A MEMS sensor amplitude measurement circuit and method

Abstract

This application provides a MEMS sensor amplitude measurement circuit and method, relating to the field of MEMS testing technology. First, the gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes are obtained. Based on the obtained parameters, the conversion coefficient between displacement and capacitance change is determined. Then, self-compensation of the positive and negative terminal coupling voltages is sequentially performed. Next, the sensor driving circuit is connected. After the sensitive chip starts oscillating and the amplitude stabilizes, the gain of the differential amplifier is adjusted until the voltage amplitude output by the differential amplifier reaches a preset upper limit value, and the correspondence between capacitance change and output voltage amplitude is determined. Finally, based on the voltage amplitude output by the differential amplifier, the conversion coefficient between displacement and capacitance change, and the correspondence between capacitance change and output voltage amplitude, the amplitude of the MEMS sensor is obtained. The solution provided in this application has the advantages of relaxed testing conditions, easy integration design, and high accuracy.

Description

Technical Field

[0001] This application relates to the field of MEMS testing technology, and more specifically, to a MEMS sensor amplitude measurement circuit and method. Background Technology

[0002] MEMS sensors, such as MEMS gyroscopes and resonant MEMS accelerometers, all operate in a resonant state. The vibration amplitude is a crucial parameter affecting key performance indicators such as the product's mechanical sensitivity and signal-to-noise ratio. Therefore, accurate measurement of the vibration displacement of sensitive structures facilitates precise theoretical calculations and design of various performance indicators during the design phase. Furthermore, it guides the specific dimensional design of sensitive structures, enabling rapid transformation from preliminary design to mass production.

[0003] Currently, there are two commonly used methods for measuring vibration amplitude: one is an image recognition-based measurement method, which uses the acquired MEMS planar motion fuzzy image sequence and fuzzy image analysis technology to measure planar motion parameters; the other is an electrical vibration measurement method based on single-sideband voltage ratio, which uses a dynamic signal analyzer to obtain the single-sideband spectrum, obtains the vibration amplitude ratio from the ratio of two adjacent single-sideband voltage amplitudes, and then determines the vibration amplitude.

[0004] However, image recognition-based measurement methods generally require completion within a cleanroom vacuum chamber, placing high demands on the testing environment and equipment. Furthermore, the sensitive structure must be exposed, while post-fabrication MEMS structures typically have a capping layer for wafer-level vacuum packaging, thus limiting the applicability of this method. Electrical vibration measurement methods based on single-sideband voltage ratios, which indirectly calculate the amplitude ratio of two adjacent single-sideband voltages through spectral analysis of the measurement signal, are usually very small, highly susceptible to noise in the test circuit, and have low measurement accuracy.

[0005] In summary, existing technologies for amplitude testing of MEMS sensors suffer from stringent testing conditions and low accuracy. Summary of the Invention

[0006] The purpose of this application is to provide a MEMS sensor amplitude measurement circuit and method to solve the problems of weak universality and accuracy in the amplitude testing of MEMS sensors in the prior art.

[0007] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows: On one hand, this application provides a method for measuring the amplitude of a MEMS sensor, applied to a MEMS sensor amplitude measurement circuit. The MEMS sensor amplitude measurement circuit includes a MEMS sensing chip, a first self-compensation module, a second self-compensation module, a first charge amplification module, a second charge amplification module, a differential amplifier, an analog-to-digital converter, and a PI controller. The MEMS sensing chip includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode. The input terminal of the first self-compensation module is connected to the output terminal of the PI controller and the detection positive electrode, respectively, and the output terminal of the first self-compensation module is connected to the excitation positive electrode. The input terminal of the second self-compensation module is connected to the output terminal of the PI controller and the detection negative electrode, respectively, and the output terminal of the second self-compensation module is connected to the excitation negative electrode. The detection positive electrode is connected to the first charge amplification module, and the detection negative electrode is connected to the second charge amplification module. The first charge amplification module and the second charge amplification module are also connected to the input terminal of the differential amplifier, respectively. The differential amplifier, the analog-to-digital converter, and the PI controller are connected in sequence. The method includes: The gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes are obtained, and the conversion coefficient between displacement and capacitance change is determined based on the obtained parameters. The positive terminal coupling voltage self-compensation and the negative terminal coupling voltage self-compensation are performed sequentially. After the MEMS sensor driving circuit is connected and the MEMS sensing chip starts to oscillate and the amplitude stabilizes, the gain of the differential amplifier is adjusted until the voltage amplitude output by the differential amplifier reaches the preset circuit upper limit value, and the correspondence between the capacitance change and the output voltage amplitude is determined. The amplitude of the MEMS sensor is obtained based on the voltage amplitude output by the differential amplifier, the conversion coefficient between the displacement and the capacitance change, and the correspondence between the capacitance change and the output voltage amplitude.

