Synchronous drive for MEMS

Abstract

The present application relates to a drive device for a mechanical oscillation of a microelectromechanical system (MEMS), a combination of a drive device according to any of the preceding claims with a microelectromechanical system capable of mechanical oscillation, a spectacle device comprising a drive device according to the invention or a combination according to the invention, and a method for driving a microelectromechanical system, in particular a MEMS scanner.

Description

[0001] Synchronous drive for MEMS

[0002] The present application relates to a drive device for a mechanical oscillation of a microelectromechanical system (MEMS), a combination of a drive device according to one of the preceding claims with a mechanically oscillatable microelectromechanical system, a spectacle device comprising a drive device according to the invention or a combination according to the invention, and a method for driving a microelectromechanical system, in particular a MEMS scanner.

[0003] Resonantly driven MEMS, especially MEMS scanners, and their drives must be particularly energy-efficient and miniaturized if they are to be integrated into eyeglasses, for example. Current solutions fail to satisfactorily meet both requirements.

[0004] Against this background, it is an object of the present invention to enable a particularly energy-efficient and miniaturized use of a MEMS, in particular a MEMS scanner. Against this background, it is particularly desirable to be able to dispense with electronic components that cannot be integrated into an integrated system.

[0005] This object is achieved according to the invention by a drive device for a mechanical oscillation of a microelectromechanical system, wherein the drive device has an electrical oscillator, wherein the electrical oscillator is designed and configured such that it generates an electrical output signal with a first frequency f1, wherein the electrical oscillator is designed and configured such that the first frequency f1 of the output signal can be set to a target frequency f1_soll, wherein the drive device is designed and configured such that the electrical oscillator is at least indirectly connectable to the microelectromechanical system in order to drive the mechanical oscillation of the microelectromechanical system with a drive signal, wherein the drive device has a control device, wherein the control device is designed and configured such thatthat the control device, when operating with a microelectromechanical system, receives an electrical feedback signal from the microelectromechanical system, wherein the control device is designed and configured such that a controlled variable R, which is dependent on the feedback signal and / or on the drive signal (and in particular is dependent on the feedback signal and the drive signal), can be set to a target value R_soll, wherein the control device is designed and configured such that it calculates the controlled variable R when operating with a microelectromechanical system, wherein the control device is designed, configured and connected to the electrical oscillator such that it sets the target frequency f 1 _soll, which can be set on the electrical oscillator, as a function of the measured controlled variable R, in order to control the controlled variable R to the target value R_soll.

[0006] The MEMS is a resonator with a high Q factor. The drive device according to the invention advantageously enables this property of the MEMS to increase the frequency stability of the exciting oscillator, for example, a voltage-controlled electrical oscillator. This is because the feedback signal can be used with the help of the control device to limit the oscillation of the exciting oscillator as far as possible to the natural frequency to be excited. Thus, no additional oscillator with a high Q factor or an oscillator with better frequency stability than that of typical RC oscillators is necessary. In particular, a quartz oscillator is therefore also not required to increase frequency stability.The exciting oscillator and the MEMS are also synchronized by the drive device according to the invention, so that the exciting oscillator consistently drives the MEMS at a specific natural frequency, even if the natural frequency changes due to thermal effects. The drive device according to the invention thus tracks the natural frequency used when using the MEMS.

[0007] In other words, an electrical oscillator within the meaning of the present invention, which is designed and configured such that the first frequency f1 of the output signal can be adjusted to a target frequency f1_soll, is designed such that a user can vary the target frequency f1_soll without having to structurally modify the electrical oscillator itself. An example of such an oscillator is a voltage-controlled electrical oscillator (VCO for short).

[0008] According to one embodiment of the drive device according to the invention, the feedback signal reflects the deflection of the mechanical oscillation of the microelectromechanical system. In particular, the MEMS can be a piezoelectric MEMS, so that the feedback signal reflects the mechanical deflection of the piezoelectric element.

[0009] According to one embodiment of the drive device according to the invention, the control device and controlled variable R are designed such that controlling the controlled variable R by the control device during operation with a microelectromechanical system to a target value R_soll causes the phase shift P between the drive signal and the feedback signal directly leaving the microelectromechanical system, which is therefore native, to be kept constant over time. This phase shift is decisive for whether the MEMS is driven resonantly or not. Therefore, this embodiment advantageously makes it possible to maintain the resonant drive of the MEMS even in the event of external disturbances, such as a thermally induced change in the natural frequency of the MEMS.

[0010] According to one embodiment of the drive device according to the invention, the amount of the phase shift P (the phase shift between the drive signal and the feedback signal directly leaving the microelectromechanical system and therefore native) to be kept constant over time is between 40 degrees and 140 degrees, preferably between 60 degrees and 120 degrees and particularly preferably between 70 degrees and 110 degrees.

