Mechanical Shock Detection and Phase and Frequency Correction of MEMS Mirrors

Abstract

Embodiments of the present disclosure generally relate to mechanical shock detection of a MEMS mirror and correction of phase and frequency. A system for driving a microelectromechanical system (MEMS) oscillating structure includes: a phase error detector configured to generate a phase error signal based on a measured event time and an expected event time of the MEMS oscillating structure oscillating about a rotation axis; a disturbance event detector configured to detect a disturbance event based on the phase error signal and a disturbance threshold; and a phase frequency detector (PFD) and a correction circuit configured to, in response to the detected disturbance event, monitor a plurality of measured crossover events of the MEMS oscillating structure oscillating about the rotation axis, and generate a first compensation signal based on at least a first measured crossover event and a second measured crossover event to correct the frequency of the MEMS oscillating structure, and generate a second compensation signal based on a third measured crossover event to correct the phase of the MEMS oscillating structure.

Description

Technical Field

[0001] The present disclosure generally relates to microelectromechanical systems (MEMS) oscillator systems and methods for operating microelectromechanical systems oscillator systems, and more particularly, to correcting the phase and frequency of a MEMS mirror after detecting a mechanical shock or other disturbance event. 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, microelectromechanical systems (MEMS) mirrors are used to scan light across the entire field of view. An array of photodetectors receives the reflections from the objects illuminated by the light and determines the time taken for the reflections to reach each sensor in the photodetector array. This is also referred to as measuring the Time of Flight (TOF). The LIDAR system forms depth measurements and makes distance measurements by mapping the distance to the object based on the calculation of the time of flight. Thus, the calculation of the time of flight can create distance and depth maps that can be used to generate an image.

[0003] LIDAR will be a key enabler for autonomous vehicles. Therefore, it is mandatory that the data obtained from the LIDAR system is reliable. To obtain correct LIDAR data, the PLL of the MEMS driver circuit must be stable. However, a MEMS mirror operating at a certain resonant frequency may be subject to a large mechanical shock. For example, if a large mechanical shock occurs to the MEMS mirror, the MEMS mirror may become unstable such that the PLL cannot detect further zero-crossing events that are used to control and stabilize the MEMS mirror. Current LIDAR systems can only restore the operating ability of the MEMS mirror by stopping and restarting the system. Therefore, it is not possible to recover without stopping the MEMS mirror during runtime (i.e., while keeping the MEMS mirror operating).

[0004] Accordingly, an improved device that can detect mechanical shock events and correct the phase and frequency of a MEMS mirror after such an event occurs may be desirable. Summary of the Invention

[0005] Embodiments provide a microelectromechanical systems (MEMS) oscillator system and a method for operating a microelectromechanical systems oscillator system, and more particularly, a method for correcting the phase and frequency of a MEMS mirror after detecting a mechanical shock.

[0006] One or more embodiments provide a system for driving a microelectromechanical system (MEMS) oscillating structure. The system includes a MEMS oscillating structure configured to oscillate about a rotation axis; a phase error detector configured to generate a phase error signal based on a measured event time and an expected event time of the MEMS oscillating structure oscillating about the rotation axis; a disturbance event detector configured to detect a disturbance event based on the phase error signal and a disturbance threshold, where the disturbance event disrupts the oscillation of the MEMS oscillating structure such that the phase error signal exceeds the disturbance threshold; and a phase frequency detector (PFD) and a correction circuit configured to, in response to the detected disturbance event, monitor a plurality of measured crossover events of the MEMS oscillating structure oscillating about the rotation axis, generate a first compensation signal based on at least a first measured crossover event and a second measured crossover event among the plurality of measured crossover events to correct the frequency of the MEMS oscillating structure, and generate a second compensation signal based on a third measured crossover event among the plurality of measured crossover events to correct the phase of the MEMS oscillating structure.

[0007] One or more embodiments provide a method for compensating a microelectromechanical system (MEMS) oscillating structure. The method includes driving a MEMS oscillating structure configured to oscillate about a rotation axis; generating a phase error signal based on a measured event time and an expected event time of the MEMS oscillating structure oscillating about the rotation axis; and detecting a disturbance event based on the phase error signal and a disturbance threshold, where the disturbance event disrupts the oscillation of the MEMS oscillating structure such that the phase error signal exceeds the disturbance threshold. The method further includes: in response to the detected disturbance event, monitoring a plurality of measured crossover events of the MEMS oscillating structure oscillating about the rotation axis; generating a first compensation signal based on at least a first measured crossover event and a second measured crossover event among the plurality of measured crossover events to correct the frequency of the MEMS oscillating structure; and generating a second compensation signal based on a third measured crossover event among the plurality of measured crossover events to correct the phase of the MEMS oscillating structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments are described herein with reference to the drawings.

[0009] Figure 1 is a schematic diagram of a LIDAR scanning system 100 according to one or more embodiments;

[0010] Figure 2 is a schematic block diagram of a LIDAR scanning system 200 according to one or more embodiments.

[0011] Figure 3 shows a schematic block diagram of a MEMS driver ASIC according to one or more embodiments.

[0012] Figure 4 illustrates a signal diagram corresponding to a MEMS oscillation structure according to one or more embodiments; and

[0013] Figure 5 shows a state diagram of a phase frequency detector and a correction circuit of an interference detection and correction system according to one or more embodiments. Detailed Description

[0014] Various embodiments will be described in detail below with reference to the accompanying drawings. It should be noted that these embodiments are for illustrative purposes only and should not be construed as restrictive. For example, although an embodiment may be described as including multiple features or elements, this should not be construed as indicating that all of these features or elements are required to implement the embodiment. Instead, in other embodiments, some features or elements may be omitted, or may be replaced by alternative features or elements. Additionally, other features or elements (such as conventional components of a sensor device) may be provided in addition to the features or elements explicitly shown and described.

[0015] Unless otherwise explicitly stated, features from different embodiments may be combined to form further embodiments. Changes or modifications described with respect to one embodiment among the embodiments may also be applied to other embodiments. In some instances, well-known structures and devices are not shown in detail in block diagram form to avoid obscuring the embodiments.

[0016] Unless otherwise specified, the connections or couplings between the elements shown in the drawings or described herein may be wired connections or wireless connections. Additionally, as long as the general purpose of the connection or coupling remains substantially the same, such as transmitting a certain signal or transmitting a certain information, then such connection or coupling may be a direct connection or coupling without additional intervening elements, or may be an indirect connection or coupling using one or more additional intervening elements.