[0008] Optionally, the conversion coefficient between the displacement and the change in capacitance satisfies the formula:

[0009] in, This is the conversion coefficient between displacement and capacitance change. The gap between the excitation electrode and the mass block. For the length of the excitation electrode, Where is the height of the excitation electrode, N is the number of excitation electrodes, and ε0 is the vacuum permittivity.

[0010] Optionally, the MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch. The first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch. The step of completing the positive terminal coupling voltage self-compensation includes: The first switching switch is closed and the second switching switch is opened. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the mass block to the excitation positive electrode until the output of the first charge amplification module is 0, so as to achieve self-compensation of the positive terminal coupling voltage.

[0011] Optionally, the MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch. The first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch. The step of completing the negative terminal coupling voltage self-compensation includes: The first switching switch is controlled to open, and the second switching switch is controlled to close. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the mass block to the excitation negative electrode until the output of the second charge amplification module is 0, so as to achieve self-compensation of the negative terminal coupling voltage.

[0012] Optionally, the relationship between the change in capacitance and the amplitude of the output voltage satisfies the formula:

[0013] in, This represents the relationship between the change in capacitance and the amplitude of the output voltage. For the gain of the differential amplifier, This represents the voltage difference between the common-mode voltage of the mass block and the detection electrode. This is the capacitance value of the feedback capacitor.

[0014] Optionally, the amplitude of the MEMS sensor satisfies the formula:

[0015] Where Vp is the voltage amplitude output by the differential amplifier. The amplitude of the MEMS sensor. This is the conversion coefficient between displacement and capacitance change. This represents the relationship between the change in capacitance and the amplitude of the output voltage.

[0016] On the other hand, embodiments of this application also provide a MEMS sensor amplitude measurement circuit for performing the above-described method; the MEMS sensor amplitude measurement circuit includes a MEMS sensing chip, a first self-compensation module, a second self-compensation module, a first charge amplification module, a second charge amplification module, a differential amplifier, an analog-to-digital converter, and a PI controller; the MEMS sensing chip includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode; the input terminal of the first self-compensation module is connected to the output terminal of the PI controller and the detection positive electrode, respectively, and the output terminal of the first self-compensation module is connected to the excitation positive electrode; the input terminal of the second self-compensation module is connected to the output terminal of the PI controller and the detection negative electrode, respectively, and the output terminal of the second self-compensation module is connected to the excitation negative electrode; the detection positive electrode is connected to the first charge amplification module, and the detection negative electrode is connected to the second charge amplification module; the first charge amplification module and the second charge amplification module are also connected to the input terminal of the differential amplifier, respectively; the differential amplifier, the analog-to-digital converter, and the PI controller are connected in sequence.

[0017] Optionally, the first self-compensation module includes: The first resistor has one end connected to the positive detection electrode and the other end connected to the inverting output of the variable gain amplifier. The feedback resistor is connected at both ends to the inverting input and output terminals of the variable gain amplifier, respectively. A variable gain amplifier with its non-inverting input grounded and its output connected to a capacitor; the output of the capacitor is connected to the positive detection electrode. The variable gain amplifier automatically adjusts its gain based on the output signal of the PI controller.

[0018] Optionally, the first charge amplification module includes: Operational amplifier; The feedback resistor is connected at both ends to the inverting input and output terminals of the operational amplifier. The feedback capacitor has its two ends connected to the inverting input and output terminals of the operational amplifier; The non-inverting input of the operational amplifier is connected to a common-mode voltage, and the output is used to output the voltage amplitude corresponding to the change in capacitance of the MEMS sensitive chip.

[0019] Optionally, the MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch, wherein the first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch.

[0020] Compared with the prior art, this application has the following advantages: This application provides a MEMS sensor amplitude measurement circuit and method. Because it compensates for the electrical feedthrough error between the excitation electrode and the detection electrode through a self-compensation circuit, it effectively suppresses parasitic coupling interference and improves measurement accuracy. At the same time, it adopts a combination of physical measurement and electrical measurement, and obtains the amplitude through direct measurement and calculation, avoiding the problem of indirect ratio measurement being greatly affected by noise, thereby achieving a high measurement accuracy.