[0011] According to one embodiment of the drive device according to the invention, the controlled variable R is the phase shift P of the drive signal and the native feedback signal, so that the control device is designed and configured such that, when operated with a microelectromechanical system, it adjusts the electrical oscillator to control the phase shift P of the drive signal and the native feedback signal to a target value for the phase shift P_desired. The phase shift as a controlled variable directly ensures that the control ensures resonant driving of the MEMS and is thus robust against changes in the system, such as those that may occur during maintenance, for example.

[0012] According to one embodiment of the drive device according to the invention, the controlled variable R is the quadrature Q of the feedback signal with respect to the drive signal as a reference signal. The control device is preferably designed and configured such that controlling the quadrature Q to a target value for the quadrature of zero results in controlling the phase shift of the drive signal and the native feedback signal to a predefined target value P_soll. This greatly simplifies the calculations required to maintain a specific phase shift constant.

[0013] This in turn increases the energy efficiency of the drive device.

[0014] According to one embodiment of the drive device according to the invention, the control device comprises a calculation unit, for example a phase detector and / or IQ demodulator (in particular an IQ demodulator), wherein the drive device is designed and configured such that the calculation unit, during operation with the microelectromechanical system, receives the drive signal or a first clock signal T1 synchronized with the drive signal and, on the other hand, receives the feedback signal of the microelectromechanical system indirectly, for example in filtered and / or amplified form and / or digitized, or directly, wherein the calculation unit is designed and configured such that during operation with a microelectromechanical system, it either time-discretely or time-continuously calculates the controlled variable R, for example

[0015] • the quadrature Q of the feedback signal relative to the drive signal as a reference signal and / or

[0016] • the phase shift between the drive signal and the native feedback signal is calculated, wherein the phase detector preferably comprises an IQ demodulator. This calculation advantageously enables control of the controlled variable R.

[0017] The calculation unit can, in particular, be designed such that the calculations performed in the calculation unit are carried out synchronously with the drive signal. This simplifies the calculations and thus increases energy efficiency.

[0018] According to one embodiment of the drive device according to the invention, the control device has a control unit, wherein the control unit and the calculation unit are designed and configured such that the control unit, during operation with the microelectromechanical system, receives the control variable calculated by the calculation unit and calculates the difference D between the calculated control variable and the target value for the control variable R_soll, wherein the control unit and the electrical oscillator are designed such that the control unit sets the target frequency f 1 _soll of the electrical oscillator as a function of the calculated difference D, wherein the control unit preferably comprises a loop filter with a transfer function specified for controlling the electrical oscillator.In particular, the control unit can be a so-called PLL control unit, i.e., a unit for controlling a phase-locked loop. According to one embodiment of the drive device according to the invention, the drive device is designed and configured such that, during operation with the microelectromechanical system, the control unit also receives the drive signal or a second clock signal T2 synchronized with the drive signal, so that the calculations performed in the control unit are synchronized with the drive signal. This enables a simplification of the calculations on the control unit and thus an increase in the energy efficiency of the drive device.

[0019] According to one embodiment of the drive device according to the invention, the drive device comprises a first clock generator, wherein the first clock generator is designed, configured, coupled to the electrical oscillator and connectable to the microelectromechanical system in such a way that the first clock generator receives the output signal of the electrical oscillator and converts it into the drive signal with a second frequency f2, wherein the first frequency f1 is an integer multiple, for example 1024 times or 512 times, of the second frequency f2, wherein the first clock generator is preferably a frequency divider or comprises such a frequency divider.

[0020] According to one embodiment of the drive device according to the invention, the drive device comprises a second clock generator. The second clock generator is designed, configured, and coupled to the electrical oscillator such that the second clock generator receives the output signal of the electrical oscillator and converts it into the first clock signal T1 with a third frequency f3, the first frequency f1 being an integer multiple of the third frequency f3. The second clock generator is preferably a frequency divider or comprises one. This enables synchronization between the drive signal and calculations on the calculation unit.

[0021] According to one embodiment of the drive device according to the invention, the drive device comprises a third clock generator. The third clock generator is designed, configured, and coupled to the electrical oscillator such that the third clock generator receives the output signal of the electrical oscillator and converts it into the second clock signal T2 with a fourth frequency f4, the first frequency f1 being an integer multiple of the fourth frequency f4. The third clock generator is preferably a frequency divider or comprises one. This enables synchronization between the drive signal and calculations on the control unit.

