Switching arrangement with efficiency-optimised oscillating circuit for controlling an actuator for driving an oscillating movement in an MEMS

Abstract

The invention relates to a switching arrangement for controlling an actuator for driving an oscillating movement of a mass element in an MEMS. The switching arrangement comprises: an electric oscillating circuit with an inductor, an MEMS capacitor and a charging connection; a controllable switching device for selectively interrupting or closing the oscillating circuit by controlling the switching device; and a resonance frequency based on a permanently closed state. The switching arrangement furthermore has a controller for controlling the switching device. The inductor is arranged in the oscillating circuit such that during charge transfer and during temporary recharging of the MEMS capacitor, the inductor is in a current path through which current flows and which extends through the MEMS capacitor. The controller is configured to set, by way of corresponding controlling, the switching device to a state in which it interrupts the oscillating circuit, and therefore the oscillation frequency is lower than the resonance frequency, this being done during an oscillation period of the oscillating circuit occurring in the closed state of the switching device temporarily at a time at which the voltage over the MEMS capacitor reaches a maximum amount.

Description

[0001] Circuit with an efficiency-optimized oscillating circuit for controlling an actuator to drive an oscillating movement in a MEMS

[0002] The present invention relates to a circuit for controlling an actuator, in particular a MEMS actuator, for driving an oscillating movement in a micro-electromechanical system (MEMS), as well as a MEMS equipped therewith. The circuit has an oscillating circuit with a variable oscillation period. The MEMS can, in particular, be a microscanner system with a deflection element (mirror) arranged to oscillate, wherein the actuator is configured to drive an oscillating movement (oscillation) of the deflection element.

[0003] Many MEMS, ie systems with multiple components, whose dimensions are typically in the range of 1 µm to 100 µm, with the MEMS themselves typically having dimensions in the range of about 10 µm to a few millimeters, have moving mechanical parts that can be driven using electrical energy, so that a microscopically small machine is present as an electromechanical system.

[0004] Oscillating mass elements of MEMS, particularly deflection elements of microscanners, can be made to oscillate in various ways. However, this always requires a driving force capable of deflecting the deflection element (e.g., a mirror plate) from its rest position. Typically, one or more actuators are used to provide such a force for MEMS (particularly small microphones, loudspeakers, or gyroscopes, microscanners, or microscanner systems comprising multiple microscanners). These actuators operate according to an electrostatic, electromagnetic, piezoelectric, thermal, or other actuator principle, or a hybrid of two or more such actuator principles.

[0005] The term “MEMS actuator,” as used herein, is to be understood in particular as an actuator that can convert electrical and / or magnetic energy into mechanical energy and / or vice versa, and that uses a MEMS for this purpose or is itself a component thereof, in particular as the MEMS itself or as a component thereof. Such a MEMS actuator can in particular be designed such that it operates on the basis of the direct or inverse piezoelectric effect. Where reference is made herein to an “actuator,” this can always in particular be a MEMS actuator. In the case of microscanners, which in technical terminology are also referred to as “MEMS scanners,” “MEMS mirrors,” or “micromirrors,” or in English in particular as “micro-scanners” or"Micro-scanning mirrors" or "MEMS mirrors" are specifically MEMS, or more precisely, micro-opto-electro-mechanical systems (MOEMS) from the class of micromirror actuators for the dynamic modulation of electromagnetic radiation, particularly visible light. Depending on the design, the modulating movement of an individual mirror can be translational or rotational about at least one axis. In the first case, a phase-shifting effect is achieved, while in the second case, the deflection of the incident electromagnetic radiation is achieved. In the following, microscanners are considered in which the modulating movement of an individual mirror is, at least partly, rotational.In contrast to mirror arrays, where the modulation of incident light occurs via the interaction of a large number of individual small mirrors on a single MEMS component, the modulation in microscanners is typically generated via a single mirror per MEMS component (microscanner).

[0006] Microscanners can therefore be used, in particular, to deflect electromagnetic radiation by modulating the deflection direction of an incident electromagnetic beam using a deflection element (“mirror”). This can be used, in particular, to create a Lissajous projection of the beam into an observation field or projection field. This allows, among other things, imaging and sensory tasks to be solved or display functionalities to be implemented. Furthermore, such microscanners can also be used to advantageously irradiate materials, particularly for their processing. Other possible applications include illuminating or illuminating certain open or closed spaces or spatial areas with electromagnetic radiation, for example, in the context of spotlight applications.

[0007] In many cases, microscanners have a mirror plate ("mirror") as a deflection element, which is suspended laterally on elastically stretchable springs. A distinction is made between single-axis mirrors, which are preferably mounted so that they can rotate around a single axis, and dual-axis and multi-axis mirrors, which allow rotations, particularly rotational oscillations, around a corresponding number of different axes, especially simultaneously.

[0008] A microscanner system for deflecting an electromagnetic beam can thus comprise, in particular, a biaxial microscanner, i.e., a microscanner with two different non-parallel, in particular mutually orthogonal, oscillation axes, or a combination of several individual, in particular two, single-axis microscanners arranged such that the incident beam can be deflected successively by the various individual microscanners of the microscanner system to generate a two-dimensional deflection pattern, in particular a Lissajous pattern. In a microscanner system with a combination of two or three single-axis microscanners, their non-parallel oscillation axes can, in particular, be orthogonal to each other in pairs.

[0009] Specifically in so-called Lissajous microscanners or Lissajous microscanner systems, two non-parallel, particularly orthogonal, oscillation axes are operated simultaneously, particularly in resonance, to generate a trajectory of the radiation deflected by the deflection element in the form of a Lissajous figure. This allows large amplitudes to be achieved in both axes.

[0010] From EP 2 514211 B1, such a deflection device for a projection system for projecting Lissajous figures onto an observation field is known, which is designed to deflect a light beam, in particular a laser beam, about at least a first and a second deflection axis for generating Lissajous figures.

[0011] Electrostatic, electromagnetic, piezoelectric, thermal, and other actuator principles are typically used to drive MEMS, such as small microphones, loudspeakers, or gyroscopes, and especially for microscanners or microscanner systems. Piezoelectric actuators, in particular, utilize the inverse piezoelectric effect to deform a piezoelectric material in an electric field generated by an (electrical) capacitance, depending on the strength of the field. If the field varies over time, particularly due to a variable voltage applied to the capacitance, the resulting field variation results in a variable deformation of the piezo material that can be controlled by the field variation. This deformation can be used as a small motor to drive a mechanical movement, especially in microscanners, an oscillating movement of the mirror.

[0012] However, particularly in the case of resonantly operated, oscillating MEMS components, such as the deflection element in a microscanner, the actuator(s) are often not powerful enough to statically deflect the oscillating MEMS component to a desired target amplitude during operation within a single activation of the actuator(s). To achieve the target deflection, at least one actuator—in the case of a piezo actuator, its piezoelectric material—must be subjected to a periodic alternating voltage whose frequency corresponds, at least to a good approximation, ideally exactly to the mechanical resonance frequency of the oscillating MEMS component.This results in small, but always timely, driving forces that are able, after a certain time, to significantly oscillate the mechanical oscillator formed by the oscillating MEMS component and its suspension or bearing, and thus gradually "charge" it with mechanical energy until the target amplitude is reached (and can possibly be maintained over a longer period of time).

[0013] From an electrical perspective, this drive process in a capacitive actuator, especially a piezo actuator, corresponds to a constant recharging of its capacitor. Especially in the case of a microscanner with a piezoelectric drive, the amplitude of the alternating voltage across the piezo actuator's capacitor significantly influences the resulting scan angle (target amplitude) of the microscanner, or the maximum achievable scan angle in the steady state.

[0014] Particularly when a MEMS is to be used in a device that only has a very limited amount of electrical energy or electrical power available to supply energy during operation, as is usually the case with a battery-operated, particularly portable device (such as a mobile, particularly portable device, e.g. smartphone, or a so-called "wearable", or AR / VR glasses or a MEMS integrated into clothing), energy-efficient drives for the MEMS are advantageous or even necessary in order to enable the longest possible, in particular a sufficiently long, application-related, self-sufficient service life of the devices.

[0015] To reduce the power consumption of the MEMS, it is therefore desirable to make the charge transfer processes on the actuator capacitor as efficient as possible. This minimizes the resulting overall power consumption for driving the MEMS and, in particular, increases the service life of the battery(ies). Furthermore, the voltage level available to the device, especially the battery voltage, is often below the voltage level required by the actuator, so voltage conversion is required to achieve it.

[0016] From FR 2 829 314 A1, a device and a method for controlling an electronically controlled piezo actuator, in particular a piezoelectric stepped fuel injection nozzle, which is controlled by the electronic injection computer of an internal combustion engine in a motor vehicle are known.

[0017] US 2005 / 0029905 A12 discloses a device for controlling a piezoelectric ultrasonic actuator, which is electronically monitored by a computer controlling a DC voltage source. The device comprises a DC-DC converter powered by the voltage source and delivering, at least at the output, a DC voltage between two end terminals, to which at least one arm is connected in parallel. The arm consists of two alternately controllable bridge switches connected in series, and the center point of which is alternately connected to the two output terminals of the DC-DC converter by a load consisting of at least one actuator connected in series with a resonant inductance.

[0018] WO 03 / 038918 A2 discloses a device and a method executable therewith for controlling at least one piezoelectric ultrasonic actuator for ultrasonic piezoelectric injectors for fuel injection in a motor vehicle heat engine. The device is electronically monitored by a control computer and a DC voltage source. The device comprises a DC / AC converter amplifier powered by the DC voltage source, consisting of a bridge or push-pull circuit, whose high-voltage output is connected to an oscillating circuit consisting of the actuator and a resonant inductor. The converter consists of a connection to at least one transformer whose primary winding is connected to the voltage source via at least one controllable switch and whose only secondary winding supplies a high-voltage and high-frequency alternating signal that excites the piezoelectric actuator.

[0019] DE 19854789 A1 describes a method and a device for charging and discharging a piezoelectric element. The method and device are characterized in that the charging current charging the piezoelectric element and the discharging current discharging the piezoelectric element are adjusted taking into account the capacitance of the piezoelectric element. This makes it possible to charge and discharge piezoelectric elements as quickly and extensively as desired under all circumstances.

[0020] DE 10 102 286 A1 discloses a circuit arrangement for controlling piezoelectric materials to generate high voltage and waveforms. It consists of a voltage source, a coil with an electronic switch, and a diode. At least four electronic switches are arranged between two connection points in the form of a bridge circuit. A piezo element is connected between the bridge balancing points, and at least one current sink is arranged parallel to each of the two electronic switches.

[0021] DE 102013 208 870 A1 discloses a circuit for bipolar charge recovery of a piezoelectric or electrostatic drive, in which a piezo actuator is connected in series with a coil. A first terminal of the piezo actuator is connected to a first and a second switch, with a first terminal of the coil being connected to a third and a fourth switch. A second terminal of the piezo actuator is connected to a second terminal of the coil, with the first switch and the third switch being connected to a first terminal of a power supply. The second switch and the fourth switch are connected to a second terminal of the power supply.

[0022] A piezoelectrically driven MEMS pump is known from US 2021 / 0099105 A1.

[0023] It is an object of the present invention to provide an improved circuit for controlling an actuator for energy-efficient and / or space-saving driving of an oscillating movement in a MEMS and a MEMS, in particular a microscanner system, equipped with such a circuit.

[0024] This object is achieved according to the teaching of the independent claims. Various embodiments and developments of the invention are the subject of the dependent claims and / or the following description, which, for the sake of clarity, is structured into sections introduced by a heading. However, this description should not be construed as a limitation of the content of the text sections falling under them or the figures described therein.

[0025] The term "MEMS capacitance," as used herein, refers to an electrical capacitance, in particular a single electrical capacitor, which is at least partially formed as a component of a MEMS actuator and configured to at least temporarily store electrical energy used to operate the actuator for its (partial) conversion into mechanical energy. In particular, such a MEMS capacitance can comprise a capacitor, in particular a plate capacitor, of a piezo actuator with a piezoelectric material as the dielectric. A MEMS capacitance can in particular be formed as an integrated component of a MEMS, in particular such that the electrodes and the dielectric of the MEMS capacitance each form a layer of a layer sequence produced in or on a semiconductor substrate.

[0026] The term "controller," as used herein, refers in particular to a process or a device (control device) configured to carry out such a process, which is designed to control one or more components of a circuit, including in particular one or more of its switching devices, in the sense of an "open-loop" or "closed-loop" control via corresponding signals. It can in particular be or comprise a computer-programmed microcontroller or a hard-wired control circuit. Such a control device can in particular itself be part of the circuit.

[0027] The term "boost converter" (also known as "step-up converter"), as used herein, refers to a form of DC-DC converter configured to convert an input voltage into an output voltage such that the magnitude of the output voltage is greater than the magnitude of the input voltage. This term is not limited to any particular topology or type of such a DC-DC converter.

[0028] The term “switching device” as used herein is to be understood as a circuit or component thereof which is or has at least one circuit or component acting as a switch. In particular, the switching device can have one or more switches. It can be implemented in particular by means of one or more semiconductor components such as transistors or diodes. For example, a single transistor or a CMOS gate can act as a switch if appropriately controlled. A diode can also act as a switch, in particular in the forward direction, if a voltage applied across it is optionally above its threshold voltage (in the forward direction) or below its breakdown voltage (in the reverse direction).

