Delay measurement, monitoring and compensation of an oscillator control system

Abstract

Embodiments of the present disclosure relate to delay measurement, monitoring, and compensation of an oscillator control system. An oscillator control system, comprising: an oscillator structure; a phase error detector configured to generate a phase error signal based on a delayed event time signal and a delayed reference signal; an analog signal path coupled between the oscillator structure and the phase error detector, the analog signal path configured to receive an event time signal and produce the delayed event time signal; a control circuit configured to generate a reference signal; a programmable delay circuit configured to receive the reference signal and induce a programmable delay on the reference signal, generating the delayed reference signal; an analog delay measurement circuit configured to inject a test signal into the analog signal path, receive a delayed test signal from the analog signal path, measure an analog delay of the delayed test signal, and generate a configuration signal configured to adjust the programmable delay according to the measured analog delay.

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to the delay measurement, monitoring, and compensation of oscillator control systems. Background Technology

[0002] Light detection and ranging (LIDAR) is a remote sensing method that uses light in the form of pulsed laser light to measure the distance (variable distance) to one or more objects in the field of view. Specifically, microelectromechanical systems (MEMS) mirrors are used to scan the light across the field of view. A photodetector array receives reflections from the illuminated object, and the time taken for the reflections to reach the individual sensors in the photodetector array is determined. This is also known as time-of-flight (TOF) measurement. The LIDAR system maps the distance to the object through time-of-flight calculations, thus forming a depth measurement and performing the distance measurement. Therefore, time-of-flight calculations can create distance and depth maps, which can be used to generate images.

[0003] A LIDAR scanning system comprises a scanning mirror and corresponding circuitry for scanning the field of view. The scanning mirror oscillates around one or more scanning axes as it scans the field of view. The ability to accurately sense the position information (e.g., rotation angle) of the scanning mirror with respect to one or more of its scanning axes is crucial for precise laser targeting. The more accurate and precise this position information, the more accurate the laser targeting and light detection at the receiver. However, the accuracy of this position information from a typical position sensing circuit is compromised by numerous analog delays introduced by the driving and sensing circuitry at the MEMS mirror and by the analog signal path extending from the driving and sensing circuitry to the MEMS driver. The analog signal path includes various analog components (current clamps, transimpedance amplifiers (TIAs), low-pass filters, etc.) and printed circuit board (PCB) interconnects. Analog delays can also vary with temperature and system lifetime. Therefore, analog delays are not static and can change over time. During the system's scanning operation, analog delays may change. If these analog delays are not properly compensated for, they will compromise the accuracy of laser targeting.

[0004] Therefore, an analog delay compensation system capable of compensating for analog delays and timing errors in real time may be needed. Summary of the Invention

[0005] One or more embodiments provide an oscillator control system, the oscillator control system comprising: an oscillator structure configured to oscillate about a rotation axis; a phase error detector configured to generate a phase error signal based on a delayed event time signal and a delayed reference signal, wherein the delayed event time signal indicates a measured event time of oscillation of the oscillator structure about the rotation axis, and the delayed reference signal indicates an expected event time of oscillation of the oscillator structure about the rotation axis; and an analog signal path coupled between the oscillator structure and the phase error detector, the analog signal path being configured to receive the event time signal indicating the measured event time and to introduce an analog delay on the event time signal, thereby generating a delayed event error signal. The system includes: a delayed event timing signal; a control circuit configured to generate a reference signal indicating the expected event time and to generate a drive signal based on a phase error signal to drive the oscillation of an oscillator structure; a programmable delay circuit configured to receive the reference signal and induce a programmable delay on the reference signal to generate a delayed reference signal; and an analog delay measurement circuit configured to inject a test signal into an analog signal path, receive a delayed test signal from the analog signal path, measure the analog delay based on the delayed test signal, and generate a configuration signal configured to adjust the programmable delay of the programmable delay circuit according to the measured analog delay.

[0006] One or more embodiments provide a method for controlling an oscillator structure configured to oscillate about a rotation axis in response to a drive signal. The method includes driving an oscillator structure to oscillate about a rotation axis according to a drive signal; generating a phase error signal based on a delayed event time signal and a delayed reference signal via a phase error detector, wherein the delayed event time signal indicates a measured event time of oscillation of the oscillator structure about the rotation axis, and the delayed reference signal indicates an expected event time of oscillation of the oscillator structure about the rotation axis; generating a delayed event time signal by inducing an analog delay on the event time signal via an analog signal path, wherein the analog signal path is coupled between the oscillator structure and the phase error detector; generating a reference signal indicating the expected event time; generating a drive signal based on the phase error signal to drive the oscillator structure to oscillate; inducing a programmable delay on the reference signal to generate a delayed reference signal; injecting a test signal into the analog signal path; inducing an analog delay on the test signal via the analog signal path to generate a delayed test signal; measuring the analog delay based on the injected test signal and the delayed test signal; and generating a configuration signal configured to adjust the programmable delay according to the measured analog delay.

[0007] One or more embodiments provide a LiDAR (Light Detection and Ranging) control system, comprising: a microelectromechanical system (MEMS) mirror configured to oscillate about a rotation axis; a phase error detector configured to generate a phase error signal based on a delayed event time signal and a delayed reference signal, wherein the delayed event time signal indicates the measured event time of the MEMS mirror oscillation about the rotation axis, and the delayed reference signal indicates the expected event time of the MEMS mirror oscillation about the rotation axis; and an analog signal path coupled between the MEMS mirror and the phase error detector, the analog signal path being configured to receive the event time signal indicating the measured event time, and at event time... The system includes: a control circuit configured to generate a reference signal indicating the expected event time and a drive signal based on a phase error signal to drive the oscillation of the MEMS mirror; a programmable delay circuit configured to receive the reference signal and generate a programmable delay on the reference signal to generate a delayed reference signal; and an analog delay measurement circuit configured to inject a test signal into the analog signal path, receive the delayed test signal from the analog signal path, measure the analog delay based on the delayed test signal, and generate a configuration signal configured to adjust the programmable delay of the programmable delay circuit according to the measured analog delay. Attached Figure Description

[0008] This document describes embodiments with reference to the accompanying drawings.

[0009] Figure 1 This is a schematic diagram of a LIDAR scanning system according to one or more embodiments;

[0010] Figure 2 This is a schematic block diagram of a LIDAR scanning system according to one or more embodiments.

[0011] Figure 3 The illustration shows signal diagrams of various signals generated by a MEMS driver based on a mirror angle θ and / or position, according to one or more embodiments;

[0012] Figure 4 A schematic block diagram of a MEMS driver according to one or more embodiments is shown; and

[0013] Figure 5 This is a schematic block diagram of a MEMS driving and position sensing system according to one or more embodiments. Detailed Implementation

[0014] 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 multiple features or elements, this should not be construed as indicating that implementing the embodiment requires all of these features or elements. Rather, in other embodiments, some features or elements may be omitted or may be replaced by alternative features or elements. Additionally, features or elements other than those explicitly shown and described may be provided, such as conventional components of a sensor device.