[0022] According to one embodiment of the drive device according to the invention, the control device has a sampling unit, wherein the drive device is designed and configured such that the sampling unit, when operating with the microelectromechanical system, firstly receives the drive signal or a third clock signal T3 synchronized with the drive signal and secondly receives the feedback signal of the microelectromechanical system indirectly, e.g. in filtered and / or amplified form, or directly, wherein the sampling unit is designed and configured such that it samples the received feedback signal in a time-discrete manner with a sampling frequency, for example with 32 samples per oscillation period of the drive signal, so that the sampling unit provides the digitized feedback signal as an output signal, wherein the sampling frequency is in particular the first frequency f1 of the drive signal,a fifth frequency f5 of the third clock signal T3 or a frequency f5' reduced or increased compared to the fifth frequency f5, wherein the latter frequency f5' can be obtained by forming an integral over a fixed number of data points of the feedback signal to be digitized, each measured at the fifth frequency, wherein the control device is preferably designed such that the sampling unit is connected upstream of a calculation unit as described above, so that the feedback signal is present in a time-discrete manner at the input of the calculation unit.

[0023] The scanning unit can be designed as an analog-to-digital converter or comprise one.

[0024] According to one embodiment of the drive device according to the invention, the drive device comprises a fourth clock generator. The fourth clock generator is designed, configured, and coupled to the electrical oscillator such that the fourth clock generator receives the output signal of the electrical oscillator and converts it into the third clock signal T3 with the fifth frequency f5, the first frequency f1 being an integer multiple of the fifth frequency f5. The fourth clock generator is preferably a frequency divider or comprises one. This enables simplified calculations in the calculation unit and thus enables an increase in energy efficiency.

[0025] According to one embodiment of the drive device according to the invention, the control device has a low-pass filter, which is preferably designed as a switched-capacitor filter, wherein the low-pass filter is designed and configured according to a first alternative such that the low-pass filter, when operating with the microelectromechanical system, exclusively receives and filters the feedback signal of the microelectromechanical system indirectly, e.g. in filtered and / or amplified form, or directly, or wherein the low-pass filter is designed and configured according to a second alternative such that the low-pass filter, when operating with the microelectromechanical system, on the one hand receives and filters the feedback signal of the microelectromechanical system indirectly, e.g.in filtered and / or amplified form, or directly and, on the other hand, receives the drive signal or a fourth clock signal T4 synchronized with the drive signal and filters it in a time-discrete manner, in particular in time with the first frequency f1 of the drive signal or in time with the sixth frequency f6 of the fourth clock signal T4, wherein the control device is preferably designed such that the low-pass filter is connected upstream of a sampling unit as described above, so that the feedback signal is low-pass filtered at the input of the sampling unit.

[0026] The design of the low-pass filter as a switched-capacitor filter allows the drive device to be configured in such a way that any change in the phase of the feedback signal caused by the low-pass filter is independent of any change in the MEMS's natural frequency. Consequently, the phase accuracy of the low-pass filter or any phase shift caused by the low-pass filter remains unaffected or unchanged when the MEMS's natural frequency changes.

[0027] According to one embodiment of the drive device according to the invention, the low-pass filter is designed according to the second alternative, wherein the drive device comprises a fifth clock generator, wherein the fifth clock generator is designed, configured and coupled to the electrical oscillator such that the fifth clock generator receives the output signal of the electrical oscillator and converts it into the fifth clock signal T4 with the sixth frequency f6, wherein the first frequency f1 is an integer multiple of the sixth frequency f6, wherein the fifth clock generator is preferably a frequency divider or comprises such a frequency divider.

[0028] According to one embodiment of the drive device according to the invention, the drive device comprises a first signal amplifier, wherein the first signal amplifier is designed, configured and arranged such that it amplifies the drive signal during operation with the microelectromechanical system and is connected upstream of the microelectromechanical system, so that the drive signal amplified by means of the first signal amplifier is present at the input of the microelectromechanical system.

[0029] According to one embodiment of the drive device according to the invention, the drive device comprises a second signal amplifier, wherein the second signal amplifier is designed, configured, and arranged such that, during operation with the microelectromechanical system, it amplifies the feedback signal and is connected upstream of the control device, such that the feedback signal amplified by the second signal amplifier is present at the input of the control device. According to one embodiment of the drive device according to the invention, the control device comprises a calculation unit designed at least as an IQ demodulator according to the above description and a sampling unit according to the above description, wherein the calculation unit is configured such that it accesses a lookup table stored in the control device for calculating the controlled variable R.This is a particularly strong simplification of a calculation and therefore particularly energy efficient.

[0030] According to one embodiment of the drive device according to the invention, the drive device comprises the second clock generator and the fourth clock generator and is designed such that the calculation unit and the sampling unit are operated with clock signals T1 and T3 that are synchronous with the drive signal. In the lookup table, each period i of the clock signal T1 or each period i of the clock signal T3 is assigned a precalculated value X(i) of at least one trigonometric function TRI, for example, a sine or cosine function. Since calculating trigonometric functions requires high computing capacity, this allows for particularly significant energy savings during the calculations.

[0031] According to one embodiment of the drive device according to the invention, the electrical oscillator is a voltage-controlled electrical oscillator.