[0029] The term "capacitively unbuffered," as used herein, refers to a current path that is not buffered by a capacitance in the sense of a voltage buffer, in particular not in the sense of a buffer capacitor. Thus, (apart from any parasitic capacitances) there is no capacitive component (in particular a capacitor) for buffering (i.e., supporting) the input voltage or input current of a component or circuit part controlled via the current path, in particular the actuator. In particular, any remaining parasitic capacitance of the current path can be in the range of less than or equal to 40 pF, in particular less than or equal to 10 pF.

[0030] The term "current source," as used herein, refers to an active two-terminal circuit that delivers an electric current at its connection points. A key property is that the strength of this current depends only slightly ("real" current source) or not at all ("ideal" current source) on the electrical voltage at its connection points.

[0031] The term "a resonant frequency related to a permanently closed state of the resonant circuit," as used herein, is understood to mean a resonant frequency of the resonant circuit that it exhibits in the steady state when it is permanently closed, i.e., at least beyond the transient process, i.e., in particular, when it is not interrupted by the first switching device. For an ideal resonant circuit (i.e., when ohmic resistances R are negligibly small), the resonant frequency f0 is: where C is the capacitance and L is the inductance of the resonant circuit. In a real resonant circuit, the resonant frequency is lower due to the ohmic losses in the resistors R, depending on the strength of this damping.

[0032] The term "boost converter," as used herein, refers to a voltage converter of any type and / or topology that generates an output voltage from an input voltage by voltage conversion, or can generate one in at least one operating mode, such that the magnitude of the output voltage is greater than the magnitude of the input voltage. For this purpose, a boost converter can, in particular, comprise one or more boost converters and / or one or more charge pumps.

[0033] The terms "comprises," "includes," "includes," "has," "has," "with," or any other variation thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a method or apparatus that includes or has a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or that are inherent in such a method or apparatus.

[0034] Furthermore, unless explicitly stated to the contrary, "or" refers to an inclusive "or" and not an exclusive "or." For example, a condition A or B is satisfied by one of the following conditions: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

[0035] The terms "a" or "an" as used herein are defined as "one or more." The terms "another" and "another," and any other variations thereof, are defined as "at least one other."

[0036] The term “configured” or “set up” to perform a specific function (and respective variations thereof), as used here, is to be understood that a relevant device or component thereof is already in a design or setting in which it can perform the function or is at least adjustable – i.e. configurable – so that it can perform the function after being set accordingly. The configuration can be carried out, for example, by appropriately setting parameters of a process sequence or of switches or the like for activating or deactivating functionalities or settings. In particular, the device can have a plurality of predetermined configurations or operating modes, such that the configuration can be carried out by selecting one of these configurations or operating modes.

[0037] The terms "first," "second," "third," and similar terms in the specification and claims are used to distinguish between similar or otherwise similarly named elements and not necessarily to describe a sequential, spatial, or chronological order. It is understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments described herein may function in orders other than those described or illustrated herein.

[0038] Circuit with boost converter (“first circuit”)

[0039] A first aspect of the solution presented here relates to a first circuit for controlling an actuator, in particular a MEMS actuator, for driving an oscillating movement of at least one movable component of a microelectromechanical system (MEMS). The first circuit can be used in particular for controlling an actuator for driving a mirror movement in a microscanner system.

[0040] It comprises a boost converter circuit with an inductance (hereinafter referred to as a "booster inductance" to distinguish it from other inductances mentioned below, in particular having one or more coils), an electrical MEMS capacitance, and a switching device controllable by means of a controller. The MEMS capacitance is designed as a component of an actuator in such a way that it forms a component of an electromechanical converter of the actuator, wherein the converter is configured to convert electrical energy stored in the MEMS capacitance into at least one mechanical variable for driving a movement of the actuator (in particular at least one component thereof). The switching device is configured to assume a first circuit configuration depending on the controller and sequentially thereafter, in particular alternating several times with the first circuit configuration, a second circuit configuration.In this case, (i) in the first circuit configuration, a first current path through the booster inductor is enabled to cause an increasing current flow through the booster inductor, fed by a supply voltage, and (ii) in the second circuit configuration, a capacitively unbuffered second current path (apart from possible parasitic capacitances) is enabled between a first pole of the booster inductor and the MEMS capacitance to charge the MEMS capacitance to a first voltage, which is equal to or higher in magnitude than the supply voltage, by means of a current flow fed at least partially by the booster inductor (in particular as a current source). The supply voltage can, in particular, be generated by the circuit itself or supplied to it externally.

[0041] In the first circuit, the electrical energy supplied via the second current path between a first pole of the booster inductance and the MEMS capacitance is available largely undiminished to charge and thus power the MEMS capacitance of the actuator and thus its function by means of a current flow fed at least partially by the booster inductance at a voltage level higher than the supply voltage. The so-called "capacitor paradox" or "two-capacitor paradox" that occurs in conventional boost converters (see Fig. 1 and the accompanying figure description), which theoretically limits efficiency to a maximum of 50% (see https: / / en.wikipedia.org / wiki / Two capacitor paradox), can be avoided here, since no configuration with two capacitors that can be connected in parallel via a switch is required in the voltage amplification path of the boost converter.

[0042] In this way, the first circuit results in a significantly reduced electrical power requirement for controlling the actuator, so that the first circuit including the actuator can be used in particular in devices for which only a very limited amount of electrical energy or electrical power is available for power supply during operation.

[0043] In the following, various exemplary embodiments of the first circuit are first described, which, unless this is expressly excluded or is technically impossible, can be combined with each other as desired and with the other aspects of the present solution described below.

[0044] In some embodiments, the control is unregulated. Consequently, there is no control within the framework of the actuation, but only pure control (in the sense of "open loop") without a control loop. Accordingly, the first circuit can be simplified compared to a regulated actuation since, in particular, no controller and no feedback (control loop) are required and the circuit components required for this can therefore be omitted. This also makes it possible to implement particularly space-saving solution variants. This is possible in particular because during periodic operation, i.e. a periodic alternating change between the two circuit configurations of the switching device, the voltage across the MEMS capacitance can essentially be modeled, i.e. to a good approximation, as a linear function of the period duration or, more precisely, the duration of the first circuit configuration.Thus, even a pure control system without closed-loop control can be sufficient to adjust the voltage across the MEMS capacitance with sufficient precision, thus controlling the actuator with good accuracy. Furthermore, the energy losses associated with closed-loop control are eliminated, allowing the power consumption of the primary circuit to be further reduced and its efficiency to be further increased.

[0045] In some embodiments, the switching device is further configured to repeatedly temporarily disconnect a third current path, in particular depending on the controller, such that the MEMS capacitance can be repeatedly, at least partially, discharged via this third current path in order to generate a supply voltage of the electromechanical converter at the MEMS capacitance whose magnitude varies over time. The continuous switching and the resulting discharging can, in particular, occur periodically. By discharging, a charge state of the MEMS capacitance can be established which leads to a lower voltage across the MEMS capacitance and thus to a correspondingly lower input voltage at the actuator than in the charged charge state (which is achieved during the second configuration of the switching device).This allows the actuator to be switched between at least two states (charged / discharged), which correspond to two different mechanical states of the actuator via electromechanical conversion. An alternating, particularly periodic, change between the two charge states can thus produce a corresponding, particularly periodic, mechanical movement in the actuator, which can be used to drive a movement, particularly an oscillatory movement, in a MEMS (such as a mirror movement, particularly mirror oscillation of a microscanner system).

[0046] In some embodiments, the third current path leads to a buffer capacitor for buffering the supply voltage in order to transfer charge from the MEMS capacitor to the buffer capacitor during its discharge. This allows the charge introduced into the MEMS capacitor during charging to be at least partially recovered and used for a subsequent charging process. In this way, the power consumption of the first circuit can be further reduced, thus further increasing its efficiency. In this variant, the third current path is also referred to as the fourth current path to distinguish it from an alternative current path according to another variant for discharging without charge return or buffering.

[0047] In some embodiments, the switching device is further configured, in particular depending on the controller, to repeatedly and temporarily open a fourth current path between the MEMS capacitance and a second pole of the booster inductance, which pole is electrically opposite to the first pole, during a period in which the second current path is not open, such that the MEMS capacitance is charged to a second voltage with a polarity opposite to the polarity of the first voltage. In this way, bipolar operation is possible in which the polarity across the MEMS capacitance changes, in particular alternately. Accordingly, when using an actuator, such as a piezo actuator, which operates in a polarization-dependent manner, different actuator states can be brought about depending on, in particular in synchronization with, the change in the polarity of the voltage across the MEMS capacitance.By using such a bipolar drive with positive and negative voltages, the power consumption can be halved again, in particular compared to a unipolar drive, using only one positive and one negative voltage, if the same voltage amplitude (V. ma x - V m in).

[0048] In some of these embodiments, the circuit device comprises: (i) a first switch, S1, for switching an electrical connection between the supply voltage and the second pole of the booster inductance; (ii) a second switch, S2, electrically connected to the first pole of the booster inductance, for switching the first current path through or interrupting it; (iii) a third switch, S3, electrically connected to the first pole of the booster inductance, for switching the second current path through or interrupting it; and (iv) a fourth switch, S4, electrically connected to the second pole of the booster inductance and the MEMS capacitance, for switching the fourth current path through or interrupting it. Thus, a bipolar implementation of the first circuit in the aforementioned sense can be achieved in a very efficient, particularly component-saving and thus space- and energy-saving manner using only four switches in the switching device.

[0049] The term “electrically connected” here means a direct electrical connection without intermediate circuit components (i.e., components) or an indirect connection via one or more intermediate circuit components (i.e., components), e.g., resistors, whereby the connection may, in particular, have the characteristic of a (small) ohmic resistance R, e.g., with R < 10 Q.

[0050] In some embodiments, the circuit further comprises a fifth switch, S5, for switching on or off a current path between the second pole of the inductance and ground.

[0051] In particular, according to some of the embodiments, the controller can be configured to put the circuit device into different switching states step by step according to the following sequence, wherein the sequence is run through at least once, preferably several times, in particular periodically:

[0052] (a) Si and S2 closed, S3 and S4 open;

[0053] (b) S1 and S3 closed, S2 and S4 open;

[0054] (c) S2 and S3 closed, S1 and S4 open;

[0055] (d) S1 and S2 closed, S3 and S4 open;

[0056] (e) S2 and S4 closed, S1 and S3 open;

[0057] (f) S2 and S3 closed, S1 and S4 open.

[0058] In some of these embodiments, the first circuit has a buffer capacitance, in particular a capacitor, for capacitive buffering of the supply voltage. The sequence also has a further switching state (b1), which lies between the switching states (b) and (c) and is characterized in that S1 and S4 are closed and S2 and S3 are open. Thus, when the MEMS capacitance is discharged, charge can be transferred from the MEMS capacitance to the buffer capacitance in order to be available for another switching cycle without the corresponding amount of charge having to be provided by the supply voltage source. In this way, the power consumption is also reduced and the efficiency of the (bipolar) first circuit is further increased.

[0059] In some embodiments, the sequence additionally (to states (a) to (f) and optionally also to (b1)) has a further switching state (b2) which lies between switching states (b) and (c) and is characterized in that S2 and S4 are closed and S1 and S3 are open in it. Thus, when the MEMS capacitance is discharged, charge from the MEMS capacitance can be conducted through the booster inductance in order to at least partially charge it with energy (in its magnetic field) for a further switching cycle, without the energy charge resulting from this current having to be subsequently made available to the booster inductance from the supply voltage source instead. In this way, power consumption can also be reduced and the efficiency of the (bipolar) first circuit can be further increased.

[0060] In some embodiments, the sequence additionally comprises a further switching state (e1) that follows the switching state (g) and precedes the switching state (f) and is characterized in that S4 and S5 are closed and S1, S2, and S3 are open. This enables energy recovery even from negative voltages across the MEMS capacitance C M (following switching state (e1)).

[0061] In some embodiments, the controller (more precisely the corresponding control device) has a multi-stage delay chain and a multiplexer for tapping the respective output signals of the stages of the delay chain in a time-staggered manner in order to generate a time-variable control signal for controlling the switching device. The delay elements of the delay chain can in particular be designed from standard cells or as specially defined (“customized”) analog components or circuit parts, wherein the required delay of the individual stages can be calculated from the quotient of the maximum necessary switch-on time (duration of the first circuit configuration) and the number of stages. The analog design would have the advantage that by setting a driver current for the delay elements (current control, cf.“current-starved” inverter), the delay time of each individual delay element can be adjusted, and thus could be optimally adjusted for any MEMS capacitors (with different capacitance values ​​and output voltages).

[0062] In particular, according to some of these embodiments, the switching device can be controlled by means of the control signal in such a way that a switching between the first switching configuration and the second switching configuration, or vice versa, can be effected by means of the control signal.

[0063] In this way, a control for the circuit, in particular for its switching device, can be implemented in a simple and energy-efficient manner.

[0064] Circuit with a pauseable efficiency-optimized oscillating circuit

[0065] ("second circuit") A second aspect of the solution relates to a second circuit for controlling an actuator, in particular a MEMS actuator, for driving an oscillatory movement of a mass element in a MEMS. The control can, in particular, be controlled or uncontrolled.

