GÜTEFAKTORKOMPENSATION IN MEMS(MICROELECTROMECHANICAL SYSTEM)-GYROSKOPEN

Abstract

Procedures, exhibiting: Received by a resonator of a MEMS (Microelectromechanical System) gyroscope, a resonator signal generated in response to a movement of the resonator; Determining the quality factor of the resonator using the resonator signal; Generating a compensation signal with at least one time characteristic determined using the quality factor of the resonator; Received by a sensor of the MEMS gyroscope, a detection signal generated in response to an angular movement of the MEMS gyroscope; and Generating a compensated acquisition signal using the acquisition signal and the compensation signal; further showing: Detecting a resonant frequency of the resonator using the resonator signal; and Driving the resonator with a drive signal determined using the resonance frequency and the quality factor; wherein driving the resonator with a drive signal determined using the resonance frequency and the quality factor involves varying an average of the drive signal based on the quality factor and / or varying an impulse density of the drive signal based on the quality factor.

Description

AREA OF REVELATION

[0001] The present disclosure relates to MEMS (Microelectromechanical System) gyroscopes. GENERAL STATE OF THE ART

[0002] MEMS (Microelectromechanical System) gyroscopes are designed to detect angular motion by sensing accelerations generated by Coriolis forces. Coriolis forces arise when a resonant mass of a MEMS gyroscope is subjected to angular motion.

[0003] DE 10 2016 105 527 A1 describes a system, a device and a method for resonator and Coriolis axis control in vibration gyroscopes.

[0004] US 2013 / 0 008 226 A1 discloses an oscillating microsystem with a loop for automatic gain control with integrated control of the quality factor.

[0005] US 2017 / 0307374A1 discloses a compensation circuit for a microelectromechanical (MEMS) resonator. BRIEF SUMMARY OF THE REVELATION

[0006] The claimed subject matter is defined in the independent claims. Advantageous further developments are described in the dependent claims.

[0007] Some aspects of this disclosure relate to circuits and methods for compensating MEMS gyroscopes for quality factor variations. Quality factor variations occur when mechanical losses are introduced into the gyroscope's resonator, for example, due to thermoelastic damping or squeeze-film damping, which can impair the gyroscope's ability to accurately detect angular velocity. Quality factor compensation can be achieved by generating a compensation signal with a decay rate that depends on the quality factor of the gyroscope's resonator. This limits artifacts that might otherwise arise in the gyroscope's output signal. Additionally or alternatively, quality factor compensation can be achieved by controlling the force with which the gyroscope's resonator is driven.In some embodiments, this can be achieved by controlling the average value of the control signal.

[0008] According to one aspect of the present disclosure, a method is described. The method may comprise: receiving, from a resonator of a MEMS gyroscope, a resonator signal generated in response to a movement of the resonator; determining a quality factor of the resonator using the resonator signal; generating a compensation signal with at least one time characteristic determined using the quality factor of the resonator; receiving, from a sensor of the MEMS gyroscope, a detection signal generated in response to an angular movement of the MEMS gyroscope; and generating a compensated detection signal using the detection signal and the compensation signal.

[0009] According to another aspect of the present disclosure, a MEMS device is described. The MEMS device may include a gyroscope comprising a sensor and a resonator; and a control circuit arrangement configured to: receive, from the resonator, a resonator signal generated in response to a movement of the resonator; determine a quality factor of the resonator using the resonator signal; generate a compensation signal with a time characteristic determined using the quality factor of the resonator; receive, from the sensor, a detection signal generated in response to an angular movement of the MEMS gyroscope; and generate a compensated detection signal using the detection signal and the compensation signal.

[0010] According to another aspect of the present disclosure, a MEMS device is described. The MEMS device may comprise: a gyroscope comprising a sensor and a resonator; a quality factor measurement circuit coupled to a motion detection electrode of the resonator; a compensation circuit with an input terminal coupled to the quality factor measurement circuit and an output terminal, wherein the compensation circuit comprises a transient compensation circuit arrangement; and a signal combination circuit arrangement coupled to the sensor and the output terminal of the transient compensation circuit arrangement. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Various aspects and embodiments of the disclosure are described with reference to the following figures. The figures are not necessarily drawn to scale. Elements appearing in several figures are designated with the same reference number in all figures in which they appear. Fig. Figure 1A is a block diagram representing a MEMS gyroscope according to some embodiments of the technology described herein. Fig. 1B is a diagram showing the spectral response of the resonator of Fig. 1A illustrated at different times according to some embodiments of the technology described herein. Fig. Figure 2 is a schematic diagram of an illustrative MEMS gyroscope, known as the MEMS gyroscope of Fig. 1A can serve, according to some embodiments of the technology described herein. Fig. Figure 3A is a block diagram illustrating a control circuit arrangement for compensating a MEMS gyroscope for quality factor fluctuations according to some embodiments of the technology described herein. Fig. Figure 3B is a flowchart illustrating a method for compensating a MEMS gyroscope for quality factor variations according to some embodiment of the technology described herein. Fig. Figures 4A-4C show illustrative examples of resonator signals with different amplitudes according to some embodiments of the technology described herein. Fig. Figures 4D-4F show illustrative examples of drive signals with different pulse densities according to some embodiments of the technology described herein. Fig. 5A is a block diagram of an illustrative compensation circuit used in the control circuit arrangement of Fig. 3A can be used according to some embodiments of the technology described herein. Fig. 5B is a block diagram of another illustrative compensation circuit used in the control circuit arrangement of Fig. 3A can be used with a transient compensation circuit, according to some embodiments of the technology described herein. Fig. 5C is a block diagram of yet another illustrative compensation circuit, which is part of the control circuit arrangement of Fig. 3A can be used with a transient compensation circuit and a blanking circuit, according to some embodiments of the technology described herein. Fig. Figure 6A is a diagram illustrating the operation of a circuit with a control circuit resonator path compensation according to some embodiments of the technology described herein. Fig. 6B is a diagram showing the operations of the compensation circuit of Fig. 5A is illustrated according to some embodiments of the technology described herein. Fig. 6C is a diagram illustrating the operations of the compensation circuit of Fig. 5B illustrates some embodiments of the technology described herein. Fig. 6D is a diagram that shows the operations of the compensation circuit of Fig. 5C is illustrated according to some embodiments of the technology described herein. DETAILED DESCRIPTION I. Overview