[0015] Unless otherwise specifically indicated, features from different embodiments may be combined to form other embodiments. Variations or modifications described with respect to one embodiment may also be applicable to other embodiments. In some instances, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the embodiments.

[0016] Furthermore, in the following description, equivalent or similar reference numerals are used to denote equivalent or similar elements or elements having equivalent or similar functions. Since identical or functionally equivalent elements in the drawings are given the same reference numerals, repeated descriptions of elements with the same reference numerals can be omitted. Therefore, the descriptions provided for elements with the same or similar reference numerals can be interchanged.

[0017] Unless otherwise stated, the connections or couplings between the elements shown in the accompanying drawings or described herein can be wired or wireless. Furthermore, as long as the connection or coupling is essentially for the general purpose of maintaining a connection or coupling for, for example, transmitting a signal or transmitting information, such a connection or coupling can be a direct connection or coupling without additional intermediate elements, or it can be an indirect connection or coupling with one or more additional inserting elements.

[0018] In this disclosure, ordinal expressions such as "first," "second," etc., can modify various elements. However, such elements are not limited by the above expressions. For example, the above expressions do not limit the sequence and / or importance of elements. The above expressions are used only for the purpose of distinguishing one element from other elements. For example, the first box and the second box indicate different boxes, but they are both boxes. For other examples, without departing from the scope of this disclosure, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element.

[0019] The embodiments relate to optical sensors and optical sensor systems, and to obtaining information about optical sensors and optical sensor systems. A sensor can refer to a component that converts a physical quantity to be measured into an electrical signal (e.g., a current signal or a voltage signal). Physical quantities can include, for example, electromagnetic radiation such as visible light, infrared (IR) radiation, or other types of illumination signals, current, or voltage, but are not limited to these. For example, an image sensor can be a silicon chip inside a camera that converts photons of light from a mirror into a voltage. The larger the active area of ​​the sensor, the more light can be collected to create an image.

[0020] As used herein, a sensor device can refer to a device that includes sensors and other components, such as biasing circuitry, analog-to-digital converters, or filters. A sensor device can be integrated onto a single chip; however, in other embodiments, multiple chips or external components can be used to implement the sensor device.

[0021] In a Light Detection and Ranging (LIDAR) system, a light source transmits light pulses into the field of view, and the light is reflected from one or more objects through backscattering. Specifically, LIDAR is a direct time-of-flight (TOF) system, in which light pulses (e.g., a laser beam of infrared light) are emitted into the field of view and an array of pixels detects and measures the reflected beams. For example, a photodetector array receives reflections from an illuminated object.

[0022] The time difference of return of each light pulse across multiple pixels in the pixel array can then be used to create a digital 3D representation of the environment or generate other sensor data. For example, a light source can emit a single light pulse, and a time-to-digital converter (TDC) electrically coupled to the pixel array can count from the time the light pulse is emitted (corresponding to the start signal) until the time the reflected light pulse is received at the receiver (i.e., the pixel array) (corresponding to the stop signal). The "time of flight" of the light pulse is then translated into distance.

[0023] In another example, an analog-to-digital converter (ADC) can be electrically coupled to a pixel array (e.g., indirectly coupled using intermediate elements therebetween) for pulse detection and Time-of-Flight (TOF) measurements. For instance, the ADC can be used to estimate the time interval between start and stop signals using appropriate algorithms. For example, the ADC can be used to detect analog electrical signals from one or more photodiodes to estimate the time interval between a start signal (i.e., the timing corresponding to the emission of a light pulse) and a stop signal (i.e., the timing corresponding to the reception of the analog electrical signal at the ADC) using appropriate algorithms.

[0024] Scanning techniques such as oscillating horizontal scanning (e.g., from left to right and from right to left in the field of view) or oscillating vertical scanning (e.g., from bottom to top and from top to bottom in the field of view) can illuminate a scene in a continuous scanning manner. Each time a laser beam is fired from the light source, a scan line is generated within the "field of view." By emitting continuous light pulses along different scanning directions, an area called the field of view can be scanned, and objects within the area can be detected and imaged. Therefore, the field of view represents a scan plane with a projection center. Raster scanning can also be used.

[0025] Figure 1 This 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 including a transmitter and a receiver. The transmitter includes an illumination unit 10, transmitter optics 11, and a one-dimensional (1D) microelectromechanical system (MEMS) reflector 12. The receiver includes a second optical component 14 and a photodetector array 15.

[0026] The illumination unit 10 includes multiple light sources (e.g., laser diodes or light-emitting diodes), which are linearly aligned in a single strip and configured to transmit light for scanning an object. The light emitted by the light sources is typically infrared light, but other wavelengths can also be used. Figure 1 As can be seen in the embodiments, the shape of the light emitted by the light source is diffused in a direction perpendicular to the transmission direction to form an elliptical beam perpendicular to the transmission direction. The illumination light emitted from the light source is guided to the emitter optics 11, which is configured to focus each laser beam onto a one-dimensional MEMS mirror 12. The emitter optics 11 can be, for example, a lens or a prism.

[0027] When reflected by the MEMS mirror 12, the light from the light source is vertically aligned to target each emitted laser beam, forming a one-dimensional vertical scan line SL or a vertical stripe of infrared light. Each light source in the illumination unit 10 contributes to a different vertical region of the vertical scan line SL. Therefore, the light sources can be simultaneously activated and deactivated to obtain light pulses with multiple segments, each segment corresponding to a corresponding light source. However, each vertical region or segment of the vertical scan line SL can also be independently activated or deactivated by turning on or off a corresponding light source of the illumination unit 10. Thus, light from part or all of the vertical scan line SL can be output from the system 100 into the field of view.

[0028] Therefore, the transmitter of system 100 is configured to generate a laser beam based on laser pulses, the laser beam having a rectangular shape extending in a direction perpendicular to the emission direction of the laser beam.

[0029] Additionally, although three laser sources are shown, it should be understood that the number of laser sources is not limited to this. For example, the vertical scan line SL can be generated by a single laser source, two laser sources, or more than three laser sources.

[0030] MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) integrated on a semiconductor chip (not shown). According to this embodiment, the MEMS mirror 12 is configured to rotate about a single scanning axis and, arguably, has only one scanning degree of freedom. Unlike 2D MEMS mirrors (2D MEMS scanners), in a 1D MEMS mirror, the single scanning axis is fixed to a non-rotating substrate and thus maintains its spatial orientation during oscillation of the MEMS mirror. Therefore, the 1D oscillating MEMS mirror is designed to be more resistant to vibration and shock than 2D MEMS mirror solutions. Due to this single scanning rotation axis, the MEMS mirror 12 is referred to as a 1D MEMS mirror or a 1D MEMS scanner.