[0066] This second circuit shows:

[0067] (i) an electrical resonant circuit, comprising: a first inductance (hereinafter referred to as "resonant circuit inductance" to distinguish it from other inductances mentioned below, in particular comprising one or more coils), a first electrical MEMS capacitance, a charging connection for temporarily supplying electrical energy from a power supply external to the resonant circuit to temporarily recharge the MEMS capacitance; and a first switching device (hereinafter also referred to as "resonant circuit switch"), which can be controlled, in particular by means of a control signal, for selectively interrupting or closing the resonant circuit depending on a control of the first switching device; and a resonant frequency related to a permanently closed state of the resonant circuit; and

[0068] (ii) a controller for controlling the first switching device.

[0069] The first inductance is arranged in the resonant circuit in such a way that it lies in a current path of the resonant circuit through which current flows and through the first MEMS capacitance both during the recharging of the first MEMS capacitance during an electrical oscillation of the resonant circuit in the closed state of the first switching device and during the temporary recharging of the first MEMS capacitance in the interrupted state of the first switching device.

[0070] The controller is configured to temporarily place the first switching device, during a respective oscillation period of the oscillating circuit running in the closed state of the first switching device, by means of a corresponding control, in particular for a specific portion of the oscillation period, at a time at which the voltage across the first MEMS capacitance reaches a maximum in terms of magnitude within the respective oscillation period, into a state in which it interrupts the oscillating circuit, so that an actual oscillation frequency of the oscillating circuit is effected which is lower than the resonance frequency.

[0071] The term "charging connection" or "charging connection point," as used herein, can be understood as any type of connection of the resonant circuit to a power supply external to the resonant circuit, via which energy is supplied to the resonant circuit to power its oscillation. In particular, this connection can be configured via a direct electrical connection, inductively, or capacitively, in order to feed energy into the resonant circuit in the form of electrical and / or magnetic energy.

[0072] With the second circuit, the effective oscillation frequency of the resonant circuit can be variably adjusted using the first switching device. Temporarily interrupting the resonant circuit causes a corresponding pause in the electrical oscillation in the resonant circuit (a "paused resonant circuit"), resulting in an effective oscillation frequency below the resonant frequency of the resonant circuit (in a permanently closed state).

[0073] Thus, the lower effective oscillation frequency can be achieved without having to increase the values ​​of the (first) MEMS capacitance C or the (first) inductance L according to relationship (1) (see section “Terminology” above). If oscillating components of a MEMS cannot or should not exceed a certain upper limit frequency with regard to their oscillation frequency, then effective oscillation frequencies can be achieved, in particular also variably adjusted, at or below the limit frequency using the above-mentioned concept of the pauseable oscillating circuit, even though values ​​for C and L are used which, according to relationship (1), result in a resonance frequency f0 above the limit frequency. In particular, smaller and thus space-saving inductances L and / or MEMS capacitances (especially capacitive loads) C can be used, thus reducing or keeping the space required for the circuit to control the actuator small.

[0074] The possibility of being able to variably adjust the effective oscillation frequency for given values ​​for C and L using the control by means of the first switching device can also be advantageously used to compensate for component tolerances, in particular in the context of mass production.

[0075] The energy in the oscillating circuit is thus, at least for the most part, stored in the MEMS capacitor in the form of electrical energy during the pause in the oscillation caused by the interruption, until the oscillation is resumed by closing the oscillating circuit. This storage during the pause of the oscillating circuit can be largely maintained over a long period of time, at least with a low-loss MEMS capacitor, so that a correspondingly wide range of values ​​for the variable, adjustable effective oscillation frequency of the oscillating circuit can be achieved without significant (particularly application-specific, unacceptable) energy losses.

[0076] Furthermore, the energy temporarily stored in the first inductor is used or co-used to recharge the MEMS capacitor and thus operate the actuator powered by it, allowing for particularly low-consumption (periodic) control of the actuator. Due to its small footprint and high energy efficiency, the circuit is particularly suitable for use in mobile applications, especially in portable devices with small dimensions (e.g., wearables).

[0077] Since the first inductor is arranged in the oscillating circuit in such a way that it is located in a current path of the oscillating circuit through which current flows and through the MEMS capacitance, not only during the recharging of the MEMS capacitance during electrical oscillation of the oscillating circuit, but also during temporary recharging of the MEMS capacitance, energy is also temporarily stored in the first inductor during recharging. The temporarily stored energy corresponds, to a first approximation, to the energy that would normally remain unused during a recharging process without the use of an inductor due to the capacitor paradox. After recharging begins, energy builds up in the first inductor in the form of a magnetic field immediately after the charging terminal is connected to the power supply circuit until the voltage level at the output of the power supply circuit and the first MEMS capacitance is in equilibrium.This is where the recharging process would normally end without the use of an inductor. However, the energy temporarily stored in the inductor is now dissipated again, causing the voltage level across the first MEMS capacitance to rise above that of the power supply circuit until the energy in the first inductor is completely dissipated. Immediately opening the current path between the power supply circuit and the first MEMS capacitance after the charging process / current flow has ended prevents the additional energy stored in the first MEMS capacitance from accidentally flowing back into the power supply circuit due to the lower voltage level there. This additional energy or charge is therefore also available for the subsequent oscillation of the resonant circuit, i.e. when the first switching device is closed again. This further optimizes the efficiency of the (second) circuit.

[0078] Various exemplary embodiments of the second circuit are described below, each of which, unless expressly excluded or technically impossible, can be combined with each other as well as with the other aspects of the solution described herein.

[0079] In some embodiments, the MEMS capacitance is configured as a component of the actuator such that it forms part of an electromechanical transducer of the actuator. The transducer is configured to convert electrical energy stored in the MEMS capacitance into at least one mechanical variable for driving a movement of the actuator. The actuator can in particular be a MEMS actuator, e.g., a piezo actuator. The voltage drop across the MEMS capacitance as part of the electrical oscillation in the resonant circuit can thus be made available to the actuator directly and without further capacitive buffering, so that a high degree of efficiency of the second circuit can be achieved.

[0080] In some embodiments, the control circuit can be configured, in particular, to place the first switching device into a state in which it interrupts the resonant circuit during a respective oscillation period of the resonant circuit when the voltage across the MEMS capacitance reaches a maximum within the oscillation period after a charge reversal of the MEMS capacitance occurs during the oscillation period. This ensures that the maximum available energy is used to recharge the capacitor, and the resonant circuit optimally reduces the total power consumption.

[0081] This can also ensure that the current in the inductance has reached a minimum or approaches zero, and thus no voltage peaks occur through the inductance. In some embodiments, in addition to the MEMS capacitance, the resonant circuit has a separately formed second MEMS capacitance with the same or different capacitance value (with respect to the first MEMS capacitance). The MEMS capacitance and the second MEMS capacitance are interconnected in the resonant circuit such that a first pole of the MEMS capacitance is electrically connected to a first pole of the second MEMS capacitance via at least one switch of the first switching device and the resonant circuit inductance, and the respective second poles of the two MEMS capacitances are electrically connected to one another such that they are held at the same (constant or time-variable) electrical potential during operation of the resonant circuit.

[0082] In this way, voltages complementary to each other in terms of their sign can be tapped from the two MEMS capacitors. To achieve a desired differential voltage between the poles of this combination of MEMS capacitors that are furthest apart in potential, it is sufficient to charge the two individual MEMS capacitors to a smaller voltage, since the two voltages add together. The aforementioned principle of the pauseable oscillating circuit remains, at least essentially, unaffected. Such a configuration can be used advantageously, in particular, to achieve a differential drive of an oscillatory MEMS, in particular a drive for the oscillating movement of a deflection element of a microscanner.

[0083] Such a drive is particularly advantageous for achieving the most uniform, jerk-free oscillation possible of the microscanner's deflection element (mirror) and / or for reducing power consumption. The second MEMS capacitor can then also be designed as a MEMS capacitor of a (particularly second) actuator and thereby form part of a converter configured to convert electrical energy stored in the second MEMS capacitor into at least one mechanical variable for driving a movement of this actuator.

[0084] In some embodiments, the second circuit further comprises a power supply circuit for temporarily supplying electrical energy to the resonant circuit via the charging connection. This allows for longer, particularly continuous, operation of the MEMS, despite losses that are unavoidable in reality (e.g., due to heat generation in parasitic, particularly ohmic, resistors of the actual circuit), radiation from electromagnetic waves at higher frequencies, or friction in the MEMS or air friction from moving parts of the MEMS), in which the power supply circuit can at least partially compensate for the energy losses. This allows the energy in the resonant circuit to be maintained or at least its dissipation to be slowed down.

[0085] In some embodiments, the power supply circuit comprises a second switching device configured, depending on a control, in particular by the controller, to temporarily connect a first feed point for electrical energy to the charging terminal of the resonant circuit in order to supply the resonant circuit with electrical energy supplied or capable of being supplied at the first feed point. This allows the energy supply to the resonant circuit to be precisely adjusted based on the control, in particular to initially oscillate it or to compensate for its energy losses during subsequent operation, and in particular to optimize its temporal progression.

[0086] Specifically, according to some embodiments, the second circuit can be configured, in particular by appropriate control, to temporarily close the second switching device (i) in a respective oscillation period of the resonant circuit when the voltage across the MEMS capacitance reaches a maximum within the oscillation period and has the same polarity as a voltage provided by the power supply circuit at the first feed point. The MEMS capacitance is recharged accordingly when it is currently maximally charged within the scope of the electrical oscillation already occurring in the resonant circuit, so that only an additional charge needs to be supplied by the power supply circuit to replenish the charge of the MEMS capacitance to a target voltage.In the aforementioned case that a second MEMS capacitance is also provided in the resonant circuit, this can be implemented accordingly there, taking into account the opposite polarity. The second circuit can (ii), in particular additionally, be configured, in particular by appropriate control, to open the second switching device in a respective oscillation period of the resonant circuit as soon as, during the temporary recharging of the first MEMS capacitance in the closed state of the second switching device, the current flow through the first inductance has dropped to a specific value corresponding to a maximum of 10% (in particular a maximum of 5% or a maximum of 1%) of its maximum value previously reached during the recharging. The value can in particular be determined such that it corresponds to a complete cessation of the current flow (i.e. to zero amperes).In particular, in conjunction with the time for closing the second switching device determined above under point (i), an optimised operation of the circuit can be achieved, particularly with regard to its energy efficiency.

[0087] In some embodiments, the second circuit is configured to temporarily connect the first feed point to the charging terminal of the resonant circuit during the respective oscillation period by means of the second switching device at a time before which two consecutive charge reversal processes of the MEMS capacitance of the resonant circuit have already occurred during the oscillation period since the first feed point was last temporarily connected to the resonant circuit by means of the second switching device. This can be particularly advantageous with regard to efficient and compact implementation, because it is then sufficient to provide only a single high-voltage source, optionally with positive or negative polarity of the output voltage. In particular, if such a high-voltage source has conventional coil-based boost converters for voltage increase, a coil can be saved on a circuit board.This can be an advantage, especially when implementing the circuit using an integrated circuit (IC, e.g. ASIC), where hardly any additional IC-external components are required.

[0088] In some embodiments, the second circuit is configurable such that the amount of electrical energy supplied to the oscillating circuit via the charging terminal from the power supply circuit in at least one oscillation period is adjustable. This can be achieved in various ways. For example, the duration of the recharging can be varied over time, the current intensity of the recharging current can be adjusted (in particular by adjusting the voltage driving it), or the frequency at which recharging occurs can be adjusted, for example, such that recharging only occurs every mth period of the electrical oscillation in the oscillating circuit, where m > 0 is a natural number.

[0089] The second circuit can in particular be configured such that the amount of electrical energy supplied to the oscillating circuit via the charging connection from the power supply circuit can be set individually for each oscillation period (e.g. by means of a control) or globally for all m-th oscillation periods, where m > 0 is again a natural number.

[0090] In some embodiments, the power supply circuit comprises an inductive coupling device, in particular an inductively coupled pair of coils, for temporarily inductively feeding electrical energy into the resonant circuit. This can be provided in addition to or as an alternative to a wired power supply to the resonant circuit. Thus, the power supply circuit can be galvanically decoupled from the resonant circuit, at least if a wired power supply is no longer available.

[0091] In some embodiments, the power supply circuit comprises a third switching device which is configured, depending on a control, to temporarily connect a second feed point for electrical energy to the resonant circuit in order to supply the resonant circuit with electrical energy supplied or supplyable at the second feed point in such a way that the polarity of a first electrical supply voltage applied to the first feed point is opposite to the polarity of a second electrical supply voltage applied at the same time to the second feed point, thus enabling a bipolar energy supply to the resonant circuit.

[0092] The generation and / or feeding of the second supply voltage can, in particular, correspond to one or more of the supply voltages supplied to the first feed-in point, in particular be identical thereto (except for the different polarity), in accordance with one or more of the methods described herein.

[0093] Combined circuit with boost converter and pauseable oscillator circuit

[0094] The aforementioned principles of the first circuit and the second circuit can also be used in combination within the solution.

[0095] According to a first approach, such a combined circuit is obtained in particular by further providing, starting from the first circuit (in particular starting from one of its embodiments described herein), a resonant circuit having a capacitance defined at least partially by the MEMS capacitance, a resonant circuit inductance, and a controllable second switching device for selectively interrupting or closing the resonant circuit depending on a control of the second switching device. The resonant circuit has a resonant frequency related to a permanently closed state of the resonant circuit.The first inductance is arranged in the resonant circuit such that, both during the recharging of the MEMS capacitance during electrical oscillation of the resonant circuit in the closed state of the second switching device and during the temporary recharging of the MEMS capacitance in the interrupted state of the second switching device, it is located in a current path of the resonant circuit through which current flows and through the MEMS capacitance. Furthermore, the controller is further configured to control the second switching device such that it temporarily opens the second switching device for a specific portion of a respective oscillation period of the resonant circuit, thereby interrupting the resonant circuit and thus causing an actual oscillation frequency of the resonant circuit that is lower than the resonant frequency.