[0012] The inventors have recognized and understand that the ability of gyroscopes to precisely detect the velocity of an angular motion to which they are subjected can be impaired by unwanted fluctuations in the quality factor of the gyroscope's resonator. The quality factor is defined here as the ratio between the resonant frequency and the bandwidth of the gyroscope's resonator.

[0013] Under certain circumstances, fluctuations in the quality factor relative to the nominal value can occur in response to mechanical losses within the resonator, which may be due to thermoelastic damping or squeeze-film damping, among other phenomena. Such mechanical losses can broaden or narrow the resonator's spectral response, resulting in a change in the quality factor. When a fluctuation in the quality factor occurs, the gyroscope's amplitude response may vary over time, even if the magnitude of the angular velocity remains constant. Such fluctuations lead to undesirable distortions in the gyroscope's output signal.

[0014] The inventors further recognize and understand that a conventional gyroscope, which may be susceptible to fluctuations in the quality factor, can be improved by compensating the gyroscope's output signal for these fluctuations. In some embodiments, the compensation can be performed by: (1) determining the quality factor of a gyroscope based on the gyroscope resonator signal; (2) generating a compensation signal using the determined quality factor; and (3) multiplying the gyroscope's detection signal by the compensation signal. In some embodiments, the compensation can be performed in real time (e.g., while angular motion is being detected). In some embodiments, a control circuit arrangement is coupled to the gyroscope and is configured to determine fluctuations in the resonator's quality factor and to generate a compensation signal while these fluctuations occur.In this way, changes in the quality factor are constantly monitored and discounted from the output signal of the gyroscope.

[0015] In some embodiments, control circuit resonator signal path compensation can be applied to the gyroscope. Control circuit resonator signal path compensation, which in some embodiments can be considered a coarse compensation technique, can be used to limit larger changes in the gyroscope's output signal resulting from fluctuations in the quality factor. In some embodiments, the control circuit resonator signal path compensation is performed by adjusting the force applied to the gyroscope's resonator. The extent to which the force is varied can depend on the extent to which the quality factor has changed. For example, the greater the extent to which the quality factor has decreased, the greater the force that can be applied to the resonator.

[0016] The inventors have further recognized and understand that the impact of quality factor variations on the sensitivity of a gyroscope can be further reduced by using sensing signal path compensation in addition to control circuit resonator signal path compensation. Accordingly, in some embodiments, the control circuit resonator signal path compensation can introduce distortions into the gyroscope's output signal, which can lead to unsatisfactory angular velocity measurements. The sensing signal path compensation, which in some embodiments can be considered a fine-tuning technique, can aim to limit the development of these distortions. For example, in some embodiments, a compensation signal with a time characteristic determined based on the resonator's quality factor can be generated. An example of a time characteristic is a decay rate.Accordingly, in a specific example, a compensation signal with a decay rate determined based on the quality factor is generated. Since the decay rate is related to the quality factor, distortions in the gyroscope's output signal that may arise due to control circuit resonator signal path compensation can be limited or even completely suppressed. To further limit distortions in the gyroscope's output signal, some embodiments can additionally force the compensation signal to a substantially constant value during a specific time period. This technique, referred to here as "blanking," can limit spikes or other features that might otherwise distort the gyroscope's output signal.

[0017] It is understood that under certain circumstances, acquisition signal path compensation can be used without the need for control circuit resonator signal path compensation. This might be the case, for example, if small fluctuations in the quality factor are expected.

[0018] It is understood that the techniques introduced above and discussed in more detail below can be implemented in any of numerous ways, since the techniques are not limited to any particular method of implementation. Examples of implementation details are provided here for illustrative purposes only. Furthermore, the techniques disclosed herein can be used individually or in any suitable combination, since aspects of the technology described herein are not limited to the use of any particular technique or combination of techniques.

[0019] Fig. Figure 1A is a block diagram illustrating a gyroscope 10 according to some embodiments. The gyroscope 10 has a resonator 12 and a sensor 14. The resonator 12 is configured to oscillate when driven by a signal with a frequency f. R The sensor 14 (which in some embodiments may be an accelerometer) is designed to detect angular velocities. When the gyroscope 10 is subjected to an angular movement (e.g., when the gyroscope is rotated relative to an axis), the angular rate at which the angular movement occurs (e.g., the rotation rate around the axis) can be detected using the sensor 14.

