Control structure for an oscillator with nonlinear frequency response

Abstract

Embodiments of the present disclosure relate to a control structure for an oscillator with a nonlinear frequency response. An oscillator control system includes: a nonlinear oscillator structure configured to oscillate about an axis; a driver circuit configured to generate a drive signal to drive the oscillator structure; a detection circuit configured to measure the angular amplitude and phase error of the oscillator structure; an amplitude controller configured to generate a reference oscillator period based on the measured angular amplitude; a period and phase controller configured to: receive the reference oscillator period and the measured phase error from the detection circuit, generate at least one control parameter of the drive signal based on the reference oscillator period and the measured phase error, and determine a drive period of the drive signal based on the reference oscillator period and the measured phase error. The driver circuit is configured to: generate the drive signal based on at least one control parameter and the drive period.

Description

Technical Field

[0001] The present disclosure relates generally to micro-electromechanical systems (MEMS) oscillating systems and methods of operating the same, and more particularly, to controlling an oscillating structure in a MEMS oscillating system. 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 (variable distance) to one or more objects in a field of view. In particular, micro-electromechanical systems (MEMS) mirrors are used to scan light across the field of view. An array of photodetectors receives reflections from objects illuminated by the light and determines the time it takes for the reflections to reach the individual sensors in the photodetector array. This is also known as measuring the time of flight (TOF). LIDAR systems form depth measurements and perform distance measurements by mapping distances to objects based on time of flight calculations. Thus, the time of flight calculation can create distance and depth maps, which can be used to generate images.

[0003] The LIDAR scanning system may include one or more scanning mirrors and corresponding circuit devices for scanning different fields of view in the horizontal direction and / or vertical direction. Each scanning mirror is a nonlinear oscillator having a correlation between angular amplitude and frequency. If an oscillator with a nonlinear frequency response is affected by an external (possibly unobservable) disturbance, the oscillator may change its oscillation amplitude and thereby change its frequency due to the nonlinear correlation of the oscillator. Typically, a phase-locked loop (PLL) driving the oscillator measures both the angular amplitude and the oscillator phase, and adapts the drive period according to the phase, and adapts some other control quantity (e.g., drive voltage) according to the amplitude. Since the noise of the amplitude measurement is often larger than the noise of the phase measurement, the drive period is adapted quite quickly, while the amplitude control is slow in comparison. Therefore, rapid changes in amplitude are not compensated. In addition, the PLL always follows the oscillator period, rather than pushing the oscillator to the desired period, and thereby to the desired amplitude.

[0004] Therefore, what is desired is an improved control structure for an oscillator having a nonlinear frequency response. Summary of the invention

[0005] Embodiments provide a control structure for angular amplitude and phase control of a nonlinear oscillator having a nonlinear correlation between amplitude and frequency.

[0006] One or more embodiments provide an oscillator control system, the oscillator control system comprising: an oscillator structure configured to oscillate about an axis, wherein the angular amplitude and frequency of the oscillator structure have a nonlinear correlation; a driver circuit configured to generate a drive signal to drive the oscillation of the oscillator structure; a detection circuit configured to measure the angular amplitude and phase error of the oscillator structure; an outer control loop including an amplitude controller, the amplitude controller configured to generate a reference oscillator period based on the measured angular amplitude; an inner control loop including a period and phase controller, the period and phase controller configured to: receive the reference oscillator period from the outer control loop and the measured phase error from the detection circuit, generate at least one control parameter of the drive signal based on the reference oscillator period and the measured phase error, and determine a drive period of the drive signal based on the reference oscillator period and the measured phase error, wherein the driver circuit is configured to: generate the drive signal based on the at least one control parameter and the drive period of the drive signal. The driver circuit is configured to: generate the drive signal based on the at least one control parameter and the drive period.

[0007] One or more embodiments provide a method for controlling an oscillator structure, wherein the oscillator structure is configured to oscillate around an axis according to a drive signal, wherein the angular amplitude and frequency of the oscillator structure have a nonlinear correlation, the method comprising: measuring the angular amplitude of the oscillator structure; measuring the phase error of the oscillator structure; generating a reference oscillator period based on the measured angular amplitude; generating at least one control parameter of the drive signal based on the reference oscillator period and the measured phase error, including: adapting at least one control parameter of the drive signal to compensate for the measured phase error; determining a drive period of the drive signal based on the reference oscillator period and the measured phase error, including: adapting the drive period to compensate for the measured phase error; and generating the drive signal based on at least one control parameter of the drive signal and the drive period.

[0008] One or more embodiments provide a light detection and ranging (LIDAR) control system, the system comprising: a microelectromechanical system (MEMS) mirror configured to oscillate about an axis, wherein the angular amplitude and frequency of the MEMS mirror have a nonlinear correlation; a driver circuit configured to generate a drive signal to drive the oscillation of the MEMS mirror; a detection circuit configured to measure the angular amplitude and phase error of the MEMS mirror; an outer control loop comprising an amplitude controller, the amplitude controller being configured to: generate a reference mirror period based on the measured angular amplitude; and an inner control loop comprising a period and phase controller, the period and phase controller being configured to: receive a reference mirror period from the outer control loop and a measured phase error from the detection circuit, generate at least one control parameter of the drive signal based on the reference mirror period and the measured phase error, and determine a drive period of the drive signal based on the reference mirror period and the measured phase error, wherein the driver circuit is configured to: generate the drive signal based on the at least one control parameter of the drive signal and the drive period. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments are described herein with reference to the accompanying drawings.

[0010] Figure 1A is a schematic diagram of a LIDAR scanning system according to one or more embodiments;

[0011] Figure 1B shows a schematic top view of an example of a reflector device according to one or more embodiments;

[0012] Figure 2 is a schematic block diagram of a LIDAR scanning system according to one or more embodiments;

[0013] Figure 3 illustrates signal graphs of various signals generated by a MEMS actuator based on a mirror angle θ and / or position according to one or more embodiments;

[0014] Figure 4A illustrates an angular amplitude-frequency response curve of a micro-mirror device according to one or more embodiments;

[0015] Figure 4B illustrates an angular amplitude-frequency response curve (top) and a phase delay-frequency response curve (bottom) of a micro-mirror device according to one or more embodiments;

[0016] Figure 5 illustrates a schematic block diagram of an oscillator control system according to one or more embodiments;

[0017] Figure 6illustrates a schematic block diagram of an oscillator control system according to one or more embodiments;

[0018] Figure 7 A schematic block diagram of an oscillator control system according to one or more embodiments is illustrated. DETAILED DESCRIPTION

[0019] In the following, 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 required to implement the embodiment. On the contrary, in other embodiments, some of the features or elements may be omitted or may be replaced with alternative features or elements. In addition, 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.

[0020] Unless otherwise specifically stated, features from different embodiments may be combined to form other embodiments. Variations or modifications described with reference to one embodiment in the embodiments may also be applicable to other embodiments. In some cases, in order to avoid making the embodiments difficult to understand, known structures and devices are shown in block diagram form rather than in detail.

[0021] Unless otherwise specified, the connection or coupling between the elements shown in the drawings or described herein may be a wire-based connection or a wireless connection. In addition, as long as the general purpose of the connection or coupling (e.g., transmitting a specific type of signal or transmitting a specific type of information) is basically maintained, such connection or coupling may be a direct connection or coupling without additional intermediate elements, or may be an indirect connection or coupling with one or more additional intermediate elements.

[0022] Embodiments relate to optical sensors and optical sensor systems, and 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). For example, the physical quantity may include electromagnetic radiation (such as visible light, infrared (IR) radiation, or other types of illumination signals), current, or voltage, but is not limited thereto. For example, an image sensor may be a silicon chip inside a camera that converts photons of light from a lens into voltage. The larger the active area of ​​a sensor, the more light can be collected to create an image.

[0023] A sensor device as used herein may refer to a device including a sensor and other components (e.g., a bias circuit device, an analog-to-digital converter, or a filter). The sensor device may be integrated on a single chip, although in other embodiments, multiple chips or components external to the chip may be used to implement the sensor device.

[0024] In a light detection and ranging (LIDAR) system, a light source transmits a light pulse into a field of view, and the light is reflected from one or more objects by backscattering. In particular, LIDAR is a direct time-of-flight (TOF) system in which a light pulse (e.g., a laser beam of infrared light) is emitted into the field of view, and an array of pixels detects and measures the reflected beam. For example, an array of photodetectors receives reflections from objects illuminated by the light.

[0025] The difference in the return time of each light pulse across multiple pixels of the pixel array can then be used to make 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) until the time the reflected light pulse (corresponding to a stop signal) is received at the receiver (i.e., at the pixel array). The "time of flight" of the light pulse is then converted to distance.

[0026] In another example, an analog-to-digital converter (ADC) can be electrically coupled to the pixel array (e.g., indirectly coupled with an intermediate element located in between) 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 emitting a light pulse) and the stop signal (i.e., corresponding to the timing of receiving the analog electrical signal at the ADC) using an appropriate algorithm.