[0031] Although the embodiments describe the use of a 1D oscillating MEMS mirror, the measurement methods described herein can also be extended to 2D MEMS mirrors. In this case, the two axes of a single 2D MEMS mirror are controlled by different phase-locked loops (PLLs), such that the 2D MEMS mirror is measured and compensated for an analog delay of the first scan axis according to any of the techniques described herein, and the 2D MEMS mirror is measured and compensated for an analog delay of the second scan axis according to any of the techniques described herein. Further, it is possible that the different PLLs are provided in separate MEMS drivers or integrated into a single MEMS driver for the 2D MEMS mirror.

[0032] MEMS mirror 12 is itself a nonlinear resonator (i.e., a resonant MEMS mirror) configured to oscillate "side-to-side" around the scan axis 13 at a resonant frequency, causing the light reflected from MEMS mirror 12 (i.e., the vertical scan line of light) to oscillate back and forth in the horizontal scan direction. MEMS mirror 12 exhibits strong nonlinearity due to the hardening of its suspension. The scan period, or oscillation period, is defined, for example, by a 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 back to the first edge. The mirror period of MEMS mirror 12 corresponds to the scan period.

[0033] Therefore, by changing the angle of the MEMS mirror 12 on its scanning axis 13, the vertical light stripe scans the field of view in the horizontal direction. For example, the MEMS mirror 12 can be configured to oscillate at a resonant frequency of 2 kHz between + / -15 degrees to manipulate the light within + / -30 degrees, thereby constituting the scanning range of the field of view. Thus, the field of view can be scanned line by line by the MEMS mirror 12 through rotation of its degree of motion. Such a sequence of motion (e.g., from -15 degrees to +15 degrees) is called a single scan or scan cycle. Multiple scans can be used by a processing unit to generate distance and depth maps and 3D images.

[0034] Although a transmission mirror is described in the context of MEMS mirrors, it should be understood that other oscillating mirrors can also be used. Additionally, the resonant frequency or rotation is not limited to 2 kHz and + / - 15 degrees, respectively, and both the resonant frequency and field of view can be increased or decreased depending on the application. Therefore, the scanning mirror is configured to oscillate about a scanning axis and guide the laser beam into the field of view in different directions. Thus, the transmission technique involves transmitting the beam from a transmission mirror oscillating about a scanning axis into the field of view, such that the beam is projected into the field of view as a vertical scan line SL, which moves horizontally across the field of view as the transmission mirror oscillates about a single scanning axis.

[0035] Upon impact with one or more objects, the transmitted vertical light stripe is backscattered and reflected toward the LIDAR scanning system 100 as a reflected vertical line. A second optical component 14 (e.g., a lens or prism) receives the reflected light at this reflected vertical line. The second optical component 14 guides the reflected light to a photodetector array 15, which receives the reflected light as a receiving 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., calculated and processed via TOF).

[0036] The receiving line is shown as a vertical light column extending along one of the pixel columns in the length direction of the pixel column. The receiving line has... Figure 1 The diagram shows three regions corresponding to the vertical scan line SL. As the vertical scan line SL moves horizontally across the field of view, the vertical light beam RL incident on the 2D photodetector array 15 also moves horizontally across the 2D photodetector array 15. When the receiving direction of the reflected beam RL changes, the reflected 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 beam RL corresponds to the transmission direction of the scan line SL.

[0037] The photodetector array 15 can be any of several photodetector types, including avalanche photodiodes (APDs), silicon photomultiplier tubes (SiPMs), photovoltaic cells, and / or other photodiode devices. Imaging sensors such as charge-coupled devices (CCDs) can also be photodetectors. In the example provided herein, the photodetector array 15 is a two-dimensional (2D) APD array comprising an array of APD pixels. In other embodiments, the photodetector array 15 can be a 1D array comprising a single column of photodiodes. Activation of the photodiodes can be synchronized with light pulses emitted by the illumination unit 10. Alternatively, a single photodetector unit / pixel opposite the array can be used. For example, a single photodetector unit / pixel can be used in the case of a 2x1D scan emitter in a coaxial LiDAR architecture.

[0038] The photodetector array 15 receives reflected light pulses as a receiving line RL and generates an electrical signal in response. Since the transmission time of each light pulse from the illumination unit 10 is known and light travels at a known speed, the distance between the object and the photodetector array 15 can be determined using the time-of-flight calculation of the electrical signal. Depth mapping can then be used to plot the distance information.

[0039] In one example, for each distance sample, the microcontroller triggers a laser pulse from each light source in the illumination unit 10 and also starts a timer in the time-to-digital converter (TDC) integrated circuit (IC). The laser pulse propagates via transmission optics, is reflected by the target field, and is captured by the APDs of the APD array 15. The APD emits short electrical pulses, which are then amplified by an electrical signal amplifier. The comparator IC identifies the pulse and sends a digital signal to the TDC to stop the timer. The TDC uses a clock frequency to calibrate each measurement. The TDC sends serial data of the differential time between the start and stop digital signals to the microcontroller, which filters out any erroneous readings, averages the multiple time measurements, and calculates the distance from the target at that particular field location. By emitting continuous light pulses in different directions established by the MEMS mirrors, the area (i.e., the field of view) can be scanned, a three-dimensional image can be generated, and objects within the area can be detected.

[0040] Alternatively, instead of using the TDC method, the 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 a start signal (i.e., the timing corresponding to the emission of a light pulse) and a stop signal (i.e., the timing corresponding to the reception of the analog electrical signal at the ADC) using an appropriate algorithm.

[0041] It should be understood that the aforementioned horizontal scanning system 100 can also be used for vertical scanning. In this case, the scanning arrangement is configured such that the scanning direction is rotated by 90°, causing the scan line SL and the receiving line RL to move vertically (i.e., from top to bottom or from bottom to top). Thus, the scan line is the horizontal scan line SL projected into the field of view, which moves vertically across the field of view as the transmission mirror oscillates about a single scanning axis. Furthermore, as the horizontal scan line SL moves vertically across the field of view, the horizontal light train RL incident on the 2D photodetector array 15 also moves vertically across the 2D photodetector array 15.

[0042] It will be further understood that a LIDAR scanning system may include multiple scanning mirrors 12 and corresponding circuitry for scanning different fields of view in the horizontal and / or vertical directions. For example, a vehicle may include multiple scanning mirrors arranged at different locations 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 in the same locations within the vehicle and configured to scan the same field of view.

[0043] Figure 2 This is a schematic block diagram of a LiDAR scanning system 200 according to one or more embodiments. Specifically, Figure 2 Additional features of the LIDAR scanning system 200 are shown, which includes example processing and control system components such as MEMS drivers, receiver circuitry, and system controllers.