[0020] In some embodiments, the gyroscope 10 is configured to detect angular velocities by sensing an acceleration resulting from the Coriolis effect. The Coriolis effect, and thus a Coriolis force, arises when: 1) the resonator 12 oscillates; and 2) the gyroscope is subjected to an angular motion. Under these circumstances, the sensor 14 can detect the acceleration resulting from the Coriolis effect. The angular rate associated with the angular motion can be deduced from the acceleration, for example, by using a detection circuit arrangement coupled to the sensor 14.

[0021] The resonator 12 and the sensor 14 can be arranged in any suitable manner. In some embodiments, the resonator 12 can contain a test mass and the sensor 14 can contain a separate test mass. In other embodiments, the resonator 12 and the sensor 14 can share the same test mass.

[0022] In some embodiments, the gyroscope's ability to precisely detect angular motion can be impaired by the fact that the quality factor of the resonator 12 fluctuates over time, which can be attributed to losses in the mechanical system. Various factors can lead to these losses, including mechanical damping, thermoelastic damping, and squeeze-film damping. The losses may depend on the ambient temperature and / or ambient pressure. Fig. Figure 1B is a diagram representing the spectral response of resonator 12 at times t1 and t2 (where t2 is later than t1), according to some embodiments. In particular, curve 20 represents the spectral response of resonator 12 at time t1, and curve 22 represents the spectral response of resonator 12 at time t2, with both curves plotted as amplitude versus frequency. As shown, both curves have maxima at frequency f. R , the resonant frequency of resonator 12. However, curve 20 has a bandwidth Δf1, while curve 22 has a bandwidth Δf2 greater than Δf1 (where the bandwidths Δf1 and Δf2 can represent the respective 3 dB bandwidths). The widening of the bandwidth between t1 and t2 can, for example, be attributed to a temperature increase. Consequently, the quality factor of the resonator (which is the ratio between f) Rand Δf is defined) deteriorates between t1 and t2. Some aspects of the technology described herein target circuits and techniques for compensating MEMS gyroscopes for quality factor variations. II. Example of a MEMS gyroscope

[0023] An example implementation of gyroscope 10 is in Fig. Figure 2 shows some embodiments. In this example, the gyroscope 100 is configured to oscillate in a direction parallel to the x-axis and to detect Coriolis forces in a direction parallel to the y-axis. However, it is understood that gyroscopes of the types described herein are not limited to any specific direction of resonance or detection.

[0024] The MEMS gyroscope 100 comprises test masses 101 and 102, armature 103, fingers 105, 107, 114, 132, and 133, and stationary electrodes 104, 108, 110, 122, and 123. The test masses 101 and 102 can be suspended above a substrate 115, which in some embodiments may be made of silicon. The substrate 115, the test masses 101 and 102, the armature 103, the fingers 105, 107, 114, 132, and 133, and the stationary electrodes 104, 108, 110, 122, and 123 can be fabricated using MEMS techniques. For example, the test masses 101 and 102 can be formed by depositing a layer of material onto a sacrificial layer. The sacrificial layer can then be etched, leaving the test materials suspended above the substrate 115. In one example, the test materials 101 and 102 are made of (doped or undoped) polysilicon. The test materials 102 and 101 can be used as resonator 12 and sensor 14, respectively (see Fig. 1A) serve.

[0025] The test mass 101 is connected to the substrate via anchors 103, which can extend in a direction parallel to the z-axis. The test mass 101 is also connected to the anchors via flexures 111. The flexures 111 allow movement of the test mass 101 in a direction parallel to the y-axis.

[0026] As shown, the test mass 102 is enclosed within the test mass 101 in the xy-plane. However, not all embodiments are limited to this arrangement. The test masses 101 and 102 are elastically coupled to each other via flexures 117. The flexures 117 allow movement of the test mass 102 in a direction parallel to the x-axis.

[0027] The function of the MEMS gyroscope 100 is based on the Coriolis effect. In the example of Fig. 2. An angular motion of the MEMS gyroscope about the z-axis can be detected by detecting an acceleration of the test mass 101 in the y-axis direction when the test mass 102 is driven to oscillate in the x-axis direction. As such, the x-axis is referred to here as the "resonator axis" and the y-axis as the "Coriolis axis." However, MEMS gyroscopes of the types described herein are not limited to detecting angular motion about the z-axis, as shown in the figure, but can be used to detect motion about any suitable axis. Furthermore, some MEMS gyroscopes can even be configured as multi-axis gyroscopes, enabling the detection of angular motion about two or three axes using a single device (e.g., a single pair of elastically coupled test masses).

[0028] The vibration of the test mass in the x-axis direction can be initiated using drivers 106 and 109 (although any other suitable number of drivers can be used). Driver 106 includes stationary electrodes 104 and fingers 105. The stationary electrodes 104 can be attached to the substrate 115 via armatures extending along the z-axis. The fingers 105 are connected to and extend away from the test mass 102. The fingers 105 and the stationary electrodes 104 are arranged in an alternating configuration, forming several capacitors. Similarly, driver 109 includes stationary electrodes 108 and fingers 107. Movement of the test mass 102 along the x-axis can be initiated by applying a signal to the capacitors formed between the stationary electrodes and the fingers.When a signal is applied to the capacitors, corresponding attractive electrostatic forces are generated, causing the test mass to move from its initial position in the x-axis direction. Applying periodic signals (e.g., sinusoidal signals) can cause the test mass to oscillate periodically. Drivers 106 and 109 can be driven by signals that are out of phase with each other (e.g., by 180°).