[0027] Scanning, such as an oscillating horizontal scan (e.g., from left to right and right to left of the field of view) or an oscillating vertical scan (e.g., from bottom to top and top to bottom of the field of view) can illuminate the scene in a continuous scanning manner. Each emission of a laser beam by a light source can produce a scan line in the "field of view". By emitting continuous light pulses in different scanning directions, an area called the field of view can be scanned, and objects within the area can be detected and imaged. The field of view thus represents a scan plane with a projection center. Raster scanning can also be used.

[0028] Figure 1A1 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 element 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.

[0029] The lighting unit 10 includes a plurality of light sources (e.g., laser diodes or light emitting diodes) linearly aligned in the form of a single bar and configured to emit light for scanning an object. The light emitted by the light source is typically infrared light, although light having another wavelength may also be used. As can be seen from the embodiment of FIG. 1 , the shape of the light emitted by the light source expands in a direction perpendicular to the transmission direction to form a light beam having a rectangular shape perpendicular to the transmission. The illumination light emitted from the light source is directed to an emitter optical element 11, which is configured to focus each laser onto a one-dimensional MEMS mirror 12. For example, the emitter optical element 11 may be a lens or a prism.

[0030] When reflected by the MEMS mirror 12, the light from the light source is aligned in the vertical direction to form a one-dimensional vertical scan line SL of infrared light or a vertical infrared light strip for each laser shot emitted. Each light source of the lighting unit 10 contributes to a different vertical region of the vertical scan line SL. Therefore, the light source can be activated and deactivated simultaneously to obtain a light pulse having a plurality of segments, each of which corresponds to a corresponding light source. However, each vertical region or each segment of the vertical scan line SL can also be independently activated or disabled by turning on or off a corresponding light source in the light sources of the lighting 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.

[0031] 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.

[0032] 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 may be generated by a single laser source, two laser sources, or more than three laser sources.

[0033] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micro-mirror) integrated on a semiconductor chip (not shown). 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, and can be said to have only one degree of freedom for movement. Due to the single axis of rotation, the MEMS mirror 12 is referred to as a 1D MEMS mirror.

[0034] In order to make a MEMS scanning mirror robust against vibrations, the mirror should have a low inertia, ie a light and rigid mirror body. Furthermore, the mirror should have a high stiffness of its suspension for all degrees of freedom (DOF) of the mirror body.

[0035] In order to achieve a light and rigid reflector body, the reflector body may include a relatively thin reflector and a thicker reinforcement structure for the reflector. The reflector body may be arranged in the reflector frame in a manner that it can rotate around an axis of rotation extending in a plane defined by the reflector frame. The axis of rotation may extend to a first end and a second end of the reflector body that are opposite to each other. The reflector may have a reflecting surface on a first main surface, and a second main surface opposite to the first main surface is provided with a reinforcement structure.

[0036] In order to achieve high stiffness suspension, such as Figure 1B As shown, the reflector body can be supported in the reflector frame using a support beam extending along the rotation axis and an additional cantilever beam or leaf spring assembly. Generally, as defined herein, a leaf spring assembly can refer to a cantilever beam assembly, and vice versa. Similarly, leaf springs and cantilever beams can be used interchangeably.

[0037] The cantilever beam assembly may have a longitudinal direction and may extend in a plane defined by the frame. The support beam may be connected between the reflector body and the frame at opposite ends of the reflector body along the rotation axis. The cantilever beam assembly may have a cantilever beam coupled to the reflector frame at a first end via a relief structure and fixed to the reflector body at a second end. The thickness of the cantilever beam perpendicular to the plane of the frame may be less than the width of the cantilever beam in the plane of the frame.

[0038] The result of the low inertia of the mirror body and the high suspension stiffness can be a high resonant frequency and good dynamic performance. These properties can also make the device, which operates at the resonant frequency around the main axis of rotation, very fast. In normal operation (i.e., at resonance), accelerations of typically 10,000 G can be achieved at the mirror tip. This can make any external vibrations negligible.

[0039] Due to the stiffness of the suspension structure (ie, cantilever beam), the MEMS mirror 12 exhibits nonlinear behavior, such that the mirror's oscillation frequency increases in a nonlinear manner as the oscillation amplitude (ie, tilt angle amplitude) increases. Thus, stiffening the suspension makes the MEMS mirror 12 more strongly nonlinear.

[0040] The MEMS mirror 12 can be assembled in Figure 2 The chip package 27 is shown to protect the mirror. For example, the MEMS mirror 12 can be sealed in the chip package at low pressure (ie, pressure below atmospheric pressure). Such low pressure can provide a low damping environment for the MEMS mirror 12 to operate.

[0041] Conceivable packages may include or differ from one or more of the following variations: different substrates (e.g., metal substrates (leadframes), ceramic substrates, organic substrates (similar to printed circuit board (PCB) materials)) and different optical covers or coverings (e.g., optical materials of glass, silicon, sapphire, etc.). In addition, the optical cover or covering may be a cover forming a cavity, may be integrated in a frame (e.g., a metal frame), or assembled to a pre-molded cavity or a ceramic cavity.

[0042] One or more methods (e.g., bonding, gluing, welding, forging, etc.) or one or more different materials (e.g., silicone, glass solder, AuSn, etc.) can be used to join one or more elements together (e.g., to connect a lid or cover to a substrate). It should be understood that the joining methods can be interchangeable across the various embodiments disclosed herein.

[0043] Alternatively, a wafer-level approach can be used so that the lid forming the cavity can be mounted directly on the MEMS chip (or even mounted at the wafer level before singulation). Here, if the lid attachment leaves the electrical pads exposed, the submounted chip / lid can be further processed into the package using a molding or casting process.

[0044] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micro-mirror) integrated on a semiconductor chip (not shown). The MEMS mirror 12 according to this embodiment is configured to rotate around a single scanning axis and can be said to have only one degree of freedom for scanning. Unlike a 2D-MEMS mirror (2D MEMS scanner), in a 1D MEMS mirror, a single scanning axis is fixed on a non-rotating substrate and thus maintains its spatial orientation during the oscillation of the MEMS mirror. Therefore, compared to a 2D MEMS mirror solution, a 1D oscillating MEMS mirror is designed to be more robust to vibration and shock. Due to this single scanning axis of rotation, the MEMS mirror 12 is referred to as a 1D MEMS mirror or a 1D MEMS scanner. Although the embodiment describes the use of a 1D oscillating MEMS mirror, the synchronization method described herein can also be extended to a 2D MEMS mirror. In this case, the two axes of a single 2D MEMS mirror are controlled by different phase locked loops (PLLs) to synchronize a first scanning direction of the 2D MEMS mirror according to a first axis according to any synchronization technique described herein, and synchronize a second scanning direction of the 2D MEMS mirror according to a second axis according to any synchronization technique described herein. Different PLLs may also be provided in separate MEMS actuators for each 2D MEMS mirror or integrated into a single MEMS actuator.

[0045] The MEMS mirror 12 itself is a nonlinear resonator (i.e., a resonant MEMS mirror) that is configured to oscillate "side-to-side" around a single scan axis 13 at a resonant frequency, so that the light reflected from the MEMS mirror 12 (i.e., a vertical scan line of light) oscillates back and forth in the horizontal scan direction. Due to the stiffening of the suspension, the MEMS mirror 12 is even more strongly nonlinear. For example, a scan period or oscillation period is defined by one complete oscillation from a first edge of the field of view (e.g., the left side) to a second edge of the field of view (e.g., the right side) and then back to the first edge again. The mirror period of the MEMS mirror 12 corresponds to the scan period.

[0046] Thus, by changing the angle of the MEMS mirror 12 on its scanning axis 13, the field of view is scanned in the horizontal direction by the vertical light bar. For example, the MEMS mirror 12 can be configured to oscillate at a resonant frequency of 2kHz between + / -15 degrees to deflect the light over + / -30 degrees, which constitutes the scanning range of the field of view. Thus, the field of view can be scanned line by line by the rotation of the MEMS mirror 12 in its degree of motion. One such sequence of traversing the degrees of motion (e.g., from -15 degrees to +15 degrees) is called a single scan or scanning cycle. Multiple scans can be used to generate distance and depth maps and 3D images by a processing unit.

[0047] Although a transmission mirror is described in the context of a MEMS mirror, it should be understood that other 1D mirrors may also be used. In addition, the resonant frequency or degree of rotation is not limited to 2kHz and + / -15 degrees, respectively, and the resonant frequency and field of view may be increased or decreased depending on the application. Thus, the one-dimensional scanning mirror is configured to oscillate around a single scanning axis and introduce the laser beam into the field of view in different directions. Thus, the transmission technique includes transmitting a light beam from a transmission mirror oscillating around a single scanning axis into the field of view, such that the light beam is projected into the field of view in the form of a vertical scan line SL that moves horizontally across the field of view as the transmission mirror oscillates around the single scanning axis.

[0048] Upon impacting one or more objects, the transmitted strip of vertical light is reflected as a reflected vertical line by backscattering toward the LIDAR scanning system 100, where the second optical component 14 (e.g., a lens or prism) receives the reflected light. The second optical component 14 directs the reflected light onto a photodetector array 15, which receives the reflected light as a receive line RL and is configured to generate an electrical measurement signal. The electrical measurement signal 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).

