Readout circuit for a MEMS gyroscope and method for operating such a readout circuit

Abstract

The present invention relates to a readout circuit for a MEMS gyroscope having an oscillating mass that can be excited to oscillate, comprising: an analog amplitude control loop / phase control loop for monitoring the oscillating motion of the oscillating mass and generating a drive signal to excite and maintain a defined oscillating motion of the oscillating mass; a sensing front end for providing measured values ​​of the MEMS gyroscope; a phase control loop for providing a demodulated clock signal for the sensing front end; and an energy management unit, which is constructed to predetermine a sensing operating mode of the MEMS gyroscope for detecting measured values ​​with the aid of the sensing front end and a standby operating mode of the MEMS gyroscope for not detecting measured values, in which the energy management unit activates the sensing front end and the phase control loop in the sensing operating mode and deactivates them in the standby operating mode, and the analog amplitude / phase control loop provides a drive signal for the MEMS gyroscope and a clock signal for the energy management unit independently of the operating mode of the MEMS gyroscope.

Description

Field of Technology

[0001] The present invention relates to a readout circuit for a MEMS gyroscope and a method for operating such a readout circuit, the MEMS gyroscope having an oscillating mass (seismische Masse) that can be excited to oscillate. Background Art

[0002] Known MEMS gyroscope units (hereinafter simply referred to as MEMS gyroscopes) are often used together with acceleration sensors in the inertial measurement units of portable terminal devices, for example, to enable applications in the field of extended reality (augmented reality) or for applications in building navigation (indoor navigation). It should be noted here to minimize energy consumption as much as possible. Compared with the energy consumption of acceleration sensors, the energy consumption of MEMS gyroscopes is relatively high because, for detection purposes, the oscillating mass of the sensor structure needs to be actively excited to oscillate in the excitation plane. Then, the rotational movement of the sensor about an axis oriented parallel to the excitation plane and perpendicular to the excitation direction can be detected as the deflection of the oscillating mass perpendicular to this excitation plane, because such rotational movement causes the Coriolis force (Corioliskraft), which acts on the oscillating mass perpendicular to the excitation plane. Generally, the oscillating mass of the MEMS gyroscope is placed in resonance oscillation. This oscillatory motion is always maintained because it takes a relatively long time to bring the oscillating mass from the rest state back into a defined oscillatory state again. This ensures that the sensor is always ready for measurement even if measurement data is not continuously detected. A known measure for reducing the energy consumption of MEMS gyroscopes is to turn off the readout circuit of the MEMS gyroscope if no measurement data is to be detected, but keep the drive circuit activated to maintain the oscillatory motion or oscillation of the oscillating mass. It is known to use a phase control loop (Phasenregelkreis) with low noise in the drive circuit because this phase control loop is not only used to generate the drive signal but also to provide a digital clock signal for the sensing front end. This phase control loop makes a decisive contribution to the energy consumption of the drive circuit and thus also to the overall energy consumption of the MEMS gyroscope because the drive circuit is always in the activated state to maintain the oscillatory motion of the oscillating mass.

[0003] A gyroscope system is known from US 9,506,757 B2, which includes a MEMS gyroscope connected to a drive system and a sensing system. The drive system keeps the MEMS gyroscope in an oscillating state, and the sensing system is kept in a state of receiving, amplifying, and demodulating the output signal of the MEMS gyroscope corresponding to the rotational speed of the MEMS gyroscope. The gyroscope system further includes a phase adjustment loop PLL, which receives a reference clock REFCLK from the drive system and generates a system clock CLK. In addition, the gyroscope system includes a control device that operates based on the system clock and determines the operating states of the drive system and the sensing system and also determines the operating state of the phase adjustment loop. Here, during a so-called protection mode, one or more system state variables are kept in a substantially unchangeable state, enabling a quick switch between a low-energy operating mode and a normal operating mode of the gyroscope system. Summary of the Invention