[0029] As described in detail below, in some embodiments it may be desirable to monitor the movement of the test mass 102 during the operation. Monitoring the movement can be achieved using a motion detector 151. The motion detector 151 comprises stationary electrodes 110 and fingers 114, which form several capacitors. For the sake of simplicity, in the exemplary embodiment of Fig. Figure 2 shows only one motion detector 151, although alternative embodiments may have additional motion detectors. When the test mass moves in response to a drive signal, the extent to which the finger 114 and the stationary electrode 110 overlap varies (due to longitudinal movement of the finger), thereby varying the capacitance of the capacitor. As such, a detection signal can be generated in the motion detector 151 in response to movement of the test mass 102. For example, the movement of the test mass can lead to an electric current in the capacitors of the motion detector 151, the amplitude of which is proportional to the actual velocity of the test mass.

[0030] When the MEMS gyroscope 100 is subjected to an angular movement about the z-axis (assuming that the test mass 102 pivots when the angular movement occurs), a Coriolis force is generated, which can lead to an acceleration in the y-axis direction. The speed at which the angular movement occurs can be deduced from the amplitude of the acceleration induced by the Coriolis force. In some embodiments, the test mass 101 can be used to detect these accelerations. In particular, in the embodiment of Fig. 2. Motion detector 112 (which has stationary electrodes 122 and fingers 132) and motion detector 113 (which has stationary electrodes 123 and fingers 133) are used to detect movement of the test mass 101 in the y-axis direction. Accordingly, movement of the test mass 101 in the y-axis direction can generate an electric current in the capacitors of motion detectors 112 and 113. The magnitude of the acceleration experienced by the test mass 101, and thus the angular acceleration of the MEMS gyroscope 101, can be deduced from the electric current generated by motion detectors 112 and 113.

[0031] The functions of the MEMS gyroscope 10 are controlled using a control circuit arrangement, which may be integrated into the same substrate as the gyroscope or into a separate substrate. The control circuit arrangement may include circuits to cause the resonator 12 to oscillate, circuits to monitor the movement of the resonator 12, circuits to detect the movement of the sensor 14, and / or circuits to stabilize the movement of the sensor 14. III. Quality Factor Compensation

[0032] Fluctuations in the resonator's quality factor can reduce the gyroscope's ability to accurately detect angular velocity. In some embodiments, the gyroscope can be compensated for quality factor fluctuations by: 1) receiving, using the control circuitry, a signal generated in response to resonator movement; 2) determining the resonator's quality factor based on the received signal while it is oscillating; 3) generating a compensation signal with a time characteristic (for example, a decay rate) determined using the quality factor; 4) receiving a detection signal generated in response to angular movement of the gyroscope; and 5) combining the detection signal with the compensation signal.

[0033] A representative control circuit arrangement is shown in Fig. 3A shown according to some embodiments. Fig. Figure 3A is a block diagram representing a MEMS gyroscope 300 that can function as a MEMS gyroscope 10 (an example of which is in Fig. 2 shown), and a control circuit arrangement 302. The MEMS gyroscope 300, here simply referred to as the “gyro”, is characterized by a resonator axis (i.e., the axis along which the resonator oscillates) and a Coriolis axis (i.e., the axis along which the sensor moves in response to a Coriolis force). Furthermore, the MEMS gyroscope 300 includes a drive electrode 306, a motion detector electrode 351, a sensing electrode 312, and a feedback electrode 314. The drive electrode 306 can be an electrode of a driver for driving the resonator of the gyro, examples of which are a stationary electrode 104 and a finger 105 (see Figure 2). Fig. 2) The motion detector electrode 351 can be an electrode of a motion detector for detecting movement of the gyro's resonator, examples of which are a stationary electrode 110 and a finger 114. The detection electrode 312 can be an electrode of a motion detector for detecting movement of the gyro's sensor, examples of which are a stationary electrode 123 and a finger 133. The feedback electrode 314 can be used to control movement of the gyro's sensor. For example, the feedback electrode can be controlled to limit movement of the sensor along the Coriolis axis. Using feedback to limit movement of the sensor can make the sensor less sensitive to variations in temperature or environmental stress. The feedback electrode can be implemented using the same electrode as the detection electrode or using a separate electrode.In embodiments where the same physical electrode is shared, the physical electrode can serve as the sensing electrode during a first time interval and can serve as the feedback electrode during a second time interval.

