, wherein each sense signal represents a capacitance of a corresponding comb drive; processing circuitry configured to detect and identify a parasitic motion mode of the MEMS scanning structure based on the sensing signal; as well as The system controller is configured to cause a reaction force to be applied to one or more of the rotor comb electrodes corresponding to the parasitic motion mode or the stator comb electrodes corresponding to the parasitic motion mode at a timing effective for damping the parasitic motion mode.

16. The scanning system of claim 15 , wherein the system controller is configured to damp the parasitic motion pattern based on the parasitic motion pattern by applying at least one damping signal to at least a subset of stator comb electrodes of the plurality of comb drives or to each rotor comb electrode of the plurality of comb drives.

17. The scanning system of claim 16, wherein the system controller selectively determines the subset of stator comb electrodes to which the at least one damping signal is applied based on the parasitic motion pattern.

18. The scanning system of claim 16, wherein the system controller is configured to superimpose the at least one damping signal on the at least one drive signal.

19. The scanning system of claim 15, wherein the system controller is further configured to: The sensing circuit is selectively coupled to at least the subset of the plurality of comb drives such that the sensing circuit receives a sensing signal from the subset based on a type of the parasitic motion pattern being evaluated.

20. The scanning system of claim 15, wherein: the plurality of comb drives comprising a first subset of comb drives and a second subset of comb drives, The sensing circuit is configured to subtract at least one sense signal provided by the second subset of comb drivers from at least one sense signal provided by the first subset of comb drivers to generate a differential measurement signal, and The processing circuit is configured to: determining an amplitude of the parasitic motion pattern relative to the at least one drive signal based on the differential measurement signal, and A phase of the parasitic motion pattern relative to the at least one drive signal is determined based on the differential measurement signal.

21. The scanning system of claim 20, wherein the system controller is further configured to: The parasitic motion pattern is damped by applying at least one damping signal, wherein the system controller adjusts an amplitude and a phase of the at least one damping signal based on the amplitude and the phase of the parasitic motion pattern.

22. The scanning system of claim 20, wherein a sign of the differential measurement signal indicates a scanning direction of the MEMS scanning structure.

23. The scanning system of claim 15, wherein the system controller is further configured to: damping the parasitic motion mode by biasing a pair of stator comb electrodes during a drive voltage off time of the drive signal to decelerate the parasitic motion mode according to the parasitic motion mode, The MEMS scanning structure is a resonant MEMS scanning structure.

24. The scanning system of claim 16, wherein the system controller is further configured to: damping the parasitic motion mode by superimposing a damping voltage on the at least one drive signal, the at least one drive signal being applied to each of the rotor comb electrodes to decelerate the parasitic motion mode, The MEMS scanning structure is a resonant MEMS scanning structure.

25. The scanning system of claim 16, wherein the system controller is further configured to: damping the parasitic motion mode by superimposing a damping voltage on the at least one drive signal applied to a pair of stator comb electrodes to decelerate the parasitic motion mode, The MEMS scanning structure is a quasi-static MEMS scanning structure.

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