Drive signal switching scheme for power optimization of oscillating MEMS mirrors

Abstract

Embodiments of the present disclosure generally relate to a power-optimized drive signal switching scheme for an oscillating MEMS mirror. An oscillator driver system includes an oscillator structure and a driver circuit. The oscillator structure includes a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, and the oscillator structure is driven about an axis of rotation according to a voltage difference between the rotor voltage and the stator voltage. The driver circuit is configured to generate a drive signal and output the drive signal as the rotor voltage, where the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the axis of rotation, and where the stator voltage is a fixed voltage. The low voltage level and the high voltage level are greater than the stator voltage, such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the low voltage level and the high voltage level, respectively.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to a power-optimized drive signal switching scheme for an oscillating MEMS mirror. BACKGROUND

[0002] There are various types of micro-electromechanical system (MEMS) mirrors, such as an oscillating one-dimensional (ID) MEMS mirror, a two-dimensional (2D) MEMS mirror, or a quasi-static MEMS mirror. In driving a high-frequency MEMS mirror using a high-voltage drive signal, the drive signal applied to the rotor of the MEMS mirror is typically switched between 0 V and a high-voltage value, with the voltage at the stator of the MEMS mirror fixed at 0 V. The switching of the drive signal between these two voltage levels creates a driving force that causes the MEMS mirror to rotate about an axis of rotation, and can be used to create an oscillating driving force in order to drive the MEMS mirror at a resonant frequency.

[0003] However, at high frequencies, power dissipation becomes an issue, particularly in low-power scanner systems such as wearable augmented reality glasses that operate using a limited power source, such as a battery.

[0004] Power is affected by the driving (actuation) frequency of the drive signal in a linear manner, and by the high-voltage level applied to the MEMS mirror in a quadratic manner. Furthermore, the torque experienced by the mirror is related to the square of the high-voltage level. Only a small fraction or even a large fraction of the required power can be lost in charging and discharging the MEMS capacitor and the parasitic capacitor, while only a small fraction of the power is converted to mechanical power for driving the MEMS oscillation.

[0005] In the case of a high-frequency MEMS mirror that requires a high voltage and a high oscillation angle, considerable power dissipation can be incurred. This power dissipation is an impediment for applications that operate using a battery, such as wearable augmented reality glasses.

[0006] Accordingly, an improved system and method that is capable of driving a MEMS mirror while limiting power dissipation can be desirable. SUMMARY

[0007] One or more embodiments provide an oscillator driver system comprising: an oscillator structure configured to oscillate about a rotational axis, wherein the oscillator structure comprises a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, and wherein the oscillator structure is driven about the rotational axis as a function of a voltage difference between the rotor voltage and the stator voltage; and a driver circuit comprising an output terminal coupled to the rotor terminal, wherein the driver circuit is configured to generate a drive signal and output the drive signal at the output terminal as the rotor voltage, wherein the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis, and wherein the stator voltage is a fixed voltage and both a magnitude of the low voltage level and a magnitude of the high voltage level are greater than a magnitude of the stator voltage, such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the low voltage level and the high voltage level, respectively.

[0008] One or more embodiments provide an oscillator driver system comprising: an oscillator structure configured to oscillate about a rotational axis, wherein the oscillator structure comprises a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, and wherein the oscillator structure is driven about the rotational axis as a function of a voltage difference between the rotor voltage and the stator voltage; and a driver circuit comprising a first output terminal coupled to the rotor terminal and a second output terminal coupled to the stator terminal, wherein the driver circuit is configured to generate a drive signal and output the drive signal at the second output terminal as the stator voltage, wherein the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis, and wherein the rotor voltage is a fixed voltage and both a magnitude of the low voltage level and a magnitude of the high voltage level are less than a magnitude of the rotor voltage, such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the high voltage level and the low voltage level, respectively.

[0009] One or more embodiments provide a method of driving an oscillator structure about a rotational axis, where the oscillator structure includes a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, the method comprising: driving the oscillator structure about the rotational axis according to a voltage difference between the rotor voltage and the stator voltage, where driving the oscillator includes generating a drive signal and providing the drive signal as the rotor voltage to the rotor terminal, where the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis; and providing a fixed voltage for the stator voltage as the drive signal is switched between the low voltage level and the high voltage level, where both the low voltage level and the high voltage level are greater than the stator voltage, such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the low voltage level and the high voltage level, respectively.

[0010] One or more embodiments provide a method of driving an oscillator structure about a rotational axis, where the oscillator structure includes a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, the method comprising: driving the oscillator structure about the rotational axis according to a voltage difference between the rotor voltage and the stator voltage, where driving the oscillator includes generating a drive signal and providing the drive signal as the rotor voltage to the rotor terminal, where the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis; and providing a fixed voltage for the stator voltage as the drive signal is switched between the low voltage level and the high voltage level, where both the low voltage level and the high voltage level are greater than the stator voltage, such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the low voltage level and the high voltage level, respectively. BRIEF DESCRIPTION OF DRAWINGS

[0011] Embodiments are described herein with reference to the accompanying drawings.

[0012] Figure 1A And Figure 1B is a schematic block diagram of a scanning system according to one or more embodiments;

[0013] Figure 2A shows a schematic diagram of a MEMS driver system 200 according to one or more embodiments;

[0014] Figure 2B shows a schematic diagram of a MEMS driver system 200 according to one or more embodiments; Figure 2A shows voltage waveforms of a rotor voltage and a stator voltage of the MEMS driver system, and an angular (rotational) position waveform of a MEMS mirror, as shown in

[0015] Figure 3A shows a schematic diagram of a MEMS driver system 200 according to one or more embodiments; and

[0016] Figure 3B The voltage waveforms of the rotor voltage and the stator voltage of the MEMS driver system shown, and the angular (rotational) position waveform of the MEMS mirror are shown. Figure 3A DETAILED DESCRIPTION

[0017] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments are for illustrative purposes only and should not be construed as limiting. For example, although the embodiments can be described as including a plurality of features or elements, this should not be construed as indicating that all of these features or elements are required in order to implement the embodiments. Rather, in other embodiments, some features or elements can be omitted, or replaced with alternative features or elements. In addition, other features or elements can be provided in addition to the features or elements explicitly shown and described, such as conventional components of a sensor device.