[0004] In one embodiment, the present invention provides a read circuit for a MEMS gyroscope having an oscillating mass that can be excited to oscillate, the read circuit comprising:

[0005] · An analog amplitude / phase adjustment loop for monitoring the oscillatory motion of the oscillating mass and for generating a drive signal for exciting and maintaining a defined oscillatory motion of the oscillating mass;

[0006] · A sensing front end that can be selectively activated and for providing a measurement value of the MEMS gyroscope;

[0007] · A phase adjustment loop that can be selectively activated and for providing a demodulation clock signal for the sensing front end;

[0008] · An energy management unit configured to,

[0009] - Preset an active sensing operating mode for the MEMS gyroscope, in which the measurement value is detected by means of the sensing front end, or

[0010] - Preset a standby operating mode for the MEMS gyroscope, in which the measurement value is not detected,

[0011] in such a way that the energy management unit activates the sensing front end and the phase adjustment loop in the sensing operating mode and deactivates the sensing front end and the phase adjustment loop in the standby operating mode, wherein the analog amplitude / phase adjustment loop provides a drive signal for the MEMS gyroscope independently of the operating mode of the MEMS gyroscope, and wherein the analog amplitude / phase adjustment loop provides a clock signal for the energy management unit.

[0012] In another embodiment, the present invention provides a method for operating a readout circuit for a MEMS gyroscope, the MEMS gyroscope having an oscillating mass that can be excited to oscillate, the method comprising the following steps:

[0013] - Monitoring the oscillatory motion of the oscillating mass by means of an analog amplitude / phase adjustment loop and generating a drive signal for exciting and maintaining a defined oscillatory motion of the oscillating mass;

[0014] - Providing a clock signal for the energy management unit by means of the analog amplitude / phase adjustment loop;

[0015] - Predetermining an active sensing operating mode or a standby operating mode for the MEMS gyroscope by means of the energy management unit by activating or deactivating the sensing front end and the phase adjustment loop, wherein, in the sensing operating mode,

[0016] - Providing a measurement value of the MEMS gyroscope by means of the activated sensing front end,

[0017] - Providing a demodulation clock signal for the sensing front end and a clock signal for the digital signal processing unit for the measurement value by means of the activated phase adjustment loop, wherein the clock signal has a higher frequency than the drive signal, for example at least 2 times, preferably at least 5 times.

[0018] In other words, a readout circuit is provided that can be operated in an alternating operating mode in a clock-driven manner, wherein the oscillating mass of the MEMS gyroscope is always kept in motion only by means of the analog amplitude / phase adjustment loop, independently of the operating mode of the sensing front end, and the sensing front end, the phase adjustment loop and the signal processing unit are switched on or operated only when measurement data of the MEMS gyroscope are required.

[0019] One of the advantages achieved thereby is that, by deactivating the phase adjustment loop in the standby operating mode, the energy consumption of the MEMS gyroscope can be significantly reduced while the oscillatory motion of the oscillating mass can be kept unaffected. Another advantage is that the analog amplitude / phase adjustment loop provides a clock signal for the energy management unit independently of the phase adjustment loop (i.e., also in the standby operating mode), and this clock signal can be used as a time base for switching between the sensing operating mode and the standby operating mode. According to the invention, the phase adjustment loop is activated only in the sensing operating mode in order to provide a demodulation clock signal for the activated sensing front end and, if necessary, a clock signal for the signal processing unit.

[0020] Other features, advantages and other embodiments of the present invention are described or disclosed hereinafter.

[0021] According to an advantageous refinement, the readout circuit is configured to detect the oscillatory movement of the oscillating mass in the form of a time-varying position signal and to provide it as an input signal to the phase adjustment loop. Correspondingly, in this embodiment of the invention, the demodulation clock signal for activating the sensing front end and, if necessary, the clock signal for the signal processing unit are derived from the frequency of the oscillatory movement of the oscillating mass, in particular from its resonance frequency.