[0049] The receiving line is shown as a vertical optical column extending along one of the pixel columns in the longitudinal direction of the pixel columns. Figure 1A As the vertical scan 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 the first edge of the photodetector array 15 to the second edge of the photodetector array 15. The receiving direction of the reflected light beam RL corresponds to the transmission direction of the scan line SL.

[0050] The photodetector array 15 can be any of a variety of photodetector types, including avalanche photodiodes (APDs), 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 including an APD pixel array. In other embodiments, the photodetector array 15 can be a 1D array including a single column of photodiodes. The activation of the photodiodes can be synchronized with the light pulses emitted by the lighting unit 10. Alternatively, in contrast to the array, a single photodetector unit / pixel can be used. For example, in the case of a 2x1D scanning transmitter in a coaxial LIDAR architecture, a single photodetector unit / pixel can be used.

[0051] The photodetector array 15 receives the reflected light pulses as receive lines RL and generates an electrical signal in response thereto. Since the transmission time of each light pulse from the lighting unit 10 is known, and since light travels at a known speed, the distance of the object from the photodetector array 15 can be determined using the time-of-flight calculation of the electrical signal. A depth map can plot the distance information.

[0052] In one example, for each distance sample, the microcontroller triggers a laser pulse from each of the light sources of the lighting unit 10 and also starts a timer in a time-to-digital converter (TDC) integrated circuit (IC). The laser pulse propagates through the transmission optical element, is reflected by the target field, and is captured by the APD in the APD array 15. The APD emits a short electrical pulse, which is then amplified by the electrical signal amplifier. The comparator IC recognizes the pulse and sends a digital signal to the TDC to stop the timer. The TDC uses the clock frequency to calibrate each measurement. The TDC sends serial data of the differential time between the start digital signal and the stop digital signal 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 emitting continuous light pulses in different directions established by the MEMS mirror, an area (i.e., field of view) can be scanned, a three-dimensional image can be generated, and objects within the area can be detected.

[0053] 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., corresponding to the timing of emitting a light pulse) and the stop signal (i.e., corresponding to the timing of receiving the analog electrical signal at the ADC) using an appropriate algorithm.

[0054] It should be understood that the above-described horizontal scanning system 100 can also be used for vertical scanning. In this case, the scanning device is arranged so that the scanning direction is rotated by 90° so that the scanning line SL and the receiving line RL move in the vertical direction (i.e., from top to bottom or from bottom to top). In this way, the scanning line is a horizontal scanning line SL projected into the field of view, and when the transmission reflector oscillates about a single scanning axis, the horizontal scanning line SL moves across the field of view in the vertical direction. In addition, as the horizontal scanning axis SL moves across the field of view in the vertical direction, the horizontal light column RL incident on the 2D photodetector array 15 also moves across the 2D photodetector array 15 in the vertical direction.

[0055] It should also be understood that the LIDAR scanning system may include multiple scanning mirrors 12 and corresponding circuit devices for scanning different fields of view in the horizontal direction and / or vertical direction. For example, a vehicle may include multiple scanning mirrors arranged at different positions on the vehicle to scan different fields of view. Alternatively, synchronized MEMS mirrors may be used in a 2x1D system (such as a Lissajous scanning system). In this case, the MEMS mirrors are mounted at the same position in the vehicle and are configured to scan the same field of view.

[0056] Figure 1B A schematic top view of an example of a reflector 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 reflector body 8. The reflector body 8 includes a reflector 12 and a reflector support 16. The reflector device also includes a frame 17. The reflector body 8 is arranged 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 major surfaces of one or more layers in which the frame 17 is formed.

[0057] The reflector body 8 can rotate around a rotation axis 13 extending in a plane defined by the frame 17. A support beam 18 (also referred to as a torsion beam) is connected between the reflector body 8 and the frame 17 along the rotation axis 13. More specifically, a first support beam 18 is connected between a first end of the reflector body 8 and the frame 17, and a second support beam 18 is connected between a second end of the reflector body 8 and the frame 17, wherein the second end of the reflector body 8 is opposite to the first end in the direction of the rotation axis 13. Figure 1BAn enlarged view of one of the support beams 18 is shown in enlarged portion C in the right hand side of FIG. It can be seen 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 rotation axis 13. The support beam 18 may be colinear with the rotation axis 13.

[0058] 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 required shapes.

[0059] The mirror frame 17 defines a mirror recess 20 in which the mirror body 8 is disposed. The mirror recess 20 is defined by a recess periphery 28 of the mirror frame 17. The mirror frame 17 is also configured to define additional recesses in which other components such as actuators and leaf spring assemblies may be disposed.

[0060] The reflector device comprises at least one leaf spring assembly 30. In the example shown, the reflector device comprises two pairs of leaf spring assemblies 30, wherein the leaf spring assemblies in each pair extend in opposite directions from the reflector body 8. In the example shown, the leaf spring assemblies 30 are arranged symmetrically with respect to the rotation axis 13.

[0061] At least one leaf spring assembly 30 includes a leaf spring 32 and a relief link 34. The relief link 34 may have one or more relief springs 35. The leaf spring 32 includes a first end 32a and a second end 32b. The first end 32a is coupled to the reflector body 8, and the second end is coupled 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 a reflector support (not shown), and the second end 32b is coupled to the frame 17 via the relief link 34. In an example, the first ends 32a of two leaf springs 32 extending in different directions from the same portion of the reflector body 8 may be connected to each other (e.g., a leaf spring on the left side of the reflector 12 or a leaf spring on the right side of the reflector 12).

[0062] In some examples, the shape of the reflector 12 may include a recess in the area of ​​the rotation axis 13, wherein a portion of the leaf spring 32 extends into the recess of the reflector 12. In some examples, the leaf spring 32 and the reflector 12 may be formed in the same material layer and may be connected to each other adjacent to the rotation axis 13.

[0063] In some examples, the leaf spring 32 can be implemented in a single crystal silicon layer in a direction having lower material stiffness, wherein the longitudinal direction of the leaf spring is aligned with the direction of lower material stiffness. <100> The axis is implemented in the silicon layer, and the longitudinal direction of the leaf spring is <100> direction, in which case the <100> Direction has lower material stiffness.

[0064] The torsional stiffness about the rotation axis 13 can be set using a leaf spring assembly 30. A pair of support beams 18 support the reflector body 8 vertically (i.e., perpendicular to the main surface of the frame 17) at the rotation axis 13. However, the effect of the support beams 18 on the torsional stiffness can be negligible, so that the natural frequency of the reflector body can be mainly 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 reflector body 8 (i.e., the reflector 12) around its rotation axis 13. The support beams 18 can define the out-of-plane rocking and vertical mode stiffness for the corresponding dynamic mode and the corresponding resonant frequency. The torsional stiffness can be decoupled from the out-of-plane rocking and vertical mode stiffness, so that the out-of-plane rocking and vertical mode frequencies can be set to desired values, such as higher values, without affecting the torsional mode stiffness and the resonant frequency. As defined herein, the Y axis is along the rotation axis 13, the X axis is perpendicular to the Y axis in the mirror plane when the mirror 12 is stationary, and the Z axis is perpendicular to the mirror plane 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.

[0065] exist Figure 1B In the example shown, at least one leaf spring 32 is connected at one end to the reflector body 8 at a position close to the rotation axis 13. The other end 32b is connected to an associated relief link 34 at a position away from the rotation axis 13. The leaf spring assembly 30 can provide torsional stiffness to the reflector body 8 about the rotation axis 13. The relief link 34 can provide a compliant or flexible coupling from the leaf spring 32 to the frame 17. The relief link 34 can be longitudinal to the leaf spring 32 (i.e., at Figure 1B The embossed link 34 has a relatively low stiffness in the X direction, which allows one end of the leaf spring 32 to move in the longitudinal direction of the leaf spring 32 when the reflector body 8 rotates about the rotation axis 13. Figure 1B The Z and Y directions have relatively high rigidity.

[0066] The resonant frequency of the mirror 12 rotating about the rotation axis 13 can be mainly defined by the inertia of the mirror body 8 and the stiffness of the leaf spring assembly 30, which can be defined by the bending stiffness of the leaf spring 32 and the torsional and translational stiffness of the relief link 34. The bending stiffness of the leaf spring 32 can be defined by the length, width, and especially the thickness of the leaf spring 32. The combined stiffness of the support beam 18 and the relief link 34 in the X direction can prevent the movement of the mirror body 8 perpendicular to the rotation axis 13 (in the X direction) during operation. More details about the relief link are provided below.

[0067] The support beam 18 is connected between the frame 17 and the reflector body 8 along the rotation axis 13 to support the reflector body 8 in the frame 17. In one example, the support beam 18 has a narrow rectangular cross-section perpendicular to the rotation axis 13, wherein the major axis of the rectangle is perpendicular to the surface of the reflector body 8 and the reflector 12, and the minor axis of the rectangle is parallel to the surface of the reflector 12. Torsional stiffness corresponding to the rotation of the reflector body 8 around the rotation axis 13 can be provided by the leaf spring assembly 30. The support beam 18 can be used only to support the reflector body 8, and the effect on the torsional stiffness can be ignored. The size of the support beam 18 can be determined so that the stiffness for the vertical displacement of the reflector body 8 (along the Z direction) and the out-of-plane translation perpendicular to the rotation axis 13 (along the X axis) is as high as possible.