[0018] Features from different embodiments can be combined to form other embodiments, unless specifically noted otherwise. Changes and modifications can be made to the described embodiments without departing from the scope of the application. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the embodiments.

[0019] In addition, in the following description, equivalent or similar elements or elements having equivalent or similar functions are denoted by equivalent or similar reference numerals. Since the same or functionally equivalent elements are given the same reference numerals in the drawings, repeated description of the elements with the same reference numerals can be omitted. Therefore, the description provided for elements with the same or similar reference numerals can be mutually interchangeable.

[0020] Unless otherwise specified, the connection or coupling between elements shown in the drawings or described herein can be a wire-based connection or a wireless connection. In addition, such a connection or coupling can be a direct connection or coupling without additional intermediate elements, or an indirect connection or coupling with one or more additional intermediate elements, as long as the general purpose of the connection or coupling (e.g., transmitting a certain signal or transferring a certain information) is essentially maintained.

[0021] In the present disclosure, expressions including ordinal numbers 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 the elements. The above expressions are used merely to distinguish an element from other elements with respect to its function. For example, a first block and a second block represent different blocks although they are both blocks. For another example, a first element can be termed a second element, and similarly, a second element can also be termed a first element without departing from the scope of the present disclosure.

[0022] ​Embodiments relate to optical transmitters and optical transmitter systems configured to transmit optical beams or pulses. The optical beams include visible light, infrared (IR) light, or other types of illumination signals. In some applications, the transmitted light can be backscattered by objects back into the system, where the backscattered light is detected by sensors. The sensors can convert the received backscattered light into electrical signals, such as current signals or voltage signals, which can be further processed by the system to generate object data and / or images.

[0023] For example, in a light detection and ranging (LIDAR) system, a light source transmits an optical beam into a field of view, and the light is reflected by backscattering from one or more objects. One or more microelectromechanical system (MEMS) mirrors can be arranged to receive the transmitted optical beam and to steer (scan) the transmitted optical beam into the field of view to perform an environmental scan.

[0024] In other applications, a MEMS mirror, such as a wearable augmented reality glasses, can be arranged to receive the transmitted optical beam and to steer (scan) the transmitted optical beam onto the retina of a human eye in order to render an image thereon.

[0025] Figure 1A and Figure 1B are schematic block diagrams of scanning systems 100A and 100B, respectively, in accordance with one or more embodiments. In particular, the scanning system 100A includes two one-dimensional (ID) MEMS mirrors 12x and 12y for steering or otherwise deflecting an optical beam (pulse) according to a scan pattern. In contrast, the scanning system 100B includes a single two-dimensional (2D) MEMS mirror 12xy for steering or otherwise deflecting an optical beam (pulse) according to a scan pattern. Of course, in certain applications, a single ID MEMS mirror (i.e., either the MEMS mirror 12x or 12y) can also be used to perform the scanning function.

[0026] The MEMS mirrors 12x and 12y are mechanically moving mirrors (i.e., MEMS micro mirrors) integrated on a semiconductor chip (not shown). The MEMS mirrors in accordance with the embodiments described herein are configured to rotate or oscillate via rotation about a single scan axis (i.e., ID MEMS mirror) or two scan axes (i.e., 2D MEMS mirror) that are generally orthogonal to each other. The oscillation of the MEMS mirror about the scan axis can be driven at a resonant frequency between two predetermined extreme deflection angles (e.g., + / - 15 degrees). A scanner with two orthogonal axes is configured to control the steering of the optical beam in two dimensions (e.g., in a horizontal x-direction and in a vertical y-direction), while a scanner with only one ID MEMS mirror is configured to control the steering of the optical beam in one dimension.

[0027] In Figure 1AIn the illustrated example, two ID MEMS mirrors 12x and 12y are used to steer the light beam in two dimensions. MEMS mirror 12x includes a first scan axis 13x that enables MEMS mirror 12x to steer light in the x-direction, and MEMS mirror 12y includes a second scan axis 13y that enables MEMS mirror 12yx to steer light in the y-direction. The two MEMS mirrors 12x and 12y are arranged sequentially along the transmission path of the light beam such that one of the MEMS mirrors (e.g., MEMS mirror 12x) first receives the light beam and steers the light beam in a first dimension, and the second MEMS mirror (e.g., MEMS mirror 12y) receives the light beam from the first MEMS mirror and steers it in a second dimension. As a result, the two MEMS mirrors 12x and 12y operate together to steer the light beam generated by illumination unit 10 in two dimensions. In this way, the two MEMS mirrors 12x and 12y can direct the light beam to a desired 2D coordinate (e.g., x-y coordinate). Multiple light beams can be steered by the two MEMS mirrors 12x and 12y at different 2D coordinates of a scan pattern.

[0028] In Figure 1B In another illustrated example, one 2D MEMS mirror 12xy is used to steer the light beam in two dimensions. MEMS mirror 12xy includes a first scan axis 13x that enables MEMS mirror 12xy to steer light in the x-direction and a second scan axis 13y that enables MEMS mirror 12xy to steer light in the y-direction. In this way, a single MEMS mirror is able to steer a light beam received from illumination unit 10 in both the x-direction and the y-direction. As a result, MEMS mirror 12xy can direct the light beam to a desired 2D coordinate (e.g., x-y coordinate). Multiple light beams can be steered by MEMS mirror 12xy at different 2D coordinates of a scan pattern.