[0096] The circuit may in particular comprise any, in particular one or more of the embodiments of the second circuit described herein.

[0097] The electrical oscillations generated in the oscillating circuit thus lead to a time-varying, in particular alternating, charge and thus voltage of the MEMS capacitance, so that the mechanical variable for driving a movement of the actuator, to which the MEMS capacitance belongs, also varies accordingly.

[0098] Such a combined circuit also results, according to a second approach, in particular by starting from the second circuit with a power supply circuit, this power supply circuit having a boost converter configured to convert an input voltage applied to the feed-in point into a higher-magnitude output voltage in order to supply the resonant circuit with electrical energy based on this output voltage when the second switching device is in a state in which it temporarily electrically connects the feed-in point to the resonant circuit. In this way, a high-voltage source can be dispensed with, and instead, only a low-voltage source can be used to provide a supply voltage for the second circuit.The boost converter may in particular comprise a boost converter circuit according to the first circuit, wherein the resonant circuit capacitance is formed at least partially by the MEMS capacitance of the boost converter circuit.

[0099] The circuit can, in particular in the case of more than one feed-in point, each feed-in point individually or equally, have each, in particular one or more, of the embodiments of the boost converter circuit described herein from the first circuit as a boost converter circuit.

[0100] MEMS, in particular a microscanner system. A third aspect of the present solution relates to a MEMS comprising: (i) a mass element configured to oscillate; (ii) an actuator for driving an oscillating movement of the mass element; and (iii) a circuit according to the first aspect or the second aspect or a circuit combined thereof, in each case for controlling the actuator such that it is thereby caused to move the oscillatable mass element in an oscillating movement.

[0101] The MEMS capacitance is designed as a component of the actuator in such a way that it itself forms a component of an electro-mechanical transducer of the actuator, and the transducer is configured to convert electrical energy stored in the MEMS capacitance into at least one mechanical variable for driving a movement of the actuator in order to thereby drive the oscillatory movement of the mass element.

[0102] In some embodiments, the MEMS comprises a microscanner system, and the mass element is configured as an oscillating deflection element of the microscanner system for deflecting electromagnetic radiation incident on the deflection element. This allows for a particularly energy-efficient drive of the movement, in particular of the deflection element, especially for scanning an electromagnetic beam (e.g., a laser beam).

[0103] The features and advantages explained with regard to the first and second aspects of the solution also apply accordingly to the microscanner system according to the third aspect of the solution.

[0104] Further advantages, features and possible applications of the present solution will become apparent from the following detailed description in conjunction with the figures.

[0105] It shows:

[0106] Fig. 1 as a starting point for the explanation of the first circuit from Fig. 2A: a conventional circuit for controlling a capacitive actuator with a regulated boost converter;

[0107] Fig. 2A shows a first exemplary embodiment of the first circuit that enables unipolar control of the actuator; Fig. 2B shows a comparison of the circuits from Figs. 1 and 2A;

[0108] Fig. 3 is a diagram showing a temporal current curve through the inductance of the circuit of Fig. 2A / 2B during its operation, while the magnetic energy is built up in the inductance;

[0109] Fig. 4 shows an exemplary embodiment of a control device for controlling a first circuit, in particular according to Fig. 2A.

[0110] Fig. 5 shows a second exemplary embodiment of the first circuit which enables bipolar control of the actuator;

[0111] Fig. 6 shows an exemplary time profile of the configuration of the switching device of the circuit from Fig. 5, in particular the switching states of its individual switches; and

[0112] Fig. 7 as a starting point for the explanation of the second circuit from Fig. 8: a conventional circuit for controlling a MEMS actuator for driving an oscillating MEMS, in which a recharging of a MEMS capacitance of the MEMS actuator is carried out by means of a half-bridge using two opposite-polarity supply voltages;

[0113] Fig. 8 shows a first exemplary embodiment of the second circuit, with an efficiency-optimized, pauseable resonant circuit and with a high-voltage source for providing a supply voltage for the circuit;

[0114] Fig. 9 is a qualitative representation of the voltage curves at the MEMS capacitance of the resonant circuit and the charging current to be supplied by the high-voltage source in the circuit of Fig. 8;

[0115] Fig. 9A is an enlarged view of the voltage and current curves at the MEMS capacitance of the circuit of Fig. 8 during the recharging process;

[0116] Fig. 9B illustrates special effects of the circuit from Fig. 8 based on a comparison of Fig. 9A with Fig. 9B: an enlarged view of the voltage and current curves at the MEMS capacitance during the recharging process in an exemplary modification of the circuit from Fig. 8, in which the resonant circuit inductance in the resonant circuit is arranged outside a recharging circuit for the resonant circuit; Fig. 10 shows a second exemplary embodiment of the second circuit with a pauseable resonant circuit and with a high-voltage source inductively coupled to the resonant circuit via a coupled pair of coils for providing a supply voltage for the circuit;

[0117] Fig. 11 shows a third exemplary embodiment of the second circuit with a pauseable resonant circuit and with a resonant circuit capacitance divided between two separate MEMS capacitances;

[0118] Fig. 12 shows a first exemplary embodiment of a circuit in which the concepts of the first circuit and the second circuit are combined to form a circuit with a unipolar boost converter and a pauseable resonant circuit;

[0119] Fig. 13 shows a second exemplary (bipolar) embodiment of a circuit in which the concepts of the first circuit and the second circuit are combined to form a circuit with a bipolar boost converter and a pauseable resonant circuit; and

[0120] Fig. 14 shows a third exemplary (bipolar) embodiment of a circuit in which the concepts of the first circuit and the second circuit are combined to form a circuit for differential and bipolar driving of a MEMS actuator.

[0121] Fig. 15 shows an exemplary embodiment of a MEMS, here specifically as a microscanner.

[0122] In the figures, like reference numerals generally designate like, similar, or corresponding elements (except in some cases when naming switching devices). Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are reproduced in such a way that their function and general purpose will be understood by those skilled in the art. Connections and couplings between functional units and elements shown in the figures can, unless expressly stated otherwise, also be implemented as indirect connections or couplings. The control or control device can, in particular, be implemented using hardware, software, or a combination of hardware and software.

[0123] Exemplary embodiments of the first circuit The following are explanations of exemplary embodiments of the first circuit, starting with the conventional circuit 100 from Fig. 1:

[0124] The circuit 100 of Fig. 1 corresponds to a typical design of an asynchronous boost converter (DC / DC converter) from the prior art and is explained here for reference purposes, in particular to identify important differences compared to circuits according to the solution.

[0125] A voltage source provides a supply voltage U v as a DC voltage and thus feeds an inductance (coil) L when a circuit is closed by the inductances. The resistance R L represents the ohmic resistance of the inductance in the sense of an equivalent circuit diagram and is not relevant for the further discussion of the circuit(s).

[0126] In a first phase of the circuit's operation, the circuit is closed by the inductance L by switching the field-effect transistor T on. This is done via a regulator Reg, which controls the transistor T via its gate. Due to the current flowing through the inductance L, it builds up a magnetic field in which the supply voltage U v provided energy is stored (in the form of magnetic energy).

[0127] If, in a second phase, the transistor T is switched off by the regulator Reg, the inductance L attempts to maintain its magnetic flux according to Lenz's law or the law of induction despite the interruption of the previous circuit by inducing a voltage, so that the current generated thereby creates a magnetic field that counteracts the change in the magnetic flux. The induced voltage leads in particular to the diode D being switched in the forward direction above its threshold voltage and the current generated from the magnetic field of the inductance L (at least proportionally in addition to the supply voltage Uv) can flow into the buffer capacitor C, so that an output voltage U A across the buffer capacitance C. The diode therefore acts like a switch.

[0128] The generation of the output voltage U Ais controlled by a control loop with a voltage divider consisting of resistors Ri and R2 and an operational amplifier OP, whose output is electrically connected to an input of the regulator Reg to close the control loop. To control the regulator Reg, the voltage at the center tap of the voltage divider is compared to a fixed reference voltage V using the operational amplifier OP. re f is compared and, depending on the result of the comparison, a variable frequency or a variable duty cycle (alternative German terms are "Tastgrad" and "Aussteuergrad") of an output signal of the controller Reg is determined, with which the transistor T is controlled. In this way, the output voltage U A at the buffer capacitor C to a substantially constant value, which depends in particular on the reference voltage V ref depends.

[0129] The output voltage U Acan now be used as a driver voltage to enable an electrical connection to a MEMS actuator by closing a switch Si in order to drive it. The MEMS actuator can - as shown - in particular have a MEMS capacitance C M and in particular be a piezo actuator in which the MEMS capacitance CM acts as a piezo element together with a piezo material arranged between its two opposite-pole electrodes. By means of a capacitor arranged parallel to the MEMS capacitance C M By switching on the switch S2, the MEMS capacitance CM can be discharged again, in particular to 0 V. By controlling the switches Si and S2 accordingly, an excitation frequency for the MEMS actuator can be set with which the MEMS capacitance C Moscillates back and forth between a charged and an uncharged state, thus causing the MEMS actuator to oscillate mechanically, which in turn can be used to drive a mechanical movement of another component. The switches Si and S2 can also be implemented using transistors.

[0130] The high voltage that can be generated by circuit 100 can be up to 200 V at a frequency of up to 100 kHz, so that switches Si and S2 must be designed accordingly as high-voltage switches. If the buffer capacitance C is connected to a constant voltage source for the supply voltage U vHowever, if the capacitor is charged, as is the case with circuit 100, the theoretical efficiency is a maximum of only 50% due to the feeding of the MEMS capacitance CM from the buffer capacitance C and the resulting occurrence of the so-called "capacitor paradox." The remaining part of the applied energy is dissipated as power loss, particularly in the resistance of the (high-voltage) switch S1, the ohmic resistance RL of the coil, and the supply lines.

[0131] Typical properties of such a conventional circuit 100 are therefore:

[0132] - Low efficiency due to the capacitor paradox - Permanent switching of the transistor T, to supply the average consumed charge for the periodic recharging of the M EMS capacitance C M (Leads to higher overall power consumption due to switching losses and can also cause noise in other circuit components)

[0133] - Relatively high power consumption due to the permanent regulation of the output voltage

[0134] - Large system volume (requires output voltage regulation and a high-voltage switch Si , which leads to high regulation and switching losses)

[0135] - High overall circuit complexity

[0136] - Requires analog components to ensure the control stability of the boost converter

[0137] - Requires a high-voltage switch Si, which is complex to construct (e.g. bootstrap circuit or similar) and is therefore not energy efficient.

[0138] Fig. 2A, on the other hand, shows a first exemplary embodiment 200 of a first circuit with which one or more of the aforementioned disadvantages can be reduced or even avoided. Fig. 2B illustrates, within the context of a comparison 205 of circuits 100 and 200, which circuit components can be eliminated in circuit 200.

[0139] In contrast to circuit 100, the transistor T is no longer controlled by a regulator (closed-loop) but by a controller (open-loop) Ctrl by means of a control signal Q and the charging current does not flow into a buffer capacitance C, from which the MEMS capacitance CM is subsequently charged, but rather it flows directly without capacitive buffering into the MEMS capacitance CM of the actuator, in particular MEMS actuator, in order to generate a drive voltage U M above the MEMS capacitance C M to build.

[0140] The MEMS capacitance C Mis designed as a component of the actuator, so that it forms a component of an electro-mechanical transducer of the actuator, wherein the transducer is configured to contain in the MEMS capacitance C Mto convert stored electrical energy into at least one mechanical variable for driving a movement of the actuator. The actuator can in particular be a piezo actuator or piezo element, in which a piezoelectric material is arranged between the electrodes of the MEMS capacitance CM SO such that, upon the occurrence of an electrical voltage UM between the electrodes, it lies in the associated electric field and deforms according to the inverse piezoelectric effect, thereby converting electrical energy into mechanical energy. The circuit 200 has a switching device, which includes the transistor T, the diode D, and the switch S2. Optionally, the further switch S2 already known from Fig. 1 can be present in order to optionally discharge the MEMS capacitance CM directly to ground, in particular after energy recovery into a supply-side buffer capacitor C B. Assuming that the supply voltage is x, e.g. 3V, then using the switch S2, an additional voltage change of x could be achieved across the MEMS capacitance C M However, switch S2 should only be closed briefly to avoid charging the inductance L by a current fed from the supply voltage Uv. Alternatively, the supply voltage Uv can be used instead during the discharge of the MEMS capacitance C M can be decoupled from the inductance L by an optional additional switch (not shown).

[0141] As can be seen particularly with regard to Fig. 2B, the circuit 200 has a significantly lower complexity compared to the circuit 100 with a significantly higher efficiency, in particular due to the avoidance of the (high-voltage) switch Si, the buffer capacitor C and the associated capacitor paradox as well as the control including the associated control loop with the voltage divider Ri, R2, the operational amplifier OP, the regulator Reg and its switching frequency generation function for the transistor T.