[0068] The mirror device may also include at least one actuator 40 to provide a torque to drive the mirror body 8 about the rotation axis 13. In one example, the actuator may include a mirror comb attached to the mirror body 8, which is interleaved with a frame comb attached to the frame 17. Applying a potential difference between the interleaved mirror combs and the frame combs may create a driving force between the mirror combs and the frame combs, which may create a torque on the mirror body 8 about the rotation axis 13. An oscillating potential may be applied to drive the mirror device at a natural frequency of the mirror device.

[0069] In other examples, actuation methods may include electromagnetic actuation and piezoelectric actuation. In electromagnetic actuation, the micromirror may be "immersed" in a magnetic field, and an alternating current through a conductive path may create an oscillating torque about the axis of rotation 13. A piezoelectric actuator may be integrated into a leaf spring, or the leaf spring may be made of a piezoelectric material, to produce an alternating beam bending force in response to an electrical signal and generate an oscillating torque.

[0070] Due to the torsional stiffness about the rotation axis 13 caused by the leaf spring assembly 30, the MEMS mirror 12 exhibits nonlinear behavior, such that the oscillation frequency of the mirror 12 increases in a nonlinear manner as the oscillation amplitude (i.e., the tilt angle amplitude) increases. Thus, the stiffening of the leaf spring 32 as the mirror rotates makes the MEMS mirror 12 more strongly nonlinear.

[0071] 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 exemplary processing and control system components, such as MEMS actuators, receiver circuits, and a system controller.

[0072] 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 components of the receiver unit 22, and receives raw data from the receiver unit 22, and performs processing on the raw data (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 device for processing data and a control circuit device (such as a microcontroller) configured to generate control signals. The LIDAR scanning system 200 may also include a temperature sensor 26.

[0073] The receiver unit 22 includes a photodetector array 15 and a receiver circuit 24. The receiver circuit 24 may include one or more circuit devices or sub-circuit devices 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 trigger control signals from the system controller 23 that trigger 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.

[0074] The transmitter unit 21 includes an illumination unit 10, a MEMS mirror 12, and a MEMS driver 25 configured to drive the MEMS mirror 12. In particular, the MEMS driver 25 actuates and senses the rotational position of the mirror, and provides position information of the mirror (e.g., a tilt angle or a degree of rotation about a rotation axis) to the system controller 23. Based on the position information, the laser source of the illumination unit 10 is triggered by the system controller 23, and a photodiode (e.g., an APD diode) is activated to sense and thereby measure the reflected light signal. Therefore, the higher accuracy of the position sensing of the MEMS mirror makes the control of other components of the LIDAR system more prepared and precise.

[0075] 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 actuator structure of the MEMS mirror 12 also includes the suspension structure discussed above. Therefore, the MEMS actuator 25 may also include measurement circuits 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) that is configured to process measurement information from the measurement circuitry to assess the mechanical health of the MEMS mirror 12 and / or the state of the chip package.

[0076] Additionally or alternatively, system controller 23 may receive measurement information from the measurement circuit of MEMS actuator 25 and perform processing on the measurement information. Therefore, 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 evaluate the mechanical health of MEMS mirror 12 and / or the status of the chip package.

[0077] By sensing the rotational position of the MEMS mirror 12 about its rotational axis 13, the MEMS driver 25 can sense a zero-crossing event of the MEMS mirror 12. A zero-crossing event is a situation when the MEMS mirror 12 has a rotational angle of 0° on its rotational axis 13. In particular, a zero-crossing event is a moment when the MEMS mirror 12 is parallel to the frame or in a neutral position. The neutral position may also be referred to as a stationary position (e.g., when the MEMS mirror 12 stops after the driving force is disconnected). Since the MEMS mirror 12 oscillates back and forth between two rotational directions (e.g., clockwise and counterclockwise), two zero-crossing events occur during one 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 may also be used instead of a zero-crossing event.

[0078] In some embodiments, the event time may correspond to a non-zero crossing event. For example, the sensed rotation angle may be some angle other than 0°. However, for purposes of explanation, the examples herein will be described in the context of sensing a zero crossing event.

[0079] 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. In particular, 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.

[0080] Figure 3 A signal diagram of various signals generated by the MEMS driver 25 based on the mirror angle θ and / or position is illustrated, including a position signal (position_L). For example, the position signal (position_L) can be a pulse signal during which a first pulse transition (e.g., a falling edge transition) is triggered at a zero crossing when the mirror oscillates in a first rotational direction (e.g., from left to right), and a second pulse transition (e.g., a rising edge transition) is triggered at a zero crossing when the mirror oscillates in a second rotational direction (e.g., from right to left). In addition, the signal is "high" when the mirror points in one direction (e.g., pointing to the left), and the signal is "low" when the mirror points in a second direction (e.g., pointing to the right). Therefore, the position signal not only indicates a zero crossing event by triggering a pulse transition, 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 also increases. Based on the position signal, the phase and / or frequency of two or more position signals can be compared.

[0081] Alternatively, at each zero crossing event, a short pulse may be generated by the MEMS driver 25 such 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, there will be no absolute phase information indicating in which direction the mirror is moving. Based on the position signal, the phase and / or frequency of two or more position signals may be compared.

[0082] The MEMS driver 25 may send position information to the system controller 23, so that the system controller 23 may 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 position information may also be used by the system controller as feedback information, so that the system controller 23 may maintain stable operation of the MEMS mirror 12 and also maintain synchronization with other MEMS mirrors via control signals provided to the MEMS driver 25.

[0083] The timing information of the zero crossing event can also be used by the MEMS driver 25 to generate a phase clock signal (Phase_CLK). The phase clock signal is a high-frequency signal (e.g., 14 MHz) with a fixed number of pulses that provides fine-grained phase information of the MEMS mirror 12. In this case, the movement of the mirror is divided into equidistant slices in the time domain (affected by the quantization error of the digitally controlled oscillator (DCO) frequency generator). A "slice" can be considered as a sub-portion of the time interval between two consecutive zero crossing events. In particular, the time interval between two zero crossing events (i.e., between two Position_L signals or pulses) is divided into the same part so that a signal pulse is generated at each part. Therefore, the phase clock signal is a pulse signal whose frequency depends on the time interval between two zero crossing events, where the shorter the time interval, the higher the frequency. Therefore, the phase clock signal divides the movement of the mirror into a clear number of phase slices. The MEMS driver 25 can generate a phase clock signal and output the phase clock signal to the system controller 23.

[0084] Figure 3 Also illustrated is a phase clock signal (Phase_CLK) comprising a plurality of pulses per oscillation period, wherein an oscillation period is defined by the time interval between two consecutive zero-crossing events.

[0085] 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 a drive voltage (i.e., an actuation signal or drive signal) is applied by a MEMS driver 25. The drive voltage can be referred to as a high voltage (HV). The drive voltage applied to the finger-shaped structure generates a corresponding capacitance. The drive voltage across the finger-shaped structure creates a driving force between the crossed mirror combs and the frame combs, which creates a torque on the mirror body about the axis of rotation. The drive voltage can be switched or toggled to generate an oscillating drive force. The oscillating drive force causes the mirror to oscillate back and forth between two extremes on the axis of rotation of the mirror. Depending on the configuration, the actuation can be adjusted or adjusted by adjusting the drive voltage disconnection time, the voltage level of the drive voltage, or the duty cycle.

[0086] 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 signal or drive signal) can be used to generate an oscillating drive force. Therefore, it should be understood that actuation voltage / drive voltage and actuation current / drive current can be used interchangeably herein to indicate an actuation signal or drive signal, and both can generally be referred to as a drive force.

[0087] As the mirror oscillates, the capacitance between the finger electrodes changes depending on the rotational position of the mirror. The MEMS actuator 25 is configured to measure the capacitance between the interdigitated finger electrodes and determine therefrom the rotational position or angular position of the MEMS mirror 12. By monitoring the capacitance, the MEMS actuator 25 can detect zero crossing events and their timing and can determine the tilt angle of the MEMS mirror 12 at any given moment. The MEMS actuator 25 can also use the measured capacitance to determine the mirror frequency and record the information in a memory at the MEMS actuator 25 or the system controller 23.

[0088] Sensing of the position of the MEMS mirror 12 is performed based on a detector configured to measure capacitance. For example, as the MEMS mirror moves, the geometry of the finger structures changes, causing the geometry of the capacitors to change. As the geometry of the capacitors changes, the capacitances themselves also change. Therefore, a specific capacitance directly corresponds to a specific position (i.e., tilt angle) of the MEMS mirror. By sensing the capacitance of the finger structures, the MEMS actuator 25 can monitor and track the oscillations of the mirror and determine specific positions of the MEMS mirror, including zero crossings.