[0029] A drive signal is used for each scan axis in order to drive the MEMS mirror about that scan axis. Thus, MEMS mirror 12x receives a drive signal for being driven about first scan axis 13x, MEMS mirror 12y receives a drive signal for being driven about second scan axis 13y, and MEMS mirror 12xy receives a first drive signal for being driven about first scan axis 13x and a second drive signal for being driven about second scan axis 13y. The drive signals produce a driving force that causes the MEMS mirror to rotate about the respective scan axis, and can be used to produce an oscillating driving force to drive the MEMS mirror about the respective scan axis at a resonant frequency.

[0030] Each MEMS mirror 12x, 12y, and 12xy can be a resonator (i.e., a resonant MEMS mirror) configured to oscillate “back and forth” around each of its scan axes at a resonant frequency, such that light reflected from the MEMS mirror oscillates back and forth in the scan direction of the respective scan axis.

[0031] For each scan axis, the MEMS mirror includes an actuator structure for driving the MEMS mirror around that scan axis. The actuator structure includes interdigitated electrodes made from interdigitated mirror combs on the rotor side and frame combs on the stator side, which are applied with a drive voltage by its driver (e.g., driver 25x or 25y). The drive voltage applied to the interdigitated structure generates a corresponding torque. Thus, the MEMS mirror itself represents a capacitor, the capacitance of which changes with the rotation angle of the MEMS mirror around its scan axis.

[0032] The drive voltage across the interdigitated structure generates a drive force between the interdigitated mirror combs and the frame combs, which generates a torque on the mirror body around the rotation axis. The drive voltage can be switched or toggled high / low, thereby generating an oscillating drive force. The oscillating drive force causes the mirror to oscillate back and forth between two extreme values on its scan axis. As the mirror oscillates, the capacitance between the interdigitated electrodes changes depending on the rotational position of the mirror. The MEMS driver is configured to measure the capacitance between the interdigitated electrodes and, from that, determine the rotational or angular position of the MEMS mirror. By monitoring the capacitance, the MEMS driver can track the rotational position of the MEMS mirror as well as detect zero-crossing events (i.e., when the rotational angle is zero) and their timing.

[0033] For example, as the MEMS mirror moves, the geometry of the interdigitated structure changes, which causes the geometry of the capacitance to change. As the geometry of the capacitance changes, the capacitance itself also changes. Thus, a particular capacitance directly corresponds to a particular position (i.e., rotational angle) of the MEMS mirror. By sensing the capacitance of the interdigitated structure, the specific position of the MEMS mirror can be determined.

[0034] One way to measure the capacitance is to measure the current flowing through the interdigitated structure, convert the measured current to a voltage, and then further correlate the voltage to the capacitance and / or rotational angle. However, any method of measuring the capacitance can be used. The rotational direction (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 or negative change indicates the relative rotational direction.

[0035] The scanning systems 100A and 100B each comprise an illumination unit 10 (i.e., a light transmitter) comprising at least one light source (e.g., at least one laser diode or light emitting diode) configured to transmit a light beam (pulse) along a transmission path towards the MEMS mirror(s). The illumination unit 10 can sequentially transmit a plurality of light pulses according to a trigger signal received from the system controller 23.

[0036] The scanning systems 100A and 100B further comprise a system controller 23 configured to control the components of the scanning system. In certain applications such as LIDAR, the system controller 23 can also be configured to receive raw data from a light sensor (not shown) and perform processing (e.g., via digital signal processing) thereon to generate object data (e.g., point cloud data). Accordingly, the system controller 23 comprises at least one processor and / or processor circuitry (e.g., comparators, time-to-digital converters (TDCs), analog-to-digital converters (ADCs), and digital signal processors (DSPs)) of a signal processing chain for processing the data, as well as control circuitry (such as a microcontroller) configured to generate control signals.

[0037] The system controller 23 is configured to generate a trigger signal for triggering the illumination unit 10 to generate a light pulse. Accordingly, the system controller 23 controls the timing of the emission of light pulses from the illumination unit 10 via the trigger signal. The system controller 23 is also configured to set the drive frequency of the MEMS mirror for each of its scan axes and is able to synchronize the oscillations about the two scan axes 13x and 13y.

[0038] The scanning systems 100A and 100B each comprise a MEMS driver 25x for driving a MEMS mirror (i.e., the MEMS mirror 12x or 12xy) about a first scan axis 13x and a MEMS driver 25y for driving a MEMS mirror (i.e., the MEMS mirror 12y or 12xy) about a second scan axis 13y. Each MEMS driver 25x, 25y actuates and senses the rotational position of the mirror about its respective scan axis and provides position information (e.g., a tilt angle or a number of rotations about the rotational axis) of the mirror to the system controller 23. Based on this position information, the laser source of the illumination unit 10 can be triggered by the system controller 23. Accordingly, a higher precision of the position sensing of the MEMS mirror results in more accurate and precise control of the other components of the scanning system.

[0039] A drive voltage (i.e., actuation or drive signal) is applied by the MEMS driver to an actuator structure of the MEMS mirror corresponding to its corresponding scan axis to drive oscillation of the MEMS mirror about the scan axis. The drive voltage can be referred to as a high voltage (HV) signal. The actuator structure can include interdigitated electrodes made of interdigitated mirror and frame combs to which the drive voltage (i.e., actuation or drive signal) is applied by the MEMS driver. The drive voltage applied to the actuator structure generates a drive force between, for example, the interdigitated mirror and frame combs that generates a torque on the mirror body about the rotation axis.

[0040] The drive voltage can be switched or toggled between two or more voltage values including a low voltage (LV) level and a high voltage (HV) to generate an oscillatory drive force to produce mirror oscillation. The oscillatory drive force causes the mirror to oscillate back and forth between two extreme values on its rotation axis. For simplicity, only a rectangular waveform with two levels (i.e., LV level and HV level) is discussed by way of example. When the HV level is generated, it can be said that the HV level is on (i.e., HV_On), and when the LV level is generated, it can be said that the HV level is off (i.e., HV_Off).