[0142] The operation of the circuit in Fig. 2A / 2B can be described as follows:

[0143] If the transistor T is switched through by means of a corresponding control by the control Ctrl (“first” circuit configuration), a first current path through the inductance L is thereby released in order to supply a voltage U vto cause an increasing current flow through the inductance L. The current through the inductance L increases (initially approximately linearly). The resistance RL represents (in the sense of an equivalent circuit) the winding resistance of the inductance L (coil).

[0144] After time t L the transistor T is switched off (“second” circuit configuration), so that a capacitively unbuffered second current path is opened between a first pole of the inductance L and the MEMS capacitance CM, via which the MEMS capacitance CM is charged directly by means of a current flow fed at least partially by the inductance L through the then forward-biased diode D to a first voltage, which is equal to or higher than the supply voltage Uv. In the process, the magnetic energy stored in the inductance L is dissipated and converted into the magnetic energy stored in the MEMS capacitance C Mbuilding up electrical energy is directly converted.

[0145] If we consider the time course 300 of the current flowing through the inductance L during the first circuit configuration, this can be given by the following relationship, as illustrated in Fig. 3:

[0146] Here, R corresponds to the sum of the parasitic series resistances of the inductance L and the path resistance of the switched-on transistor T (the intermediate paths are idealized here as having only a negligible resistance) and U v is again the supply voltage, which also corresponds to the voltage drop across this series circuit. I o is a maximum current (limit current) to which the charging current l(t) asymptotically approaches over time. The limit current is calculated as:

[0147] I o = (3)

[0148] To simplify equation (2), it can be linearized at the origin at time t = 0 by its derivative:

[0149] At time t = 0 this relationship simplifies to:

[0150] By inserting (3) into (5) we obtain with the linearization at time t L , at which the second circuit configuration is switched, for the current I through the inductance:

[0151] The stored energy E in the inductance L at time t = t L results in: EM = -2U t L ) (7)

[0152] Correspondingly, the energy E M the MEMS capacity C M , where U M which is above C M The capacitor voltage is:

[0153] If we equate the two equations (7) and (8) and replace / (t L) by the expression from equation (6), the voltage U M , to which the MEMS capacitance C M is charged due to the energy transfer from the inductance L, to:

[0154] This is how the voltage U scales M above the MEMS capacitance C M in good approximation proportional to the time period in which the transistor is switched on, also proportional to the supply voltage U v , and root-shaped with the inverse of values ​​for the inductance L and the MEMS capacitance C MThis approximation is particularly valid when the sum of all parasitic resistances (e.g., series resistance of the coil, series resistance of the MEMS capacitor CM, and track resistances) is comparatively small in absolute terms. Otherwise, these would ultimately lead to a lower charging voltage of the MEMS capacitor CM, since the energy stored in the coil is not only transferred to the MEMS capacitor but also partially converted into heat.

[0155] The voltage U M above the MEMS capacitance C M can thus at least approximately be described as a linear function of the time period t L Since all components within the circuit, especially L and C M , are known, the output voltage U M solely via the controllable switch-on time t Lof the transistor T. This allows the regulator Reg to be omitted, which leads to a significant simplification of the circuit 200 compared to the conventional circuit 100.

[0156] The switch S2 for discharging the MEMS capacitance C M can either be connected in parallel to CM (third current path) as shown in Fig. 1 or - as shown - in a fourth current path leading back to the supply voltage source (then referred to as switch S2 to indicate this different arrangement). The supply voltage source (but not the second current path between inductance and MEMS capacitance C M ) is connected via a buffer capacitor C B buffered, in which the charges flowing back through switch S2 when CM is discharged can be temporarily stored and reused for another activation cycle of the actuator. This further increases the efficiency of circuit 200.

[0157] Fig. 4 shows an exemplary embodiment 400 of the control device Ctrl for controlling a circuit according to the solution, in particular according to Fig. 2A. It serves to control the switch-on time or duration of the transistor T and thus also the output voltage UM ZU and is implemented with a delay chain 405 with several delay elements 405-1, ..., 405-n connected in series, a multiplexer 410 and a flip-flop.

[0158] In this example, n = 255 is selected. The delay elements 405-1, ... , 405-255 can be implemented using standard cells or customized, particularly application-specific, analog circuitry. The required delay time of each individual delay element can be calculated from the quotient of the maximum required turn-on time and the number of delay elements. For simplicity, the same delay time of 8 ns was selected for all delay elements 405-1, ... , 405-255 in this example.

[0159] An analog design has the particular advantage that the delay time of each individual delay element can be individually adjusted via a current control and can thus be optimally adjusted for any MEMS capacitors (with different capacitance values ​​and output voltages).

[0160] Each clock pulse of a clock signal CLK applied to the control device 400 is thus divided evenly according to the number of delay elements 405-1, ..., 405-255.

[0161] By applying a selection signal SEL to the multiplexer 410, the desired stage of the delay chain can be selected, which is output to the R input of the RS flip-flop 415. When the clock signal CLK is at the "1" or "high" level, the output signal Q (e.g., with the "1" level) switches the transistor T on. However, as soon as the output signal of the multiplexer 410 subsequently changes according to the selected delay (e.g., to the "1" level), the output signal Q changes (e.g., to the "0" level) in such a way that the transistor T is blocked. By selecting the delay using the selection signal SEL, the time period t Lduring which the inductance L is “charged” with magnetic energy. Since the level of the voltage U M over MEMS capacity C M again depends on the time period t L depends, the level of the voltage U can be determined using the selection signal SEL. M and thus control the activity of the actuator.

[0162] In Fig. 5, a circuit 500 for bipolar control of an actuator with a controlled boost converter is shown as a second exemplary embodiment.

[0163] In the circuit 500, which represents a modification or further development of the circuit 200, the switching device is further configured to be repeatedly and temporarily switched on in a period of time in which the voltage between a first pole of the inductance L and the MEMS capacitance C Mlying second current path is not enabled, to enable a fourth current path between the MEMS capacitance and a second pole P2 of the inductance L which is electrically opposite to the first pole Pi in such a way that the MEMS capacitance C M is charged to a second voltage with a polarity opposite to the polarity of the first voltage.

[0164] For this purpose, the switching device of circuit 500 has four switches Si to S4. The switch Si is located in the current path between the supply voltage U vand the second pole P2 of the inductance L. The switch S2 is located in the first current path between the first pole Pt of the inductance L and ground. In particular, it can be implemented - as in Fig. 2A - by a transistor T (or several transistors and / or diodes). The same applies to all other switches. The third switch S3 is located in the second current path between the first pole P1 of the inductance L and the MEMS capacitance Cm. The fourth switch S4 is located in a further ("fourth") current path between the MEMS capacitance C M and the supply voltage U v or their buffer capacitor C B and corresponds to switch S2, from Fig. 2B.

[0165] Optionally, another switch S5 can be provided between the second pole P2 and ground.

[0166] The operation of circuit 500 is illustrated in Fig. 6 using the time profile 600 of the configuration of the switching device of circuit 500, in particular the switching states of its individual switches S1 to S4. The switching states of the switching device are gradually shifted to different switching states by a controller (not shown) over time according to the following sequence with the successive time intervals t0bis, where "1" in the diagrams indicates a closed switch and "0" an open switch, and the sequence is run through at least once:

[0167] Fig. 6 shows a special case in which this sequence is repeated periodically (the transitions between successive periods P are indicated by vertical dashed lines). As shown in the table (but not illustrated in Fig. 6), after each charging or discharging of the MEMS capacitance CM, a rest state is established until the inductance L needs to be recharged, in which all switches are open (“idle” state) and the MEMS capacitance CM is “floating,” meaning that, due to the lack of connection to a defined electrical potential, it itself has no defined electrical potential.

[0168] This serves to prevent the charge stored in the MEMS capacitance CM during charging from flowing away again, especially towards the supply source, or to prevent the just discharged MEMS capacitance C Mis immediately (partially) recharged. Conversely, this also means that the control device should be designed so that the relevant switch(es) (e.g., S3) is / are opened immediately as soon as the coil's energy has been completely consumed. Alternatively, this function can be performed by a corresponding design of the switch itself.

[0169] Before the time interval t0, all switches are open (“idle” state) and the MEMS capacitance C M therefore has no defined electrical potential (floating). In the time interval to, the "first" circuit configuration is present, in which only the switches S1 and S2 are closed, so that the first current path through the inductance L is closed and due to a voltage supplied by the supply voltage U vA magnetic field with the associated magnetic energy is created along the first current path in the inductance L. The coil is thus "charged" with energy.

[0170] During the transition to the following time interval ti, while switch S1 remains closed, switch S2 is opened and switch S3 is closed instead, resulting in a “second” circuit configuration in which the second current path from a first pole of the inductance L via the closed switch S3 to the MEMS capacitance CM is enabled, so that the magnetic energy stored in the inductance L in the meantime causes a current flow along the second current path, by means of which the MEMS capacitance C M to the positive voltage U M = +V is charged.

[0171] This is followed by an idle state (not illustrated in Fig. 6) in which all switches are open to avoid the MEMS capacitance CM now stored charge again to the voltage source for the supply voltage U v can flow away.

[0172] In the subsequent time interval t2 (which is optional), switch S3 is opened again and switch S4 is closed instead, so that a further current path is enabled via switch S4 (corresponding in particular to the claimed “fourth” current path), via which the MEMS capacitance CM is at least partially fed into the buffer capacitance C B (for buffering the supply voltage U v ) to a lower voltage U M = +V1. This allows for "charge recycling" in the sense that part of the charge of the buffer capacitance CB can be reused for the next buildup of a magnetic field in the inductance L, thus increasing the efficiency of the circuit 500.

[0173] Alternatively, by closing switches S2 and S4 while switches S1 and S3 are open, charge recovery from the MEMS capacitance C M can be used directly to build up magnetic energy in the inductance L by causing a corresponding current through the inductance L (not illustrated).

[0174] In the time interval t3, only the switches S2 and S3 are closed, so that the MEMS capacitance C M can be completely discharged to ground (this step can be omitted in the aforementioned alternative, since the MEMS capacitance C M is already discharged there in the time interval t2).

[0175] This is followed by an “idle state” (not illustrated in Fig. 6) in which all switches are open to prevent the MEMS capacitor C M is now (partially) charged again in an uncontrolled manner.

[0176] During the subsequent time interval t4, only switches S1 and S2 are closed, so that, as in time interval t0, the inductance is charged with magnetic energy via the first current path. The current flow through the inductance L is fed from the supply voltage Uv and partially from the buffer capacitance CB.

[0177] In the time interval t5, with switch S2 still closed, switch S1 is opened and switch S4 is closed, so that charge flows from the MEMS capacitance CM via S4 through the inductance L and via S2. Due to the inductance L's tendency to maintain the original current flow through it (Lenz's law), the current flow continues until the MEMS capacitance CM is charged to a negative voltage value, which in terms of magnitude can correspond in particular to the positive voltage value +V and thus be -V.

[0178] This is followed by an idle state (not illustrated in Fig. 6) in which all switches are open to prevent the charge now stored in the MEMS capacitor CM from returning to the voltage source for the supply voltage U v can flow away.

[0179] Finally, in time interval t6, only switches S2 and S3 are closed again, allowing the MEMS capacitance CM to be completely discharged to ground at 0V. A new cycle can then be initiated, repeating the sequence.

[0180] The optional switch S5 can be used as follows, in particular, to recover charges at negative voltages, analogous to the charge recovery described above at positive voltages: If the MEMS capacitance CM is to be discharged from -V to 0, for example, S5 and S3 can be closed. A current then builds up again in the inductance L.

[0181] If the MEMS capacitance CM is empty, S5 and S3 can be opened immediately and S1 and S2 closed instead, allowing the current in the inductor L to continue to rise. Then everything proceeds as described above.

[0182] Exemplary embodiments of the second circuit

[0183] The following are further explanations of exemplary embodiments of the second circuit, starting with the conventional circuit 700 from Fig. 7:

[0184] The circuit 700 of Fig. 7 represents a so-called half-bridge circuit. It has two supply voltage sources 705 and 710, which supply mutually complementary voltages. The central circuit branch of the circuit 700 has a component to be driven by the half-bridge circuit, in this example a capacitive MEMS actuator, such as a piezo actuator. The MEMS capacitance of the MEMS actuator is denoted here as CM An ohmic resistance of the central circuit branch occurring in reality is represented, here in the sense of an equivalent circuit diagram, by the resistance R, which, however, plays no role in the further explanations.

[0185] Furthermore, the circuit has two switching devices 715 and 725, which can each be controlled by an associated control voltage source 720 or 730 of variable control voltage, so that depending on this respective control voltage, the associated switching device (e.g. switch or switching transistor) 715 or 725 forms a current path between the associated supply voltage source 705 or 715 and the MEMS capacitance C M By alternately temporarily switching the two current paths through the switching devices 715 and 725, the MEMS capacitance C Malternately recharged to a positive or negative voltage V+ or V-, whereby the MEMS actuator can execute or drive a corresponding alternating movement.

[0186] However, this type of circuit is not very energy efficient. On average, the circuit 700 must consume the total power Ptotai — CM ' U during its operation. 2 ' f (10) are applied by the supply voltage sources 705 and 710.

[0187] Here, CM describes the capacitance value of the MEMS capacitance, U the peak-to-peak voltage across the MEMS capacitance, and f the frequency of the resulting square wave voltage. For example, a microscanner as a MEMS with a typical MEMS capacitance of 100 pF for its actuator to drive the deflection element, a voltage swing of 200 V (±100 V), and a frequency of 25 kHz would result in a theoretical power consumption of 100 mW.