[0017] Embodiments relate to optical sensors and optical sensor systems, and to obtaining information about optical sensors and optical sensor systems. A sensor may refer to a component that converts a physical quantity to be measured into an electrical signal (such as a current signal or a voltage signal). The physical quantity may include, but is not limited to, electromagnetic radiation (such as visible light, infrared (IR) radiation, or other types of illumination signals (current or voltage)). For example, an image sensor may be a silicon chip inside a camera that converts a photograph of light from a lens into a voltage. The larger the effective area of the sensor, the more light can be collected to create an image.

[0018] As used herein, a sensor device may refer to a device that includes a sensor and other components, such as a biasing circuit system, 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 also be used to implement the sensor device.

[0019] In a light detection and ranging (LIDAR) system, a light source emits light pulses 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 light pulses (e.g., laser beams of infrared light) are emitted into the field of view, and a pixel array detects and measures the reflected light beam. For example, a photodetector array receives the reflection from an object illuminated by light.

[0020] Currently, photodetector arrays can be used to measure the reflected light. The photodetector array can be a one-dimensional (1D) array composed of multiple rows of photodetectors (pixels) arranged in a single column, or a two-dimensional (2D) array composed of multiple rows and columns of photodetectors arranged in a similar grid arrangement. Each pixel row or group of adjacent pixel rows can be read out as a measurement signal in the form of raw analog data. Each measurement signal can include data from a single pixel column or from two or more pixel columns corresponding to the selected (multiple) pixel rows.

[0021] The difference in the return time of each light pulse for multiple pixels across the pixel array can then be used to create a digital 3D representation of the environment or generate other sensor data. For example, the light source can emit a single light pulse, and a time-to-digital converter (TDC) electrically coupled to the pixel array can start counting from the time the light pulse is emitted (corresponding to a start signal) until the time the reflected light pulse is received at the receiver (i.e., the pixel array) (corresponding to a stop signal). Then, the "time of flight" of the light pulse is translated into a distance. In another example, an analog-to-digital converter (ADC) can be electrically coupled to the pixel array (e.g., indirectly coupled with intervening elements 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 through an appropriate algorithm.

[0022] Scanning such as oscillatory horizontal scanning (e.g., from left to right, from right to left in the field of view) can illuminate the scene in a continuous scanning manner. Each time the light source emits a laser beam, a scan line is produced in the "field of view". By emitting continuous light pulses in different scan directions, an area called the field of view can be scanned, and objects within the area can be detected and imaged. Thus, the field of view represents a scanning plane with a projection center. Raster scanning can also be used.

[0023] Figure 1is 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, and the LIDAR scanning system 100 includes: a transmitter, including an illumination unit 10, transmitter optics 11, and a one-dimensional (1D) MEMS mirror 12 (1D MEMS scanner); and a receiver, including primary optics 14 and an optical receiver 15. The optical receiver 15 in the illustration is a 2D photodetector array 15, but alternatively can be a 1D photodetector array. The receiver may further include receiver circuitry, such as data acquisition / readout circuitry and data processing circuitry, as will be described further according to Figure 2 as described further.

[0024] Although this arrangement represents an example arrangement of a LIDAR system, it should be understood that the 1D scanning mirror 12 can be rotated to scan in different scan directions. For example, the LIDAR scanning system 100 can be rotated 90° to scan in the vertical direction instead of the horizontal direction.

[0025] The illumination unit 10 includes a plurality of light sources (e.g., laser diodes or light emitting diodes) arranged in a single strip linear array and configured to emit light that is used to scan an object. The light emitted by the light sources is typically infrared light, although light of other wavelengths can also be used. As can be seen from the Figure 1 embodiment, the shape of the light emitted by the light sources spreads in a direction perpendicular to the emission direction to form a rectangular light beam perpendicular to the emission direction. The illumination light emitted from the light sources is directed to the transmitter optics 11, which is configured to focus each laser onto the one-dimensional MEMS mirror 12.

[0026] The transmitter optics 11 can be, for example, a lens or a prism. When reflected by the MEMS mirror 12, the light from the light sources is arranged vertically to form a one-dimensional vertical scan line of infrared light or a vertical strip of infrared light. Each light source of the illumination unit 10 contributes to a different vertical region of the vertical scan line. Although five laser sources are shown, it should be understood that the number of laser sources is not limited thereto. For example, the vertical scan line can be generated by a single laser source, two laser sources, etc. It should also be understood that the light sources can be arranged in a matrix form.

[0027] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) integrated on a semiconductor chip (not shown). The MEMS mirror 12 according to this embodiment is configured to rotate about a single scanning axis and can be said to have only one degree of freedom for scanning. Different from a 2D-MEMS mirror (2D MEMS scanner), in a 1D MEMS mirror, the single scanning axis is fixed on a non-rotating substrate and thus maintains its spatial orientation during the oscillation of the MEMS mirror. Due to this rotating single scanning axis, the MEMS mirror 12 is referred to as a 1D MEMS mirror or a 1D MEMS scanner.

[0028] The MEMS mirror 12 is configured to oscillate “left and right” about a single scanning axis 13 such that the light reflected from the MEMS mirror 12 (i.e., the vertical scan line) oscillates back and forth in the horizontal scan direction. The scan period or oscillation period is defined as, for example, one full oscillation from the first edge (e.g., the left side) of the field of view to the second edge (e.g., the right side) of the field of view and then back to the first edge. The mirror period of the MEMS mirror 12 corresponds to the scan period.

[0029] Thus, by changing the angle of the MEMS mirror 12 with respect to its scanning axis 13, the field of view is scanned horizontally by the vertical bars of light. For example, the MEMS mirror 12 can be configured to oscillate at + / -15 degrees in the horizontal scan direction to direct light within + / -30 degrees (i.e., 60 degrees), thereby constituting the horizontal scan range of the field of view. Thus, the field of view can be scanned row by row by the rotation (depending on its degree of movement) of the MEMS mirror 12. One such sequence, depending on its degree of movement (e.g., from -15 degrees to +15 degrees and vice versa), is referred to as a single scan. Thus, two scans are used for each scan period. Multiple scans can be used to generate distance and depth maps as well as 3D images obtained by a processing unit. The horizontal resolution of the depth map and the image depends on the incremental step size of the rotation angle of the MEMS mirror 12 taken between two scans.

[0030] Although mirrors are described in the context of MEMS mirrors, it should be understood that other 1D mirrors or even 2D mirrors can also be used. Additionally, the degree of rotation is not limited to + / -15 degrees, and the field of view can be increased or decreased according to the application. Thus, a one-dimensional scanning mirror is configured to oscillate about a single scanning axis and direct laser beams in different directions into the field of view. Thus, the emission technique includes emitting a light beam from a mirror that oscillates about a single scanning axis into the field of view such that the light beam is projected as a vertical scan line into the field of view, and the light beam moves horizontally across the entire field of view as the mirror oscillates about the single scanning axis.