[0021] Secondly, this method can be tested directly after packaging, without exposing sensitive structures or completing the test in a cleanroom vacuum chamber, which greatly reduces the requirements for the testing environment and equipment, making the testing conditions more relaxed and the environmental adaptability stronger.

[0022] Furthermore, the measurement circuit does not have a high-frequency carrier, omitting modules such as carrier generation, demodulation, and filtering. Compared with traditional carrier-based CV detection circuits, its circuit structure is simpler, easier to integrate, and reduces the requirements for operational amplifier bandwidth, which is beneficial for on-chip integrated design of measurement and control circuits.

[0023] Finally, the variable gain amplifier is automatically adjusted by a PI controller to achieve self-compensation of electrical feedthrough error, eliminating the need for manual intervention and improving testing efficiency.

[0024] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a circuit diagram of the MEMS sensor amplitude measurement circuit provided in the embodiments of this application.

[0027] Figure 2 An exemplary flowchart of a MEMS sensor amplitude measurement method provided in an embodiment of this application.

[0028] Figure 3 This is a circuit diagram of the self-compensation module provided in an embodiment of this application.

[0029] Figure 4 This is a circuit diagram of the charge amplification module provided in an embodiment of this application.

[0030] In the picture: 110 - MEMS sensing chip; 120 - First self-compensation module; 130 - Second self-compensation module; 140 - First charge amplification module; 150 - Second charge amplification module; 160 - Differential amplifier; 170 - Analog-to-digital converter; 180 - PI controller; 190 - First switching switch; 200 - Second switching switch. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0033] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Some embodiments of this application are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] As described in the background section, existing technologies for amplitude testing of MEMS sensors typically employ image recognition-based measurement methods or electrical vibration measurement methods based on single-sideband voltage ratios. However, image recognition-based methods generally require completion within a cleanroom vacuum chamber, placing high demands on the testing environment and equipment. Furthermore, the sensitive structure must be exposed, while post-fabrication MEMS structures usually have a capping layer to achieve wafer-level vacuum encapsulation, ensuring a high vacuum level in the sensitive structure's vibration chamber and achieving a high Q value. Therefore, this method has limited applicability. As for electrical vibration measurement methods based on single-sideband voltage ratios, these methods indirectly calculate the ratio of adjacent single-sideband voltage amplitudes through spectral analysis of the measurement signal. This ratio is typically very small and highly susceptible to noise from the test circuit, resulting in low measurement accuracy.

[0036] In view of this, this application provides a method for measuring the amplitude of a MEMS sensor. It should be noted that the method provided in this application is applied to a MEMS sensor amplitude measurement circuit. Please refer to [link to relevant documentation]. Figure 1 The MEMS sensor amplitude measurement circuit includes a MEMS sensing chip 110, a first self-compensation module 120, a second self-compensation module 130, a first charge amplification module 140, a second charge amplification module 150, a differential amplifier 160, an analog-to-digital converter 170, and a PI controller 180. The MEMS sensing chip 110 includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode. The input terminal of the first self-compensation module 120 is connected to the output terminal of the PI controller 180 and the detection positive electrode, respectively. The output terminal of 120 is connected to the excitation positive electrode; the input terminal of the second self-compensation module 130 is connected to the output terminal of the PI controller 180 and the detection negative electrode, respectively, and the output terminal of the second self-compensation module 130 is connected to the excitation negative electrode; the detection positive electrode is connected to the first charge amplification module 140, and the detection negative electrode is connected to the second charge amplification module 150; the first charge amplification module 140 and the second charge amplification module 150 are also connected to the input terminal of the differential amplifier 160, respectively; the differential amplifier 160, the analog-to-digital converter 170 and the PI controller 180 are connected in sequence.

[0037] As an optional implementation, please refer to Figure 2 The method includes: S102, obtain the gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes, and determine the conversion coefficient between displacement and capacitance change based on the obtained parameters.

[0038] S104 sequentially performs self-compensation of the positive terminal coupling voltage and self-compensation of the negative terminal coupling voltage.