[0188] A primary reason for the rather low energy efficiency of circuit 700 is that, due to the so-called "capacitor paradox" or "two-capacitor paradox" (see https: / / en.wikipedia.orq / wiki / Two capacitor paradox), which occurs here and is familiar from general circuit technology, at least 50% of the absorbed power is directly converted into heat when charging or recharging the MEMS capacitance CM. This is also the case when the line resistance (e.g., but also R) becomes infinitesimally small.

[0189] A second reason is that the remaining portion of the supplied power is required for building up the different energy levels in the MEMS capacitance CM, ie for the alternating recharging, whereby, however, during recharging, charge flowing out of the MEMS capacitance CM is diverted to ground or through the voltage sources without being recovered for further use.

[0190] Fig. 8 shows a first exemplary embodiment 800 of the second circuit, which enables bipolar control of the actuator, more precisely of the MEMS capacitance C M , is possible. However, a single supply voltage source 805 is sufficient here, which can correspond in particular to the supply voltage source 705 in its construction and can provide a DC voltage as supply voltage U vof the circuit 800, in particular at a feed point Ei. Given the voltage requirements of the actuator, this is typically a high-voltage source (in the present context, therefore, a voltage source that can supply a supply voltage that is higher than the typical supply voltages of logic circuits, in particular semiconductor circuits). The supply voltage can be greater than 10 V in magnitude, in particular at or above 100 V. Instead of the second supply voltage source 710, however, an inductance L is provided in the circuit 800. s (“Resonant circuit inductance”), which together with the MEMS capacitance CM (and R) and a switching device 825 forms an oscillating circuit. _The inductance L additionally shown in Fig. 8 S 2 is not included in the circuit 800. Rather, L S 2 only an alternative placement of the resonant circuit inductance Ls which will be discussed further below with reference to Figure 9B). The switching device 825 can correspond in its construction in particular to one of the previously described switching devices 715 and 725. The resonant circuit is electrically connectable at a charging connection (point) A via a switching device 815 to the feed-in point Ei fed by the supply voltage source 805, so that when the switching device 815 is closed and the switching device 825 is simultaneously open, electrical energy can be transferred from the supply voltage source 805 to the resonant circuit in a recharging circuit 835 defined thereby. Thus, the MEMS capacitance C Mbe recharged. The oscillation of the resonant circuit following the recharging, in which the MEMS capacitance CM is repeatedly, in particular periodically, recharged, takes place in a recharge circuit 840 of the circuit 800 corresponding to the resonant circuit itself, with the switching device 825 then closed and the switching device 815 then open.

[0191] The arrangement of the resonant circuit inductance L s in the resonant circuit is specially selected so that it is used both during the above-mentioned recharging of the MEMS capacitance C M via the charging connection A (with the switching device 815 closed and the switching device 825 open) as well as during repeated recharging of the MEMS capacity C M during electrical oscillation of the oscillating circuit (with switching device 815 open and switching device 825 closed) from the respective through the MEMS capacitance C M flowing current flows through it.

[0192] During recharging, the resonant circuit inductance L s thus (magnetic) energy, which it makes available at least partially (another portion is consumed in the resistor R in the real case) until the switching device 815 opens, for further recharging of the MEMS capacitance CM (in particular, beyond the voltage level of the power supply circuit) by temporarily continuing the charging current (cf. Lenz's law). The duration of the closed state of the switching device 815 occurring per oscillation period can in particular be optimized such that the supply of additional energy takes place with maximum efficiency. The switching device 815 is then controlled such that it connects the supply voltage source 805 to the charging terminal A of the resonant circuit and thus (indirectly) to the MEMS capacitance CM precisely when the voltage across the MEMS capacitance C Mhas a first maximum Ui with Ui < Uv and it has the same polarity as the voltage Uv provided by the supply voltage source 805.

[0193] When the switching device 815 is subsequently opened again, the current flow from the supply voltage source 805 into the oscillating circuit is interrupted and the charging current jn the MEMS capacitance C M As a result, the current flow is also interrupted or, at least, uncontrolled, if there is still an additional inductively induced current flow in the resonant circuit. The switching device 815 should therefore advantageously remain closed until the charging current has (again) dropped to zero and then be opened precisely at that time, so that the voltage level in the MEMS capacitance, which is now higher than the supply voltage Uv from the supply voltage source 805, does not subsequently lead to an unwanted current flow back to the supply voltage source 805.

[0194] The duration of the recharging process is thus predefined. It should not normally be varied, as otherwise there is a risk that the current path will be interrupted and the current through the coil will cause voltage spikes. As a setting for the resulting MEMS voltage, it is therefore possible to use a variable supply voltage U instead. v from the supply voltage source 805.

[0195] If the switching device 825 were not present or permanently closed, then the oscillation frequency of the resonant circuit would be determined by its values ​​of C according to the relationship (1) (see above). M and L s conditional resonance frequency fo is given.

[0196] Especially in the case of microscanners, typical resonance frequencies of deflection elements (mirror plates) are in the range of up to a maximum of 100 kHz. The capacitance of the piezoelectric material is typically in the range of up to approximately 150 pF. The primary inductance of the resonant circuit could be L s choose a coil with a suitable inductance value so that the resonance frequency fo of the electrical oscillating circuit exactly corresponds to the resonance frequency of the deflection element.

[0197] However, it turns out that according to the equation (1), solved for L, impractically large inductance values ​​result:

[0198] Such large inductance values ​​for L sHowever, in combination with small winding resistances, this would be very space-consuming and therefore unsuitable for products where the smallest possible MEMS design is important, such as AR / VR glasses. The smaller the resonance frequency fo and / or the value for C M is specified, the greater the required inductance L s . At fo = 30 kHz and CM = 100 pF, L s already a value of almost 300 mH.

[0199] If Ls has to be kept small, especially for space reasons, a circuit implementation with a classic, permanently closed resonant circuit is therefore unfavorable or even impossible.

[0200] As shown in Fig. 9 based on the current and voltage curves 900 at the MEMS capacitance C Millustrated, the operation of the circuit 800 can therefore be carried out in particular as follows, wherein a controller (not shown), such as a computer program-controlled microcontroller or a hard-wired control circuit, is used to control the switching devices: First, with the switching device 815 closed and the switching device 825 simultaneously open, a current path is established from the supply voltage source 805 via the charging terminal A and the resonant circuit inductance L s the initially uncharged MEMS capacitance C M enabled to charge the MEMS capacitance CM for the first time to a voltage level +V using a charging current l2 from the supply voltage source 805. With sufficient charging time, the voltage across the MEMS capacitance CM rises above the level of the supply voltage +V = U v(see the enlarged section of the voltage curve shown in Fig. 9A). The charging time is essentially determined by the respective values ​​of L s and C m certainly.

[0201] The oscillating circuit is now supplied with energy and begins to oscillate in a damped oscillation after the switching device 815 is opened and the switching device 825 is closed. However, this oscillation is modulated and thus changed to a lower oscillation frequency by opening the switching device 825 for a specific time portion of the oscillation period in each oscillation period when the voltage U M on the MEMS capacitance C M during the oscillation process has just reached a maximum and thus the voltage present in the oscillating circuit, between CM and L s back and forth oscillating energy currently, at least largely, as electrical energy in C MThe time component of the oscillation period can be approximately 50%, i.e., roughly half the period duration. More precisely, it would be 50% minus the time the oscillating circuit needs to transfer charge between two voltage levels.

[0202] Meanwhile, the energy lost in the oscillating circuit, especially at the resistor R and the lines due to, in particular, ohmic losses (hence damped oscillation), can now be recovered by regularly temporarily closing the switching device 815 and opening the switching device 825 by recharging C M be compensated with a temporary charging current l2. This recharging preferably occurs when the voltage U M above the MEMS capacitance C Mduring the oscillation process, the voltage has just reached its maximum value in the current oscillation period. However, this does not necessarily have to occur in every oscillation period or after each recharging. Rather, it is also possible to recharge only after several recharging cycles in between or only after several oscillation periods, e.g., every mth time, with m e.g. with m = 2.

[0203] Recharging can generally take place with a positively polarized high-voltage source at times when the oscillating circuit is paused and the voltage across the MEMS is at its maximum, as well as with a negatively polarized high-voltage source at times when the oscillating circuit is paused and the voltage across the MEMS capacitance C M is just minimal. In this case, a somewhat more uniform voltage signal results across the MEMS capacitance C M .

[0204] The oscillating circuit is thus paused regularly in order to maintain its oscillation frequency fs, which is determined from the value of C M and L s conditional resonance frequency fo of the oscillating circuit (in the permanently closed case) is reduced, and on the other hand to recharge the energy lost during the electrical oscillation.

[0205] A significant advantage of this circuit is that the voltage generated when recharging C M The flowing charges are no longer simply diverted to ground, but remain available for continued electrical oscillation in the resonant circuit. Furthermore, the negative effects of the capacitor paradox during recharging of CM are reduced by diverting the recharging current through the resonant circuit inductance L sand abrupt voltage changes across CM are avoided. This allows for higher efficiency and thus higher energy efficiency than in circuit 700 of Fig. 7. In addition, the values ​​of CM and L s smaller than would be required in a conventional resonant circuit to achieve the desired oscillation frequency fs. This allows for particularly space-saving circuit implementations and eliminates dependence on component tolerances.

[0206] The functional principle of the circuit 800 of Fig. 8 during recharging will now be described in more detail with reference to Fig. 9A, which, according to an embodiment, shows the time course of the current I and the voltage U M on the MEMS capacity C M during reloading while swinging and a subsequent reloading process in more detail:

[0207] During the recharging of the MEMS capacitance CM, the switching device 815 is open and the switching device 825 is closed, so that the recharging circuit 840 and thus the resonant circuit are also closed. The recharging occurs with alternating signs of current and voltage during the oscillation in the resonant circuit. In Fig. 9A, the wave denoted by h (recharging current) in the temporal course of the current I represents a recharging of the MEMS capacitance C. M , in which it is recharged in the same polarity as the supply voltage Uv. This recharging process causes the MEMS capacitance C M to the voltage value U M = Ui, which is still below the supply voltage U v lies (Ui < U v ). This is because losses occur in the real resonant circuit (represented here by the ohmic parasitic resistance R).

[0208] Subsequently, in the same oscillation period, a recharging process takes place, which serves to compensate for the losses that have occurred by supplying energy from the supply voltage source 805. For this purpose, the recharging current circuit 835 is closed by closing the switching device 815 and opening the switching device 825, and a recharging current l2 fed from the supply voltage source 805 is generated therein, which on the one hand increases the resonant circuit inductance L s and on the other hand the MEMS capacity C M charges with energy.

[0209] If the voltage U M above the MEMS capacitance C M the same value as provided by the supply voltage source 805 at the charging terminal A, the inductance L s The energy stored in the resonant circuit inductance L sstored energy leads to the MEMS capacitance CM being increased to a higher voltage level U M = U2, which is even higher than the voltage level Uv provided by the supply voltage source 805 (U2> Uv). The switching device 815 remains continuously closed during this time, but as soon as the energy in the resonant circuit inductance is depleted, it is opened by the controller. The time period in which the switching device 815 is closed corresponds approximately to half the period of the resonant frequency of the resonant circuit (which would result if the resonant circuit were permanently closed).

[0210] In this way, the charging losses caused by the "capacitor paradox" or, in general, by direct recharging (without an intermediate inductance) via a voltage source can be minimized or even completely eliminated. This is possible because the special arrangement of the resonant circuit inductance L s in the resonant circuit (ie a position that lies in both the recharging circuit 835 and the recharging circuit 840) the resonant circuit inductance L s can act as an inductive temporary “current supplier” in both circuits, which avoids abrupt voltage changes across CM and thus the basis for the capacitor paradox.

[0211] Another advantage of such an arrangement of the resonant circuit inductance L scan also consist in a more uniform (filtered or smoothed) current curve being obtained during the recharging process. This can be seen from a comparison of the two Figures 9A and 9B, where Fig. 9B shows current and voltage curves at the MEMS capacitance CM corresponding to the curves shown in Fig. 9A, which would be shown in an exemplary modification of the circuit 800 from Fig. 8 if the resonant circuit inductance L s to the one marked “L S 2". In this modification, the recharging of the MEMS capacitance CM would be carried out directly via the switching device 815, ie without an interposed resonant circuit inductance L s in the recharging circuit. Due to the elimination of the inductive effect of the resonant circuit inductance L s During recharging, the recharging current l2 would initially increase rapidly and then flatten out exponentially.

[0212] In the circuit 800 of Fig. 8, however, as can be seen in Fig. 9A compared to Fig. 9B, the current flow l2 builds up during recharging via the resonant circuit inductance L s It initially rises more slowly and then falls more slowly. In between, the current k follows a characteristic typical of sine waves near their maximum.

[0213] Furthermore, the recharging time is based on half the period that would result if the switching device 825 were permanently closed (resonance case). The (half) period is primarily determined by the resonant circuit inductance L s and MEMS capacitance CM. For example, with a resonant circuit inductance Ls = 47 pH and a MEMS capacitance CM = 100 pF, the following half period T / 2 would result: ■ 100 pF = 215 ns

[0214] The resulting recharging time (in the case of Figures 8 and 9A) is therefore typically significantly longer than in the case of direct recharging without resonant circuit inductance L s in the recharging circuit 840 (case of Fig. 9B) (based on 5 RC time constants T), which is only limited by the parasitic resistance value R:

[0215] 5 ■ T = 5 ■ RC = 5 ■ 50 £1 ■ 100 pF = 25 ns

[0216] Compared to the case of Fig. 9B, in the case of Figs. 8 and 9A, the longer recharging duration leads not only to a more uniform current profile but also to a lower peak value of the recharging current. The lower-frequency and weaker components in the spectrum of the recharging current l2, as well as the additionally more uniform profile, are therefore advantageous overall because they tend to cause less interference in neighboring electrical circuits.