[0041] The level of the drive signal can be adjusted to limit (e.g., reduce) power dissipation. This power dissipation is caused by RC charging / discharging losses that should be optimized while keeping the delivered mechanical power constant. According to Equation 1, the power dissipation is proportional (~) to the drive (i.e., actuation) frequency f_actuation in a linear manner and proportional (~) to the voltage difference (AV = Vrotor - Vstator) between the voltage level applied to the MEMS mirror in a quadratic manner:

[0042] Power_dissipated ~ f_actuation * (Vrotor - Vstator)2* capacitance Equation 1,

[0043] where capacitance is the capacitance of the MEMS mirror. Note that in some embodiments, Vrotor and Vstator can be interchanged.

[0044] Moreover, according to Equation 2, the torque experienced by the mirror is related (~) to the square of the voltage level:

[0045] Torque ~ Vstator2 - Vrotor2 Equation 2.

[0046] For example:

[0047] Vrotor: HV-On: 121 V;

[0048] Vrotor: HV-Off: 0V;

[0049] Vstator: 0V;

[0050] f_actuation: 25 kHz;

[0051] capacitance: 120 pF (image capacitance + parasitic capacitance); and

[0052] power dissipation: 87.85 mW.

[0053] Here, AV is switched between 0V and 121V, resulting in a large power dissipation.

[0054] One or more embodiments propose an alternative HV switching scheme that significantly reduces the power dissipation of the system. Rather than switching the drive signal applied to the rotor of the MEMS mirror between zero (HV-Off) and a HV level with an x value (HV-On), the mirror drive signal applied to the rotor is switched between HV and HV / 2 or some other fraction, such that the LV level (e.g., HV / 2) is greater than zero.

[0055] For example, AV is switched between 140V and 70V, the resulting mirror torque corresponds to the 121V and 0V HV switching scheme. However, the power dissipation of the 140V / 70V scheme is only 29.40 mW, while the power dissipation of the 121V / 0V scheme is 87.85 mW.

[0056] Furthermore, by adjusting the HV level as well as the LV level, the same level of torque can be achieved for parametric oscillations of different operating frequencies. Specifically, the maximum total energy injected into the MEMS mirror is defined by Equation 2. Thus, if the LV level is selected, a corresponding HV level can be selected to maintain the maximum deflection angle amplitude of the mirror. If the LV level is increased, the unadjusted HV level results in a smaller AV (i.e., HV-LV) and can result in different phase conditions and even mirror drop out, as the energy injected is not sufficient to attain the target mirror amplitude. Thus, if the LV level is increased from a previous LV value set for a preselected torque, it is desirable that the HV level is increased from a previous HV value, but the voltage difference AV between them is decreased to achieve the same maximum energy injection. If the LV level is decreased from a previously set LV value, the HV level is also decreased from a previous HV value, but the voltage difference between them is increased to achieve the same maximum energy injection. Of course, different levels of maximum injected energy can be achieved by adjusting the LV and HV levels.

[0057] Figure 2AA schematic diagram of a MEMS driver system 200 is shown in accordance with one or more embodiments. The MEMS driver system 200 comprises a MEMS mirror 12 configured to rotate around a scan axis 13, and a driver circuitry 30. In this example, the driver circuitry 30 is a voltage doubler (e.g., a voltage multiplier) provided with a positive supply voltage V+ (i.e., HV / 2 or LV of the drive signal) and a reference supply voltage (e.g., ground GND). The driver circuitry 30 doubles the positive supply voltage V+ and comprises an output node 36 that outputs the positive supply voltage V+ or a predetermined multiple thereof based on a control signal Ctrl provided by a system controller 23. For example, the positive supply voltage V+ can be doubled.

[0058] It should be understood that in some embodiments, the power supply can be reversed, where the positive supply voltage V+ is at the negative supply. In the reversed case, the “high voltage” will be more negative (i.e., have a greater magnitude) than the “low voltage”, which is also negative, but not as negative as the “high voltage”. Furthermore, the rotor / stator terminals can be interchanged, which means that the connections to the two terminals 31 and 32 can be interchanged. This connection exchange to the two terminals is independent of the implementation described in Figure 2A and Figure 3A described in.

[0059] The actuator of the MEMS mirror 12 comprises a rotor terminal 31 that receives a rotor voltage Vrotor (i.e., the drive signal) and a stator terminal 32 that receives a stator voltage Vstator (i.e., ground GND). The drive voltage across the rotor terminal 31 and the stator terminal 32, and in particular the oscillating voltage difference AV between them, generates a drive force between the interdigitated mirror comb and the frame comb of the actuator structure, which generates a torque on the mirror body around the rotation axis 13.

[0060] The driver circuitry 30 provides the positive supply voltage V+ as a low voltage (LV) level of the drive signal to the MEMS mirror 12 during the LOW phase (HV Off) and provides (via doubling the positive supply voltage V+) a high voltage (HV) level of the drive signal during the HIGH phase (HV On). The drive signal is switched between these two voltage levels LV and HV at a drive frequency f actuation. Thus, during the HIGH phase, the voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator is maximized to a maximum or high voltage difference. Conversely, during the LOW phase, the voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator is minimized to a minimum or low voltage difference. Thus, three different voltage levels are applied to the terminals of the MEMS mirror 12 to generate a switching or toggling voltage difference AV, where HV and LV are applied as a toggling rotor voltage Vrotor and 0V is applied as a fixed stator voltage Vstator.

[0061] During the LOW phase, less energy is injected into the MEMS mirror. In contrast, during the HIGH phase, more energy is injected into the MEMS mirror. Typically, the MEMS mirror 12 operates like a pendulum and the HV always acts as a pulling force. When the MEMS mirror 12 reaches its maximum deflection angle, the pulling force of the HV acts to accelerate the MEMS mirror 12 during the swing down until it reaches its zero angle position. After its zero angle position, the pulling force of the HV acts to decelerate the MEMS mirror 12 during the swing up. From a control perspective, there are actually three phases, including: an acceleration phase from the maximum deflection angle to the zero-crossing during the swing down; a deceleration phase from the zero-crossing to an intermediate deflection angle between zero and the maximum deflection angle during the swing up; and an idle / deceleration phase from the intermediate deflection angle to the maximum maximum deflection angle during the swing up.