[0031] A 2D scanning mirror that uses laser dots to scan the field of view requires more emitter illuminations to scan the field of view. Compared with a 2D scanning mirror, a LIDAR system using a 1D scanning mirror can use a more relaxed illumination rate of the illumination unit 10 (i.e., the emitter). Additionally, when compared with a 2D scanning mirror, a LIDAR system using a 1D scanning mirror is generally more robust in resisting shock and vibration and is thus more suitable for automotive applications.

[0032] When illuminating one or more objects, the emitted vertical light stripe is backscattered as a vertical reflection line and returns to be reflected to the LIDAR scanning system 100, where the second optical component 14 (e.g., a lens or a prism) receives the reflected light. The second optical component 14 guides the reflected light onto the photodetector array 15, which receives the reflected light as a received 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).

[0033] The photodetector array 15 can be any one of many photodetector types (including avalanche photodiodes (APDs), photocells, and / or other photodiode devices). An imaging sensor such as a charge-coupled device (CCD) can be a photodetector. In the examples provided herein, the photodetector array 15 is a two-dimensional (2D) APD array including an array of APD pixels. In other embodiments, the photodetector array 15 can be a one-dimensional array including a single column of photodiodes. The activation of the photodiodes can be synchronized with the light pulses emitted by the illumination unit 10.

[0034] The photodetector array 15 receives the reflected light pulses as received lines and generates electrical signals in response to the light pulses. Since the emission time of each light pulse from the illumination unit 10 is known and because light travels at a known speed, the time-of-flight calculation using the electrical signals can determine the distance of the object from the photodetector array 15. A depth map can plot the distance information.

[0035] In one example, for each distance sample, the microcontroller triggers a laser pulse from each light source of the illumination unit 10 and also starts a timer in the time-to-digital converter (TDC) integrated circuit (IC). The laser pulse propagates through the emission optics, is reflected by the target field, and is captured by one or more receiving photodiodes of the photodetector array 15. Each receiving photodiode emits a short electrical pulse that is read out by an analog readout circuit. Each signal read out from the analog readout circuit can be amplified by an electrical signal amplifier.

[0036] The comparator IC identifies 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 error readings, averages multiple time measurements, and calculates the distance to the target at that particular field position. By emitting consecutive light pulses in different directions established by the MEMS mirror 12, an 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.

[0037] The signal processing chain of the receiver may also include an ADC for each photodiode or group of photodiodes. The ADC is configured to convert the analog electrical signal from the photodiode or group of photodiodes into a digital signal for further data processing.

[0038] Alternatively, the ADC can be used for signal detection and ToF measurement instead of using the TDC method. For example, each ADC can be used to detect the analog electrical signal in one or more photodiodes and use an appropriate algorithm to estimate the time interval between the start signal (i.e., the time corresponding to the emitted light pulse) and the stop signal (i.e., the time corresponding to the reception of the analog electrical signal at the ADC).

[0039] 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 the LIDAR scanning system 200 are shown, including example processing and control system components such as the MEMS driver ASIC, the receiver circuit, and the system controller.

[0040] The LIDAR scanning system 200 includes a transmitter unit 21 responsible for the emitter 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 the raw data from the receiver unit 22 and perform processing (e.g., via digital signal processing) on the raw data to generate object data (e.g., point cloud data). Thus, the system controller 23 includes at least one processor and / or processor circuitry for processing data, and control circuitry (such as a microcontroller) configured to generate control signals.

[0041] The receiver unit 22 includes a photodetector array 15 and a receiver circuit 24. The receiver circuit 24 may include one or more circuitry or sub-circuitry for receiving and / or processing information. The receiver circuit 24 may receive an analog electrical signal from the APD diodes of the photodetector array 15 and transmit the electrical signal as raw digital data to the system controller 23, for example, after converting the analog electrical signal to a digital signal via an ADC. Thus, in order to transmit the raw data as digital data, the receiver circuit 24 may further include an ADC and a field programmable gate array (FPGA). The receiver circuit 24 may also receive a trigger control signal from the system controller 23 to trigger the 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.

[0042] The transmitter unit 21 includes an illumination unit 10, a MEMS mirror 12, and a MEMS driver ASIC 25 configured to drive the MEMS mirror 12. In particular, the MEMS driver ASIC 25 actuates and senses the rotational position of the mirror and provides the position information of the mirror (e.g., the angle of rotation 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 and a photodiode (e.g., an APD diode) is activated to sense and thus measure the reflected light signal. Thus, a higher precision sensing of the MEMS mirror position results in a more accurate and precise control of the other components of the LIDAR system.

[0043] By sensing the rotational position of the MEMS mirror 12 about its axis of rotation 13, the MEMS driver ASIC 25 can sense the zero-crossing event of the MEMS mirror 12. The zero-crossing event is the situation when the angle of rotation of the MEMS mirror 12 about its axis of rotation 13 is 0°. Specifically, this is the moment when the MEMS mirror 12 is flat. Since the MEMS mirror 12 oscillates back and forth between two rotational directions, two zero-crossing events occur during a scanning period, once when the mirror oscillates in the first rotational direction and once when the mirror oscillates in the second rotational direction.

[0044] In some embodiments, the event time may correspond to a non-zero-crossing event. For example, the sensed angle of rotation may be some angle other than 0°. However, for illustrative purposes, the examples herein will be described in the context of sensing zero-crossing events.

[0045] The MEMS actuator ASIC 25 is configured to detect each zero-crossing event and record the timing for each event. Then, the MEMS actuator ASIC 25 can compare this timing information (i.e., the measured zero-crossing times) with the expected zero-crossing times for each zero-crossing to detect an asymmetry in the movement of the MEMS mirror 12 with respect to the two rotational directions. For example, due to the asymmetry of the mirror, the clockwise travel of the mirror may be faster or slower than the counterclockwise travel of the mirror. The MEMS actuator ASIC 25 can also send position information to the system controller 23 such that the system controller 23 can use the position information to control the triggering of the laser pulses of the illumination unit 10 and the activation of the photodiodes of the photodetector array 15.