[0032] According to one embodiment of the drive device according to the invention, the drive device is at least partially and preferably completely designed as an integrated electronic circuit.

[0033] According to one embodiment of the drive device according to the invention, the control device has a bandpass filter, wherein the bandpass filter receives the feedback signal, filters it and provides the filtered feedback signal, wherein the drive device preferably comprises a calculation unit designed as a phase detector (as described above) and the bandpass filter is arranged upstream of the phase detector, so that the phase detector receives the bandpass-filtered feedback signal.

[0034] The object underlying the invention is also achieved by a combination of a drive device according to one of the previously described embodiments with a mechanically oscillatable microelectromechanical system (MEMS).

[0035] According to one embodiment of the combination according to the invention, the drive device is designed and configured such that the electrical oscillator is at least indirectly connected to the microelectromechanical system in order to drive the mechanical oscillation of the microelectromechanical system with the drive signal, wherein the mechanical oscillation of the microelectromechanical system generates the feedback signal, wherein the controlled variable R is preferably designed such that the regulation of the controlled variable R to the target value R_soll causes a resonant drive of the oscillation of the microelectromechanical system, wherein the microelectromechanical system can in particular be a piezoelectric-microelectromechanical system and / or a micro-optoelectromechanical system. The MEMS thereby increases the frequency stability of the electrical oscillator.

[0036] According to one embodiment of the combination according to the invention, the microelectromechanical system is a MEMS scanner, preferably a resonantly driven MEMS scanner.

[0037] The object underlying the invention is also achieved by a spectacle device comprising a drive device according to one of the previously described embodiments and / or a combination according to one of the previously described embodiments.

[0038] According to one embodiment of the spectacle device according to the invention, it has an imaging device for projecting images into the field of vision of the user of the spectacle device, wherein the spectacle device preferably does not comprise a quartz oscillator.

[0039] The object underlying the invention is also achieved by a method for driving a microelectromechanical system, in particular a MEMS scanner, with the following steps: a) Providing a drive signal and driving a mechanical oscillation of the microelectromechanical system with the drive signal, b) Measuring a feedback signal of the mechanical oscillation of the microelectromechanical system, c) Setting a target value P_soll for the phase shift P between the drive signal and the native feedback signal, d) Setting a target value R_soll for a controlled variable R that is dependent on the drive signal and / or the feedback signal, wherein the target value R_soll of the controlled variable is selected such that when it is reached, the target value P_soll for the phase shift P is also reached, e) Determining the controlled variable R, f) Determining the difference D of the controlled variable R to the target value R_soll of the controlled variable,g) modifying the drive signal for step a), in particular modifying the frequency of the drive signal as a function of the difference D determined in step f) in order to minimize the difference D.

[0040] Preferably, the controlled variable depends on both the drive signal and the feedback signal.

[0041] According to one embodiment of the method according to the invention, steps e), f) and g) are continuously repeated in the form of a control loop.

[0042] According to one embodiment of the method according to the invention, the modification in step g) is carried out according to a predefined transfer function which depends on the difference D.

[0043] According to one embodiment of the method according to the invention, the determination of the controlled variable R in step e) takes place periodically and synchronously with driving the mechanical oscillation of the microelectromechanical system with the drive signal.

[0044] According to one embodiment of the method according to the invention, the controlled variable R is the phase shift P itself or the quadrature Q of the feedback signal with respect to a clock signal serving as a reference signal and formed synchronously with the drive signal.

[0045] Lists and numbering such as "second clock generator" do not imply a number, but serve only to uniquely identify the elements described. Therefore, if, for example, a reference is made to a "second clock generator," this should be understood as a name and does not necessarily mean that two clock generators are present.

[0046] When referring to a signal such as the feedback signal, this description refers to the native signal as well as any form of the signal further developed through filtering, amplification, or similar processing. When referring to the native signal—in other words, the original signal—this term is explicitly used.

[0047] The features of the previously described embodiments can be combined with one another, unless expressly excluded. Further advantages, features, and embodiments are apparent from the figure shown and its description.

[0048] Fig. 1 shows a schematic circuit diagram of an embodiment of an inventive combination of a MEMS, in particular a MEMS scanner (therefore called MEMS here and also referred to below as MEMS scanner) with a drive device.

[0049] Fig. 1 shows a schematic circuit diagram of an electrical oscillator according to the present invention in the form of a trimmable oscillator (here referred to as a VCO), which provides an output signal AuSi with a frequency fvco (f1). A timing block is connected downstream to generate all clock signals required in the system for the discrete-time circuits based on a common reference clock (here referred to as "clock generation including start logic").In this example, clock signals are provided for: the analog-to-digital converter (ADC for short), the clock signal T3 with the frequency fADc (corresponds to the frequency f5 described above); the IQ demodulator with low-pass filter (here called "IQ demodulation with LPF"), the clock signal T1 with the frequency f1Q (corresponds to the frequency f3 described above); the PLL controller, the clock signal T2 with the frequency fpLL (corresponds to the frequency f4 described above); and of course the MEMS scanner, the drive signal AnSi with the frequency fMEMs (corresponds to the frequency f2 described above). However, it is conceivable that, for example, the low-pass filter (LPF) is also implemented in a time-discrete manner before the ADC and thus also receives a clock signal.