[0039] S106 is connected to the MEMS sensor driving circuit. After the MEMS sensing chip starts oscillating and the amplitude stabilizes, the gain of the differential amplifier is adjusted until the voltage amplitude output by the differential amplifier reaches the preset circuit upper limit value, and the correspondence between the capacitance change and the output voltage amplitude is determined.

[0040] S108 obtains the amplitude of the MEMS sensor based on the voltage amplitude output by the differential amplifier, the conversion coefficient between displacement and capacitance change, and the correspondence between capacitance change and output voltage amplitude.

[0041] This application constructs a MEMS sensor amplitude measurement method that combines direct measurement of physical parameters with closed-loop feedback control of electrical signals, eliminating the need for high-frequency carrier modulation and actively suppressing electrical feedthrough interference. Utilizing the measurability of the structural parameters of the MEMS sensing chip 110 and the deterministic physical relationship between capacitance and displacement, the mechanical quantity of amplitude is converted into a precisely calibrable voltage amplitude. Furthermore, a dual-terminal independent self-compensation mechanism eliminates unwanted voltage coupling from the excitation electrode to the detection electrode. This achieves high signal-to-noise ratio and high repeatability electrical inversion of vibration amplitude without relying on high-precision external instruments or harsh testing environments.

[0042] In this process, the method first obtains the gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes. Based on these parameters, it determines the conversion coefficient between displacement and capacitance change. This conversion coefficient reflects the physical constraint of the MEMS structure geometry on the capacitance response sensitivity, and its value is determined by the vacuum dielectric constant, electrode size, and initial spacing. These parameters can be obtained directly using conventional process inspection equipment such as a scanning electron microscope (SEM), without relying on dynamic excitation or complex calibration processes.

[0043] Subsequently, positive-terminal coupling voltage self-compensation and negative-terminal coupling voltage self-compensation are performed sequentially: a sinusoidal voltage with a frequency approximately 1 kHz away from the natural frequency of the mass block and an amplitude of Vac is applied to the excitation positive electrode. Simultaneously, the output of the first charge amplification module 140 is monitored in real time using the PI controller 180, and the gain of the variable gain amplifier in the first self-compensation module 120 is automatically adjusted until the output approaches zero. Similarly, the same form of excitation signal is applied to the excitation negative electrode, and through the coordinated action of the second self-compensation module 130 and the PI controller 180, the output of the second charge amplification module 150 also approaches zero. This process essentially utilizes the self-compensation module to inject a cancellation signal of equal magnitude but opposite phase to the feedthrough voltage picked up by the detection electrode into the excitation electrode, thereby actively eliminating the electrical response noise caused by parasitic capacitive coupling between the excitation and detection ends without altering the intrinsic vibration state of the MEMS.

[0044] Next, the MEMS sensor driving circuit is connected. After the MEMS sensing chip 110 starts oscillating and the oscillation amplitude stabilizes, the gain of the differential amplifier 160 is adjusted until its output voltage amplitude Vp reaches the preset circuit upper limit value. At this time, the system is working in the optimal range of linear dynamic range, which is beneficial to improving the signal-to-noise ratio. Based on this, the correspondence between the capacitance change and the output voltage amplitude is established. This relationship is determined by the gain of the differential amplifier 160, the common-mode voltage difference, and the capacitance value of the feedback capacitor.

[0045] Finally, based on the voltage amplitude Vp output by the differential amplifier 160, the determined conversion coefficient between displacement and capacitance change, and the established correspondence between capacitance change and output voltage amplitude, the amplitude of the MEMS sensor is calculated by substituting these parameters. The entire calculation process is based on a clear physical model and measurable structural parameters, avoiding the problem of being easily interfered with by circuit noise due to the small single-sideband voltage amplitude ratio in spectrum analysis, and also avoiding the strict dependence of image recognition methods on exposed structures and vacuum chambers.

[0046] As can be seen, this application achieves independent, synchronous, and closed-loop compensation for the electrical feedthrough error at both ends by setting up a first self-compensation module 120 and a second self-compensation module 130 corresponding to the positive and negative excitation channels, respectively, and having their gains uniformly controlled by the same PI controller 180. Simultaneously, it eliminates the high-frequency carrier generation, demodulation, and filtering stages required in traditional CV testing, making the entire vibration measurement circuit free of any carrier-related modules, significantly simplifying the circuit structure, reducing the bandwidth performance requirements of the operational amplifier, and improving system integration and robustness. Furthermore, this method decomposes amplitude calculation into two independently verifiable stages: physical measurement of structural parameters and closed-loop calibration of the electrical response. This ensures the accuracy of the theoretical model and enhances the reliability of the measured results, ultimately enabling high-precision quantitative amplitude measurement in a typical laboratory environment, significantly reducing dependence on the testing environment and high-end equipment.