[0044] 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 configured to control the components of the transmitter unit 21 and the receiver unit 22, and to receive raw data from the receiver unit 22 and perform processing thereon (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 circuitry for processing the data, and control circuitry, such as a microcontroller, configured to generate control signals. The LIDAR scanning system 200 may also include a temperature sensor 26.

[0045] MEMS reflector 12 can be assembled Figure 2 The chip package 27 shown is used to protect the reflector. For example, the MEMS reflector 12 can be sealed in the chip package under low pressure (i.e., below atmospheric pressure). This low pressure provides a low-damping environment for the MEMS reflector 12 to operate therein.

[0046] Receiver unit 22 includes a photodetector array 15 and receiver circuitry 24. Receiver circuitry 24 may include one or more circuits or sub-circuits for receiving and / or processing information. Receiver circuitry 24 may receive analog electrical signals from the APD diodes of photodetector array 15 and transmit the electrical signals as raw analog data or raw digital data to system controller 23. To transmit the raw signals as digital signals, receiver circuitry 24 may include an ADC and a field-programmable gate array (FPGA). Receiver circuitry 24 may also receive trigger control signals from system controller 23 to activate one or more APD diodes. Receiver circuitry 24 may also receive gain setting control signals for controlling the gain of one or more APD diodes.

[0047] 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. Specifically, the MEMS driver 25 actuates and senses the rotational position of the mirror and provides the mirror's position information (e.g., tilt angle or rotation angle about the axis of rotation) to the system controller 23. Based on this 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 thus measure the reflected light signal. Therefore, higher accuracy in the position sensing of the MEMS mirror leads to more accurate and precise control of other components of the LIDAR system.

[0048] The MEMS driver 25 can also measure and record the frequency and current of the reflector using the capacitive changes in the comb-shaped drive rotor and stator of the actuator structure used to drive the MEMS reflector 12. The actuator structure of the MEMS reflector 12 also includes a suspension structure suspending the MEMS reflector 12 within the reflector frame body. Therefore, the MEMS driver 25 may also include measurement circuitry configured to measure one or more characteristics of the MEMS reflector 12 described herein. The MEMS driver 25 may also include processing circuitry including at least one processor (e.g., analog signal processing circuitry and / or digital signal processing circuitry) configured to process measurement information from the measurement circuitry to evaluate the mechanical health status and / or the state of the chip package of the MEMS reflector 12.

[0049] Additionally or alternatively, the system controller 23 may receive measurement information from the measurement circuitry of the MEMS driver 25 and perform processing thereon. Therefore, the 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), the processor being configured to process the measurement information from the measurement circuitry to assess the mechanical health of the MEMS mirror 12 and / or the state of the chip package.

[0050] By sensing the rotational position of the MEMS mirror 12 about its rotation axis 13, the MEMS driver 25 can sense zero-crossing (ZC) events of the MEMS mirror 12. A zero-crossing event is an instance where the MEMS mirror 12 has a rotation angle of 0° on its rotation axis 13. Specifically, this is the moment when the MEMS mirror 12 is parallel to the frame or in an intermediate position. The intermediate position can also be referred to as the stationary position (e.g., when the MEMS mirror 12 stops after the driving force is turned off). Since the MEMS mirror 12 oscillates back and forth between two rotational directions (e.g., clockwise and counterclockwise), two zero-crossing events occur during the scan – 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 angular crossover event of another predetermined angle can also be used instead of a zero-crossing event.

[0051] In some embodiments, the event time may correspond to a non-zero-crossing event. For example, the sensed rotation angle may be any angle other than 0°. However, for illustrative purposes, the examples herein will be described in the context of sensing a zero-crossing event.

[0052] MEMS driver 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 system controller 23 as position information. Specifically, at each zero-crossing event or angle crossing event, MEMS driver 25 triggers a change in the output of the position signal (Position_L).

[0053] Figure 3The diagram illustrates a signal graph of various signals (including a position signal (Position_L)) generated by the MEMS driver 25 based on the mirror angle θ and / or position. 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 rotation 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 rotation direction (e.g., from right to left). Furthermore, the signal is "high" when the mirror is pointing in one direction (e.g., to the left) and "low" when the mirror is pointing in a second direction (e.g., to the right). Therefore, the position signal indicates zero-crossing events not only by triggering pulse transitions but also by indicating the directional tilt of the mirror. The frequency of the position signal increases as the interval between zero-crossing events increases. Based on this position signal, the phase and / or frequency of two or more position signals can be compared.

[0054] Alternatively, at each zero-crossing event, a short pulse can be generated by the MEMS driver 25, such that a pulse 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, the absolute phase information indicates the direction in which no mirror movement will occur. Based on this position signal, the phase and / or frequency of two or more position signals can be compared.

[0055] The MEMS driver 25 can send position information to the system controller 23, enabling the system controller 23 to use the position information to control the triggering of laser pulses in the illumination unit 10 and the activation of photodiodes in the photodetector array 15. The position information can also be used by the system controller as feedback information, allowing the system controller 23 to maintain stable operation of the MEMS mirror 12 via control signals provided to the MEMS driver 25, and to synchronize with other MEMS mirrors.

[0056] The timing information of the zero-crossing events 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., 14MHz) with a fixed number of pulses, providing fine-grained phase information for the MEMS mirror 12. In this case, the mirror's movement is divided into equidistant segments in the time domain (affected by the quantization error of the digitally controlled oscillator (DCO) frequency generator). A "slice" can be considered a sub-part of the time interval between two consecutive zero-crossing events. Specifically, the time interval between two zero-crossing events (i.e., between two Position_L signals or pulses) is divided into equal parts, such that signal pulses are generated at each part. Therefore, the phase clock signal is a pulse signal whose frequency is related to the time interval between two zero-crossing events, where the shorter the time interval, the higher the frequency. Thus, the phase clock signal divides the mirror's movement into a well-defined number of phase segments. The MEMS driver 25 can generate the phase clock signal and output it to the system controller 23.

[0057] Figure 3 The diagram also illustrates a phase clock signal (Phase_CLK) that comprises several pulses per oscillation cycle, where the oscillation cycle is defined by the time interval between two consecutive zero-crossing events.

[0058] MEMS mirror 12 includes an actuator structure for driving the mirror. The actuator structure includes interdigitated finger electrodes made of interdigitated mirror combs and frame combs, to which a driving voltage (i.e., an actuation or drive signal) is applied by a MEMS driver 25. This driving voltage may be referred to as a high voltage (HV). The driving voltage applied to the finger structure generates a corresponding capacitance. The driving voltage across the finger structure creates a driving force between the interdigitated mirror combs and frame combs, which in turn creates torque on the mirror body about its axis of rotation. The driving voltage HV can be switched on or off (HV on / off), thereby generating an oscillating driving force. This oscillating driving force causes the mirror to oscillate back and forth between two extreme values ​​on its axis of rotation. Depending on the configuration, this actuation can be adjusted or modified by adjusting the driving voltage cutoff time, the voltage level of the driving voltage, or the duty cycle.