[0217] Fig. 10 illustrates a second exemplary embodiment 1000 of the second circuit, with a pauseable resonant circuit and with a high-voltage source 1005 inductively coupled to the resonant circuit via a coupled pair of coils for providing a supply voltage U v for the circuit 1000. The voltage source 1005 can alternatively be a low-voltage source, depending on the turns ratio of the coil pair.

[0218] Specifically, the circuit 1000 comprises two galvanically decoupled circuit parts, preferably including decoupled first and second masses 1045 and 1050, which are connected via a first coupling coil L v and a second coupling coil L s existing coil pair are inductively coupled. The second coupling coil L srepresents both the resonant circuit inductance of the resonant circuit and the charging terminal A, through which the energy for recharging the resonant circuit can be inductively fed in. The coupling coils also each have an ohmic resistance Rv and R s , which is shown here in the sense of an equivalent circuit diagram. The first circuit part has a circuit loop, which, in addition to the high-voltage source 1005 and the first coupling coil L v (with R v ) also contains a first switching device 1015 with an associated control voltage source 1020 for its time-variable control. Depending on the current switching state of the switching device 1015, the loop and thus the current path through the first coupling coil L v closed or interrupted, so that the inductive effect of the first coupling coil L vand thus an inductive energy transfer to the second coupling coil L s in the oscillating circuit.

[0219] The resonant circuit has, in addition to the second coupling coil L provided as resonant circuit inductance, s the MEMS capacitance CM of a MEMS actuator to be controlled (along with its ohmic resistance R), as well as a second switching device 1025 with an associated control voltage source 1030 for its time-variable control. Similar to the switching device 825 in Fig. 8, the resonant circuit can be paused with the second switching device 1025.

[0220] In addition, the resonant circuit also has a circuit branch connected in parallel to the second switching device 1025 with a diode D and a third switching device 1035 with an associated control voltage source 1040 for its time-variable control.

[0221] If switching devices 1015 and 1035 are open, interrupting the current paths passing through them, while switching device 1025 is closed, the resonant circuit is closed and "oscillates." However, if the resulting energy losses need to be compensated (see Fig. 9), then switching devices 1015 and 1035 are closed and switching device 1025 is opened.

[0222] Now, by means of a single current pulse (or by means of several consecutive current pulses with corresponding multiple closing and opening of the switching device 1015), a time-variable current, in particular alternating current, can be passed through the first coupling coil L vgenerated, which, through inductive energy transfer via the coil pair, causes an induced current in the second circuit section, which runs via the switching device 1035 and is rectified via the diode D. In this way, the MEMS capacitance CM can be recharged with direct current (which can be variable over time). This occurs during a period in which the voltage UM across the MEMS capacitance CM resulting from the previous oscillation in the oscillating circuit is at its maximum and has the same polarity as the induced voltage generated in the second coupling coil Ls. If the direction of the diode is reversed, it is analogously possible to "recharge" the oscillating circuit when the voltage across the MEMS capacitance is at its minimum. An additional current path also offers the option of bipolar recharging.

[0223] Instead of the DC voltage source 1005, an AC voltage source can also be used, so that the generation of DC pulses for generating a time-varying current through the first coupling coil L v can be omitted.

[0224] Fig. 11 illustrates a third exemplary embodiment 1100 of the second circuit with a pauseable resonant circuit, which results from the circuit 800 of Fig. 8 by converting the single resonant circuit capacitance and at the same time MEMS capacitance CM there to two separate MEMS capacitances C Mi and C M 2. In circuit 1100, for comparison with circuit 800, supply voltage source 1105 corresponds to supply voltage source 805, and switching devices 1115 and 1125 (with associated control voltage sources 1120, 1130) correspond to switching devices 815 and 825 (with associated control voltage sources 820 and 830), respectively.

[0225] Due to the division of the resonant circuit capacitance into the two separate MEMS capacitances CMI and CM2 in the arrangement shown, where the resonant circuit inductance L s and the switching device 1125 are connected between the two MEMS capacitors CMI and CM2, voltages U Mi or U M 2 at the MEMS capacities CMI and C M 2, which are phase-shifted from each other and can have the same amplitude, especially with the same capacitance values. The MEMS capacitances CMI and C M 2 can, in particular, be part of a single MEMS actuator, enabling differential drive. For example, the MEMS capacitors CMI and CM2 can each be configured as components of a piezo actuator in such a way that they produce piezoelectric forces acting in opposite directions, phase-shifted by, in particular, 180°.

[0226] Exemplary embodiments for a combination of first circuit and second circuit

[0227] As already mentioned, the previously introduced circuit types "first circuit" and "second circuit" can also be advantageously combined. While the first circuit, in particular, allows the high voltages required for the operation of actuators, in particular MEMS actuators, to be provided without using a high-voltage source as such, and instead uses a low-voltage source, which can be provided in particular by a primary or secondary battery of a mobile device, the second circuit, in particular, allows a space-saving design of the circuit. Furthermore, both circuits serve to increase energy efficiency.

[0228] Fig. 12 illustrates a first exemplary embodiment 1200 of such a combined circuit for controlling an actuator, in particular a MEMS actuator, for driving an oscillatory movement in a MEMS.

[0229] The circuit 1200 can be regarded as a further development or variant of the first circuit from Fig. 2A, so that only the differences will be discussed below.

[0230] A key difference is that, in accordance with the concept of the second circuit, circuit 1200 contains a pauseable resonant circuit with the MEMS capacitance CM as the resonant circuit capacitance. The resonant circuit also contains a resonant circuit inductance L s and a switching device S7 for temporarily interrupting (pausing) the oscillating circuit.

[0231] To recharge the MEMS capacitance CM, when it has reached its maximum voltage value within the current oscillation period, the oscillating circuit is interrupted (paused) by means of the switching device S7 and by closing the further switching device S6 a current path is created between the boost converter circuit shown in the left part of Fig. 12 and the oscillating circuit, in particular the MEMS capacitance C M , closed.

[0232] The oscillating circuit can therefore be supplied with energy solely by means of a low-voltage source to provide the supply voltage Uv, without the need for a high-voltage source.

[0233] The feedback loop via the switching device S2 and the buffer capacity C Bfrom circuit 200 of Fig. 2A can also be eliminated, since the energy in the resonant circuit is essentially retained except for the typical, particularly ohmic, losses, so buffering is no longer necessary. Fig. 13 illustrates a second exemplary embodiment 1300 of a combined circuit for controlling an actuator, in particular a MEMS actuator, for driving an oscillatory movement in a MEMS.

[0234] The circuit 1300 can be regarded as a further development or variant of the first circuit from Fig. 5, so that only the differences will be discussed below.

[0235] A key difference is that in the circuit 1300, a pauseable oscillating circuit with the MEMS capacitance C M as resonant circuit capacitance and a resonant circuit inductance L sand a switching device S7 for temporarily interrupting (pausing) the oscillating circuit.

[0236] To recharge the MEMS capacitance CM, the oscillating circuit is interrupted (paused) by means of the switching device S7 once it has reached its maximum positive voltage value within the current oscillation period. By closing at least one of the switching devices S3 and S4, a current path is closed between the boost converter circuit shown in the left part of Fig. 13 and the oscillating circuit, in particular the MEMS capacitance CM. The boost converter circuit is configured with regard to its switch positions (e.g., Si and S3 closed, S2 and S4 open, or Si and S4 closed, S2 and S3 open) such that it supplies a supply voltage to the oscillating circuit, or more precisely, the MEMS capacitance C M , which is copolar to the (positive) voltage U M above the MEMS capacitance C M is.

[0237] On the other hand, for (additional) recharging of the MEMS capacity C M When it has reached its maximum negative voltage value within the current oscillation period, the oscillating circuit is interrupted (paused) again by means of the switching device S7 and by closing at least one of the switching devices S3 and S4, a current path is created between the boost converter circuit and the oscillating circuit, in particular the MEMS capacitance C M, closed. The boost converter circuit is configured with respect to its switch positions (e.g.: S2 and S4 closed, Si and S3 open, or: S2 and S3 closed, Si and S4 open) such that it supplies a supply voltage to the resonant circuit, or more precisely, the MEMS capacitance CM, which is copolar to the (negative) voltage UM across the MEMS capacitance CM. In circuit 1300, the resonant circuit can also be supplied with energy solely by means of a low-voltage source for providing the supply voltage U v without the need for a high-voltage source. In addition, the buffer capacity C B from the circuit 500 of Fig. 5 are eliminated again, since the energy in the resonant circuit is essentially retained except for the typical, particularly ohmic, losses, so that buffering is no longer necessary.

[0238] Fig. 14 shows a third exemplary embodiment 1400 of a circuit in which the concepts of the first circuit and the second circuit are combined to form a circuit for bipolar and differential control of a MEMS actuator, in particular a microscanner.

[0239] The circuit 1400 comprises, in addition to an oscillating circuit 1425, which can be interrupted by means of a switching device 1405 and thus paused, two boost converter circuits 1415 and 1420, which here each correspond to the concept of the circuit in Fig. 13 and which serve to supply two differently poled, boosted supply voltages +U V or -U v for the pauseable resonant circuit 1425, one each at an assigned feed-in point Ei or E2 (here each equivalent to a respective charging connection A).

[0240] The recharging of the MEMS capacitors CMI and CM2 preferably occurs when they have reached their absolute maximum voltage value, which is the same polarity as the assigned supply voltage, within the current oscillation period. The oscillating circuit is temporarily interrupted (paused) by a switching device 1415 with an associated control voltage source 1420. The first MEMS capacitor CMI is thus charged in a first polarity (+), while at the same time the second MEMS capacitor C M 2 is charged with a polarity opposite to the first polarity (-). The operation of the circuit is identical to that of Fig. 13 with respect to each of the polarities, with an additional index 1 or 2 being introduced in the reference numerals to distinguish the components of the two boost converters 1415 and 1420, which can be designed identically.

[0241] The control of circuit 1400 is configured such that while boost converters 1415 and 1420 are operating, switching device 1405 is open, allowing both boost converters 1415 and 1420 to operate separately to charge the MEMS capacitors CMI and CM2 to mutually opposite voltage levels. If the oscillating circuit is subsequently activated, both boost converters 1415 and 1420 are placed in the "idle" state, so that they do not impair the function of the then oscillating oscillating circuit 1425.

[0242] The resonant circuit inductance L s According to a first variant, this can be provided on only one side of the switching device 1405 (asymmetric case) and is thus either by L Sa or L S b, while the other inductance L S b or L Sa According to a second variant, the resonant circuit inductance L sbut at the same time the two inductances L Sa and L S b as partial inductances (symmetrical case). Lsa and Lsb can, in particular, have the same inductance and therefore be identical in construction.

[0243] Fig. 15 schematically shows a MEMS 1500 comprising a microscanner system with a microscanner 1501. The microscanner 1501 comprises a support structure 1505 made from a semiconductor substrate in the form of a frame (chip frame) that surrounds a deflection element (mirror) 1510 on all sides, the base of which is made from the same semiconductor substrate as the support structure 1505. The deflection element 1510 is suspended from the support structure 1505 by means of one or more spring elements, in the present example, these are the two spring elements 1515a and 1515b attached to opposite sides of the deflection element 1510. This suspension is designed such that the deflection element 1505 can oscillate rotationally at least about one oscillation axis. This oscillation axis runs along the straight line (which runs vertically in the image of Fig. 15) through the two attachment points of the spring elements 1515a and 1515b on the deflection element 1510.With suitable excitation, it is also possible to excite an oscillation about a second oscillation axis orthogonal to the first oscillation axis, i.e., horizontal in the image of Fig. 15. In particular, to promote such a two-dimensional oscillation, instead of the suspension shown here with two opposing meandering spring elements, differently shaped and arranged spring elements can also be provided, in particular several spiral-shaped ones.

[0244] On each of the spring elements 1515a and 1515b there is a piezo element 1520 or 1525, whereby these piezo elements differ in terms of their piezo material and their tasks.

[0245] The first piezo element 1520 serves as a piezo actuator for driving the oscillatory movement of the deflection element 1510 and is therefore formed as a dielectric based on a first piezo material, such as PZT, which exhibits a particularly strong piezo effect. The electrodes of the piezo element 1520, separated from each other by the piezo material, simultaneously form the electrodes of its MEMS capacitance CM. Thus, with a suitable selection of the spring strengths of the spring elements 1515a and 1515b, the first piezo element 1520 is particularly suitable for enabling large deflections and thus scanning angles of the microscanner 100, in particular up to ± 90° (optical scanning angle) or even more.

[0246] The second piezo element 1525, on the other hand, serves as a piezo sensor for measuring and thus determining the time-dependent position, i.e. specifically the orientation or phase position of the oscillation, of the deflection element 1510.