[0022] According to another advantageous refinement, the analog amplitude / phase adjustment loop has an analog 90° phase shifter and a comparator connected downstream, the analog 90° phase shifter for the detected position signal and in particular in the form of an all-pass filter, the comparator generating a clock signal for the energy management unit from the position signal. Thus, in this case, the clock signal for the energy management unit is also derived from the frequency of the oscillatory movement of the oscillating mass, in particular from its resonance frequency.

[0023] According to another advantageous refinement, the analog amplitude / phase adjustment loop includes an amplitude demodulation unit to which the position signal and the clock signal are fed in order to obtain information about the amplitude of the oscillatory movement of the oscillating mass, wherein an analog control unit for adjusting the amplitude of the oscillatory movement of the oscillating mass is connected downstream of the amplitude demodulation unit, the analog control unit in particular in the form of a PD regulator or a PID regulator, wherein the analog amplitude / phase adjustment loop is configured to modulate the output signal of the control unit with the clock signal in order to generate a drive signal for the oscillating mass. The advantage of this is that, as a result, a drive signal for amplitude adjustment and phase adjustment of the MEMS gyroscope can be generated completely analogously and without the contribution of the phase adjustment loop.

[0024] According to another advantageous refinement, the oscillatory movement of the oscillating mass is detected capacitively. In this case, the analog amplitude / phase adjustment loop includes a capacitance-voltage converter for the capacitive position signal. The output of the capacitance-voltage converter is fed to the phase adjustment loop, the analog 90° phase shifter and the amplitude demodulation unit. It should be noted in the present case that the oscillatory movement of the oscillating mass can also be detected in other ways, for example piezoelectrically or piezoresistively. Then, other converter elements will replace the capacitance-voltage converter.

[0025] According to another advantageous refinement, the digital energy management unit is configured to use the clock signal as a time base for switching between the sensing operating mode and the standby operating mode of the MEMS gyroscope. As already mentioned, in this variant, the time base for the energy management unit is derived from the frequency of the oscillatory movement of the oscillating mass, in particular from its resonance frequency.

[0026] According to another advantageous expansion scheme, the readout circuit has a digital signal processing unit that can be selectively activated and is used for the measurement values of the MEMS gyroscope provided by the sensing front end. Here, the energy management unit is configured to activate the digital signal processing unit in the sensing operating mode and disable the digital signal processing unit in the standby operating mode. In addition, the phase adjustment loop is configured to provide a clock signal for the digital signal processing unit, and this clock signal has a higher frequency than the drive signal, for example, at least 2 times, preferably at least 5 times.

[0027] Other important features and advantages of the present invention result from the preferred embodiments, from the drawings, and from the associated description of the drawings.

[0028] It can be understood that, without departing from the scope of the present invention, the above-mentioned features and the features to be described below can be used not only in the combinations separately described, but also in other combinations or alone. Description of the Drawings

[0029] The preferred embodiments and implementations of the present invention are shown in the drawings and further elaborated in the following description, where the same reference numerals refer to the same or similar or functionally identical components or elements.

[0030] Shown here:

[0031] Figure 1 Showing a readout circuit for a MEMS gyroscope according to an embodiment of the present invention;

[0032] Figure 2 Showing a block diagram for showing the operation mode of an energy management unit according to an embodiment of the present invention. Detailed Description of the Invention

[0033] In Figure 1The gyroscope system 1 is shown in detail. The gyroscope system 1 includes a MEMS gyroscope 2 having an oscillating mass that can be excited to oscillate. The MEMS gyroscope 2 is connected to an analog amplitude / phase adjustment circuit 3 and a sensing front end 4. The analog amplitude / phase adjustment circuit 3 receives a position signal 103, for example in the form of a capacitance change (which describes the oscillating movement of the oscillating mass), from the MEMS gyroscope 2 and supplies a drive signal 100 to the MEMS gyroscope 2 in order to excite and maintain a defined oscillating movement of the oscillating mass, that is, with a defined frequency and amplitude. For reasons of energy efficiency, the oscillating mass is usually excited to produce a resonant oscillation. The MEMS gyroscope 2 detects the rotational rate of a rotational movement and supplies a corresponding measurement signal 101 with the aid of the sensing front end 4. These measurement signals are fed to a digital signal processor 6a, which is part of a digital circuit 6. The digital circuit also includes a digital energy management unit 6b for the gyroscope system 1.