[0059] In other embodiments, an electromagnetic actuator can be used to drive the MEMS mirror 12. For the electromagnetic actuator, a drive current (i.e., an actuation or drive signal) can be used to generate an oscillating drive force. Therefore, it will be understood that drive voltage and drive current are used interchangeably herein to indicate an actuation signal or a drive signal, and both can generally be referred to as drive force.

[0060] As the mirror oscillates, the capacitance between the interdigitated electrodes changes according to the mirror's rotational position. The MEMS driver 25 is configured to measure the capacitance between the interdigitated electrodes and thereby determine the rotational or angular position of the MEMS mirror 12. By monitoring the capacitance, the MEMS driver 25 can detect zero-crossing events and their timing, and can determine the tilt angle of the MEMS mirror 12 at any given time. The MEMS driver 25 can also use the measured capacitance to determine the mirror frequency and record the information in memory at either the MEMS driver 25 or the system controller 23.

[0061] Position sensing 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 structure changes, causing a change in the geometry of the capacitance. As the geometry of the capacitance changes, the capacitance itself also changes. Therefore, a particular capacitance directly corresponds to a specific position (i.e., tilt angle) of the MEMS mirror. By sensing the capacitance of the finger structure, the MEMS driver 25 can monitor and track the oscillations of the mirror and determine the specific position (including zero crossings) of the MEMS mirror.

[0062] One method for measuring capacitance is to measure the current flowing through the finger structure, convert the measured current into a voltage, and then further correlate the voltage with capacitance and / or rotation angle. However, any method for measuring capacitance can be used. The direction of rotation (e.g., positive or negative, left to right or right to left, clockwise or counterclockwise, etc.) can also be detected by measuring the change in capacitance over time, where a positive or negative change indicates the relative direction of rotation. The MEMS driver 25 can also record the current and voltage measured during the capacitance measurement. Therefore, increasing the accuracy of the mirror's position sensing can improve the overall accuracy of the LIDAR system.

[0063] Because the mirror is driven at an oscillation frequency (e.g., 2 kHz), when the mirror rotates in a first rotational direction (e.g., from left to right or clockwise), it crosses the zero position (i.e., 0°) at some point in time. The same is true when the mirror rotates in a second rotational direction (e.g., from right to left or counterclockwise), the mirror will cross the zero position at some point in time. These instances of crossing the zero position can be referred to as zero-crossing events occurring at the zero-crossing time.

[0064] Figure 4A schematic block diagram of a MEMS driver according to one or more embodiments is illustrated. The MEMS driver 25 includes an analog core 31, a phase error detector 32, an error detection and compensation unit 33, a loop filter 34, a digitally controlled oscillator (DCO) 35, and a mirror driver 36 arranged in the loop. This loop, together with the MEMS mirror 12, forms a phase-locked loop (PLL) that follows the frequency of the MEMS mirror 12. The MEMS driver 25 also includes a direction signal generator 37 and a chopper signal generator 38. It will be understood that the direction signal generator 37 and the chopper signal generator 38 may also be provided externally to the MEMS driver 25. The MEMS driver 25 electrically communicates with the MEMS mirror 12 and the system controller 23 via an electrical connection used for transmitting signals therebetween.

[0065] Therefore, the MEMS driver 25 implements analog and digital circuitry. The analog circuitry (i.e., the analog core 31) includes one or more inputs and outputs connected to the MEMS mirror 12. For example, one or more inputs of the analog core 31 can receive analog signals related to the position and rotation direction of the MEMS mirror 12. Additionally, one or more outputs of the analog core 31 can provide control signals to the MEMS mirror 12 to control the oscillation of the mirror.

[0066] The analog core 31 includes analog circuitry configured to measure the capacitance of the finger structure of the MEMS mirror actuator to measure timing-critical events, such as zero-crossing events, using a comparator. Therefore, the analog circuitry measures the position of the MEMS mirror 12 about a rotation axis and determines the zero-crossing time in a first rotation direction and a second rotation direction. The analog circuitry is also configured to generate direction information DL1L and DL1R associated with the rotation direction of the MEMS mirror 12 (e.g., clockwise or counterclockwise). The remaining digital circuitry enables chip intelligence (mirror control, laser pulse triggering, photodiode activation triggering, etc.). This method enables digital signal processing solutions to detect systematic and non-systematic error sources, which can then be compensated for.

[0067] The analog core 31 is configured to generate and output the zero-crossing time ZCmeas measured by the MEMS mirror 12, which is received by the phase error detector 32. The analog core 31 is also configured to provide direction information DL1L and DL1R to the direction signal generator 37, which is related to the rotation direction of the MEMS mirror 12 (e.g., clockwise or counterclockwise). The direction signal generator 37 is configured to generate a direction signal d(n) (e.g., +1 or -1) based on the direction information DL1L and DL1R.

[0068] Phase error detector 32 is configured to receive the measured zero-crossing time ZCmeas from analog core 31 and the reference zero-crossing time ZCref from mirror driver 36. The reference zero-crossing time ZCref is the expected zero-crossing time of MEMS mirror 12 based on the mirror's oscillation frequency. The reference zero-crossing time ZCref is generated by mirror driver 36 (i.e., by PLL).

[0069] The phase error detector 32 includes a comparator circuit configured to compare the measured (actual) zero-crossing time ZCmeas with a reference zero-crossing time ZCref and output the difference. Therefore, the phase error detector 32 is configured to compare the measured zero-crossing timing with the expected zero-crossing timing and generate an error signal p(n) representing the difference between the measured and expected zero-crossing timing. In other words, the phase error signal p(n) represents the phase error between the measured zero-crossing time ZCmeas and the reference zero-crossing time ZCref. The phase error signal p(n) is effectively output for each zero-crossing of the MEMS mirror 12.

[0070] For example, if the measured zero-crossing time is equal to the expected zero-crossing time, the phase error signal p(n) will be zero. Otherwise, the phase error signal will be a non-zero value corresponding to the difference between the measured zero-crossing time and the expected zero-crossing time.

[0071] Additionally, the phase error signal p(n) is generated for both rotation directions of the mirror. For example, in the presence of asymmetry, the phase error detector 32 can generate a phase error signal p(n) with a value of +3 corresponding to the first rotation direction, and can generate a phase error signal p(n) with a value of -3 corresponding to the second rotation direction. Asymmetry exists as long as the values ​​in the two rotation directions are not equal.

[0072] Each stroke of the MEMS mirror (i.e., from left to right or from right to left) generates a value of the phase error signal p(n). Specifically, the timing of the zero-crossing is measured whenever the MEMS mirror 12 rotates past the zero-crossing point, and the phase error signal p(n) is generated based on its comparison with the expected zero-crossing time. Therefore, the PLL error spectrum represents the output of the phase detector as a function of time (i.e., the phase error signal as a function of time).