[0062] As a result, the drive signal input to the rotor terminal 31 switches between two non-zero voltage levels, while the stator terminal 32 is fixed at 0V. This results in the voltage difference AV between the rotor terminal 31 and the stator terminal 32 switching or oscillating between two non-zero voltage difference levels at the actuation frequency f actuation, which generates the driving force to drive (e.g., oscillate) the MEMS mirror 12 around its scan axis at half the actuation frequency f actuation. Thus, the stator voltage Vstator serves as a reference voltage with respect to the rotor voltage Vrotor that receives the drive signal.

[0063] The driver circuitry 30 includes a transistor half-bridge 33 comprising a complementary transistor pair 34 and 35 connected in series between a positive supply voltage V+ and a reference supply voltage (e.g., ground GND), where “transistor complementary pair” means that when one transistor is turned on, the other transistor is turned off in a complementary manner. The transistor half-bridge 33 receives a control signal Ctrl (e.g., a pulse trigger signal) that controls the conduction path through the transistor half-bridge 33 and thereby controls the waveform of the drive signal LV / HV.

[0064] For example, the control signal Ctrl can switch between two control voltages 0V and 3.3V (i.e., low and high control voltages) sufficient to control the on / off state of the transistors 34 and 35.

[0065] The driver circuitry 30 further comprises a diode-capacitor network for generating the drive signal and modulating the drive voltage across the rotor terminals 31 and the stator terminals 32. Here, the diode-capacitor network comprises a diode Dl and a capacitor Cl that generate an output voltage LV and HV at an output node 36 of the driver circuitry 30 and, thus, the voltage level of the drive signal LV / HV. The diode-capacitor network in the present example is configured to double the positive supply voltage V+, but can be designed to have a multiplication factor different from 2.

[0066] When the control signal Ctrl is low, the transistor 34 is on and the transistor 35 is off. As a result, the capacitor Cl is in a charging phase and the positive supply voltage V+ is passed to the output node 36 of the driver circuitry 30 as the LV level of the drive signal. In other words, when the control signal Ctrl is low, the drive signal is equal to the positive supply voltage V+.

[0067] When the control signal Ctrl is high, the transistor 35 is on and the transistor 34 is off. As a result, the capacitor Cl is in a supply phase and, due to the diode Dl, the capacitor Cl provides a voltage across its terminals to the output node 36 of the driver circuitry 30 in addition to the positive supply voltage V+. The voltage across the capacitor Cl is equal to the positive supply voltage V+. In this way, the voltage at the output node 36 is doubled and provides the HV level of the drive signal. Thus, the HV level is twice the positive supply voltage V+ (i.e., twice the LV level). In other words, when the control signal Ctrl is high, the drive signal is equal to twice the positive supply voltage V+.

[0068] The control signal Ctrl is switched between its control values with the actuation frequency f actuation, thereby switching the drive signal between LV and HV with the actuation frequency f actuation. Because the stator voltage Vstator is fixed at 0 V, the voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator is also switched with the actuation frequency f actuation and drives the oscillation of the MEMS mirror 12 at half of this frequency.

[0069] Figure 2B Fig. 1 shows a schematic diagram of a MEMS mirror 12 according to Figure 2AThe voltage waveforms of the rotor voltage Vrotor and the stator voltage Vstator of the illustrated MEMS driver system 200, and the angular (rotational) position waveform of the MEMS mirror. The angular (rotational) position waveform represents the angular value Qmirror of the deflection or tilt angle of the MEMS mirror 12, where a positive value corresponds to the deflection angle when the MEMS mirror is tilted in the positive direction (e.g., right), and a negative value corresponds to the deflection angle when the MEMS mirror is tilted in the negative direction (e.g., left). The angular value Qmirror of the MEMS mirror 12 oscillates at half the drive frequency f_actuation.

[0070] In one example, the positive supply voltage V+ can be set to 70 V as the LV value, which results in the voltage difference AV to switch between 70 V and 140 V. The two voltage levels of the drive signal are always greater than the fixed stator voltage Vstator during the drive operation. In the inverted case where the negative supply voltage is used instead of the positive supply voltage V+, the two voltage levels of the drive signal are always less than the fixed stator voltage Vstator during the drive operation, as the voltage levels are negative voltage levels. Thus, it can be said that the magnitude (i.e., absolute value) of the voltage levels of the drive signal is always greater than the magnitude of the fixed stator voltage Vstator during the drive operation.

[0071] Figure 3A A schematic diagram of a MEMS driver system 300 is shown, in accordance with one or more embodiments. The MEMS driver system 300 includes a MEMS mirror 12 configured to rotate about a scan axis 13, and a driver circuitry 40. In this example, the driver circuitry 40 is a voltage doubler provided with a positive supply voltage V+ (i.e., HV of the drive signal) and a reference supply voltage (e.g., ground GND) (which is also the LV of the drive signal).

[0072] It should be appreciated that in some embodiments, the power supply can be inverted, where the positive supply voltage V+ it is a negative supply. In the inverted case, the “high voltage” will be more negative (i.e., have a greater magnitude) than the “low voltage”, which is also negative, but not as negative as the “high voltage”. Furthermore, the rotor / stator terminals can be interchanged, which means that the connections to the two terminals 31 and 32 can be interchanged. This connection swapping to the two terminals is independent of the inversion of the power supply. Figure 2A and Figure 3A as described in the implementations described in

[0073] Unlike the MEMS driver system 200, in which the drive signal is applied to the rotor terminals 31 and the fixed voltage is applied to the stator terminals 32, in the MEMS driver system 300 the drive signal is applied to the stator terminals 32 and the fixed voltage is applied to the rotor terminals 31. Both voltage levels of the drive signal are smaller than the fixed rotor voltage Vrotor. The driver circuitry 40 is configured to generate the fixed rotor voltage Vrotor from the positive supply voltage V+, wherein the fixed rotor voltage Vrotor is twice the positive supply voltage V+, so that it is always greater than the voltage levels of the drive signal during the drive operation or always smaller than the voltage levels of the drive signal during the drive operation in case of inversion. Thus, it can be said that the magnitude (i.e. the absolute value) of the fixed rotor voltage Vrotor is always greater than the voltage levels of the drive signal during the drive operation.