[0046] The MEMS mirror 12 includes an actuator structure that is used to drive the mirror. The actuator structure includes crossed finger electrodes made of crossed mirror combs and frame combs, and the MEMS actuator ASIC 25 applies a drive voltage (e.g., 100 V) across the crossed finger electrodes. The drive voltage applied across the finger structure generates a corresponding capacitance. The drive voltage across the finger structure creates a driving force between the crossed mirror combs and the frame combs, thereby generating a torque on the mirror body about the axis of rotation. The drive voltage can be switched or toggled between on and off, thereby creating an oscillating driving force. The oscillating driving force causes the mirror to oscillate back and forth about its axis of rotation between two extreme positions. As the mirror oscillates, the capacitance between the finger electrodes changes according to the rotational position of the mirror. The MEMS actuator ASIC 25 is configured to measure the capacitance between the crossed finger electrodes and thereby determine the rotational position or angular position of the MEMS mirror 12. By monitoring this capacitance, the MEMS actuator ASIC 25 can detect the zero-crossing event and the timing of the zero-crossing event.

[0047] As will be described in further detail, sensing of the position of the MEMS mirror 12 is performed based on a mirror phase error detector configured to measure capacitance. For example, as the MEMS mirror moves, the geometry of the finger structure changes, resulting in a change in the geometry of the capacitance. As the geometry of the capacitance changes, the capacitance itself also changes. Thus, the specific capacitance directly corresponds to the specific position (i.e., the rotational angle) of the MEMS mirror. By sensing the capacitance of the finger structure, the specific position of the MEMS mirror can be determined.

[0048] One method of 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 the capacitance and / or the rotational angle. However, any method of 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.) is also detected by measuring the change in capacitance over time, where a positive change or a negative change indicates opposite rotational directions.

[0049] Improving the accuracy of mirror position sensing will improve the overall accuracy of the LIDAR system. For example, the accuracy requirement may be to irradiate a laser within + / -2 millidegrees (i.e., a range of 4 millidegrees) of a vertical target line while the mirror oscillates at a frequency of, for example, 2 kHz. This translates to having to emit the laser to the mirror with an acceptable timing error or error budget of approximately 20 nanoseconds to be within + / -2 millimeters of the target line. Therefore, to meet this requirement, it is important to accurately sense the position of the mirror.

[0050] Since the mirror is driven at a set oscillation frequency, 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. When the mirror rotates in a second rotational direction (e.g., from right to left or counterclockwise), it can be said that the same occurs, and 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 that occur at zero-crossing times.

[0051] However, due to variability introduced during manufacturing and as the mirror ages, there may be asymmetries in the mirror and they can change over time. These asymmetries result in a timing difference between the motion in the first rotational direction compared to the motion in the second rotational direction. In other words, the time interval between the two zero-crossings at the later of the two zero-crossings can be different in the case of the first rotational direction compared to the case of the second rotational direction. Additionally, one or both of the zero-crossings can deviate from the expected zero-crossing calculated based on the oscillation frequency.

[0052] Figure 3 A schematic block diagram of a MEMS driver ASIC 25 according to one or more embodiments is shown. The MEMS driver ASIC 25 includes an analog core 31, a phase error detector 32 (i.e., a phase detector (PD)), an error detection and compensation unit 33, a loop filter 34, a digitally controlled oscillator (DCO) 35, and a mirror driver 36 arranged in a loop. This loop forms a phase-locked loop (PLL) that follows the frequency of the MEMS mirror 12 together with the MEMS mirror 12. The MEMS driver ASIC 25 also includes a direction signal generator 37 and a phase frequency detector (PFD), as well as a correction circuit 38. However, it should be understood that the direction signal generator 37 and the PFD and the correction circuit 38 can also be provided external to the MEMS driver ASIC 25. The MEMS driver ASIC 25 communicates electrically with the MEMS mirror 12 and the system controller 23 via an electrical connection that is used to transmit signals between them.

[0053] Therefore, the MEMS actuator ASIC 25 implements an analog circuit system and a digital circuit system. The analog circuit system (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 may receive analog signals related to the position and rotation direction of the mirror from the MEMS mirror 12. Additionally, one or more outputs of the analog core 31 may provide control signals to the MEMS mirror 12 for controlling the oscillation of the mirror.

[0054] The analog core 31 includes an analog circuit system that is configured to measure the capacitance of the finger structures of the MEMS mirror actuator in order to measure timing-critical events (such as zero crossings) with the aid of a comparator. Thus, the analog circuit system measures the position of the MEMS mirror 12 about the axis of rotation and determines the zero-crossing times in the first and second rotation directions. The analog circuit system is also configured to generate direction information DL1L and DL1R related to the rotation direction of the MEMS mirror 12 (e.g., clockwise or counterclockwise). The remaining digital circuit system implements the intelligence of the chip (control of the mirror, triggering of laser pulses, triggering of photodiode activation, etc.). This approach enables a digital signal processing solution to detect systematic and non-systematic error sources, which can then be compensated for.

[0055] The analog core 31 is configured to generate and output the measured zero-crossing time ZCmeas of the MEMS mirror 12, which is received by the phase error detector 32. The analog core 31 is also configured to provide the direction information DL1L and DL1R related to the rotation direction of the MEMS mirror 12 (e.g., clockwise or counterclockwise direction) to the direction signal generator 37, which is configured to generate a direction signal d(n) (e.g., +1 or -1) based on the direction information DL1L and DL1R.

[0056] The phase error detector 32 is configured to receive the measured zero-crossing time ZCmeas from the analog core 31 and the reference zero-crossing time ZCref from the mirror driver 36. The reference zero-crossing time ZCref is the expected zero-crossing time of the MEMS mirror 12 based on the mirror oscillation frequency. The reference zero-crossing time ZCref is generated by the mirror driver 36 (i.e., by the PLL).

[0057] The phase error detector 32 includes a comparator circuit system (e.g., a phase detector) configured to compare the measured (actual) zero-crossing time ZCmeas with a reference zero-crossing time ZCref and output their difference. In particular, this difference is a value representing the number of clock cycles between ZCmeas and ZCref. Thus, the phase error detector is configured to compare the measured zero-crossing timing with the expected zero-crossing timing and generate a phase error signal p(n) representing the difference between the measured zero-crossing timing and the 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 detected zero-crossing of the MEMS mirror 12.

[0058] For example, if the measured zero-crossing time ZCmeas is equal to the expected zero-crossing time ZCref, then 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.

[0059] In addition, the phase error signal p(n) is generated for both rotational directions of the mirror. For example, in the presence of asymmetry, the phase error detector 32 may generate a phase error signal p(n) with a value of +3 corresponding to the first rotational direction and may generate a phase error signal p(n) with a value of -3 corresponding to the second rotational direction. As long as the values for the two rotational directions are not equal, there is asymmetry.