[0034] The control circuit arrangement 302 includes a resonator signal path controller 320, a Coriolis feedback loop 348, a quality factor (Q) measurement circuit 330, a compensation circuit 340, and a combiner 344. The resonator signal path controller 320 comprises a receiver (RX) 319, a phase-locked loop (PLL) 321, and a drive circuit 323. The RX 319 receives a resonator signal generated in response to movement of the gyro's resonator and may include a voltage amplifier, a current amplifier, a transimpedance amplifier, a filter, and / or other suitable circuit components. The PLL 321 may be configured to determine the resonant frequency of the gyro's resonator based on the resonator signal received by the RX 319. For example, the PLL 321 may be configured to synchronize with the fundamental frequency of the resonator signal.Alternatively or additionally, the PLL 321 can be used to ensure that the gyro's resonator is driven at its resonant frequency. The gyro's resonator can be driven by the drive circuit 323, which may include an amplifier, a current generator, a transconductance amplifier, and / or other suitable circuit components. The signal path between the motion detector electrode 351 and the drive electrode 306 is referred to as the "control circuit resonator signal path." This path is defined as a control circuit path because it does not control the amplitude of the resonator signal to force it to a constant value, as would otherwise be the case in a closed-loop control arrangement. In the example of... Fig. 3 The control circuit resonator signal path includes the RX 319, the PLL 321 and the drive circuit 323, although more or fewer components may be included in other embodiments.

[0035] The Coriolis feedback loop 348 can include a circuit arrangement for controlling the functions of the gyro sensor. For example, the Coriolis feedback loop 348 can limit the sensor's movement along the Coriolis axis, thereby reducing the sensor's susceptibility to temperature fluctuations. The Coriolis feedback loop 348 can include an amplifier, such as a signal amplifier (SA), and analog and / or digital circuitry for driving the feedback electrode 314 to limit sensor movement. The output signal of the Coriolis feedback loop can be an amplified and / or digitized version of the sensing signal or a copy of the sensing signal. It is understood that under circumstances where the gyro's resonator experiences a change in its quality factor, such a change may be reflected in the sensing signal, thereby distorting the angular velocity detection.The path between the measuring electrode 312 and the output of the control circuit arrangement 302 (i.e. the compensated sensing signal) is referred to herein as the ‘sensing signal path’.

[0036] The quality factor measurement circuit 330 is designed to determine the quality factor of the gyro's resonator from the resonator signal. In one example, the quality factor measurement circuit 330 receives the resonator signal from the RX 319 and determines whether the quality factor has fallen below a threshold or whether the decay rate of the quality factor is greater than a threshold rate. Once it has been determined that the quality factor has fallen below a threshold or has varied at a rate greater than a threshold rate, compensation can be performed using the compensation circuit 340. It should be understood, however, that not all embodiments are limited to using thresholds to initiate compensation. For example, in some embodiments, compensation is performed in a free-running manner, whereby compensation is carried out continuously even when fluctuations in the quality factor are minimal.

[0037] Gyroscope compensation can be performed in numerous ways using the compensation circuit 340. In some embodiments, compensation can be achieved by varying a characteristic of the drive signal based on a specific quality factor (referred to as "control circuit resonator path compensation"). As such, the compensation circuit 340 can have an output terminal coupled to a control terminal of the drive circuit 323. The signal used to control the drive circuit 323 is referred to as the control signal. Additionally or alternatively, compensation can be performed by combining (e.g., by multiplying or dividing) the acquisition signal with a compensation signal having one or more time characteristics determined using the quality factor (referred to as "acquisition signal path compensation").As such, the compensation circuit 340 can have an output connection that is coupled to a combiner 344. The combiner 344 can have a second connection that is coupled to the control loop sensing path.

[0038] An illustrative method for compensating a gyroscope is described in Fig. Figure 3B shows some embodiments. The compensation method 350 begins at action 352, in which a resonator signal is received from a resonator of a MEMS gyroscope. For example, the resonator signal can be received from the motion detector electrode 351 of Fig. 3A can be received. The resonator signal can be generated in response to movement of the resonator. In operation 354, the quality factor of the resonator can be determined using the resonator signal, for example, using the quality factor measurement circuit 330. The quality factor can be determined in the time domain or in the frequency domain. When determined in the time domain, the quality factor can be deduced from the rate at which the resonator signal (or the envelope of the resonator signal) varies over time. When determined in the frequency domain, the quality factor can be deduced from the bandwidth of the resonator signal relative to its peak frequency.

[0039] Optionally, in step 356, one or more characteristics of the drive signal (the signal used to drive the resonator) can be determined using a control signal based on the quality factor determined in step 354. The characteristic(a) of the drive signal can be such that, when varied by the control signal, it leads to a fluctuation in the electrostatic force acting on the resonator. In some embodiments, the characteristic that is varied depending on the quality factor is the mean of the drive signal, the pulse density, the duty cycle of the drive signal, and / or the amplitude of the drive signal. Accordingly, the inventor understands that increasing the mean, pulse density, duty cycle, and / or amplitude of the drive signal can lead to an increase in the electrostatic force driving the resonator.The extent to which the electrostatic force is varied by mean modulation, pulse density modulation, duty cycle modulation, and / or amplitude modulation can be adjusted depending on the variation in the quality factor. In some embodiments, the compensation circuit 340 can be designed such that the mean, pulse density, duty cycle, and / or amplitude of the drive signal increase in response to a decrease in the quality factor.

[0040] In Action 358, a compensation signal with one or more time characteristics determined using the quality factor obtained in Action 354 can be generated. A specific example of a time characteristic is the rate at which the compensation signal decays over time. In this example, the compensation signal can be varied from a high level to a low level, and the rate at which this variation occurs can be controlled based on the quality factor. For example, in some embodiments, the decay rate can be set proportionally to the quality factor. In another example, the decay rate can be set to be equal to the inverse of the resonator's bandwidth. Examples of compensation signals are shown below.