[0247] In Fig. 15, the corresponding connecting lines 1535a, b and 1545a, b, respectively, as well as the connecting pads (bond pads) 1530a, b and 1540a, b coupled thereto for establishing a respective electrical connection to external drive or measurement electronics, e.g., via wire bonds, are also shown for both piezo elements 1520 and 1525. It is also conceivable that, in addition to the two illustrated piezo elements, further piezo elements could be provided as piezo actuators or piezo sensors.

[0248] The base is an SOI (silicon-on-insulator) substrate. A SiO2 or other electrical passivation layer is created on this substrate, onto which the piezoelectric layer stacks are applied. The piezoelectric layer stacks consist of a bottom electrode, usually made of metal, the piezoelectric material, and a top electrode, usually made of metal. An additional electrical passivation layer is used between the top and bottom electrodes to prevent electrical short-circuiting.

[0249] To control the first piezo element 1520 (and optionally to process measurement signals from the second piezo element 1525), the MEMS 1500 additionally has a circuit 1550 according to one of the aforementioned circuit-related aspects of the present solution, e.g., according to one of Figures 8 or 10 to 14. Depending on the circuit used, the piezo elements can be non-differential or differential. LIST OF REFERENCE SYMBOLS

[0250] 100 conventional regulated boost converter circuit

[0251] 200 first (unipolar) embodiment of a circuit according to the solution

[0252] 205 Comparison of circuits 100 and 200

[0253] 300 Time course of the current through the inductance L during the first

[0254] Circuit configuration

[0255] 400 Embodiment of a control device Ctrl

[0256] 405 Delay chain

[0257] 405-x Delay elements of the delay chain 405

[0258] 410 multiplexers

[0259] 415 RS flip-flop

[0260] 500 second (bipolar) embodiment of a circuit according to the solution

[0261] 600 Time course of the configuration of the switching device of the circuit 500

[0262] 700 conventional half-bridge circuit

[0263] 705, 710 supply voltage sources

[0264] 715, 725 Switchgear

[0265] 720, 730 control voltage sources

[0266] 800 first exemplary embodiment of the second circuit

[0267] 805 supply voltage source

[0268] 815, 825 switching devices

[0269] 820, 830 control voltage sources

[0270] 835 Recharging circuit

[0271] 840 recharging circuit, oscillating circuit

[0272] 900 Current and voltage waveforms at the MEMS capacitance of the circuit 800

[0273] 1000 second exemplary embodiment of the second circuit

[0274] 1005 Supply voltage source

[0275] 1015, 1025 Switchgear

[0276] 1020, 1030 control voltage sources

[0277] 1035 additional switching device

[0278] 1040 Control voltage source for switching device 1035

[0279] 1045 first mass

[0280] 1050 second mass

[0281] 1100 third exemplary embodiment of the second circuit

[0282] 1105 Supply voltage source

[0283] 1115, 1125 Switchgear

[0284] 1120, 1130 Control voltage sources 1200 First exemplary embodiment of a combined circuit 1300 Second exemplary embodiment of a combined circuit

[0285] 1400 third exemplary embodiment of a combined circuit 1405 switching device

[0286] 1410 Control voltage source for switching device 1405

[0287] 1415 first boost converter

[0288] 1420 second boost converter

[0289] 1425 resonant circuit

[0290] 1500 MEMS

[0291] 1501 microscanner (system)

[0292] 1505 Support structure (chip frame)

[0293] 1510 Deflection element (mirror)

[0294] 1515a first spring element

[0295] 1515b second spring element

[0296] 1520 first piezo element, piezo actuator

[0297] 1525 second piezo element, piezo sensor

[0298] 15530a, b Connection pads for the first piezo element 135a, b Connection lines for the first piezo element

[0299] 1540a, b Connection pads for the second piezo element

[0300] 1545a, b Connecting cables for the second piezo element

[0301] 1550 circuit

[0302] A charging port (point)

[0303] C Buffer capacity in conventional circuit

[0304] C B Buffer capacitor for supply voltage source

[0305] CM MEMS capacity

[0306] CMI , CM2 separate MEMS capacities

[0307] Clk clock signal (Clock)

[0308] Ctrl control or control device

[0309] D-diode

[0310] Ei , E2 Feed-in points for electrical energy

[0311] I Charging current

[0312] 10 Limiting current

[0313] 11 Transfer current

[0314] 12Recharge current

[0315] L (second) inductance, especially booster inductance

[0316] L s Resonant circuit inductance, second coupling inductance LS2 Positioning of the resonant circuit inductance in the case of Fig. 9B

[0317] L Sa Resonant circuit inductance or first resonant circuit partial inductance in Fig. 14

[0318] Lsb resonant circuit inductance or second resonant circuit partial inductance in Fig. 14

[0319] L v first coupling inductance

[0320] OP operational amplifier

[0321] P Period or period duration

[0322] PT first pole of the inductance L

[0323] P2second pole of the inductance L

[0324] Q Output signal from Ctrl

[0325] R, S inputs of the RS flip-flop 415

[0326] Reg Controller

[0327] Ri, R2Ohm resistors that form voltage dividers

[0328] RL, RM , RL2Ohmic resistance of the associated inductance L, Li or L2

[0329] R s , Rv Ohmic resistances of the coupling inductances, especially Ohmic resistance in the resonant circuit according to the equivalent circuit diagram

[0330] R Sa Ohmic resistance or first partial resistance in the resonant circuit according to the equivalent circuit diagram in Fig. 14

[0331] R S b Ohmic resistance or second partial resistance in the resonant circuit according to the equivalent circuit diagram in Fig. 14

[0332] Sr S7Switching devices, in particular switching transistors

[0333] SEL selection signal

[0334] T transistor t time variable to.-.- .te time intervals

[0335] Ui voltage across buffer capacity C

[0336] U2Voltage across buffer capacity C

[0337] UA voltage across buffer capacity C

[0338] UM voltage over MEMS capacitance

[0339] U v Supply voltage or supply voltage source

[0340] Vref reference voltage

[0341] +V, -V alternating voltage levels of UM

Claims

CLAIMS 1. A circuit (800; 1000; 1100; 1200; 1300; 1400) for controlling an actuator (1520) for driving an oscillating movement of a mass element in a MEMS, the circuit (800; 1000; 1100; 1200; 1300; 1400) comprising: an electrical oscillating circuit (840; 1425) comprising: a first inductance (Ls), a first electrical MEMS capacitance (CM); a charging terminal (A) for temporarily supplying electrical energy from a power supply (805; 1005; 1105) external to the oscillating circuit to temporarily recharge the MEMS capacitance (CM; CM1); a controllable first switching device (825) for selectively interrupting or closing the resonant circuit (840; 1425) depending on a control of the first switching device (825); and a resonant frequency related to a permanently closed state of the resonant circuit (840; 1425); and a controller for controlling the first switching device (825);wherein the first inductance (Ls) is arranged in the oscillating circuit (840; 1425) in such a way that, both during the recharging of the first MEMS capacitance (CM; CM1) during an electrical oscillation of the oscillating circuit (840; 1425) in the closed state of the first switching device (825) and during the temporary recharging of the first MEMS capacitance (CM; CM1) in the interrupted state of the first switching device (825), it lies in a current path of the oscillating circuit (840; 1425) through which current flows and through the first MEMS capacitance (CM; CM1); and wherein the controller is configured to temporarily control the first switching device (825) during a respective oscillation period of the oscillating circuit (840; 1425) running in the closed state of the first switching device (825) by means of a corresponding control at a time at which the voltage across the first MEMS capacitance (CM;CM1) reaches a maximum in terms of amount within the respective oscillation period, into a state in which it interrupts the oscillating circuit (840; 1425), so that an actual oscillation frequency of the oscillating circuit (840; 1425) is caused which is lower than the resonance frequency; 2. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 1, wherein: the first MEMS capacitance (CM; CM1) is configured as a component of the actuator (1520) such that it forms a component of an electromechanical transducer of the actuator (1520); and the transducer is configured to convert electrical energy stored in the first MEMS capacitance (CM; CM1) into at least one mechanical variable for driving a movement of the actuator (1520).

3. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of the preceding claims, wherein the controller is configured to put the first switching device (825) into a state in which it interrupts the resonant circuit (840; 1425) in a respective oscillation period of the resonant circuit (840; 1425) when the voltage across the first MEMS capacitance (CM; CM1) reaches a maximum in terms of amount within the oscillation period after a charge reversal of the first MEMS capacitance (CM; CM1) taking place during the oscillation period.

4. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of the preceding claims, wherein: the resonant circuit (840; 1425) has, in addition to the first MEMS capacitance (CM; CM1), a second MEMS capacitance (CM2) formed separately from the first MEMS capacitance (CM; CM1); the first and the second MEMS capacitance (CM; CM1) in the resonant circuit (840; 1425) are connected in such a way that a first pole of the first MEMS capacitance (CM; CM1) is electrically connected to a first pole of the second MEMS capacitance (CM2) via at least one switch of the first switching device (825) and the first inductance (Ls), and the respective second poles of the two MEMS capacitances are electrically connected to one another in such a way that they are kept at the same electrical potential during operation of the resonant circuit (840; 1425).

5. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of the preceding claims, further comprising a power supply circuit for temporarily supplying electrical energy to the resonant circuit (840; 1425) via the charging terminal (A).

6. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 5, wherein the power supply circuit comprises a second switching device (815) configured to switch a feed point in response to a control for temporarily connecting electrical energy to the charging terminal (A) of the oscillating circuit (840; 1425) in order to supply the oscillating circuit (840; 1425) with electrical energy supplied or capable of being supplied at the feed-in point.

7. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 6, wherein the Circuit (800; 1000; 1100; 1200; 1300; 1400) is configured to generate the second Switching device (815): to be temporarily closed when the voltage across the first MEMS capacitance (CM; CM1) reaches a maximum within the oscillation period and has the same polarity as a voltage provided by the power supply circuit at the feed-in point; and / or to be opened as soon as, during the temporary recharging of the first MEMS capacitance (CM; CM1), in the closed state of the second switching device, the current flow through the first inductance (Ls) has dropped to a specific value which corresponds to a maximum of 10% of its maximum value previously reached during the recharging.

8. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 6 or 7, wherein the circuit (800; 1000; 1100; 1200; 1300; 1400) is configured to temporarily connect the feed point to the charging terminal (A) of the resonant circuit (840; 1425) in the respective oscillation period by means of the second switching device at a time before which two consecutive charge reversal processes of the first MEMS capacitance (CM; CM1) of the resonant circuit (840; 1425) have already taken place in the oscillation period since the feed point was last temporarily connected to the resonant circuit (840; 1425) by means of the second switching device.

9. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of claims 5 to 8, wherein the circuit (800; 1000; 1100; 1200; 1300; 1400) is configurable such that the amount of electrical energy supplied to the oscillating circuit (840; 1425) in at least one oscillation period via the charging terminal (A) from the power supply circuit is adjustable.

10. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 9, wherein the circuit (800; 1000; 1100; 1200; 1300; 1400) is configurable to that the amount of electrical energy supplied to the oscillating circuit (840; 1425) via the charging terminal (A) from the energy supply circuit can be set individually for each oscillation period or globally for all m-th oscillation periods, where m > 0 is a natural number.

11. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of claims 5 to 10, wherein the power supply circuit comprises an inductive coupling device (LV, LS) for the temporary inductive feeding of electrical energy into the resonant circuit (840; 1425).

12. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to one of claims 5 to 11, further comprising a boost converter configured to convert an input voltage applied to the feed point into a higher output voltage in order to supply the resonant circuit (840; 1425) with electrical energy based on this output voltage when the second switching device (815) is in a state in which it temporarily electrically connects the feed point to the resonant circuit (840; 1425).

13. Circuit (800; 1000; 1100; 1200; 1300; 1400) according to claim 12, wherein: the boost converter comprises a boost converter circuit with a second inductance (L) and a third switching device (T) that can be controlled by the controller and a third MEMS capacitance that is formed at least partially by the first and / or the second MEMS capacitance (CM; CM1; CM2);wherein the third switching device (T) is configured to assume a first circuit configuration depending on the controller and sequentially subsequently a second circuit configuration, so that in the first circuit configuration a first current path through the second inductance (L) is enabled to cause an increasing current flow through the second inductance (L) fed by a supply voltage (UV), and in the second circuit configuration a capacitively unbuffered second current path between a first pole of the second inductance (L) and the third MEMS capacitance is enabled to charge the third MEMS capacitance to a first voltage by means of a current flow fed at least partially by the second inductance (L), the amount of which is equal to or higher than the supply voltage (UV).

14. A MEMS (1500), comprising: a mass element (1510) configured to oscillate; an actuator (1520) for driving an oscillatory movement of the mass element; and a circuit (800; 1000; 1100; 1200; 1300; 1400) according to any one of the preceding claims for controlling the actuator (1520) such that it is thereby caused to move the oscillatory mass element (1510) in an oscillatory movement; wherein the MEMS capacitance (CM) of the circuit (800; 1000; 1100; 1200; 1300; 1400) is designed as a component of the actuator (1520) in such a way that it itself forms a component of an electromechanical transducer of the actuator (1520), and the transducer is configured to convert electrical energy stored in the MEMS capacitance (CM) into at least one mechanical variable for driving a movement of the actuator (1520) in order to thereby drive the oscillatory movement of the mass element (1510).

15. The MEMS (1500) according to claim 14, wherein the MEMS (1500) comprises a microscanner system (1501); and the mass element (1510) is configured as an oscillatory deflection element of the microscanner system (1501) for deflecting electromagnetic radiation incident on the deflection element.

Images