[0060] Each travel 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). In particular, any time the MEMS mirror 12 rotates through a zero-crossing, the timing of the zero-crossing is measured and a phase error signal p(n) is generated based on its comparison with the expected zero-crossing time. Thus, the PLL error spectrum represents the output of the phase detector over time (i.e., the phase error signal over time).

[0061] The zero-crossing time deviation for the first rotational direction can be different from the zero-crossing time deviation for the second rotational direction. Thus, the phase error signal p(n) for the zero-crossing time in the first rotational direction can be different from the phase error signal p(n) for the zero-crossing time in the second rotational direction. This asymmetry in the zero-crossing timing results in a periodic jitter component in the PLL error spectrum. Due to this asymmetry in the zero-crossing timing, at least a portion of the error budget required to meet the accuracy requirements can be consumed. Thus, it is desirable to remove this error from the output of the phase error detector 32 so that it is not introduced into the position information of the MEMS mirror 12.

[0062] Furthermore, chopping is a technique used to compensate for the analog offset of operational amplifiers used in the analog core 31 of the LIDAR system. However, this chopping technique can also introduce periodic errors into the PLL error spectrum generated by the phase error detector. Moreover, these periodic jitter components (also known as chopping errors) should be removed from the output of the phase error detector 32 to improve the accuracy of the position information of the MEMS mirror 12.

[0063] Errors caused by both mirror asymmetry and chopping are introduced into the PLL error spectrum on a periodic basis as periodic jitter.

[0064] The error detection and compensation unit 33 is configured to receive the phase error signal p(n) from the phase error detector 32, detect the periodic jitter component, and remove the periodic jitter component 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 the direction signal d(n) from the direction signal generator 37.

[0065] The compensated phase error signal pcorr(n) effectively reduces the jitter of the PLL, which enables higher accuracy in sensing and controlling the MEMS mirror 12, and higher accuracy in controlling the illumination unit 10. Specifically, removing the jitter component from the phase error signal p(n) enables the mirror position signaling (i.e., mirror position information) to be more accurate, which enables more precise laser illumination and more precise control of the mirror.

[0066] The error detection and compensation unit 33 includes a DSP structure composed of coupled circuit system logic (such as adders, subtracters, multipliers, integrators, dividers, etc.) to form a signal processing chain configured to detect and compensate for periodic jitter components. In particular, the DSP structure is configured to measure and compensate for the periodic jitter caused by the two main error sources of mirror asymmetry and chopping.

[0067] The corrected phase detector signal pcorr(n) is used to derive the signal f of the DCO 35 DCO, and form the basis of the mirror position information generated by the mirror driver 36. In particular, the error detection and compensation unit 33 outputs the corrected phase detector signal pcorr(n) to the loop filter 34, and the loop filter 34 implements proportional-integral (PI) or proportional-integral-derivative (PID) control to increment the DCO counter 35a of the DCO 35. The DCO counter 35a is responsible for the braking frequency of the mirror 12. Therefore, the loop filter 34 generates / regulates the DCO increment, which is then output to the DCO counter 35a. The DCO counter 35a adjusts the DCO counter value, and the DCO 35 adjusts the actuation frequency of the MEMS mirror 12 (i.e., the signal f DCO ).

[0068] Because there is no periodic jitter component in the corrected phase detector signal pcorr(n), the phase of the signal f DCO of the DCO 35 is not affected by these jitter components and more accurately corresponds to the phase of the MEMS mirror 12. The DCO 35 provides the signal f DCO to the mirror driver 36 based on the value of the DCO counter 35a.

[0069] The mirror driver 36 is a mirror scheduler that determines the mirror timing of the MEMS mirror 12 based on the signal f DCO . Therefore, the mirror driver 36 includes at least one processor (shown as the mirror timing controller 36a) for performing timing analysis and scheduling, and also includes a sub-timing counter 36b. The sub-timing counter 36b tracks the expected zero-crossing time and is reset to the zero-crossing counter value (e.g., 0x0000) to coincide with the time when the zero-crossing event is expected and is responsible for the phase of the mirror (i.e., the position of the mirror). The zero-crossing counter value can be referred to as the crossing event counter value that covers both zero-crossing and non-zero-crossing events.

[0070] Based on the sub-timing counter 36b, the mirror timing controller 36a is configured to generate a drive voltage HV as a control signal for controlling the oscillation of the MEMS mirror 12. More specifically, as described previously, the drive voltage HV (e.g., 100V) is turned on and off and applied to the actuator structure of the MEMS mirror 12. The mirror driver 36 is not only configured to turn on and off the drive voltage HV, but can also be configured to drive the voltage to any level (e.g., fully on, half off - fully off, etc.).

[0071] The mirror driver 36 is based on the signal f DCODetermine the mirror position information and output the mirror position information 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 of the photodetector array 15.

[0072] The mirror driver 36 can also determine an expected zero-crossing time ZCref based on the mirror position information.

[0073] The system controller 23 can also be used to configure the mirror driver 36 with certain parameters (e.g., during startup).

[0074] In addition to removing the periodic jitter component, the MEMS driver ASIC 25 is configured to detect interference events (such as large mechanical shocks or mechanical vibrations) that disrupt the resonance of the MEMS mirror 12 and the PLL can no longer maintain the correct phase and frequency of the mirror. The MEMS driver ASIC 25 is also configured to correct the phase and frequency of the MEMS mirror 12 after detecting such an interference event. This correction of the phase and frequency and the restoration of the overall operation of the MEMS mirror 12 are performed during the operation of the MEMS mirror 12 without stopping the MEMS mirror 12 (i.e., while maintaining the operation of the MEMS mirror 12).

[0075] As a first step, the phase error detector 32 includes an interference event detector 32a that performs, for example, shock detection. In particular, the interference event detector 32a compares the absolute value of the phase error signal p(n) with an interference threshold and detects whether the absolute value of the phase error signal p(n) is greater than the interference threshold. As an example, the interference threshold can be 200 clock cycles, but is not limited thereto.

[0076] If the absolute value of the phase error signal p(n) is greater than the interference threshold, the interference event detector 32a detects an interference event. If the absolute value of the phase error signal p(n) is not greater than the interference threshold, no interference event is detected and the MEMS driver ASIC 25 operates as described above. Essentially, the interference event detector 32a detects whether the zero-crossing time ZCmeas deviates too much from the reference zero-crossing time ZCref such that the restoration of the operation of the MEMS mirror 12 is ensured.