[0089] One method of measuring capacitance is to measure the current flowing through the finger-like structure, convert the measured current into a voltage, and then also relate the voltage to the capacitance and / or the rotation angle. However, any method of measuring capacitance can be used. The rotation direction (e.g., positive or negative, from left to right or from right to left, clockwise or counterclockwise, etc.) is detected by measuring the change in capacitance over time, where a positive or negative change indicates the opposite rotation direction. The MEMS driver 25 can also record the current and voltage measured during the measurement of capacitance. Therefore, improving the accuracy of the position sensing of the reflector can improve the overall accuracy of the LIDAR system.

[0090] Since the mirror is driven at an oscillating frequency (e.g., 2 kHz), when the mirror rotates in a first rotation direction (e.g., from left to right or clockwise), the mirror crosses the zero position (i.e., 0°) at a specific time point. Similarly, when the mirror rotates in a second rotation direction (e.g., from right to left or counterclockwise), the mirror will cross the zero position at a specific time point. These cases of crossing the zero position can be referred to as zero crossing events occurring at zero crossing times.

[0091] Figure 4A The angular amplitude-frequency response curve of the micro-mirror device according to one or more embodiments is illustrated. In particular, Figure 4A The mirror angle θ of the MEMS mirror 12 is plotted mirror With the mirror frequency f mThe relationship between the amplitude and the amplitude is shown in FIG. 2 . Both axes in the figure are arbitrary units. The complete response curve includes a top response curve (1) and a bottom response curve (0). The top response curve (1) can also be referred to as an operational response curve, in which the frequency sweeps across the operational range. In contrast, the bottom response curve (0) can be referred to as a non-operational response curve, which exists before the amplitude operating range is reached. The complete response curve can be measured and stored in the memory of the LIDAR system 200 (e.g., in the system controller 23).

[0092] The operation flow of the MEMS mirror from point 1 to point 7 will now be described, during which a constant drive voltage is applied to the MEMS mirror 12 by the MEMS actuator 25. Here, "constant drive voltage" means that the drive voltage is the same voltage when actuated (i.e., turned on). However, it should be understood that the drive voltage is turned on and off to produce the mirror oscillation.

[0093] As described in the previous paragraph, all points on the graph are operated at the same drive voltage provided by MEMS actuator 25. The drive voltage simply stretches or compresses the curve (ie, higher frequencies and larger tilt angles can be achieved due to more energy being put in by a higher drive voltage).

[0094] The operation of the MEMS mirror starts at the starting frequency f on the bottom response curve (0). start Here, the MEMS actuator 25 starts the drive voltage signal to the MEMS mirror 12. In response, the MEMS mirror 12 will start The value of starts to move slightly (e.g., at a low angle). From the starting frequency f start Initially, the mirror frequency is swept downward (ie, decreasing, from right to left).

[0095] The frequency is reduced to synchronize the mirror with the applied drive signal (i.e., reduce the phase offset between the two). As more energy is applied over time (i.e., constant drive voltage), the mirror continues to move slightly out of resonance until the jump frequency f jump (Point 2). That is, the mirror frequency continues to decrease until the instability point is found, and the amplitude of the mirror oscillation increases at point 2 (180° phase shift, hence the jump). At the jump frequency, the mirror phase changes from θ jump0 (Point 2) shifted 180 degrees to θ jump1 (Point 3), where the input energy is converted into motion.

[0096] At point 4, the mirror frequency f mStart sweeping the frequency upward (i.e., increasing, from left to right). Along the top response curve, the mirror phase can continue to increase. At point 5, the mirror is in the stable operating region (in phase, but offset). The mirror can be in optimal resonance at point 5. However, if the mirror frequency continues to increase to point 6, the mirror phase is at the fallback frequency f fb The fallback phase is reached at 0 = θ fb1 Therefore, before this critical point of point 6, the inclination angle of the reflector is the largest.

[0097] Back-off frequency f fb is the maximum frequency that the mirror can sustain at the established drive voltage. The back-off point or critical point is the point where the potential energy input into the mirror system by the drive voltage is equal to the kinetic energy of the mirror system resisting that potential energy (in phase, no offset), and pushing it past this point disturbs the equilibrium and the resonance is lost. Thus, at point 6, there is not enough energy in the system to maintain the mirror phase, and the phase is offset by 180 degrees, and at the back-off phase θ fb0 The value falls back to the bottom response curve (0).

[0098] Point 7 is the back-off point on the bottom response curve (0) and is the phase angle to which the mirrors are backed off. This phase angle is not necessarily zero degrees since the drive voltage is still present, but the mirrors are no longer in phase. The cycle can start again at point 7 or point 1.

[0099] Figure 4B The angular amplitude steady-state response curve (top) and the phase delay steady-state response curve (bottom) of a micro-mirror device according to one or more embodiments are illustrated. For both figures, the frequency response is shown when a 60V square wave actuation with a 50% duty cycle is used. The frequency of the drive signal is the mirror frequency f m The delay is defined by the time between the zero crossing of the mirror and the negative edge of the drive signal (ie, if the zero crossing of the mirror occurs before the negative drive edge, the phase is positive).

[0100] Embodiments are directed to control structures for angular amplitude and phase control of nonlinear oscillators having a correlation between angular amplitude and frequency, where an amplitude-frequency (AF) correlation may be significant. If only relatively noisy amplitude measurements are available, oscillator frequency changes may be used as an alternative to amplitude error estimation, which allows for higher control bandwidth. The control bandwidth defines how fast the system can track a reference signal (e.g., a feedback signal).

[0101] Figure 5 A schematic block diagram of an oscillator control system 500 is illustrated according to one or more embodiments. Figure 5 right Figure 6 and Figure 7 In general, the oscillator control system 500 includes a cascade control structure including a slow outer control loop and a faster inner control loop. In particular, the oscillator control system 500 includes: an amplitude controller 51, which represents the outer control loop; a period and phase controller 52, which represents the inner control loop; and an oscillator 53, which includes an oscillating structure driven by the period and phase controller 52. The oscillating structure of the oscillator 53 is a nonlinear oscillator, which has a correlation between angular amplitude and frequency. The oscillator 53 may include, for example, a MEMS mirror 12 as its oscillating structure.

[0102] Thus, the two controllers 51 and 52 are cascaded in that the output of the amplitude controller 51 is provided as an input to the period and phase controller 52. The period and phase controller 52 is a multiple-input multiple-output (MIMO) controller 52 configured to generate control signals U and T for driving the oscillator 53. dr The two outputs of the controller 52 are generated and adjusted based on the two inputs of the controller 52. In addition, the controller 52 is configured to have a control bandwidth higher than the control bandwidth of the controller 51.

[0103] The variable A is the angular amplitude received at the amplitude controller 51. Since the amplitude controller 51 uses the noisy amplitude measurement A, the amplitude controller 51 has a low control bandwidth. The angular amplitude A is measured by a detection circuit (not shown).

[0104] The variable Tref is a reference oscillator period generated by the amplitude controller 51 based on the measured angular amplitude A, wherein the outer control loop controls the amplitude error to be zero on average (ie, the average amplitude error is zero) when the MEMS mirror 12 oscillates.

[0105] The variable ΔT is the phase error received at the period and phase controller 52. The phase error ΔT is measured by a detection circuit (not shown).

[0106] The variable U represents one or more control parameters (e.g., voltage level, duty cycle, reference phase for phase control, etc.) generated by the period and phase controller 52 in response to the reference oscillator period Tref and the phase error ΔT. The period and phase controller 52 varies the control parameter U based on the reference oscillator period Tref and the phase error ΔT, which in turn varies based on the amplitude measurement A. In particular, the period and phase controller 52 varies the control parameter U in conjunction with the drive period Tdr so as to meet the reference oscillator period Tref and achieve zero phase error.

[0107] The variable Tdr is the drive period (i.e., oscillation period) applied by the period and phase controller 52. The period and phase controller 52 may include a drive PLL that adapts Tdr to compensate for the phase error ΔT and achieve a reference oscillator period Tref. The period and phase controller 52 adapts Tdr with a high control bandwidth due to a high signal-to-noise ratio (SNR) phase detection signal. However, the change or compensation of the drive period Tdr may be slower than the compensation of the control parameter U. In this case, the control parameter U changes rapidly, while the drive period Tdr is only moderately adapted at a slower speed than the control parameter U.

[0108] The period and phase controller 52 simultaneously generates the control parameter U and the drive period Tdr to drive the oscillator 53 to the reference oscillator period Tref and to simultaneously compensate for the phase error ΔT with a high control bandwidth.

[0109] In view of the above, the oscillator control system 500 includes a slow outer loop 51 that uses the (possibly noisy) amplitude measurement A to derive a reference oscillator period Tref corresponding to a desired amplitude (i.e., a reference amplitude), where the amplitude error averages to zero. The inner loop then controls the phase and oscillator period error (and hence the amplitude) with high bandwidth. As a result, the oscillator control system 500 uses the accurately measurable oscillator period Tm as an amplitude equivalent parameter (Af effect), and compensates for deviations from the desired period and phase.