[0050] The clock signals are designed in such a way that all clock signals are linked to the frequency of the drive signal via a respective natural number N. All discrete-time circuits thus run synchronously with the MEMS.

[0051] The drive signal generated by the timing block is then amplified in a downstream block (here referred to as the "drive signal amplifier"). This is necessary to supply the MEMS scanner with a drive signal of the appropriate amplitude for the desired operating point. The amplified drive signal with frequency f M EMs are then used to excite the MEMS scanner.

[0052] If the frequency is correctly selected, the MEMS scanner begins to oscillate mechanically. The high quality of the MEMS now contributes to filtering the drive signal AnSi. This means that the oscillation frequency of the MEMS corresponds to the average frequency of the drive signal AnSi, but with lower temporal jitter, thus improving frequency stability (similar to a discrete quartz oscillator).

[0053] The feedback signal FeSi generated by the MEMS scanner, also called sense signal, represents the instantaneous deflection angle of the mirror plate integrated in the MEMS scanner and thus directly corresponds to the current phase position of the MEMS with respect to its drive signal AnSi.

[0054] For further signal processing, the feedback signal FeSi is first amplified continuously (referred to here as the "feedback signal amplifier"), which can be achieved, for example, with a charge amplifier or a transimpedance amplifier. This is necessary to apply electrical stress to the feedback signal FeSi through the subsequent blocks.

[0055] The amplified feedback signal FeSi is then filtered through an anti-aliasing low-pass filter (LPF) and then digitized using an analog-to-digital converter (ADC). The low-pass filter can be implemented as continuous-time or discrete-time. In the latter case, however, the low-pass filter must be supplied with a suitable clock, which can also be generated by the timing block described above. The advantage of a discrete-time filter is a more stable phase response. However, this advantage must be individually weighed against the disadvantage of a potentially increased noise level.

[0056] It should be emphasized here that the ADC in this embodiment represents the transition between the analog and digital environments. However, a fully analog implementation of the synchronous drive device shown is also conceivable, for which no ADC is required.

[0057] After the feedback signal FeSi has been sampled by the ADC synchronously with the MEMS movement, a discrete-time and synchronized IQ demodulation with integrated low-pass filtering is performed. This extracts the instantaneous phase (and amplitude) of the largely sinusoidal feedback signal FeSi with respect to the MEMS excitation frequency, the frequency fMEMs (f2), which serves as the input for the subsequent phase control. The integrated low-pass filter helps filter out the unwanted frequency components generated during demodulation.

[0058] Due to the fact that the sampling of the feedback signal is synchronized and thus always occurs at well-defined times, the mathematical calculations carried out during signal processing can be massively simplified and thus the power consumption of the signal processing can also be reduced.

[0059] To close the phase-locked loop shown in Fig. 1, the phase shift P of the MEMS scanner (i.e., the native feedback signal) with respect to the drive signal AnSi, known from demodulation, is passed to the phase-locked loop control block ("PLL control"). In this block, the measured phase shift P is compared with the desired target phase shift P_target. Alternatively, an equivalent controlled variable can be compared with its target value if the effect is the same—namely, controlling the phase shift P to resonantly drive the MEMS.

[0060] The task of the PLL control unit is to minimize the calculated phase error, the difference D. To achieve this, the VCO's input variable f_soll and thus also the frequency f1 of the output signal AuSi are varied depending on the instantaneous phase error.

[0061] If the frequency of the VCO's output signal AuSi is temporarily too high, for example, due to the typically suboptimal frequency stability of a VCO, the MEMS scanner cannot immediately follow these spontaneous frequency changes and therefore continues to oscillate at a constant frequency. This leads to a measurable phase error, which in turn causes the control of the phase-locked loop - the PLL control - to reduce the VCO's target frequency (in the context of this invention, f1_soll). In this way, the MEMS acts as a stabilizing element of the entire synchronous drive concept and thus improves the frequency stability of the integrated oscillator (e.g., VCO) without the need to use a discrete (quartz) oscillator with higher power consumption and a larger installation space.

[0062] The process scheme described above repeats periodically, so that a largely defined phase shift P is established between the drive signal AnSi and the native feedback signal FeSi of the MEMS scanner.

[0063] If we now assume that the resonance frequency of the MEMS scanner changes over time, for example, due to external temperature fluctuations, this would also lead to a measurable phase error (a difference D in the sense of the present invention), which is corrected by the control loop. Thus, the entire system remains synchronized at all times.