[0077] In response to detecting an interference event, the interference event detector 32a is configured to generate a correction enable signal CorrEn and a high voltage enable signal HVEn. For example, the interference event detector 32a is further configured to disable the phase detector of the phase error detector 32 while enabling the correction enable signal CorrEn and the high voltage enable signal HVEn in response to detecting an interference event.

[0078] The correction enable signal CorrEn is configured to enable the PFD and the correction circuit 38. Thus, the PFD and the correction circuit 38 are inactive until an interference event occurs. Immediately after the interference event occurs, the PFD and the correction circuit 38 are activated and turned on. In response to being activated, the PFD and the correction circuit 38 are configured to disable the phase error detector 32. In particular, in response to receiving the correction enable signal CorrEn, the PFD and the correction circuit 38 generate a control signal SwitchEn to disconnect the switch SW1.

[0079] In the case where the switch SW1 is disconnected or disabled, the loop filter 34 is disconnected from the DCO 35, such that the DCO no longer receives the DCO increment from the loop filter 34, and thus effectively disables the output of the phase error detector 32 and the control loop of the PLL. Thus, the switch SW1 is disabled after detecting an interference event, and after the mirror frequency and the mirror phase are corrected by the PFD and the correction circuit 38, the switch SW1 will be re-enabled via the control signal SwitchEn.

[0080] The high voltage enable signal HVEn is configured to instruct the mirror driver 36 to turn on the high voltage, and the mirror driver 36 in turn sends an HVOn command to the analog core 31. In particular, the mirror driver 36 includes a shock HV (On / Off) controller 36a, which is configured to receive the high voltage enable signal HVEn. The high voltage enable signal HVEn triggers the shock HV (On / Off) controller 36c to turn on the drive voltage HV for a predetermined duration of at least two mirror periods. As a result, the shock HV (On / Off) controller 36c overrides the normal sub-timing operation of controlling the mirror driver 36, such that the correction of the MEMS mirror 12 can be performed.

[0081] Since the zero-crossing event can only be measured when the drive voltage HV is turned on, the drive voltage HV is turned on. To fully restore the operation of the MEMS mirror 12, at least three consecutive zero-crossing events will be detected. Thus, the predetermined duration should be long enough to detect three consecutive zero-crossing events. Generally, the duration of two mirror periods ensures that at least three consecutive zero-crossing events can be detected.

[0082] In view of the above, in response to detecting an interference event, the interference event detector 32a disables the phase error detector 32, enables the PFD and correction circuit 38, and turns on the drive voltage HV.

[0083] The PFD and correction circuit 38 is configured to receive the measured zero-crossing time ZCmeas from the analog core 31 to detect zero-crossing events. Using the detected zero-crossing events, the PFD and correction circuit 38 is configured to detect the current phase and frequency of the MEMS mirror 12 after the interference event and calculate a new frequency DCO increment.

[0084] In particular, the PFD and correction circuit 38 includes: a PFD that includes a zero-crossing timing counter (ZCTC); and a correction circuit that generates a compensation signal based on calculations using measurements made by the PFD. The compensation signal includes a corrected DCO increment signal (DCOcorr) and a corrected phase counter signal (PCcorr). The corrected DCO increment signal (DCOcorr) provides a corrected DCO increment, while the corrected phase counter signal (PCcorr) provides a corrected phase counter value (e.g., 0x0000) to the sub-timing counter 36b. Alternatively, the corrected phase counter signal (PCcorr) can trigger the sub-timing counter 36b to reset to the zero-crossing counter value (e.g., 0x0000) without explicitly providing the corrected phase counter value. In either case, the sub-timing counter 36b resets to the zero-crossing counter value. In response to receiving the corrected phase counter value, the sub-timing counter 36b is reset to the corrected phase counter value.

[0085] During a predetermined duration, the PFD and correction circuit 38 is enabled, and the PFD is configured to detect zero-crossing events of the mirror 12. The PFD and correction circuit 38 uses these detected zero-crossing events to determine the mirror frequency and mirror phase of the mirror during the predetermined duration.

[0086] To determine the mirror frequency, the PFD waits for the first zero-crossing event after the interference event occurs. Once the PFD detects the first zero-crossing event, the PFD starts the ZCTC, and the ZCTC count increments up to the second zero-crossing event after the interference event is detected. Note that the period between the first zero-crossing event and the second zero-crossing event represents one and a half mirror cycles of the mirror 12, and the period between the first zero-crossing event and the third zero-crossing event represents one full mirror cycle of the mirror 12.

[0087] The correction circuit of the PFD and correction circuit 38 uses the counter value of the ZCTC (which coincides with the second zero-crossing event and represents the time period between the first zero-crossing event and the second zero-crossing event) to determine the mirror frequency of the mirror 12 at that time. More specifically, the counter value of the ZCTC represents half of the full mirror period and is used by the correction circuit to calculate the corrected DCO counter increment DCOcorr. The corrected DCO counter increment DCOcorr represents the actuation frequency of the mirror (i.e., the frequency of the HVon / off signal).

[0088] The correction circuit of the PFD and correction circuit 38 stores the DCO counter maximum value (DCOmax) of the DCO counter 35a and the sub-timing counter range of the sub-timing counter 36b, and uses these values together with the counter value of the ZCTC to calculate the corrected DCO counter increment DCOcorr based on the following equation (1):

[0089]

[0090] According to equation (1), the DCO counter maximum value DCOmax is multiplied by the sub-timing counter range, and the product is divided by the counter value of the ZCTC to obtain the corrected DCO counter increment DCOcorr.

[0091] Next, the PFD and correction circuit 38 is configured to wait until a third zero-crossing event occurs after detecting an interference event to set the mirror frequency and mirror phase. In particular, when the third zero-crossing event occurs, the PFD and correction circuit 38 is configured to set the mirror frequency by outputting the corrected DCO counter increment DCOcorr to the DCO counter 35a. Therefore, the DCOcorr signal sets the DCO counter increment. The DCO counter value consists of the previous DCO counter value plus the DCO increment.

[0092] In addition, when the third zero-crossing event occurs, the PFD and correction circuit 38 is configured to set the mirror phase by resetting the sub-timing counter value of the sub-timing counter 36b to its zero-crossing counter value (e.g., 0x0000).

[0093] When the PFD and correction circuit 38 calculates the DCO counter increment DCOcorr in response to the second zero-crossing event, waiting until the third zero-crossing event to set the mirror frequency and mirror phase ensures that the PFD and correction circuit 38 has sufficient processing time to complete the calculation of the corrected DCO counter increment DCOcorr. Therefore, waiting until the third zero-crossing event ensures that the mirror frequency and mirror phase are set simultaneously.