[0110] It should be mentioned that, unlike e.g. a cantilever beam with a dynamic tip-surface interaction, the amplitude-to-frequency dependence of the oscillator 53 is assumed to be constant or at least slowly changing. Even in the presence of external disturbances, the reference oscillator period Tref for the inner loop 52 still exhibits the desired amplitude on a short time scale. In addition, unlike other oscillator control systems that require both amplitude and frequency (or phase) measurements to be accurate in order to achieve a high control bandwidth, the embodiments described herein require only an accurate phase measurement (i.e., phase error ΔT), while the amplitude measurement A can be noisy and less accurate.

[0111] Figure 6A schematic block diagram of an oscillator control system 600 according to one or more embodiments is illustrated. In particular, the oscillator control system 600 includes a fully cascaded control structure including a slow outer control loop and a faster inner control loop. Therefore, similar to the oscillator control system 500, the oscillator control system 600 includes: an amplitude controller 51, which represents a part of the outer control loop; a period and phase controller 52, which represents a part of the inner control loop; and an oscillator 53, which is driven by the period and phase controller 52. The oscillator 53 includes the MEMS mirror 12 as a nonlinear oscillator, which has a correlation between its angular amplitude and its frequency. The oscillator 53 also includes a detection circuit 61, which is configured to measure the angular amplitude θ (corresponding to the angular amplitude of the MEMS mirror 12) Figure 5 The angular amplitude A) and phase error ΔT in.

[0112] Due to the nonlinearity of the comb-actuated MEMS mirror, the MEMS mirror shows a significant nonlinear dependence between amplitude and frequency, such as Figure 4B The open loop frequency response is shown in FIG. 1. At high amplitudes (eg, greater than 8 A), the behavior is dominated by the top response curve (ie, the backbone curve), which represents the purely mechanical behavior of the mirror.

[0113] Therefore, the mirror period reflects the amplitude of the mirror and can be estimated from the phase detection signal driving the PLL according to equation (1).

[0114]

[0115] in is the estimated half-period of the ith mirror, is the ith applied drive cycle, is the corresponding i-th measured phase error, and is the corresponding i-1th measured phase error (i.e., the previously measured phase error). Therefore, and represents two consecutive phase errors used to calculate the mirror period. The previous phase error can be stored in memory for use in equation (1). The controller 52 calculates the phase error based on the measured phase error, the reference oscillator period T m,ref The driving period Tdr and the additional control parameter U are calculated based on the estimated mirror period Tm calculated by the controller 52 using equation (1).

[0116] For general description, the phase error is defined as the difference between the measured (actual) zero crossing of the MEMS mirror 12 and the expected zero crossing given by the inner control loop 52. According to the limit, through to calculate the subsequent expected zero crossing, where is the i+1th applied drive cycle, and so on. Therefore, if is the current applied drive cycle, then is the next applied drive cycle. Therefore, the next applied drive cycle consists of two consecutive zero crossings limited.

[0117] Furthermore, in this embodiment, it is assumed that feedback measurements θ and ΔT are available at the expected zero crossing event or at least after a short processing time (which is negligible relative to the mirror period). For example, shift registers 62 and 63 can store measurement samples θ and ΔT, respectively, which produce a unit sampling delay time period (z -1 ).

[0118] The fully cascaded structure of the oscillator control system 600 is preferred if equation (2) is satisfied:

[0119]

[0120] where θ is the nominal amplitude of the mirror, and σ θ and are the standard deviation of the amplitude measurement and the standard deviation of the mirror period estimate, respectively.

[0121] exist Figure 6 In the measurement, the amplitude noise and phase noise are measured by and These inputs correspond to the noise characteristics of the detector and are naturally added to their corresponding amplitude and phase error measurements. For example, the actual measured phase error value includes the true value (e.g., ΔT) and the noise / uncertainty In addition, Δd ext,i+1 represents the external disturbance (e.g., vibration) applied to the MEMS mirror 12. Mirror period gradient can be measured (e.g., from Figure 4B d response curve), calculated from the mirror dynamics, or estimated from the measured amplitude and mirror period errors. If equation (2) is satisfied, the mirror period is a better estimate of the mirror amplitude variation than the mirror measurement itself. Therefore, the environmental fluctuations Δd can be better handled by using only the phase detection signal of the PLL driven by equation (1). ext,iRapid changes in the mirror's amplitude caused by vibrations, such as

[0122] The slow outer loop includes an angle amplitude error generator 64 and an amplitude controller 51. The angle amplitude error generator 64 is configured to receive the i-th measured angle amplitude θi and the reference angle amplitude θref from the feedback path (e.g., from the register 62), and generate an amplitude error measurement based on the i-th measured angle amplitude θi and the reference angle amplitude θref. Specifically, the reference angular amplitude θref is subtracted from the i-th measured angular amplitude θi to generate an amplitude error measure Amplitude error measurement This can be any measurement related to amplitude (eg, 6° to 0° time).

[0123] The angle amplitude error generator 64 may also receive the i-th amplitude noise measurement and generates an amplitude error measurement based on three inputs In particular, from the ith measured angular amplitude θi and the ith amplitude noise measurement The reference angle amplitude θref is subtracted from the sum to produce an amplitude error measurement

[0124] The amplitude controller 51 determines the amplitude error based on the received amplitude error measurement. Generate reference mirror period where if the mirror oscillates, the amplitude error averages to zero. Since the outer loop can be quite slow, the amplitude error measurement Accuracy In the measurement of a set, accuracy refers to how close the measurement is to a particular value, while precision refers to how close the measurements are to each other.

[0125] The faster inner loop includes a phase error generator 65 and a period and phase controller 52. As described above, phase noise is naturally added to the true phase error. The phase error generator 65 is configured to receive the i-th measured phase error ΔT from a feedback path (e.g., from register 63). i And receive phase noise measurement And generate the added phase error representing the total phase error of the i-th measurement

[0126] The period and phase controller 52 is configured to receive the added phase error And by using equation (1) to drive the MEMS mirror 12 to the reference mirror period provided by the outer loop And compensate the phase error ΔT iIn particular, the period and phase controller 52 is configured to make the phase error ΔT and and The period and phase controller 52 is based on the reference oscillator period T m,ref This is done by generating the control parameter U from the phase error ΔT and is also based on the reference oscillator period T m,ref The control parameter U and the drive period Tdr are both dependent on two inputs: the reference oscillator period T m,ref and phase error ΔT.

[0127] Specifically, the period and phase controller 52 calculates the estimated mirror period Tm using equation (1), and then calculates the mirror period error as the difference between the estimated mirror period Tm and the reference mirror period Tm. m,ref The period and phase controller 52 uses both the phase error ΔT and the period error of the MEMS mirror 12 to generate, adjust and / or compensate for the control parameter U and the driving period Tdr.

[0128] According to equation (1), the period and phase controller 52 is configured to estimate the oscillator period of the oscillator structure based on the measured phase error and the sum of the drive period minus the previously measured phase error. Therefore, the period and phase controller 52 is configured to estimate the oscillator period of the oscillator structure, determine the oscillator period error based on the estimated oscillator period and the reference oscillator period, and adapt the drive period and at least one control parameter of the drive signal to compensate for the measured phase error and the determined oscillator period error. The determined oscillator period error is the difference between the estimated oscillator period and the reference oscillator period.

[0129] As a result, the controller 52 drives the oscillator 53 to the reference oscillator period T m,ref To correct the period error and simultaneously compensate for the phase error ΔT. The standard deviation is low), so the mirror amplitude and mirror phase can be controlled quickly.

[0130] The oscillator control system 600 includes a driver circuit 66 configured to generate a modulated (eg, pulse width modulated (PWM)) drive signal V drive(i.e., drive voltage) to drive the MEMS mirror 12. The driver circuit 66 includes a variable / configurable oscillator that drives the PLL, where the variable / configurable oscillator is used to drive the MEMS mirror 12 and maintain the MEMS mirror 12 in a stable state. The PLL includes a phase detector, a loop filter / controller, and a variable oscillator, and the detection circuit 61 can extract signals from different stages of the driving PLL to make measurements related to the operation of the MEMS mirror 12. For example, the detection circuit 61 can measure the angular amplitude, the mirror period, the mirror frequency, and the mirror phase. Therefore, the detection circuit 61 can be integrated with the driver circuit 66, such as Figure 2 (see MEMS driver 25). It should be noted that the period and phase controller 52 is part of the driving PLL as well as the configurable oscillator.

[0131] The driver circuit 66 uses the drive PLL to modulate the drive signal V based on one or more control parameters generated by and received from the cycle and phase controller 52. drive The driver circuit 66 may use the control parameters to change the voltage level, duty cycle, period, and / or reference phase of the drive voltage. For example, the control parameters U may include a voltage level for setting the drive signal. and includes a switching parameter for modulating the timing of switching of the drive signal and in addition, is another switching parameter, which sets the driving period of the driving signal, which is determined by the switching period at t 0i and t 0i+1 The time limit of two consecutive expected zero crossings at . Set the on-time of the driving voltage in the signal cycle, and Set the off time of the driving voltage in the signal cycle. The on time defines the dr The transition from low voltage level to high voltage level within the drive period T dr The transition from high voltage level to low voltage level within the device.

[0132] Control parameters and T dr At least two of the control parameters in the reference oscillator depend on the reference oscillator period T m,ref and phase error ΔT, and is adapted by the controller 52 to minimize the phase and period errors. In some cases, all control parameters are adapted based on the two inputs and are used to minimize the phase and period errors. In some cases, at least one of the drive period Tdr and the control parameter U is adapted based on the two inputs and is used to minimize the phase and period errors.