Claims

P a t e n t a n s p r ü c h e 1. A drive device for a mechanical oscillation of a microelectromechanical system, wherein the drive device comprises an electrical oscillator, wherein the electrical oscillator is designed and configured such that it generates an electrical output signal (AuSi) with a first frequency (f1), wherein the electrical oscillator is designed and configured such that the first frequency (f1) of the output signal (AuSi) can be set to a target frequency (f1_soll), wherein the drive device is designed and configured such that the electrical oscillator is at least indirectly connectable to the microelectromechanical system in order to drive the mechanical oscillation of the microelectromechanical system with a drive signal (AnSi), wherein the drive device comprises a control device, wherein the control device is designed and configured such thatthat the control device, when operating with a microelectromechanical system, receives an electrical feedback signal (FeSi) from the microelectromechanical system, wherein the control device is designed and configured such that a controlled variable (R), which is dependent on the feedback signal (FeSi) and / or on the drive signal (AnSi), can be set to a target value (R_soll), wherein the control device is designed and configured such that, when operating with a microelectromechanical system, it calculates the controlled variable (R), wherein the control device is designed, configured and connected to the electrical oscillator such that it sets the target frequency (f1_soll) adjustable on the electrical oscillator as a function of the measured controlled variable (R) in order to control the controlled variable (R) to the target value (R_soll).

2. Drive device according to the preceding claim, wherein the feedback signal reflects the deflection of the mechanical oscillation of the microelectromechanical system.

3. Drive device according to one of the preceding claims, wherein the control device and controlled variable (R) are designed such that a control of the controlled variable (R) by the control device during operation with a microelectromechanical system to a target value (R_soll) causes a temporal constant-keeping of the phase shift between the drive signal (AnSi) and the feedback signal (FeSi) leaving the microelectromechanical system and therefore native.

4. Drive device according to the preceding claim, wherein the amount of the phase shift P which is kept constant over time is between 40 degrees and 140 degrees, preferably between 60 degrees and 120 degrees and particularly preferably between 70 degrees and 110 degrees.

5. Drive device according to one of the preceding claims, wherein the controlled variable is the phase shift (P) of the drive signal (AnSi) and the native feedback signal (FeSi), so that the control device is designed and configured such that, in operation with a microelectromechanical system, it adjusts the electrical oscillator to control the phase shift (P) of the drive signal (AnSi) and the native feedback signal FeSi to a target value for the phase shift (P_soll).

6. Drive device according to one of the preceding claims, wherein the controlled variable (R) is the quadrature (Q) of the feedback signal (FeSi) with respect to the drive signal (AnSi) as a reference signal, wherein the control device is preferably designed and configured such that a control of the quadrature to a target value for the quadrature of zero effects a control of the phase shift of the drive signal (AnSi) and the native feedback signal (FeSi) to a predefined target value (P_soll).

7. Drive device according to one of the preceding claims, wherein the control device comprises a calculation unit, for example a phase detector and / or IQ demodulator, wherein the drive device is designed and configured such that the calculation unit, when operating with the microelectromechanical system, receives, on the one hand, the drive signal (AnSi) or a first clock signal (T1) synchronized with the drive signal (AnSi) and, on the other hand, the feedback signal (FeSi) of the microelectromechanical system indirectly, e.g. in filtered and / or amplified form and / or digitalized, or directly, wherein the calculation unit is designed and configured such that, in operation with a microelectromechanical system, it either time-discretely or time-continuously receives the controlled variable R, for example • the quadrature Q of the feedback signal (FeSi) related to the drive signal as reference signal and / or • the phase shift between the drive signal (AnSi) and the native feedback signal (FeSi) is calculated, wherein the phase detector preferably comprises an IQ demodulator.

8. Drive device according to the preceding claim, wherein the control device has a control unit, wherein the control unit and the calculation unit are designed and configured such that the control unit, in operation with the microelectromechanical system, receives the controlled variable calculated by the calculation unit and calculates the difference (D) between the calculated controlled variable and the target value for the controlled variable (R_soll), wherein the control unit and the electrical oscillator are designed such that the control unit sets the target frequency (f 1 _soll) of the electrical oscillator depending on the calculated difference (D), wherein the control unit preferably comprises a loop filter with a transfer function specified for the control of the electrical oscillator.

9. Drive device according to the preceding claim, wherein the drive device is designed and configured such that the control unit, during operation with the microelectromechanical system, also receives the drive signal (AnSi) or a second clock signal (T2) synchronized with the drive signal (AnSi), so that the calculations performed in the control unit are carried out synchronously with the drive signal (AnSi).