[0047] As one implementation method, the conversion coefficient between displacement and capacitance changes satisfies the formula:

[0048] in, This is the conversion coefficient between displacement and capacitance change. The gap between the excitation electrode and the mass block. For the length of the excitation electrode, Where is the height of the excitation electrode, N is the number of excitation electrodes, and ε0 is the vacuum permittivity.

[0049] This application combines the geometric parameters of the MEMS sensitive structure with the physical model of a classic parallel plate capacitor to construct a conversion coefficient for displacement and capacitance changes that can be directly calculated from actual process measurement data. This establishes a quantitative mapping relationship between vibration displacement and electrical signal without the need for additional calibration equipment or dynamic excitation.

[0050] The conversion coefficient between displacement and capacitance change is used to characterize the change in equivalent capacitance between the detection electrode and the mass block when the mass block undergoes a unit displacement in the vertical direction. The gap, length, and height mentioned above can be obtained by directly measuring the cross-sectional image using a scanning electron microscope.

[0051] In practical applications, this conversion coefficient is entirely based on physical modeling and actual process measurements of static structural parameters. The process involves: after deep silicon etching of the structural layers in the MEMS structure, selecting a typical chip slice, and obtaining measured values ​​of the gap between the excitation electrode and the mass block, as well as the length of the excitation electrode, under a scanning electron microscope; combining the designed electrode height ensured by the wafer thinning process, and the number of excitation electrodes specified in the layout, substituting these values ​​into the above formula allows for the one-time calculation of the conversion coefficient between displacement and capacitance changes. This process does not involve any dynamic signal acquisition, spectrum analysis, or external vibration sources, and is therefore unaffected by factors such as test system noise, environmental temperature drift, or excitation distortion.

[0052] As one implementation, the MEMS sensor amplitude measurement circuit also includes a first switching switch 190 and a second switching switch 200. A first self-compensation module 120 is connected to the output of a PI controller 180 via the first switching switch 190, and a second self-compensation module 130 is connected to the output of a PI controller 180 via the second switching switch 200. The steps for completing the positive terminal coupling voltage self-compensation include: The first switching switch 190 is closed and the second switching switch 200 is opened. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the excitation positive electrode until the output of the first charge amplification module 140 is 0, so as to achieve self-compensation of the positive terminal coupling voltage.

[0053] The steps to complete negative terminal coupling voltage self-compensation include: The first switching switch 190 is opened and the second switching switch is closed. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the mass block to the excitation negative electrode until the output of the second charge amplification module 150 is 0, so as to achieve self-compensation of the negative terminal coupling voltage.

[0054] This embodiment achieves independent, path-by-path, crosstalk-free compensation for the electrical feedthrough error between the excitation and detection electrodes by setting a physically isolated switching control mechanism between the positive and negative excitation channels, combined with a time-sharing excitation application and closed-loop adjustment strategy. This accurately eliminates coupling interference generated by the positive and negative terminals without introducing additional noise sources or disrupting the system's static operating point. Furthermore, this structure ensures that the same output signal of the PI controller 180 can only unidirectionally and selectively drive either the first self-compensation module 120 or the second self-compensation module 130, preventing simultaneous action on both modules. This avoids the superposition, interference, or competition between the positive and negative compensation signals, ensuring that each compensation process targets a single excitation path.

[0055] In practical applications, the first charge amplification module 140 continuously monitors the electrical signal picked up by the positive electrode and sends the signal to the differential amplifier 160 and the subsequent analog-to-digital converter 170. Then, the PI controller 180 automatically adjusts the gain of the variable gain amplifier in the first self-compensation module 120 according to the digital feedback result until the output of the first charge amplification module 140 approaches zero. In this state, the first self-compensation module 120 has injected a cancellation signal that is equal in magnitude and opposite in phase to the current positive terminal power supply voltage into the excitation positive electrode, thereby achieving real-time zeroing of the net coupling voltage on the detection positive electrode side.

[0056] Similarly, the second charge amplification module 150 monitors the response signal of the negative electrode and adjusts the gain of the second self-compensation module 130 through the closed loop of the PI controller 180 until the output of the second charge amplification module 150 approaches zero, thereby completing the independent compensation for the negative terminal power supply error.