[0073] The error detection and compensation unit 33 is configured to receive a phase error signal p(n) from the phase error detector 32, detect periodic jitter components, and remove the periodic jitter components from the phase error signal p(n) to generate a compensated phase error signal pcorr(n). The error detection and compensation unit 33 also receives a direction signal d(n) from the direction signal generator 37.

[0074] The compensated phase error signal pcorr(n) effectively reduces the jitter of the PLL, thereby enabling higher precision in sensing and controlling the MEMS mirror 12, and in controlling the illumination unit 10. Specifically, removing the periodic jitter component from the phase error signal p(n) enables more accurate mirror position signaling (i.e., mirror position information), which allows for more precise laser firing and more accurate control of the mirror.

[0075] The error detection and compensation unit 33 includes a DSP structure composed of circuit logic (e.g., adders, subtractors, multipliers, integrators, dividers, etc.), which is coupled to form a signal processing chain configured to detect and compensate for periodic jitter components. Specifically, the DSP structure is configured to measure and compensate for the two main error sources: mirror asymmetry and periodic jitter caused by chopping.

[0076] The calibrated phase detector signal pcorr(n) was used to derive the signal F of DCO 35. DCO This forms the basis for the mirror position information generated by the mirror driver 36. Specifically, the error detection and compensation unit 33 outputs the calibrated phase detector signal pcorr(n) to the loop filter 34, which implements proportional-integral (PI) or proportional-integral-derivative (PID) control to increment DCO 35 to adjust the phase of DCO 35.

[0077] Because the calibrated phase detector signal pcorr(n) does not contain periodic jitter components, the signal F of DCO 35... DCO The phase is unaffected by these jitter components and corresponds more accurately to the phase of the MEMS mirror 12. The DCO35 provides the FDCO signal to the mirror driver 36 based on the value of the DCO counter 35a.

[0078] The mirror driver 36 is based on signal F DCO A mirror scheduler is used to determine the sub-timing of the MEMS mirror 12. Therefore, the mirror driver 36 includes at least one processor for performing timing analysis and scheduling. Based on the sub-timing, the mirror driver 36 is configured to generate a drive voltage HV as a control signal to control the oscillation of the MEMS mirror 12. More specifically, the drive voltage HV (e.g., 100V) is turned on and off, and as previously described, is applied to the actuator structure of the MEMS mirror 12. The mirror driver 36 is not only configured to turn the drive voltage HV on and off, but can also drive the voltage to any level (e.g., fully on, half-fully off, etc.).

[0079] The mirror driver 36 is based on signal F DCOThe mirror position information is determined and output to the system controller 23. The mirror position information effectively indicates the position of the MEMS mirror 12. The system controller 23 can use the mirror position information to control the timing of the laser pulses of the illumination unit 10. The mirror position information can also be used to control the activation timing of the diodes in the photodetector array 15.

[0080] The mirror driver 36 can also determine the expected zero-crossing time ZCref based on the mirror position information.

[0081] Figure 5 This is a schematic block diagram of a MEMS driving and position sensing system 500 according to one or more embodiments. Specifically, the MEMS driving and position sensing system 500 can at least partially... Figure 2 and Figure 4 The MEMS driver 25 shown is implemented therein. The MEMS driving and position sensing system 500 also includes a MEMS mirror 12 to which the MEMS driving and position sensing circuitry of the system 500 is coupled.

[0082] As described above, the MEMS mirror 12 itself includes an actuator structure for driving the mirror around a scanning axis. The actuator structure also includes a drive capacitor, which the sensing circuitry uses to measure its capacitance to detect the rotational or angular position of the MEMS mirror 12. A portion of the total analog delay when sensing position information may be caused by the drive capacitor.

[0083] The MEMS driving and position sensing system 500 includes a phase error detector 32 (e.g., a phase comparator) as an input to a phase-locked loop (PLL) circuit used to synchronize the MEMS mirror 12. The phase error detector 32, which can be an analog or digital phase detector, is coupled to a sensing feedback path used to detect the actual zero crossing of the MEMS mirror 12. The sensing feedback path is an analog signal path S that includes various analog components (current clamps, transimpedance amplifiers (TIAs), low-pass filters, etc.) and printed circuit board (PCB) interconnects. A Each of the various analog components and printed circuit boards (PCBs) contributes a portion of the total analog delay when sensing position information (e.g., zero-crossing information). The analog sensing circuitry of the sensing feedback path (including analog core 31) is configured to detect zero-crossing at MEMS mirror 12 and output a zero-crossing signal ZCmeas indicating that a zero-crossing event has occurred.

[0084] Therefore, an analog delay block 42 is provided in the sensing feedback path and represents the total analog delay occurring between the MEMS mirror 12 and the phase error detector 32. Thus, the timing of the actual zero-crossing signal corresponding to the actual zero-crossing detected during the oscillation of the MEMS mirror 12 is delayed by the analog delay block 42. This delay by the analog delay block 42 results in a delayed zero-crossing signal (DZCmeas) received by the phase error detector 32. If the total analog delay of the delayed zero-crossing signal is appropriately compensated, the sensed zero-crossing signal of the MEMS mirror 12 is sent to the laser firing circuitry in a precise manner. However, as mentioned above, the analog delay is not static and needs to be monitored in real time during scanning operations and throughout the entire lifecycle of the LIDAR system.

[0085] The MEMS drive and position sensing system 500 also includes a controller 43, which may be a digital controller, an analog controller, or a hybrid thereof. In the current example, the controller 43 is implemented as a digital controller and may be the digital portion of a PLL including a phase error detector 32. Therefore, the digital controller 43 may include an error detection and compensation unit 33, a loop filter 34, a DCO 35, and a mirror driver 36 arranged in a feedback loop having a MEMS mirror 12, an analog delay block 42, and a phase error detector 32. It should be noted that the MEMS mirror 12 and the analog delay block 42, which at least partially represent the analog core 31, are part of the feedback path of the PLL.

[0086] The digital controller 43 generates a zero-crossing reference signal ZCref, which indicates the expected zero-crossing time of the oscillating MEMS mirror 12. For example, the digital controller 43 (i.e., the mirror driver 36) can determine the expected zero-crossing time of the expected MEMS mirror 12 based on the oscillation frequency it drives, sub-timing information, and the system model.

[0087] The programmable delay circuit 44 receives a zero-crossing reference signal ZCref from the digital controller 43 and compensates for the zero-crossing reference signal ZCref by inducing a delay on the signal, for example, based on an expected analog delay. The expected analog delay is programmed into the programmable delay circuit 44 and can be configured as a programmable analog delay. In some examples, the programmable delay may incorporate both analog and / or digital delays.