[0074] Using the example values above, the positive supply voltage V+ can be set to 70 V as the HV value of the drive signal, 0 V can be set as the LV of the drive signal, and the fixed rotor voltage Vrotor can be set to 140 V. This setting results in a voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator that is switched between 70 V and 140 V. Thus, the rotor voltage Vrotor serves as a reference voltage with respect to the stator voltage Vstator that receives the drive signal.

[0075] The oscillating voltage difference AV generates a drive force between the interdigital mirror comb and the frame comb of the actuator structure that generates a torque on the mirror around the rotation axis 13. Thus, three different voltage levels are applied to the terminals of the MEMS mirror 12 to generate the switching or toggling voltage difference AV, wherein HV and LV are applied as the switching stator voltage Vstator and the higher voltage (2HV) is applied as the fixed rotor voltage Vrotor.

[0076] The driver circuitry 40 doubles the positive supply voltage V+ and comprises an output node 36 that outputs the positive supply voltage V+ or its double based on a control signal Ctrl. The driver circuitry 40 provides the positive supply voltage V+ as the high voltage (HV) level of the drive signal to the MEMS mirror 12 during the LOW phase (HV Off) and the reference supply voltage GND as the low voltage (LV) level of the drive signal to the MEMS mirror 12 during the HIGH phase (HV ON). The drive signal LV / HV is toggled between these two voltage levels LV and HV at the drive frequency f actuation. Thus, the voltage difference AV is maximum during the HIGH phase and minimum during the LOW phase.

[0077] As a result, the drive signal input into the stator terminal 32 switches between two voltage levels, while the rotor terminal 31 is fixed at a higher voltage (e.g., 140 V). This results in the voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator switching or oscillating between two non-zero voltage difference levels at the actuation frequency f actuation, which produces a driving force to drive (e.g., oscillate) the MEMS mirror 12 about its scan axis at half the actuation frequency f actuation.

[0078] The driver circuitry 40 includes a transistor half-bridge 33 comprising a complementary pair of transistors 34 and 35 connected in series between a positive supply voltage V+ and a reference supply voltage (e.g., ground GND), where by “complementary pair of transistors” we mean that when one of the transistors is on, the other is off in a complementary fashion. The transistor half-bridge 33 receives a control signal Ctrl (e.g., a pulsed trigger signal) that controls the conduction path through the transistor half-bridge 33 and thereby controls the waveform of the drive signal LV / HV.

[0079] For example, the control signal Ctrl can switch between two control voltages 0 V and 3.3 V (i.e., low and high control voltages) sufficient to control the on / off state of the transistors 34 and 35.

[0080] The driver circuitry 40 also includes a diode-capacitor network for generating the drive signal and modulating the drive voltage across the rotor terminal 31 and the stator terminal 32. Here, the diode-capacitor network includes a diode Dl and a capacitor Cl that generate first and second modulated voltages HV and 2HV at a node 36 of the driver circuitry 40. The modulated voltages HV and 2HV, where 2HV is twice the level of HV (i.e., twice the positive supply voltage V+). The diode-capacitor network in this example is configured to double the positive supply voltage V+, but can be designed to have a multiplication factor other than 2.

[0081] The driver circuitry 40 operates in a similar manner to the driver circuitry 30, where the capacitor Cl is used to produce twice the positive supply voltage V+ (2HV) when the control signal Ctrl is high (e.g., 3.3 V), such that transistor 35 is on and transistor 34 is off. At this time, the voltage at the node 36 is 2HV and the output voltage at the output node 38 is HV, where the voltage across the capacitor Cl is equal to HV. Thus, the output node 38 is pulled up to the positive supply voltage V+ (HV) via the transistor 35, which is in an on state, and outputs the HV level of the drive signal LV / HV to the stator terminal 32. However, the voltage difference AV is actually at a minimum during this phase, which indicates that the driver circuitry 40 is in the LOW phase when the control signal Ctrl is high.

[0082] When the control signal Ctrl is low (e.g. 0 V), transistor 34 is on and transistor 35 is off. The output voltage at output node 38 is pulled down to 0 V (GND) as the LV level of the drive signal LV / HV provided to the stator terminal 32. Thus, the driver circuitry 40 generates the second modulation voltage LV / HV as the drive signal at the output node 38 based on the control signal Ctrl. However, the voltage difference AV is actually at its maximum value during this phase, which indicates that the driver circuitry 40 is in the HIGH phase when the control signal Ctrl is low.

[0083] The diode-capacitor network of the driver circuitry 40 further comprises a diode D2 and a buffer capacitor C2 that generates a fixed output voltage 2HV at an output node 37 coupled to the rotor terminal 31. Thus, when the voltage at node 36 is switched between HV and 2HV, the buffer capacitor C2 is charged such that the output voltage at the output node 37 is fixed at the doubled voltage value 2HV.

[0084] The control signal Ctrl is switched between its control values at an actuation frequency f actuation, thereby causing the drive signal to be switched between LV and HV at the actuation frequency f actuation. Because the rotor voltage Vrotor is fixed at 2HV, the voltage difference AV between the rotor voltage Vrotor and the stator voltage Vstator is also switched at the actuation frequency f actuation and drives the oscillation of the MEMS mirror 12 at half of this frequency.