[0133] It should also be noted that although a square wave drive is used in this example, it should be understood that other waveforms may be used. For example, a sine wave may be used, and the control parameter U may include a value set by the controller 52 based on the reference oscillator period T m,ref The amplitude, frequency and phase are set by the and phase error ΔT.

[0134] In order to change the driving voltage level To achieve fast amplitude control, a low settling time should be used so that However, if the drive voltage can be changed quickly, the bandwidth will increase as (where the second term should ideally be zero), phase detection via current sensing may be noisy.

[0135] To achieve a large control bandwidth without introducing more noise in the current sensing, the drive voltage V drive It is considered that it can only be in two voltage levels (for example, 0V and a voltage value different from 0V (i.e., )) and control is achieved by adjusting the timing of the switching (i.e., using control parameters and However, in order to compensate for slow drifts of environmental conditions (eg pressure changes and aging), the non-zero state of the drive voltage may also be adapted slowly without compromising the sensing.

[0136] The amplitude controller 51 and the period and phase controller 52 can be nonlinear or linear controllers designed by a suitable MEMS mirror model. A possible solution is to use a simple low-gain proportional-integral (PI) controller as the amplitude controller 51 and a linear quadratic Gaussian (LQG) regulator as the period and phase controller 52 designed at the desired operating point by linearizing the model. Also, a feed-forward algorithm providing, for example, fast amplitude changes can be implemented.

[0137] In order to reduce the control degree of freedom (DoF), the driving voltage V drive The switch-on can be fixed as Therefore, the voltage is turned on at the point of maximum angle (i.e., point of maximum amplitude) where the comb drive produces no appreciable torque. The remaining control degree of freedom is the off time and drive cycle

[0138] Due to the drive cycle defines the next expected zero crossing, so it directly affects the next phase error, while By injecting or draining energy, only the dynamic characteristics of the mirror are affected. In order to achieve a reference mirror period T m,ref The fast convergence of the drive cycle and the low variation of the drive cycle due to the sensing noise are also achieved, which is consistent with the Compared with the response Should react faster to phase and period errors.

[0139] In view of the above, the outer loop adjusts the mirror reference mirror period for the inner loop The amplitude error becomes zero on average. The inner loop drives the MEMS mirror 12 to the desired mirror reference period and uses the control parameter U and the drive period T dr The two are used to compensate for the residual phase error ΔT i .

[0140] Figure 7 FIG. 7 is a schematic block diagram of an oscillator control system 700 according to one or more embodiments. In particular, the oscillator control system 700 includes a hybrid cascade control structure including a slow outer control loop and a faster inner control loop. In addition to the oscillator control system 700 including the supplementary feedback path 70, the oscillator control system 700 and Figure 6 Similar to the oscillator control system 600 depicted in FIG. 1 , the supplemental feedback path 70 is coupled to the output of the angle amplitude error generator 64 at one end and to the input of the period and phase controller 52 at the other end. Thus, the supplemental feedback path 70 bypasses the amplitude controller 51 and the amplitude error measurement is directly provided to the period and phase controller 52, which uses the received amplitude error measurement and the estimated mirror period error to control the parameters Tdr and U. The estimated mirror period error is the difference between the estimated mirror period Tm and the reference mirror period T m,ref The difference between.

[0141] When equation (2) is not satisfied, the supplemental feedback path 70 is used. For example, if Or at least for some external influencing conditions, the mirror period variation cannot correctly represent the amplitude, then the hybrid cascade implementation is preferred, because the combination of direct and indirect amplitude measurement leads to a better detection SNR. Therefore, as shown, the amplitude error measurement is forwarded to the inner loop.

[0142] As a result, Figure 6 As described above, the period and phase controller 52 receives the reference mirror period The phase error after adding and amplitude error measurement The period and phase controller 52 uses the amplitude error measurement To reduce the uncertainty of the measurement, and calculate the control parameter U and the driving period Tdr, so as to drive the MEMS mirror 12 to the reference mirror period T m,ref And minimize the phase error.

[0143] In systems 500, 600 and 700, the amplitude controller 51 and the period and phase controller 52 may include a combination of a feed-forward algorithm and a feedback algorithm. The feedback signal may be a cycle-by-cycle measurement or a continuous / sampled signal. The feed-forward and feedback algorithms may be designed from an oscillator model, which may be derived from a measured oscillator response or from a mathematical model.

[0144] Additionally, an offline model identification or an online model identification performed by a dedicated identification procedure and algorithm may be implemented. Offline model identification may use a nonlinear model of the MEMS mirror 12 or use a linearized model that is valid near the desired operating point of the MEMS mirror 12. The identification is done once, and the MEMS mirror 12 is operated with the same parameters. Online model identification may use a nonlinear model of the MEMS mirror 12 or use a linearized model that is valid near the desired operating point of the MEMS mirror 12. The identification is performed during operation of the MEMS mirror 12 by observing dedicated parameters.

[0145] The regulation loop (e.g., detection circuit 61 and system controller 23) compares the measured reaction of the MEMS mirror 12 to the regulation process with the expected reaction and, based on the comparison, determines the so-called actual amplitude / frequency characteristic of the MEMS mirror 12 during operation. If this characteristic changes over time compared to the oscillator model, and if the change cannot be explained by temperature dependence, this may indicate mechanical degradation of the MEMS mirror 12. This may be reported to the system controller 23 to signal a request for timely replacement of the MEMS mirror 12 before the MEMS mirror 12 breaks during operation. Thus, replacement of the MEMS mirror 12 may be anticipated by monitoring operational deviations from the expected model.

[0146] One example of online identification is to estimate the local mirror amplitude over frequency behavior (ie, Af effect). Using the signal extracted from the driving PLL, the detection circuit 61 measures the angular amplitude and the mirror period, and the system controller 23 evaluates, for example, the following equation where Θ m and T m are vectors containing the measurements for the angular amplitude and the mirror period, respectively, and is an observed scalar parameter (e.g., fitted by the least squares method). The incremental symbol Δ at a variable indicates the deviation from its nominal value, and is therefore the incremental value of the measured value and the corresponding nominal value. In other words, Δθ m and ΔT m is the error value for the measured angular amplitude and mirror period. The nominal value is defined by the desired operating point at which the mirror should operate. If the observed parameter If the observed parameter changes suddenly It can be used for control or fatigue detection. Sudden changes in parameters (e.g. When the value of the MEMS mirror 12 exceeds the threshold, the system controller 23 may generate a warning signal indicating that the MEMS mirror 12 should be replaced.

[0147] Although the embodiments described herein relate to a MEMS device having a mirror, it should be understood that other embodiments may include optical devices other than MEMS mirror devices (including other nonlinear oscillating structures), including those 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 present a description of the corresponding method, where the box or device corresponds to the method step or a feature of the method step. Similarly, the various aspects described in the context of the method step also present a description of the corresponding box or item or feature of the corresponding apparatus. Some or all of the method steps can be performed by (or using) a hardware device (e.g., a microprocessor, a programmable computer, or an electronic circuit). In some embodiments, such a device can perform one or more of the method steps.

[0148] Although various embodiments have been described, it will be apparent to those skilled in the art that more embodiments and implementations are possible within the scope of the present disclosure. Thus, the present invention is not restricted except in accordance with the appended claims and their equivalents. With respect to the various functions performed by the components or structures (assemblies, devices, circuits, systems, etc.) described above, unless otherwise indicated, the terms used to describe these components (including references to "means") are intended to correspond to any component or structure that performs the specified function of the described component (i.e., it is functionally equivalent), even if it is not structurally equivalent to the disclosed structure that performs the function in the exemplary embodiments of the invention illustrated herein.

[0149] In addition, the attached claims are hereby incorporated into the detailed description, wherein each claim may exist separately as a separate exemplary embodiment. Although each claim may exist separately as a separate exemplary 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 exemplary embodiments may also include a combination of a dependent claim with each other's dependent claims or the subject matter of an independent claim. Unless it is indicated that a specific combination is not intended, such a combination is proposed herein. In addition, it is intended that the features of a claim are also included in any other independent claim, even if the claim is not directly subordinate to the independent claim.

[0150] It should also be pointed out that the methods disclosed in the specification or claims can be implemented by a device having means for performing each of the individual actions of these methods.

[0151] It should also be understood that the disclosure of multiple actions or functions disclosed in the specification or claims may not be interpreted as being in a specific order. Therefore, unless these actions or functions are not interchangeable due to technical reasons, the disclosure of multiple actions or functions does not limit them to a specific order. In addition, in some embodiments, a single action may include or may be decomposed into multiple sub-actions. Unless explicitly excluded, these sub-actions may be included and are part of the disclosure of the single action.

[0152] 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 devices. Thus, the term "processor" or "processing circuit device" as used herein refers to one of the aforementioned structures or any other structures suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules. Furthermore, the techniques may be fully implemented in one or more circuits or logic elements.

[0153] 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 circuit devices, as well as any combination of these components.