[0094] In addition, upon occurrence of a third zero-crossing event, the PFD and correction circuit 38 are configured to close or enable switches SW2 and SW3 via another control signal SwitchEN, such that the corrected signals DCOcorr and PCcorr can be transmitted to the DCO 35 and the mirror driver 36, respectively. Once the corrected signals DCOcorr and PCcorr are output from the PFD and correction circuit 38, the PFD and correction circuit 38 disable switches SW2 and SW3, re-enable switch SW1 to resume normal operation, and become inactive until the next correction enable signal CorrEn is received.

[0095] The DCO 35 includes a DCO counter 35a, and the value of the DCO counter represents the actuation frequency of the mirror. Additionally, the mirror driver 36 includes a sub-timing counter 36b that represents the mirror phase. The drive voltage HV is turned on and off based on the sub-timing counter value. Figure 4 A signal diagram of the mirror angle of the mirror is illustrated, where the left position signal Position_L indicating when the mirror tilts to the left is opposite to tilting to the right, and the direction signal Direction_L indicating when the mirror moves in the left direction (e.g., rotates counterclockwise) oscillates opposite to moving in the right direction (e.g., rotates clockwise).

[0096] In addition, Figure 4 An example of the sub-timing value of the sub-timing counter 36b of the mirror driver 36 is illustrated. Here, it is shown that the sub-timing counter is reset to the zero-crossing counter value (e.g., 0x0000) at each zero-crossing, and counts up until the next zero-crossing. The sub-timing counter is synchronized with the zero-crossing such that the sub-timing counter starts from 0x0000 and counts up to 0x3FFF, after which it is reset to 0x000 and counts up again. After an interference event occurs, there is a shift in the mirror phase and frequency. As a result, the zero-crossing no longer occurs synchronously with 0x0000, but may occur at any value between 0x0000 and 0x3FFF, as indicated by 0xXXXX in the figure. The sub-timing counter is corrected after compensation is performed by the PFD and correction circuit 38, and normal operation of the mirror resumes without stopping and restarting the mirror. Thus, during operation of the mirror, the frequency and phase of the mirror are corrected, and the zero-crossing is synchronized with the sub-timing counter value 0x0000 again.

[0097] Figure 4 The signal diagram also shows the point at which the interference event occurs, the PFD start point corresponding to the first zero-crossing event after the interference event, and the PFD correction point corresponding to the third zero-crossing event after the interference event.

[0098] Figure 5is a state diagram 500 of the PFD and correction circuit 38 according to one or more embodiments. In particular, the state diagram 500 includes an initial (INIT) state during which all values at the PFD and correction circuit 38 (including ZCTC) are reset and the PFD and correction circuit 38 waits for a correction enable signal CorrEn (i.e., the PFD and correction circuit 38 waits for a disturbance event monitored by the disturbance event detector 32a). After receiving the correction enable signal CorrEn, the PFD and correction circuit 38 are enabled and enter state 1.

[0099] During state 1, the PFD and correction circuit 38 emit an enable signal HVEn, emit a control signal SwitchEn, and monitor for a first zero-crossing event. State 1 continues until the PFD and correction circuit 38 detect the first zero-crossing event, at which point the PFD and correction circuit 38 enter state 2.

[0100] During state 2, the ZCTC count is incremented while the PFD and correction circuit 38 monitor for a second zero-crossing event. State 2 continues until the PFD and correction circuit 38 detect the second zero-crossing event, at which point the PFD and correction circuit 38 stops the ZCTC counter and enters state 3.

[0101] During state 3, the PFD and correction circuit 38 use the counter value of ZCTC to calculate a DCO counter increment DCOcorr and monitor for a third zero-crossing event. State 3 continues until the PFD and correction circuit 38 detect the third zero-crossing event, at which point the PFD and correction circuit 38 enter state 4.

[0102] During state 4, switches SW2 and SW3 are enabled and the corrected signals DCOcorr and PCcorr are generated and emitted. After emitting the correction signals DCOcorr and PCcorr, the PFD and correction circuit 38 return to the INIT state, at which point switches SW2 and SW3 are disabled, switch SW1 is re-enabled, and all values at the PFD and correction circuit 38 are reset for the next disturbance event.

[0103] Although the embodiments described herein relate to MEMS devices with mirrors, it should be understood that other implementations may include optical devices other than MEMS mirror devices or other MEMS oscillating structures. Additionally, although some aspects have been described in the context of apparatuses, it is evident that these aspects also represent a description of corresponding methods, where boxes or devices correspond to method steps or features of method steps. Similarly, aspects described in the context of method steps also represent a description of corresponding boxes or items or features of corresponding apparatuses. Some or all of the method steps may be performed by (or with) a hardware device (e.g., a microprocessor, a programmable computer, or an electronic circuit). In some embodiments, one or more of the method steps may be performed by such a device.

[0104] Depending on the requirements of certain implementations, the embodiments provided herein may be implemented in hardware or software. The implementation may be performed using a digital storage medium (e.g., a floppy disk, a DVD, a Blu-ray, a CD, a ROM, a PROM, an EPROM, an EEPROM, or a FLASH memory) having electronically readable control signals stored thereon that cooperate (or are capable of cooperating) with a programmable computer system such that the corresponding method is performed. Thus, the digital storage medium may be computer-readable.

[0105] The instructions may be executed by one or more processors, such as one or more central processing units (CPUs), digital signal processors (DSPs), general microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, as used herein, the term "processor" refers to any of the foregoing structures or any other structure 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. Similarly, the techniques may be fully implemented in one or more circuits or logic elements.

[0106] The above-described exemplary embodiments are merely illustrative. It should be understood that modifications and variations of the devices and details described herein will be apparent to other technicians in the art. Thus, this document is intended to be limited only by the scope of the appended patent claims and not by the specific details presented by the description and interpretation of the embodiments herein.

Claims

1. A system for driving a Micro-Electro-Mechanical System (MEMS) oscillation structure, comprising: The MEMS oscillation structure is configured to oscillate about a rotation axis; A phase error detector configured to generate a phase error signal based on a measured event time and an expected event time of the MEMS oscillation structure oscillating about the rotation axis; An interference event detector configured to detect an interference event based on the phase error signal and an interference threshold, wherein the interference event disrupts the oscillation of the MEMS oscillation structure such that the phase error signal exceeds the interference threshold; And A phase frequency detector (PFD) and a correction circuit configured to, in response to the detected interference event, monitor a plurality of measured crossing events of the MEMS oscillation structure oscillating about the rotation axis, generate a first compensation signal based on at least a first measured crossing event and a second measured crossing event among the plurality of measured crossing events to correct the frequency of the MEMS oscillation structure, and generate a second compensation signal based on a third measured crossing event among the plurality of measured crossing events to correct the phase of the MEMS oscillation structure.