[0085] Figure 3B Voltage waveforms of the rotor voltage Vrotor and the stator voltage Vstator of the MEMS driver system 300 shown in Fig. 3 are shown in Fig. 4. The angular (rotational) position waveform of the MEMS mirror is shown in Fig. 5. Figure 3A The voltage waveforms of the rotor voltage Vrotor and the stator voltage Vstator of the MEMS driver system 300 shown in Fig. 3 are shown in Fig. 4. The angular (rotational) position waveform of the MEMS mirror is shown in Fig. 5.

[0086] In one example, the positive supply voltage V+ can be set to 70V as the HV value, which results in the voltage difference AV switching between 70V and 140V. The two voltage levels of the drive signal are always less than the fixed rotor voltage Vrotor (2HV) during the drive operation. In the inverted case where a negative supply voltage is used instead of the positive supply voltage V+, the two voltage levels of the drive signal are always greater than the fixed rotor voltage Vrotor (i.e., no fixed rotor voltage Vrotor negative) during the drive operation, since the voltage levels are negative voltage levels. Thus, it can be said that the magnitude (i.e., absolute value) of the voltage levels of the drive signal are always less than the magnitude of the fixed rotor voltage Vrotor.

[0087] The two MEMS driver systems 200 and 300 significantly reduce power dissipation, since only the voltage switching difference between HV On and HV LOW phases creates power dissipation (parasitic RC losses). They also can sense the mirror current throughout the mirroring, to further enable rotational position sensing. They also relax the requirements on discrete components involved in the high voltage part (e.g., in this example, only 70V switches are needed instead of 121V).

[0088] While the embodiments described herein relate to MEMS devices having at least one MEMS mirror, it should be understood that other implementations can include other optical devices other than MEMS mirror devices, including other non-MEMS oscillating structures for steering light. Moreover, while some aspects have been described in the context of an apparatus, it is clear that separate aspects also represent a description of corresponding method steps, where a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method step also represent a description of corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps can be performed by (or using) a hardware apparatus, like, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some one or more of the method steps can be performed by such an apparatus.

[0089] It should also be noted that the disclosure of the method steps and / or actions of the disclosure can not be interpreted as causing a dependency on the particular sequence of the steps and / or actions. Accordingly, the disclosure of multiple steps and / or actions should not be interpreted as a dependency on a particular sequence of the steps and / or actions. Furthermore, the disclosure of a single step and / or action can encompass or can be split into multiple sub-steps and / or sub-actions. Unless explicitly stated otherwise, such sub-steps and / or sub-actions can be included and are part of the disclosure of the single step and / or action.

[0090] 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 gate arrays (FPGAs), programmable logic controllers (PLCs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term "processor" or "processing circuitry" can generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry or any other equivalent circuitry. A control unit comprising hardware can also perform one or more of the techniques of this disclosure. The control unit can use electrical and digital algorithms to perform its receiving, analyzing, and control functions, which can also include correction functions. Such hardware, software, and firmware can be implemented within the same device or within separate devices to support the various techniques described in this disclosure.

[0091] One or more aspects of the present disclosure can be implemented as a non-transitory computer-readable recording medium having recorded thereon a program embodying a method / algorithm for instructing a processor to execute the method / algorithm. Accordingly, the non-transitory computer-readable recording medium can have stored thereon an electronically readable control signal that cooperates with (or is capable of cooperating with) a programmable computer system to perform the corresponding method / algorithm. The non-transitory computer-readable recording medium can be, for example, a CD-ROM, a DVD, a Blu-ray disc, a RAM, a ROM, a PROM, an EPROM, an EEPROM, a flash memory, or an electronic memory device.

[0092] While various embodiments have been disclosed, it will be apparent to those of ordinary skill in the art that many modifications, and the like will be made thereto without departing from the spirit and scope of the present application. It will be readily apparent to those of ordinary skill in the art that other components performing the same functions can be suitably substituted. It will be understood that other embodiments can be utilized and structural or logical changes can be made without departing from the scope of the present application. It is intended that the appended claims cover all such modifications and changes as fall within the scope of the application.

Claims

1. An oscillator driver system, comprising: an oscillator structure configured to oscillate about a rotational axis, wherein the oscillator structure includes a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, and wherein the oscillator structure is driven about the rotational axis according to a voltage difference between the rotor voltage and the stator voltage; and a driver circuit including an output terminal coupled to the rotor terminal, wherein the driver circuit is configured to generate a drive signal and output the drive signal at the output terminal as the rotor voltage, wherein the drive signal is switched between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis, wherein the stator voltage is a fixed voltage and both a magnitude of the low voltage level and a magnitude of the high voltage level are greater than a magnitude of the stator voltage such that the voltage difference is switched between a low voltage difference and a high voltage difference as the drive signal is switched between the low voltage level and the high voltage level, respectively.

2. The oscillator driver system of claim 1, wherein: the driver circuit is configured to receive a first supply voltage and a second supply voltage, and the driver circuit includes a voltage multiplier circuit configured to generate the drive signal at the output terminal, wherein the voltage multiplier circuit is configured to output the first supply voltage as the low voltage level of the drive signal and apply a multiplication factor to the first supply voltage to generate a multiple of the first supply voltage as the high voltage level of the drive signal.

3. The oscillator driver system of claim 2, wherein the voltage multiplier circuit is a voltage doubler configured to double the first supply voltage and output the doubled first supply voltage as the high voltage level of the drive signal.

4. The oscillator driver system of claim 2, wherein the stator voltage is fixed at the second supply voltage.

5. The oscillator driver system of claim 2, wherein the second supply voltage is ground.

6. The oscillator driver system of claim 2, further comprising: a controller configured to generate a control signal that is switched between a first control value and a second control value at the actuation frequency, wherein the voltage multiplier circuit is configured to receive the control signal and switch the drive signal between the low voltage level and the high voltage level according to the control signal.

7. The oscillator driver system of claim 6, wherein the voltage difference is set to the low voltage difference in response to the control signal having the first control value and the voltage difference is set to the high voltage difference in response to the control signal having the second control value.

8. The oscillator driver system of claim 6, wherein the voltage multiplier circuit includes a diode capacitor circuit that defines the multiplication factor of the first supply voltage.