[0041] In action 360, a detection signal generated in response to a Coriolis force caused by an angular movement of the gyroscope is received. This detection signal can be received, for example, by the measuring electrode 312. Optionally, a stabilizing movement of the gyroscope sensor can be performed using the Coriolis feedback loop 348.

[0042] In action 362, a compensated detection signal can be obtained using the detection signal received in action 360 and the compensation signal generated in action 358. The detection signal and the compensation signal can be combined in any suitable way, such as multiplication, mixing, or division. The compensated detection signal can be output by the control circuit arrangement 302 and can indicate the rate of angular motion detected by the gyroscope.

[0043] In some embodiments, compensation of the gyroscope for fluctuations in the quality factor can be achieved, at least partially, by varying the electrostatic force driving the resonator. An increase in the electrostatic force can be achieved by increasing the time-averaged value of the drive signal. Conversely, an increase in the signal average can be achieved by increasing the pulse density, duty cycle, and / or amplitude of the signal.

[0044] Fig. Figures 4A-4F are diagrams illustrating how fluctuations in a characteristic of the drive signal can affect the resonator signal according to some embodiments. In particular, they illustrate Fig. 4A the resulting resonator signal when the drive signal from Fig. 4D is created, illustrates Fig. 4B the resulting resonator signal when the drive signal from Fig. 4E is created, and Fig. 4C illustrates the resulting resonator signal when the drive signal from Fig. 4F is applied. The curves of Fig. 4A, Fig. 4B and Fig. 4C are shown with respect to the voltage V of the resonator signal over time. The curves of the Fig. 4D, Fig. 4E and Fig. 4F are shown with respect to the amplitude of the control signal (for example, the voltage of the control signal) over time.

[0045] In this example, the pulse density is determined by the control signal from Fig. 4D to the one from Fig. 4E and back to the one from Fig. 4F increased. That is, the number of pulses present in each period of the signal (where 1 / f) M the periodicity of the signal), is determined by Fig. 4D to Fig. 4F increased. As a result, the amplitude of the resonator decreases from Fig. 4A to Fig. 4B and back to Fig. 4C. As shown, the envelope of the resonator signal lies between V1 and V2 in Fig. 4A, between V3 and V4 in Fig. 4B and between V5 and V6 in Fig. 4C (where V5 > V3 > V1 and V6 > V4 > V2). The pulse density of the control signal (or more generally, the mean of the control signal) can be, as in Fig. 4D-4F is shown to be increased in response to a decrease in the quality factor, as determined by the quality factor measurement circuit 330.

[0046] Representative operations of the control circuit arrangement 302, when compensation is performed by adjusting the electrostatic force driving the resonator (but without adjusting the compensation signal based on the quality factor), are described in Fig. 6A shown. Fig. 6A exhibits the following six curves: 1) the quality factor of the resonator, 2) the pulse density of the drive signal, 3) the average amplitude of the resonator signal, 4) the output signal Q provided by the quality factor measurement circuit 330 meas 5) the compensation signal and 6) the compensated detection signal. All such quantities are plotted as a function of time. As shown in curve 1, the quality factor of the resonator decays over time, for example, due to mechanical losses introduced by thermoelastic damping or squeeze-film damping, or due to a temperature increase. As the quality factor decays, the signal Q meas a downward slope similar to that of curve 1 (the slopes can be proportional to each other) (curve 4). As further shown in curve 2, the fluctuation at Q can meastriggers a fluctuation in a characteristic of the drive signal (the pulse density in this example, although other characteristics can be varied, such as the mean, duty cycle, and / or amplitude). In particular, the pulse density is increased from "pulse density 1" to "pulse density 2". As the pulse density increases, the mean amplitude of the resonator signal also increases (curve 3). It is understood that, because the resonator has a finite quality factor, the mean amplitude of the resonator increases according to a non-step function in response to the fluctuation in pulse density. Curve 3 has an inset that shows how the actual amplitude of the resonator signal varies over time (with a peak-to-peak amplitude equal to ΔV). As a side effect of the fluctuation in pulse density, Q measan undesired feature 610 (in this example, a triangular tip) is present. The compensation signal of curve 5 is constant, since the compensation signal is not used in this embodiment. As shown in curve 6, the compensated measurement signal exhibits a downward slope due to the decrease in the quality factor. In contrast to the quality factor, however, the compensated detection signal exhibits an increase 612 resulting from the change in the pulse density. It is understood that the increase 612 occurs with a delay t. D relative to a change in momentum density. The increase 612 compensates for the change in the quality factor at least for a certain time period.

[0047] To further improve the compensation, a compensation signal with a time characteristic determined using the quality factor obtained in action 354 can be used. The generation of the compensation signal can be carried out using the compensation circuit 340 ( Fig. 3A). Fig. Figures 5A-5C illustrate further possible implementations for the compensation circuit 340 according to some embodiments. As shown, each embodiment receives information indicating the quality factor in the form of a signal Q. meas from the quality factor measuring unit 330. In addition, each embodiment outputs a compensation signal and optionally a control signal for controlling the control circuit 323.