[0154] The controller including the hardware may also perform one or more of the techniques described in the present disclosure. Such hardware, software, and firmware may be implemented in the same device or in separate devices to support the various techniques described in the present disclosure. The software may be stored on a non-transitory computer-readable medium such that the non-transitory computer-readable medium includes a program code or program algorithm stored thereon that, when executed, causes the controller to perform method steps via a computer program.

[0155] Although various exemplary embodiments have been disclosed, it is obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention, which realize some of the advantages of the concepts disclosed herein. It is obvious to those skilled in the art that other components performing the same functions may be appropriately replaced. It should 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 mentioned that even in features not explicitly mentioned, features explained with reference to a particular drawing may be combined with features of other drawings. Such modifications to the general inventive concept are intended to be covered by the appended claims and their legal equivalents.

Claims

1. An oscillator control system, comprising: an oscillator structure configured to oscillate about an axis, wherein an angular amplitude and a frequency of the oscillator structure have a non-linear correlation; a driver circuit configured to generate a drive signal to drive oscillation of the oscillator structure; a detection circuit configured to measure the angular amplitude and phase error of the oscillator structure; an outer control loop including an amplitude controller configured to generate a reference oscillator period based on the measured angular amplitude; as well as an inner control loop, comprising a period and phase controller, the period and phase controller being configured to: receive the reference oscillator period from the outer control loop and the measured phase error from the detection circuit; generate at least one control parameter of the drive signal based on the reference oscillator period and the measured phase error; and determine a drive period of the drive signal based on the reference oscillator period and the measured phase error, wherein the driver circuit is configured to generate the drive signal based on the at least one control parameter of the drive signal and the drive period, wherein the period and phase controller is configured to: estimate an oscillator period of the oscillator structure; determining an oscillator period error based on the estimated oscillator period and the reference oscillator period; and adapting the drive period and the at least one control parameter of the drive signal to compensate for both the measured phase error and the determined oscillator period error, and The determined oscillator period error is the difference between the estimated oscillator period and the reference oscillator period.

2. The oscillator control system of claim 1, wherein: The outer control loop further includes an amplitude error generator configured to receive the measured angular amplitude and a reference angular amplitude and generate an amplitude error measurement based on a difference between the measured angular amplitude and the reference angular amplitude, and The amplitude controller is configured to receive the amplitude error measurement and generate the reference oscillator period based on the amplitude error measurement.

3. The oscillator control system of claim 2, wherein the amplitude controller is configured to generate the reference oscillator period based on the amplitude error measurement such that the amplitude error measurement becomes averaged to zero while the oscillator structure oscillates.

4. The oscillator control system of claim 2, further comprising: a supplemental feedback path coupled to an output of the amplitude error generator and configured to transmit the amplitude error measurement to the period and phase controller, Wherein the period and phase controller is configured to receive the amplitude error measurement, the reference oscillator period and the measured phase error, and to generate the at least one control parameter of the drive signal and the drive period based on the received amplitude error measurement, the received reference oscillator period and the measured phase error.

5. The oscillator control system of claim 1, wherein the period and phase controller is configured to estimate the oscillator period of the oscillator structure based on the measured phase error, the drive period, and a previously measured phase error.

6. The oscillator control system of claim 1, wherein: The inner control loop further comprises a phase error generator configured to receive a noise measurement and the measured phase error and to generate a summed phase error from the noise measurement and the measured phase error, and The period and phase controller is configured to determine the drive period of the drive signal and the at least one control parameter of the drive signal based on the added phase error, wherein the period and phase controller adapts the drive period and the at least one control parameter of the drive signal to compensate for the added phase error.

7. An oscillator control system according to claim 1, wherein the phase error measured is defined by the time difference between a measured time at which a zero crossing of the oscillator structure occurs and an expected time at which the zero crossing of the oscillator structure is expected to occur.

8. The oscillator control system of claim 1, wherein the drive period is defined by two consecutive expected zero crossing times of the oscillator structure.

9. The oscillator control system of claim 1, wherein the amplitude controller has a first control bandwidth and the period and phase controller has a second control bandwidth greater than the first control bandwidth.

10. The oscillator control system of claim 1, wherein the at least one control parameter comprises at least one of: a voltage level of the drive signal, a duty cycle of the drive signal, or a reference phase of the drive signal.

11. The oscillator control system of claim 10, wherein the drive signal is a pulse width modulation (PWM) signal that switches between a low voltage level and a high voltage level, The drive circuit is configured to adjust at least one of the low voltage level or the high voltage level of the drive signal based on the at least one control parameter.

12. The oscillator control system of claim 10 , wherein the drive signal is a pulse width modulation (PWM) signal that switches between a low voltage level and a high voltage level, The drive circuit is configured to adjust at least one of an on-time or an off-time of the drive signal, wherein the on-time defines a transition from the low voltage level to the high voltage level within the drive cycle, and the off-time defines a transition from the high voltage level to the low voltage level within the drive cycle.

13. A method for controlling an oscillator structure, the oscillator structure being configured to oscillate about an axis in response to a drive signal, wherein the angular amplitude and frequency of the oscillator structure have a non-linear correlation, the method comprising: measuring the angular amplitude of the oscillator structure; measuring a phase error of the oscillator structure; generating a reference oscillator period based on the measured angular amplitude; determining an estimated oscillator period of the oscillator structure; determining an oscillator period error as a difference between the estimated oscillator period and the reference oscillator period; Generating at least one control parameter of the drive signal based on the oscillator period error and the measured phase error, comprising: adapting the at least one control parameter of the drive signal to compensate for the measured phase error; Determining a drive period of the drive signal based on the oscillator period error and the measured phase error, comprising: adapting the drive period to compensate for the measured phase error; and The drive signal is generated based on the at least one control parameter of the drive signal and the drive period.

14. The method according to claim 13, further comprising: generating an amplitude error measurement based on a difference between the measured angular amplitude and a reference angular amplitude; as well as The reference oscillator period is generated based on the amplitude error measurement.

15. The method of claim 14, wherein generating the amplitude error measure comprises: The reference oscillator period is generated based on the amplitude error measurement such that the amplitude error measurement averages to zero while the oscillator structure oscillates.

16. The method according to claim 14, further comprising: The at least one control parameter of the drive signal and the drive period are generated based on the amplitude error measurement, the reference oscillator period and the measured phase error, wherein the amplitude error measurement and the reference oscillator period are used as separate inputs for generating the at least one control parameter and for determining the drive period.

17. The method according to claim 13, further comprising: generating an added phase error from the noise measurement and the measured phase error, Wherein determining the driving period of the driving signal comprises: determining the driving period of the driving signal based on the added phase error, comprising: adapting the driving period to compensate for the added phase error, and The generating of the at least one control parameter comprises: generating the at least one control parameter based on the added phase error, and comprising: adapting the at least one control parameter to compensate for the added phase error.

18. The method of claim 13, wherein the measured phase error is defined by a time difference between a measured time at which a zero crossing of the oscillator structure occurs and an expected time at which the zero crossing of the oscillator structure is expected to occur.

19. The method of claim 13, wherein the drive period is defined by two consecutive expected zero crossing times of the oscillator structure.

20. The method of claim 13, wherein the at least one control parameter comprises at least one of: a voltage level of the drive signal, a duty cycle of the drive signal, or a reference phase of the drive signal.

21. The method of claim 20, wherein the drive signal is a pulse width modulation (PWM) signal that switches between a low voltage level and a high voltage level, the method further comprising: At least one of the low voltage level or the high voltage level of the drive signal is adjusted based on the at least one control parameter.

22. The method of claim 20, wherein the drive signal is a pulse width modulation (PWM) signal that switches between a low voltage level and a high voltage level, the method further comprising: Adjust at least one of an on-time or an off-time of the drive signal, wherein the on-time defines a transition from the low voltage level to the high voltage level within the drive cycle, and the off-time defines a transition from the high voltage level to the low voltage level within the drive cycle.

23. A light detection and ranging LIDAR control system, comprising: a micro-electromechanical system (MEMS) mirror configured to oscillate about an axis, wherein the angular amplitude and frequency of the MEMS mirror have a non-linear correlation; a driver circuit configured to generate a drive signal to drive oscillation of the MEMS mirror; a detection circuit configured to measure the angular amplitude and phase error of the MEMS mirror; an outer control loop comprising an amplitude controller configured to: generate a reference mirror period based on the measured angular amplitude; and an inner control loop, comprising a period and phase controller, the period and phase controller being configured to: receive the reference mirror period from the outer control loop and the measured phase error from the detection circuit; generate at least one control parameter of the drive signal based on the reference mirror period and the measured phase error; and determine a drive period of the drive signal based on the reference mirror period and the measured phase error, Wherein the period and phase controller is configured to: determining an estimated oscillator period of the MEMS mirror, determining an oscillator period error as a difference between the estimated oscillator period and the reference oscillator period, generating the at least one control parameter of the drive signal based on the determined oscillator period error and the measured phase error, and determining the drive period of the drive signal based on the determined oscillator period error and the measured phase error, and The driver circuit is configured to generate the drive signal based on the at least one control parameter of the drive signal and the drive period.

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