9. The oscillator driver system of claim 8, wherein the voltage multiplier circuit comprises a transistor half-bridge configured to receive the control signal and charge a capacitor of the diode-capacitor circuit when the control signal has the first control value and to provide a stored voltage of the capacitor to the rotor terminal when the control signal has the second control value.

10. The oscillator driver system of claim 2, wherein the voltage multiplier circuit comprises: a diode-capacitor circuit configured to generate the drive signal, wherein the diode-capacitor circuit defines the multiplication factor of the first supply voltage; and a transistor half-bridge configured to control the diode-capacitor circuit to generate the drive signal at the actuation frequency.

11. An oscillator driver system, comprising: an oscillator structure configured to oscillate about a rotation axis, wherein the oscillator structure comprises a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, and wherein the oscillator structure is driven about the rotation axis according to a voltage difference between the rotor voltage and the stator voltage; and a driver circuit comprising a first output terminal coupled to the rotor terminal and a second output terminal coupled to the stator terminal, wherein the driver circuit is configured to generate a drive signal and output the drive signal at the second output terminal as the stator voltage, wherein the drive signal switches between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotation axis, wherein the rotor voltage is a fixed voltage and both the magnitude of the low voltage level and the magnitude of the high voltage level are smaller than the magnitude of the rotor voltage, such that the voltage difference switches between a low voltage difference and a high voltage difference as the drive signal switches between the high voltage level and the low voltage level, respectively.

12. The oscillator driver system of claim 11, wherein: the driver circuit is configured to receive a first supply voltage and a second supply voltage, and the driver circuit comprises a voltage multiplier circuit configured to generate the rotor voltage at the first output terminal and the drive signal at the second output terminal, wherein the voltage multiplier circuit is configured to apply a multiplication factor to the first supply voltage to generate a multiple of the first supply voltage as the rotor voltage.

13. The oscillator driver system of claim 12, wherein the voltage multiplier circuit is a voltage doubler configured to double the first supply voltage and output the doubled first supply voltage as the rotor voltage. ​ 14. The oscillator driver system of claim 12, wherein the voltage multiplier circuit is configured to output the first supply voltage at the second output terminal as the high voltage level of the drive signal and to output the second supply voltage at the second output terminal as the low voltage level of the drive signal.

15. The oscillator driver system of claim 14, wherein the second supply voltage is ground.

16. The oscillator driver system of claim 14, further comprising: a controller configured to generate a control signal that switches between a first control value and a second control value at the actuation frequency, wherein the voltage multiplier circuit is configured to receive the control signal and to cause the drive signal to switch between the low voltage level and the high voltage level in accordance with the control signal.

17. The oscillator driver system of claim 16, wherein the voltage difference is set to the high voltage difference in response to the control signal having the first control value and the voltage difference is set to the low voltage difference in response to the control signal having the second control value.

18. The oscillator driver system of claim 16, wherein the voltage multiplier circuit comprises a diode capacitor circuit that defines the multiplication factor of the first supply voltage.

19. The oscillator driver system of claim 18, wherein the voltage multiplier circuit comprises a transistor half-bridge configured to receive the control signal and charge a first capacitor of the diode capacitor circuit when the control signal has the first control value and to provide a stored voltage of the first capacitor to the rotor terminal when the control signal has the second control value.

20. The oscillator driver system of claim 19, wherein the transistor half-bridge is configured to connect the second output terminal to the second supply voltage when the control signal has the first control value and to connect the second output terminal to the first supply voltage when the control signal has the second control value.

21. The oscillator driver system of claim 20, wherein: the second supply voltage is ground and the low voltage level of the drive signal, and the first supply voltage is the high voltage level of the drive signal.

22. The oscillator driver system of claim 19, wherein the capacitor circuit comprises a second capacitor coupled to the first output terminal, the first output terminal being coupled between the first capacitor and the rotor terminal, wherein the second capacitor is configured to maintain the rotor voltage at the fixed voltage when the drive signal switches between the low voltage level and the high voltage level.

23. The oscillator driver system of claim 12, wherein the voltage multiplier circuit comprises: a diode-capacitor circuit configured to generate the drive signal, wherein the diode-capacitor circuit defines the multiplication factor of the first supply voltage; and a transistor half-bridge configured to control the diode-capacitor circuit to generate the drive signal at the actuation frequency.

24. A method of driving an oscillator structure about a rotational axis, wherein the oscillator structure comprises a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, the method comprising: driving the oscillator structure about the rotational axis according to a voltage difference between the rotor voltage and the stator voltage, wherein driving the oscillator comprises generating a drive signal and providing the drive signal as the rotor voltage to the rotor terminal, wherein the drive signal switches between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis; and providing a fixed voltage for the stator voltage as the drive signal switches between the low voltage level and the high voltage level, wherein the magnitude of the low voltage level and the magnitude of the high voltage level are both greater than the magnitude of the stator voltage, such that the voltage difference switches between a low voltage difference and a high voltage difference as the drive signal switches between the low voltage level and the high voltage level, respectively.

25. A method of driving an oscillator structure about a rotational axis, wherein the oscillator structure comprises a rotor terminal configured to receive a rotor voltage and a stator terminal configured to receive a stator voltage, the method comprising: driving the oscillator structure about the rotational axis according to a voltage difference between the rotor voltage and the stator voltage, wherein driving the oscillator comprises generating a drive signal and providing the drive signal as the stator voltage to the stator terminal, wherein the drive signal switches between a low voltage level and a high voltage level at an actuation frequency to drive the oscillator structure about the rotational axis; and providing a fixed voltage for the rotor voltage as the drive signal switches between the low voltage level and the high voltage level, wherein the magnitude of the low voltage level and the magnitude of the high voltage level are both less than the magnitude of the rotor voltage, such that the voltage difference switches between a low voltage difference and a high voltage difference as the drive signal switches between the high voltage level and the low voltage level, respectively.

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