[0088] As a result, the programmable delay circuit 44 generates a delayed zero-crossing reference signal (DZCref) based on the zero-crossing reference signal and the expected analog delay. The expected analog delay is designed to match the total analog delay of the analog delay block 42, such that the delay of the delayed zero-crossing reference signal (DZCref) is equal to the delay of the delayed zero-crossing signal (DZCmeas). When the delays are equal, the phases of the delayed zero-crossing reference signal (DZCref) and the delayed zero-crossing signal (DZCmeas) should be aligned to zero phase difference.

[0089] Phase error detector 32 is configured to receive a delayed zero-crossing reference signal (DZCref) and a delayed zero-crossing signal (DZCmeas), compare their phases, and generate an error signal p(n) based on the phase difference or phase error between the two signals. Digital controller 43 is configured to receive the error signal p(n) and adjust the drive voltage HV based on the drive voltage HV to synchronize the PLL and MEMS mirror 12. For example, the output of the DCO can be adjusted to maintain phase matching between the delayed zero-crossing reference signal (DZCref) and the delayed zero-crossing signal (DZCmeas).

[0090] The digital controller 43 is also configured to generate a position signal (Position_L) and a phase clock signal (Phase_CLK) based on signals extracted from the PLL. The digital controller 43 can also generate a direction signal (Direction_L) based on the position signal (Position_L), where the direction signal (Direction_L) indicates the rotation direction of the MEMS mirror 12. These signals are transmitted to the system controller 23 to improve the firing accuracy (i.e., timing accuracy) of the transmitted laser beam relative to the angular position of the MEMS mirror 12.

[0091] The MEMS driving and position sensing system 500 also includes an analog delay measurement circuit 45. The delay measurement circuit 45 is configured to periodically generate trigger pulses (i.e., test signals) during normal operation of the MEMS mirror 12 and inject the trigger pulses (i.e., test signals) along the analog signal path S. A (e.g., a sensing feedback path) or one or more injection points. For example, the triggered signal pulse may be injected at the MEMS mirror 12 into a driver circuit device (e.g., a drive capacitor), into a signal line on the PCB, or into the path along the analog signal path S. A One or more components (current clamp, TIA, low-pass filter, etc.) are arranged. When a pulse is injected into the driver circuit of the MEMS mirror 12, the injection is limited to the case where the drive voltage HV is cut off and the drive capacitor is discharged.

[0092] The injected pulse eventually leaves the analog delay block 42 by propagating through at least a portion of the analog signal path SA and is received by the delay measurement circuit 45. Due to delays caused by one or more analog components, the injected pulse is delayed on the same principle, causing the zero-crossing signal ZCmeas to be delayed. The delay measurement circuit 45 is configured to receive the delayed pulse and measure the delay period, which is the time between transmitting the injected pulse and receiving the delayed pulse. This delay period represents the distance the injected trigger pulse has traveled through the analog signal path S. A The part corresponds to the simulation delay being processed.

[0093] The delay measurement circuit 45 is also configured to adapt or reprogram the programmable analog delay (i.e., the expected analog delay) of the programmable delay circuit 44. For this purpose, the delay measurement circuit 45 can use the configuration signal S... C The signal is transmitted to programmable delay circuit 44, which sets the programmable analog delay based on the measured analog delay. As a result, the programmable analog delay can be periodically updated during the operation of MEMS mirror 12 to accommodate dynamically changing analog delays. This allows the phase of the delayed zero-crossing reference signal to be periodically re-aligned with the phase of the delayed zero-crossing signal (DZCmeas), and precise MEMS position information can be provided to system controller 23 and its laser firing circuitry.

[0094] Furthermore, the delay measurement circuit 45 is also configured to compare the measured analog delay with a expected delay range (e.g., a expected delay threshold). If the measured analog delay exceeds (e.g., is greater than) the expected delay threshold, the delay measurement circuit 45 can be configured to generate a functional safety (FuSa) alarm, indicating that the correct operation of the entire system cannot be guaranteed due to, for example, component failure or aging. The FuSa alarm can, for example, be transmitted to the vehicle's electronic control unit (ECU), which warns the user that the LIDAR system needs maintenance. Therefore, the delay measurement circuit 45 can be used to monitor the overall functional safety of the LIDAR system and to improve compensation for analog delays in the circuitry of the MEMS mirror 12 and MEMS driver 25.

[0095] The techniques described in this disclosure can be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the described techniques can be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), programmable logic controllers (PLCs), or any other equivalent integrated or discrete logic circuit devices, and any combination of such components. The terms "processor" or "processing circuit device" can generally refer to any of the aforementioned logic circuit devices, either alone or in combination with other logic circuit devices or any other equivalent circuit devices. A control unit, including hardware, can also perform one or more of the techniques of this disclosure. The control unit can use electrical signals and digital algorithms to perform its receiving, analyzing, and controlling functions, which may also include correction functions. Such hardware, software, and firmware can be implemented within the same device or in separate devices to support the various techniques described in this disclosure.

[0096] One or more aspects of this disclosure can be implemented as a non-transitory computer-readable recording medium on which a program is recorded, the program embodying a method / algorithm for instructing a processor to execute the method / algorithm. Therefore, the non-transitory computer-readable recording medium may have electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system to cause the corresponding method / algorithm to be executed. The non-transitory computer-readable recording medium can be, for example, a CD-ROM, DVD, Blu-ray disc, RAM, ROM, PROM, EPROM, EEPROM, FLASH memory, or electronic memory device.

[0097] Although various embodiments have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made to achieve some of the advantages of the concepts disclosed herein without departing from the spirit and scope of the invention. It will be apparent to those skilled in the art that other components performing the same function can be suitably replaced. It should be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of the invention. It should be mentioned that even features not explicitly mentioned, those interpreted with reference to specific drawings, can be combined with features in other drawings. Such modifications to the overall 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 a rotational axis; a phase error detector configured to generate a phase error signal based on a delayed event time signal and a delayed reference signal, wherein the delayed event time signal is indicative of a measured event time of the oscillator structure oscillating about the rotational axis, and the delayed reference signal is indicative of an expected event time of the oscillator structure oscillating about the rotational axis; an analog signal path coupled between the oscillator structure and the phase error detector, the analog signal path configured to receive an event time signal indicative of the measured event time and to induce an analog delay on the event time signal, thereby generating the delayed event time signal; a control circuit configured to generate a reference signal indicative of the expected event time and to generate a drive signal based on the phase error signal to drive oscillation of the oscillator structure; a programmable delay circuit configured with a programmable delay, the programmable delay circuit configured to receive the reference signal and to induce the programmable delay on the reference signal, thereby generating the delayed reference signal; and an analog delay measurement circuit configured to inject a test signal into the analog signal path, to receive a delayed test signal from the analog signal path, to measure the analog delay based on the delayed test signal, and to generate a configuration signal configured to adjust the programmable delay of the programmable delay circuit according to the measured analog delay.