[0034] As already implemented, with the aid of the analog amplitude / phase adjustment circuit 3, a defined oscillatory movement of the oscillating mass of the MEMS gyroscope 2 is excited or maintained with a constant amplitude. In the embodiment shown here, the oscillatory movement is detected capacitively, i.e., the position of the oscillating mass of the MEMS gyroscope 2. The corresponding position signal 103 is fed to the capacitance-voltage converter 3a of the analog amplitude / phase adjustment circuit 3 and converted into a corresponding voltage signal. The sinusoidal output signal of the capacitance-voltage converter 3a is passed to the analog phase shifter 3b and the amplitude demodulation unit 3d, which is also part of the amplitude adjustment circuit / phase adjustment circuit 3. The analog phase shifter 3b shifts the phase of the voltage signal by 90°. The analog phase shifter can be provided, for example, in the form of an all-pass filter. The voltage signal with a 90° phase shift is then converted by the comparator 3c into a rectangular clock signal 104. Then, on the one hand, this clock signal 104 is fed to the amplitude demodulation unit 3d, and on the other hand, this clock signal 104 is also provided to the digital energy management unit 6b. The amplitude information of the voltage signal output by the capacitance-voltage converter 3a is provided again by means of the amplitude demodulation unit 3d. For this purpose, the amplitude demodulation unit 3d can, for example, sample the sinusoidal voltage signal and in particular sample its extreme values and / or use a mixer. The amplitude information thus obtained is provided to the analog control unit 3e, which adjusts the amplitude of the oscillatory movement to the reference value Ref. Here, mostly a temperature-independent reference voltage is involved, which corresponds to a predefined desired amplitude. The control unit 3e can work proportionally or proportional-integratively. The signal output by the analog control unit 3e is a DC voltage signal, which is then modulated with the aid of the clock signal output by the comparator 3c in order to obtain the corresponding maximum energy input from the usually present drive electrodes to the oscillating mass of the gyroscope 2.

[0035] As already mentioned, the clock signal 104 is also fed to the energy management unit 6b, which uses this clock signal 104 as a time base for the user-defined automatic switching on and off of the measurement function of the gyroscope system 1, which is also referred to as "duty cycle". In the embodiment described here, the gyroscope system 1 can either operate in an active sensing operating mode (in which the measurement signals are detected and processed) or in a standby operating mode (in which no measurement signals are detected). The energy management unit 6b predefines the corresponding operating mode in such a way that it activates the sensing front end 4, the phase adjustment circuit 5, and the digital signal processor 6a for the sensing operating mode and disables these for the standby operating mode. The activation and deactivation are carried out with the aid of the control signal 106, which is also done by Figure 2is shown. Regardless of this, energy is always supplied to the amplitude adjustment circuit / phase adjustment circuit 3. The amplitude adjustment circuit / phase adjustment circuit is always active in order to maintain the oscillatory motion of the oscillating mass of the MEMS gyroscope 2 independently of the operating mode, and to generate a clock signal 104 as a time base for the energy management unit 6b independently of the operating mode.

[0036] The output signal of the capacitance-voltage converter 3a is fed to the phase adjustment circuit 5, from which, on the one hand, a demodulation clock signal 102 with low noise for the sensing front end 4 is derived, and on the other hand, a high-frequency clock signal 105 for the signal processor 6a, typically greater than 1 MHz. This is associated with a relatively high current consumption, but only takes place in the sensing operating mode, since the phase adjustment circuit 5 is disabled in the standby operating mode.

[0037] The sensing front end 4 converts the measurement signal of the MEMS gyroscope 2 into a digital signal 101 for the digital signal processor 6a using the demodulation clock signal 102. The digital signal processor 6a can then, for example, filter the digital sensor signal 101, perform temperature compensation and / or correction in terms of the offset or gain of the data.