[0048] The embodiment of Fig. Section 5A contains a lookup table (LUT) that includes data representing characteristics (e.g., mean, amplitude, duty cycle, and pulse density) that can be assigned to the drive signal. These characteristics can be mapped in the LUT as a function of the quality factor. That is, each value of the quality factor can correspond to a specific characteristic value. Mapping the quality factor to characteristics can be performed as part of a calibration routine to determine how the resonator is appropriately driven based on different quality factors.

[0049] Furthermore, the embodiment includes a delay unit t D a multiplier 512, a divider 514, and a reference generator "Ref". The delay unit t D can introduce a delay that corresponds to the delay t D essentially corresponds to, for example, in Fig. Figure 6A, curve 6 is shown. In some embodiments, the divider 514 can be configured to generate the compensation signal such that it is proportional to the Ref / Q ratio. meas For example, the compensation signal can be given by: Ref / (Q meas *Impulse density (tt) D )), where pulse density is the real-time pulse density of the drive signal.

[0050] Operations of the embodiment of Fig. 5A are in the six curves of Fig. 6B is shown. In contrast to Fig. 6A will be the compensation signal from Fig. 6B in response to a change in signal Q meas varies ( Fig. 6B, Curve 5). In particular, under this condition, the compensation signal exhibits an upward slope due to the decrease in the quality factor. As further shown in Curve 5, the compensation signal exhibits an undesired feature 614, which arises in response to feature 610. Furthermore, the compensation signal exhibits a discontinuity 616 in response to the change in pulse density. As shown in Curve 6, the compensated measurement signal is essentially flat (in contrast to the compensated acquisition signal of Fig. 6A, which has a downward slope) thanks to the upward slope of the compensation signal. However, the compensated measurement signal also exhibits a feature 624 (as a reaction to feature 614) and a peak 626 (as a reaction to the discontinuity 616).

[0051] The embodiment of Fig. 5 features a transient compensation circuit arrangement 550, which can be configured to limit or eliminate the spike 626 or other abrupt fluctuations in the compensated sensing signal that occur when the pulse density (or other characteristics) of the drive signal is varied from one value to another. In some embodiments, the components of the Fig. 5A-5C can be implemented as digital circuits. However, it is understood that analog implementations are also possible for at least some of these components.

[0052] The transient compensation circuit arrangement 550 can have a circuit arrangement to compensate for the transients in Fig. Figure 6B, Curve 5, to make the discontinuity shown more gradual. In some embodiments, the transient compensation circuit arrangement 550 can have an impulse response with a decay rate τ that depends on the quality factor determined in Figure 354. In one example, the decay rate τ of the transient compensation circuit arrangement 550 is proportional to the quality factor. In another example, the decay rate τ is equal to the inverse of the bandwidth Δf of the resonator. The transient compensation circuit arrangement 550 can be implemented in any of numerous ways, comprising a digital filter (e.g., a first-order filter, a second-order filter, or any type of higher-order filter). When implemented as an analog circuit, the filter can include a lossy element (e.g., a resistive element) whose loss varies depending on the quality factor to produce different decay rates.Operations of the embodiment of . Fig. 5 are in the six curves of Fig. Figure 6C illustrates this. In particular, as shown in curve 5, the discontinuity 616 has been replaced by a slowly decaying variation 618 (e.g., an exponentially decaying response) with a decay time rate τ. In contrast to the embodiment of Fig. 5A and Fig. 6B shows that the compensated detection signal generated in this way has no peak 626 (see Fig. 6C, curve 6), which reduces signal distortion.

[0053] The embodiment of Fig. 5C features a Q-factor blanking circuit 560, which can be configured to limit or eliminate feature 640 from the compensated measurement signal, thereby keeping the sensitivity of the gyroscope substantially constant. In some embodiments, the Q-blanking circuit can be configured to force the compensation signal to a substantially constant value for a predefined period (such as the duration of feature 610, or a duration between τ and 20τ, between 5τ and 20τ, between 10τ and 20τ, between 15τ and 20τ, between τ and 10τ, between 5τ and 10τ, or within any suitable range within such ranges). The duration of the predefined period can be related to the Q-factor. In some embodiments, the Q blanking circuit 560 is implemented using one or more capacitors or digitally using one or more registers.The operations of the embodiment of . Fig. 5C are in Fig. Figure 6D illustrates how the compensation signal (in contrast to the compensation signal of Fig. 6C) during the duration of Q meas -peak is kept at a constant value, thereby eliminating feature 614. As a result, the compensated measurement signal ( Fig. 6D, curve 6) during the period of Q meas The peak is essentially constant, thus eliminating feature 624. As a result, the sensitivity of the compensated signal to quality factor variations is essentially limited without introducing unwanted distortions.

[0054] Circuits and methods for compensating MEMS (microelectromechanical system) gyroscopes for quality factor variations are described. Quality factor variations can arise when mechanical losses are introduced into the gyroscope's resonator, for example, due to thermoelastic damping or squeeze-film damping, which can impair the gyroscope's ability to accurately measure angular velocity. Quality factor compensation can be achieved by generating a compensation signal with a decay rate that depends on the resonator's quality factor. This limits artifacts that might otherwise appear in the gyroscope's output signal. Additionally or alternatively, quality factor compensation can be achieved by controlling the force driving the gyroscope's resonator. This can be accomplished, for example, by controlling the average value of the drive signal. IV. Concluding Remarks

[0055] Aspects of the technology described herein may provide one or more advantages, some of which have been described previously. A non-limiting example of an advantage is now described. It is understood that not all aspects and embodiments necessarily provide the described advantage. It is further understood that aspects of the technology described herein may provide additional advantages beyond those just described. Some aspects of the technology described herein provide MEMS gyroscopes with a substantially reduced susceptibility to quality factor variations originating in the gyroscope resonator.