10. Drive device according to one of the preceding claims, wherein the drive device comprises a first clock generator, wherein the first clock generator is designed, arranged, coupled to the electrical oscillator and connectable to the microelectromechanical system, that the first clock generator receives the output signal (AuSi) of the electrical oscillator and converts it into the drive signal (AnSi) with a second frequency (f2), wherein the first frequency (f1) is an integer multiple, for example 1024 times or 512 times, of the second frequency (f2), wherein the first clock generator is preferably a frequency divider or comprises such a frequency divider.

11. Drive device according to one of claims 7 to 10, wherein the drive device comprises a second clock generator, wherein the second clock generator is designed, configured and coupled to the electrical oscillator such that the second clock generator receives the output signal (AuSi) of the electrical oscillator and converts it into the first clock signal (T1) with a third frequency (f3), wherein the first frequency (f1) is an integer multiple of the third frequency (f3), wherein the second clock generator is preferably a frequency divider or comprises such a frequency divider.

12. Drive device according to one of claims 9 to 11, the drive device comprises a third clock generator, wherein the third clock generator is designed, configured and coupled to the electrical oscillator such that the third clock generator receives the output signal (AuSi) of the electrical oscillator and converts it into the second clock signal (T2) with a fourth frequency (f4), wherein the first frequency (f1) is an integer multiple of the fourth frequency (f4), wherein the third clock generator is preferably a frequency divider or comprises such a frequency divider.

13. Drive device according to one of the preceding claims, wherein the control device has a sampling unit, wherein the drive device is designed and configured such that the sampling unit, when operating with the microelectromechanical system, firstly receives the drive signal (AnSi) or a third clock signal (T3) synchronized with the drive signal (AnSi) and secondly receives the feedback signal (FeSi) of the microelectromechanical system indirectly, e.g. in filtered and / or amplified form, or directly, wherein the sampling unit is designed and configured such that it samples the received feedback signal (FeSi) in a time-discrete manner with a sampling frequency, for example with 32 Samples per oscillation period of the drive signal, so that the sampling unit provides the digitized feedback signal (FeSi) as an output signal, wherein the sampling frequency can be, in particular, the first frequency (f1) of the drive signal (AnSi), a fifth frequency (f5) of the third clock signal (T3), or a frequency (f5') reduced or increased compared to the fifth frequency (f5), wherein the latter frequency (f5') can be obtained by forming an integral over a fixed number of data points of the feedback signal to be digitized, measured at the fifth frequency, wherein the control device is preferably designed such that the sampling unit is connected upstream of a calculation unit, in particular a calculation unit according to claim 7, so that the feedback signal is present in a time-discrete manner at the input of the calculation unit,wherein the scanning unit is particularly preferably designed as an analog-digital converter or comprises such a converter., 14. Drive device according to the preceding claim, wherein the drive device comprises a fourth clock generator, wherein the fourth clock generator is designed, configured and coupled to the electrical oscillator such that the fourth clock generator receives the output signal (AuSi) of the electrical oscillator and converts it into the third clock signal (T3) with the fifth frequency (f5), wherein the first frequency (f1) is an integer multiple of the fifth frequency (f5), wherein the fourth clock generator is preferably a frequency divider or comprises such a frequency divider.

15. Drive device according to one of the preceding claims, wherein the control device has a low-pass filter, which is preferably designed as a switched capacitor filter, wherein the low-pass filter is designed and configured according to a first alternative such that the low-pass filter, when operating with the microelectromechanical system, exclusively receives and filters the feedback signal (FeSi) of the microelectromechanical system indirectly, e.g. in filtered and / or amplified form, or directly, or wherein the low-pass filter is designed and configured according to a second alternative such that the low-pass filter, when operating with the microelectromechanical system, on the one hand receives and filters the feedback signal (FeSi) of the microelectromechanical system in filtered and / or amplified form, or directly, and on the other hand receives the drive signal (AnSi) or a fourth clock signal (T4) synchronized with the drive signal (AnSi) and filters it in a time-discrete manner, in particular in time with the first frequency (f1) of the drive signal (AnSi) or in time with the sixth frequency (f6) of the fourth clock signal (T4), wherein the control device is preferably designed such that the low-pass filter is connected upstream of a sampling unit, in particular the sampling unit according to claim 13, so that the feedback signal is present in a low-pass filtered manner at the input of the sampling unit.

16. Drive device according to the preceding claim, wherein the low-pass filter is designed according to the second alternative, wherein the drive device comprises a fifth clock generator, wherein the fifth clock generator is designed, configured and coupled to the electrical oscillator such that the fifth clock generator receives the output signal (AuSi) of the electrical oscillator and converts it into the fifth clock signal (T4) with the sixth frequency (f6), wherein the first frequency (f1) is an integer multiple of the sixth frequency (f6), wherein the fifth clock generator is preferably a frequency divider or comprises such a frequency divider.