[0038] The following explains in combination Figure 1 and 2 the mode of operation or operation of the readout circuit for the MEMS gyroscope 2 described.

[0039] The oscillatory motion of the oscillating mass of the MEMS gyroscope 2 is continuously monitored in order to excite or maintain a defined oscillatory motion by generating a corresponding drive signal 100, that is to say, independently of the respective operating mode of the gyroscope system 1. The drive signal 100 is generated by means of an analog amplitude / phase adjustment circuit 3.

[0040] Also independently of the respective operating mode of the gyroscope system 1, the amplitude adjustment circuit / phase adjustment circuit 3 generates a clock signal 104 as a time base for the energy management unit 6b. The energy management unit predefines the operating mode of the gyroscope system 1, that is to say, predefines the active sensing operating mode or the standby operating mode by activating or deactivating the sensing front end 4, the phase adjustment circuit 5 and the digital signal processor 6a.

[0041] In the sensing operating mode, the activated sensing front end 4 generates a digitized sensor signal 101 from the sensor signal detected by the MEMS gyroscope 2. For this purpose, the activated phase adjustment circuit 5 generates a demodulation clock signal 102 and supplies this demodulation clock signal to the sensing front end 4. In addition, the phase adjustment circuit 5 generates a high-frequency clock signal 105 for the digital signal processing unit 6a and feeds the digital sensor signal 101 to this digital signal processing unit for further signal processing.

[0042] The above measures according to the present invention enable a significant reduction in the current consumption of a MEMS gyroscope in "duty cycle" mode even without shutting off the actuation circuit or drive circuit for the oscillating mass. According to the present invention, the drive circuit is implemented in the form of a pure analog amplitude / phase regulation loop. In addition to the drive signal for the MEMS gyroscope, this amplitude regulation loop / phase regulation loop also provides a clock signal as the time base for the energy management unit, which is derived from the oscillation frequency of the oscillating mass. Here, it generally relates to the resonance frequency, which is typically in the range of 20 kHz to 50 kHz. The noise requirements for the demodulation clock signal for the sensing front end are relatively high, that is, only very low noise is allowed. Therefore, the energy consumption of the phase regulation loop providing this demodulation clock signal is relatively high. Therefore, according to the present invention, the phase regulation loop is only activated in the sensing operating mode, that is, when the measured values should actually be detected and called.

[0043] Although the present invention has been described based on preferred embodiments, the present invention is not limited thereto, but can be modified in various ways.

Claims

1. A readout circuit (1) for a MEMS gyroscope (2), the MEMS gyroscope having an oscillating mass that can be excited to oscillate, the readout circuit at least comprises: an analog amplitude / phase adjustment loop (3) for monitoring the oscillatory motion of the oscillating mass and for generating a drive signal (100) for exciting and maintaining a defined oscillatory motion of the oscillating mass; a sensing front end (4) that can be selectively activated and for providing a measurement value (101) of the MEMS gyroscope (2); a phase adjustment loop (5) that can be selectively activated and for providing a demodulation clock signal (102) for the sensing front end (4); an energy management unit (6b) configured to predetermine an active sensing operating mode for the MEMS gyroscope (2) in which the measurement value (101) is detected, predetermine a standby operating mode for the MEMS gyroscope (2) in which the measurement value (101) is not detected, in such a way that the energy management unit (6b) activates the sensing front end (4) and the phase adjustment loop (5) in the active sensing operating mode and deactivates the sensing front end and the phase adjustment loop in the standby operating mode, wherein the analog amplitude / phase adjustment loop (3) provides the drive signal (100) for the MEMS gyroscope (2) independently of the operating mode of the MEMS gyroscope (2), and wherein the analog amplitude / phase adjustment loop (3) provides a clock signal (104) for the energy management unit (6b).