2. The oscillator control system of claim 1, wherein: the measured event time is measured as a zero-crossing time at which a rotational angle of the oscillator structure is 0° as the oscillator structure oscillates about the rotational axis, and the expected event time is an expected zero-crossing time at which the rotational angle of the oscillator structure is expected to be 0°.

3. The oscillator control system of claim 2, wherein the phase error detector is configured to determine a timing difference between the measured zero-crossing time and the expected zero-crossing time, wherein a timing difference is determined for each of the measured zero-crossing times and a respective one of the expected zero-crossing times, and to generate the phase error signal representing the determined timing differences.

4. The oscillator control system of claim 1, wherein: the analog delay measurement circuit is configured to inject the test signal into the analog signal path as the oscillator structure oscillates about the rotational axis; and the programmable delay circuit is configured to adjust the programmable delay as the oscillator structure oscillates about the rotational axis.

5. The oscillator control system of claim 1, wherein: the analog delay measurement circuit is configured to periodically inject the test signal into the analog signal path as the oscillator structure oscillates about the rotational axis, and the programmable delay circuit is configured to adjust the programmable delay as the oscillator structure oscillates about the rotational axis. The programmable delay circuit is configured to periodically adjust the programmable delay as the oscillator structure oscillates about the rotation axis.

6. The oscillator control system of claim 1, wherein the analog signal path comprises an analog circuit device coupled to the oscillator structure.

7. The oscillator control system of claim 1, wherein the programmable delay circuit is configured to receive the configuration signal, adjust the programmable delay, and generate the delayed reference signal based on the adjusted programmable delay and the reference signal.

8. The oscillator control system of claim 1, wherein: the analog delay measurement circuit is configured to compare the measured analog delay to a delay threshold, and generate an alarm signal indicating a system fault on condition that the measured analog delay exceeds the delay threshold.

9. A method for controlling an oscillator structure configured to oscillate about a rotation axis in accordance with a drive signal, the method comprising: driving the oscillator structure to oscillate about a rotation axis in accordance with a drive signal; generating, by a phase error detector, a phase error signal based on a delayed event time signal and a delayed reference signal, wherein the delayed event time signal is indicative of a measured event time of the oscillator structure oscillating about the rotation axis, and the delayed reference signal is indicative of an expected event time of the oscillator structure oscillating about the rotation axis; inducing, by an analog signal path, an analog delay on the event time signal, thereby generating the delayed event time signal, wherein the analog signal path is coupled between the oscillator structure and the phase error detector; generating a reference signal indicative of the expected event time; generating the drive signal based on the phase error signal to drive oscillation of the oscillator structure; inducing a programmable delay on the reference signal, thereby generating the delayed reference signal; injecting a test signal into the analog signal path; inducing, by the analog signal path, the analog delay on the test signal, thereby generating a delayed test signal; measuring the analog delay based on the injected test signal and the delayed test signal; and generating a configuration signal configured to adjust the programmable delay in accordance with the measured analog delay.

10. The method of claim 9, wherein: the measured event time is measured as a zero-crossing time at which a rotation angle of the oscillator structure is 0° as the oscillator structure oscillates about the rotation axis, and the expected event time is an expected zero-crossing time at which the rotation angle of the oscillator structure is expected to be 0°.

11. The method of claim 9, wherein: injecting the test signal into the analog signal path is performed as the oscillator structure oscillates about the rotation axis, and adjusting the programmable delay is performed as the oscillator structure oscillates about the rotation axis.

12. The method of claim 9, further comprising: ​ periodically injecting the test signal into the analog signal path as the oscillator structure oscillates about the rotation axis; and periodically adjusting the programmable delay as the oscillator structure oscillates about the rotation axis.

13. The method of claim 9, further comprising: generating the delayed reference signal based on the adjusted programmable delay and the reference signal.

14. The method of claim 9, further comprising: comparing the measured analog delay to a delay threshold; and generating an alarm signal indicating a system fault on condition that the measured analog delay exceeds the delay threshold.

15. A light detection and ranging (LIDAR) control system, comprising: a microelectromechanical system (MEMS) mirror configured to oscillate about a rotation axis; a phase error detector configured to generate a phase error signal based on a delayed event time signal and a delayed reference signal, wherein the delayed event time signal is indicative of a measured event time of the MEMS mirror oscillating about the rotation axis, and the delayed reference signal is indicative of an expected event time of the MEMS mirror oscillating about the rotation axis; an analog signal path coupled between the MEMS mirror and the phase error detector, the analog signal path configured to receive an event time signal indicative of the measured event time, and to induce an analog delay on the event time signal, thereby generating the delayed event time signal; a control circuit configured to generate a reference signal indicative of the expected event time, and to generate a drive signal based on the phase error signal to drive oscillation of the MEMS mirror; a programmable delay circuit configured with a programmable delay, the programmable delay circuit configured to receive the reference signal, and to induce the programmable delay on the reference signal, thereby generating the delayed reference signal; and an analog delay measurement circuit configured to inject a test signal into the analog signal path, to receive a delayed test signal from the analog signal path, to measure the analog delay based on the delayed test signal, and to generate a configuration signal configured to adjust the programmable delay of the programmable delay circuit as a function of the measured analog delay.

16. The LIDAR control system of claim 15, wherein: the measured event time is measured as a zero-crossing time at which a rotation angle of the MEMS mirror is 0° as the MEMS mirror oscillates about the rotation axis, and the expected event time is an expected zero-crossing time at which the rotation angle of the MEMS mirror is expected to be 0°. ​ 17. The LIDAR control system of claim 16, wherein the phase error detector is configured to: determine a timing difference between the measured zero-crossing times and the expected zero-crossing times, wherein a timing difference is determined for each of the measured zero-crossing times and a respective one of the expected zero-crossing times; and generate the phase error signal representing the determined timing differences.

18. The LIDAR control system of claim 15, wherein: the analog delay measurement circuit is configured to inject the test signal into the analog signal path while the MEMS mirror oscillates about the rotation axis, and the programmable delay circuit is configured to adjust the programmable delay while the MEMS mirror oscillates about the rotation axis.

19. The LIDAR control system of claim 15, wherein: the analog delay measurement circuit is configured to periodically inject the test signal into the analog signal path while the MEMS mirror oscillates about the rotation axis; and the programmable delay circuit is configured to periodically adjust the programmable delay while the MEMS mirror oscillates about the rotation axis.

20. The LIDAR control system of claim 15, wherein the analog signal path includes an analog circuit device coupled to the MEMS mirror.

21. The LIDAR control system of claim 15, wherein the programmable delay circuit is configured to receive the configuration signal, adjust the programmable delay, and generate the delayed reference signal based on the adjusted programmable delay and the reference signal.

22. The LIDAR control system of claim 15, wherein: the analog delay measurement circuit is configured to compare the measured analog delay to a delay threshold, and on a condition that the measured analog delay exceeds the delay threshold, generate an alarm signal indicating a system fault. ​

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