2. The system according to claim 1, wherein: The measured event time is a zero-crossing time measured when the rotation angle of the MEMS oscillation structure is 0° while the MEMS oscillation structure oscillates about the rotation axis, and The expected event time is an expected zero-crossing time when the rotation angle of the MEMS oscillation structure is expected to be 0°.

3. The system according to 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 the timing difference is determined for each of the measured zero-crossing times and the corresponding expected zero-crossing times among the measured zero-crossing times, and generate the phase error signal representing the determined timing difference.

4. The system according to claim 1, wherein: After the detected interference event, when the MEMS oscillation structure oscillates about the rotation axis, the first measured crossing event, the second measured crossing event, and the third measured crossing event occur sequentially, wherein the second measured crossing event occurs after the first measured crossing event, and the third measured crossing event occurs after the second measured crossing event.

5. The system according to claim 1, wherein a first time difference between the first measured crossing event and the second measured crossing event represents a half-oscillation period of the MEMS oscillation structure, and a second time difference between the first measured crossing event and the third measured crossing event represents a full-oscillation period of the MEMS oscillation structure.

6. The system according to claim 1, wherein: The first compensation signal includes a corrected Numerically Controlled Oscillator (DCO) counter increment, and The PFD and correction circuit are configured to determine a time period between the first measured crossing event and the second measured crossing event, and calculate the corrected DCO counter increment based on the determined time period.

7. The system according to claim 6, further comprising: A DCO counter configured to receive the first compensation signal and update a DCO counter value used to set the frequency of the MEMS oscillating structure based on the corrected DCO counter increment.

8. The system according to claim 6, wherein: The second compensation signal is a corrected phase counter signal configured to reset a sub-timing counter to a crossing event counter value, where the sub-timing counter is used to drive the MEMS oscillating structure about the axis of rotation, and The PFD and correction circuit are configured to emit the first compensation signal and the second compensation signal in response to detecting the third measured crossing event.

9. The system according to claim 8, wherein: The first measured crossing event, the second measured crossing event, and the third measured crossing event are zero-crossing events when the rotation angle of the MEMS oscillating structure is 0° while the MEMS oscillating structure oscillates about the axis of rotation.

10. The system according to claim 1, wherein: The second compensation signal is a corrected phase counter signal configured to reset a sub-timing counter to a crossing event counter value, where the sub-timing counter is used to drive the MEMS oscillating structure about the axis of rotation, and The PFD and correction circuit are configured to emit the second compensation signal in response to detecting the third measured crossing event.

11. The system according to claim 10, further comprising: A driver configured to drive the MEMS oscillating structure about the axis of rotation, the driver including the sub-timing counter configured to control the phase of the MEMS oscillating structure.

12. The system according to claim 1, further comprising: A driver configured to switch the drive voltage on and off to drive the MEMS oscillating structure about the axis of rotation, wherein, in response to the detected interference event, the PFD and correction circuit are configured to control the driver to maintain the drive voltage on for at least two oscillation periods of the MEMS oscillating structure.

13. The system according to claim 12, wherein the PFD and correction circuit are configured to monitor the plurality of measured crossing events while the driver maintains the drive voltage on for at least two mirror periods.

14. The system according to claim 1, wherein: In response to the detected interference event, the PFD and correction circuit are configured to disable a signal path corresponding to the phase error signal until at least the third measured crossing event, and In response to the third measured crossing event, the PFD and correction circuit are configured to enable the signal path corresponding to the phase error signal.

15. The system according to claim 1, further comprising: An illumination device configured to emit pulsed light; An optoelectronic detector array configured to detect the received light and generate an electrical signal based on the received light; A driver configured to drive the MEMS oscillating structure about the axis of rotation; And A controller configured to control at least one of the illumination device, the optoelectronic detector array, and the driver based on the phase error signal.

16. The system according to claim 1, wherein the interference event is a mechanical shock.

17. A method for compensating a microelectromechanical system (MEMS) oscillating structure, the method comprising: Driving the MEMS oscillating structure configured to oscillate about an axis of rotation; Generating a phase error signal based on a measured event time and an expected event time of the MEMS oscillating structure oscillating about the axis of rotation; Detecting an interference event based on the phase error signal and an interference threshold, wherein the interference event disrupts the oscillation of the MEMS oscillating structure such that the phase error signal exceeds the interference threshold; And In response to the detected interference event: Monitoring a plurality of measured crossing events of the MEMS oscillating structure oscillating about the axis of rotation; Generating a first compensation signal based on at least a first measured crossing event and a second measured crossing event among the plurality of measured crossing events to correct the frequency of the MEMS oscillating structure; And Generating a second compensation signal based on a third measured crossing event among the plurality of measured crossing events to correct the phase of the MEMS oscillating structure.

18. The method according to claim 17, wherein the first compensation signal includes a corrected numerically controlled oscillator (DCO) counter increment, The method further comprising: Determining a time period between the first measured crossing event and the second measured crossing event; And Calculating the corrected DCO counter increment based on the determined time period.

19. The method according to claim 18, further comprising: Updating a DCO counter value used to set the frequency of the MEMS oscillating structure based on the corrected DCO counter increment of the first compensation signal.

20. The method according to claim 18, wherein the second compensation signal is a corrected phase counter signal configured to reset a sub-timing counter to a crossing event counter value, wherein the sub-timing counter is used to drive the MEMS oscillating structure about the axis of rotation, The method further comprising: Emitting the first compensation signal and the second compensation signal in response to the detected third measured crossing event.

21. The method according to claim 20, wherein the first measured crossing event, the second measured crossing event, and the third measured crossing event are zero-crossing events when the rotation angle of the MEMS oscillating structure is 0° while the MEMS oscillating structure oscillates about the rotation axis.

22. The method according to claim 17, wherein the second compensation signal is a corrected phase counter signal configured to reset a sub-timing counter to a crossing event counter value, wherein the sub-timing counter is used to drive the MEMS oscillating structure about the rotation axis. The method further comprises: transmitting the second compensation signal in response to detecting the third measured crossing event.

23. The method according to claim 17, further comprising: disabling a signal path corresponding to the phase error signal in response to a detected interference event until at least the third measured crossing event; and enabling the signal path corresponding to the phase error signal in response to the third measured crossing event.

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