2. The readout circuit according to claim 1, wherein the readout circuit (1) is configured to detect the oscillatory motion of the oscillating mass as a time-varying position signal (103) and to provide the position signal as an input signal to the phase adjustment loop (5).

3. The readout circuit according to claim 2, wherein the analog amplitude / phase adjustment loop (3) has an analog 90° phase shifter (3b) for the detected position signal (103), and the analog amplitude / phase adjustment loop (3) has a comparator (3c) connected downstream, the comparator generating the clock signal (104) from the position signal (103).

4. The readout circuit according to claim 3, wherein The analog amplitude / phase adjustment circuit (3) includes an amplitude demodulation unit (3d) to which the position signal (103) and the clock signal (104) are fed in order to obtain information about the amplitude of the oscillatory motion of the oscillating mass. Behind the amplitude demodulation unit (3d), an analog control unit (3e) is connected, which is used to adjust the amplitude of the oscillatory motion of the oscillating mass. The analog amplitude / phase adjustment circuit (3) is configured to modulate the output signal of the analog control unit (3e) by means of the clock signal (104) in order to generate the drive signal (100).

5. The reading circuit according to claim 4, wherein, the oscillatory motion of the oscillating mass is capacitively detected, and the analog amplitude / phase adjustment circuit (3) includes a capacitance-voltage converter (3a) for the capacitive position signal (103), and the output of the capacitance-voltage converter (3a) is fed to the phase adjustment circuit (5), the analog 90° phase shifter (3b), and the amplitude demodulation unit (3d).

6. The reading circuit according to any one of claims 1 to 5, wherein, the energy management unit (6b) is configured to use the clock signal (104) as a time base for switching between the active sensing operating mode and the standby operating mode of the MEMS gyroscope (2).

7. The reading circuit according to any one of claims 1 to 5, the reading circuit having a digital signal processing unit (6a) which can be selectively activated and is used for the measurement values (101) provided by the sensing front end (4) of the MEMS gyroscope (2), wherein, the energy management unit (6b) is configured to activate the digital signal processing unit (6a) in the active sensing operating mode and to deactivate the digital signal processing unit (6a) in the standby operating mode, and the phase adjustment circuit (5) is configured to provide a clock signal (105) for the digital signal processing unit (6a), which clock signal has a higher frequency than the drive signal (100).

8. The reading circuit according to claim 3, wherein, the analog 90° phase shifter (3b) is configured in the form of an all-pass filter.

9. The reading circuit according to claim 4, wherein, the analog control unit (3e) is configured in the form of a PD regulator or a PID regulator.

10. The reading circuit according to claim 7, wherein, the clock signal (105) has a higher frequency than the drive signal (100), and the frequency of the clock signal (105) is at least twice the frequency of the drive signal (100).

11. The reading circuit according to claim 7, wherein, The clock signal (105) has a higher frequency than the drive signal (100), and the frequency of the clock signal (105) is at least five times the frequency of the drive signal (100).

12. A method for operating a readout circuit (1) for a MEMS gyroscope (2), the MEMS gyroscope having an oscillating mass that can be excited to oscillate, the method comprising the following steps: monitoring the oscillatory movement of the oscillating mass by means of an analog amplitude / phase adjustment loop (3) and generating a drive signal (100) for exciting and maintaining a defined oscillatory movement of the oscillating mass; providing a clock signal (104) for an energy management unit (6b) by means of the analog amplitude / phase adjustment loop (3); predetermining an active sensing operating mode or a standby operating mode for the MEMS gyroscope (2) by means of the energy management unit (6b) by activating or deactivating a sensing front end (4) and a phase adjustment loop (5); and in the active sensing operating mode: providing a measurement value (101) of the MEMS gyroscope (2) by means of the activated sensing front end (4); providing a demodulation clock signal (102) for the sensing front end (4) and a clock signal (105) for a digital signal processing unit (6a) for the measurement value (101) by means of the activated phase adjustment loop (5), wherein the clock signal (105) has a higher frequency than the drive signal (100).

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