[0056] The terms "approximately", "essentially", and "about" may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and within ±2% of a target value in some embodiments. The terms "approximately" and "about" may include the target value.

Claims

[1] Method, comprising: Received by a resonator of a MEMS (Microelectromechanical System) gyroscope, a resonator signal generated in response to a movement of the resonator; Determining the quality factor of the resonator using the resonator signal; Generating a compensation signal with at least one time characteristic determined using the quality factor of the resonator; Received by a sensor of the MEMS gyroscope, a detection signal generated in response to an angular movement of the MEMS gyroscope; and Generating a compensated acquisition signal using the acquisition signal and the compensation signal; further showing: Detecting a resonant frequency of the resonator using the resonator signal; and Driving the resonator with a drive signal determined using the resonance frequency and the quality factor; wherein driving the resonator with a drive signal determined using the resonance frequency and the quality factor involves varying an average of the drive signal based on the quality factor and / or varying an impulse density of the drive signal based on the quality factor. [2] Method according to claim 1, wherein generating a compensation signal with at least one time characteristic determined using the quality factor of the resonator comprises generating a compensation signal with a time decay rate determined using the quality factor of the resonator. [3] Method according to a preceding claim, wherein generating a compensated detection signal using the detection signal and the compensation signal comprises generating a compensated detection signal by multiplying the detection signal with the compensation signal. [4] Methods, comprising: Received by a resonator of a MEMS (Microelectromechanical System) gyroscope, a resonator signal generated in response to a movement of the resonator; Determining the quality factor of the resonator using the resonator signal; Generating a compensation signal with at least one time characteristic determined using the quality factor of the resonator; Received by a sensor of the MEMS gyroscope, a detection signal generated in response to an angular movement of the MEMS gyroscope; and Generating a compensated acquisition signal using the acquisition signal and the compensation signal; furthermore, exhibiting the keeping of the compensation signal essentially constant during a predefined time period. [5] Method according to claim 4, further comprising setting a duration of the predefined time period based on the quality factor. [6] MEMS (Microelectromechanical System) device comprising: a gyroscope comprising a sensor and a resonator; and a control circuit arrangement designed to: Received by the resonator, a resonator signal generated in response to a movement of the resonator; Determining the quality factor of the resonator using the resonator signal; Generating a compensation signal with a time characteristic determined using the quality factor of the resonator; Received by the sensor, a detection signal generated in response to an angular movement of the MEMS gyroscope; and Generating a compensated acquisition signal using the acquisition signal and the compensation signal; wherein the control circuit arrangement is further configured to: Detecting a resonant frequency of the resonator based on the resonator signal; and Driving the resonator with a drive signal determined using the resonance frequency and the quality factor; wherein the control circuit arrangement is configured to control the resonator with a control signal determined using the resonance frequency and the quality factor, at least partially by varying an average of the control signal based on the quality factor and / or at least partially by varying an impulse density of the control signal based on the quality factor. [7] MEMS device of claim 6, wherein the control circuit arrangement is configured to generate a compensation signal with a time characteristic determined using the quality factor of the resonator, at least partially by generating a compensation signal with a time decay rate determined using the quality factor of the resonator. [8] MEMS device according to one of claims 6 to 7, wherein the control circuit arrangement is configured to generate a compensated detection signal using the detection signal and the compensation signal at least partially by generating a compensated detection signal by multiplying the detection signal with the compensation signal. [9] MEMS (Microelectromechanical System) device comprising: a gyroscope comprising a sensor and a resonator; and a control circuit arrangement designed to: Received by the resonator, a resonator signal generated in response to a movement of the resonator; Determining the quality factor of the resonator using the resonator signal; Generating a compensation signal with a time characteristic determined using the quality factor of the resonator; Received by the sensor, a detection signal generated in response to an angular movement of the MEMS gyroscope; and Generating a compensated acquisition signal using the acquisition signal and the compensation signal; wherein the control circuit arrangement is further designed to keep the compensation signal essentially constant during a predefined time period. [10] MEMS (Microelectromechanical System) device comprising: a gyroscope comprising a sensor and a resonator; a quality factor measurement circuit coupled to a motion detection electrode of the resonator; a compensation circuit with an input terminal coupled to the quality factor measurement circuit and an output terminal, wherein the compensation circuit comprises a transient compensation circuit arrangement; and a signal combination circuit arrangement coupled to the sensor and the output terminal of the transient compensation circuit arrangement. [11] MEMS device according to claim 10, wherein the transient compensation circuit arrangement includes a filter. [12] MEMS device according to claim 10 or 11, further comprising a pulse density modulator coupled to the transient compensation circuit arrangement and the resonator. [13] MEMS device according to one of claims 10 to 12, wherein the compensation circuit comprises a quality factor blanking circuit. [14] MEMS device according to any one of claims 10 to 13, wherein the sensor has a first mass and the resonator has a second mass elastically coupled to the first mass.

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