17. Drive device according to one of the preceding claims, wherein the drive device comprises a first signal amplifier, wherein the first signal amplifier is designed, configured and arranged such that it amplifies the drive signal (AnSi) during operation with the microelectromechanical system and is connected upstream of the microelectromechanical system, so that the drive signal (AnSi) amplified by means of the first signal amplifier is present at the input of the microelectromechanical system.

18. Drive device according to one of the preceding claims, wherein the drive device comprises a second signal amplifier, wherein the second signal amplifier is designed, configured and arranged such that it amplifies the feedback signal (FeSi) during operation with the microelectromechanical system and is connected upstream of the control device, so that the feedback signal (FeSi) amplified by means of the second signal amplifier is present at the input of the control device.

19. Drive device according to one of the preceding claims, wherein the control device comprises a calculation unit designed at least as an IQ demodulator according to claim 7 and a sampling unit according to claim 13, wherein the calculation unit is configured such that it accesses a lookup table stored in the control device for calculating the controlled variable R.

20. Drive device according to the preceding claim, wherein the drive device comprises the second clock generator according to claim 11 and the fourth clock generator according to claim 14 and is designed such that the calculation unit and the sampling unit are operated with clock signals T1 and T3 which are synchronous to the drive signal, wherein in the lookup table a precalculated value X(i) of at least one trigonometric function TRI, for example a sine or a cosine function, is assigned to each period i of the clock signal T1 or each period of the clock signal T3.

21. Drive device according to one of the preceding claims, wherein the electrical oscillator is a voltage-controlled electrical oscillator.

22. Drive device according to one of the preceding claims, wherein the drive device is at least partially and preferably completely designed as an integrated electronic circuit.

23. Drive device according to one of the preceding claims, wherein the control device has a bandpass filter, wherein the bandpass filter receives the feedback signal, filters it and provides the filtered feedback signal, wherein the drive device preferably comprises a calculation unit designed as a phase detector according to claim 7 and the bandpass filter is arranged upstream of the phase detector, so that the phase detector receives the bandpass-filtered feedback signal.

24. Combination of a drive device according to one of the preceding claims with a mechanically oscillatable microelectromechanical system (MEMS), wherein the drive device is designed and configured such that the electrical oscillator is at least indirectly connected to the microelectromechanical system is connected to drive the mechanical oscillation of the microelectromechanical system with the drive signal (AnSi), wherein the mechanical oscillation of the microelectromechanical system generates the feedback signal, wherein the controlled variable (R) is preferably designed such that the regulation of the controlled variable (R) to the target value (R_soll) effects a resonant driving of the oscillation of the microelectromechanical system, wherein the microelectromechanical system can in particular be a piezoelectric microelectromechanical system and / or a micro-optoelectromechanical system.

25. Combination according to the preceding claim, wherein the microelectromechanical system is a MEMS scanner, preferably a resonantly driven MEMS scanner.

26. A spectacle device comprising a drive device according to any one of claims 1 to 23 and / or a combination according to any one of claims 24 and 25.

27. A spectacle device according to the preceding claim, comprising an imaging device for projecting images into the field of vision of the user of the spectacle device, wherein the spectacle device does not comprise a quartz oscillator.

28. A method for driving a microelectromechanical system, in particular a MEMS scanner, comprising the following steps: h) providing a drive signal (AnSi) and driving a mechanical oscillation of the microelectromechanical system with the drive signal, i) measuring a feedback signal (FeSi) of the mechanical oscillation of the microelectromechanical system, j) defining a target variable (P_soll) for the phase shift (P) between the drive signal (AnSi) and the native feedback signal (FeSi), k) defining a target variable (R_soll) for a controlled variable (R) that is dependent on the drive signal (AnSi) and / or the feedback signal (FeSi), wherein the target variable (R_soll) of the controlled variable is selected such that when it is reached, the target variable (P_soll) for the phase shift (P) is also reached, l) determining the controlled variable (R), m) determining the difference (D) of the controlled variable (R) to the target value (R_setpoint) of the controlled variable, n) modifying the drive signal (AnSi) for step a), in particular modifying the frequency of the drive signal (AnSi) as a function of the difference (D) determined in step f) in order to minimize the difference (D).

29. Method according to the preceding claim, wherein steps e), f) and g) are continuously repeated in the form of a control loop.

30. Method according to one of claims 28 or 29, wherein the modification in step g) is carried out according to a predefined transfer function dependent on the difference (D).

31. Method according to one of claims 28 to 30, wherein the determination of the controlled variable in step e) takes place periodically and synchronously with driving the mechanical oscillation of the microelectromechanical system with the drive signal.

32. Method according to one of claims 28 to 31, wherein the controlled variable (R) is the phase shift (P) itself or the quadrature (Q) of the feedback signal with respect to a clock signal serving as a reference signal and formed synchronously with the drive signal.

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