[0057] Since the excitation positive electrode and excitation negative electrode of the MEMS sensing chip 110 usually drive the mass block vibration in a differential manner, there is an unavoidable parasitic capacitance coupling path between the two and the detection positive and detection negative electrodes, i.e., electrical feedthrough. If the positive and negative terminals are not compensated independently, but instead a shared compensation channel or simultaneous excitation is used, the feedthrough voltage of the positive and negative terminals may be superimposed or incompletely canceled due to phase difference, amplitude mismatch or circuit nonlinearity, or even generate new common-mode interference, which will cause the subsequent differential amplification stage to be unable to accurately extract the capacitance change signal caused by the real vibration.

[0058] Therefore, this application implements a time-division multiplexing operation process by setting a first switching switch 190 and a second switching switch 200, and first turning on the first switching switch 190 and then turning off the second switching switch 200 to complete positive-end compensation; then turning off the first switching switch 190 and turning on the second switching switch 200 to complete negative-end compensation. This application not only decouples the feedthrough errors of the positive and negative excitation paths, but also gives the entire compensation process clear timing boundaries and repeatable operation logic. This design avoids the stability risks caused by concurrent adjustment of multiple signals and ensures the physical verifiability of each compensation result; that is, as long as the output of the corresponding charge amplification module returns to zero, it can be confirmed that the feedthrough of that path has been effectively suppressed. This compensation mechanism significantly improves the anti-interference capability and engineering robustness of the measurement system, providing reliable technical support for achieving high-precision and high-consistency MEMS amplitude calibration in ordinary laboratory environments.

[0059] As one implementation method, the amplitude of a MEMS sensor satisfies the formula:

[0060] Where Vp is the voltage amplitude output by differential amplifier 160. The amplitude of the MEMS sensor. This is the conversion coefficient between displacement and capacitance change. This represents the relationship between the change in capacitance and the amplitude of the output voltage.

[0061] Optionally, this embodiment converts the physical quantity of mechanical vibration amplitude of the sensitive structure of the MEMS sensor into a voltage signal that can be directly measured by the circuit, and uses a pre-calibrated electromechanical mapping relationship for reverse calculation, thereby achieving high-precision, non-contact electrical measurement of the amplitude.

[0062] It should be understood that when a MEMS sensor is working, its internal mass undergoes a tiny resonant motion around its equilibrium position. The amplitude of this motion, known as the vibration amplitude, directly affects the sensor's sensitivity, signal-to-noise ratio, and other key performance characteristics. This amplitude is extremely small (e.g., on the nanometer to submicrometer scale) and cannot be directly read by conventional instruments; it must be indirectly reflected by the resulting capacitance change. In this process, the detection electrodes and the mass form a variable parallel-plate capacitor. When the mass is displaced, the electrode spacing changes, causing a change in capacitance. A definite physical relationship exists between this capacitance change and the displacement, determined by the structural geometric parameters, namely the conversion coefficient between displacement and capacitance change.

[0063] Specifically, the conversion factor is determined by the gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes, and is related to the vacuum dielectric constant. The gap, length, and number can be directly observed by scanning electron microscopy (SEM), while the height is precisely controlled by the wafer thinning process and adopts the design value. Therefore, the conversion factor is an inherent parameter that can be accurately known after the device is manufactured and before testing, and does not depend on real-time circuit response or external environmental conditions.

[0064] It should be noted that the capacitance change itself is still a weak analog signal, which needs to be converted into a voltage signal that is easy to acquire and calculate through circuitry. For this purpose, the circuit sequentially includes a charge amplification module, a differential amplifier 160, and an analog-to-digital converter 170. The charge amplification module linearly converts the charge change output from the detection electrode into a first-stage voltage signal. The differential amplifier 160 performs differential processing on the outputs of the positive and negative detection electrode channels to suppress common-mode interference. By adjusting its gain, the final output voltage amplitude Vp reaches a better range of the circuit's dynamic range (e.g., close to full scale but not saturated). That is, the voltage amplitude output by the differential amplifier 160 described in this application reaches a preset circuit upper limit value, thereby improving the signal-to-noise ratio. The correspondence between the capacitance change and the output voltage amplitude established after this gain adjustment is a deterministic electrical transfer characteristic of the circuit under the current configuration. Therefore, the amplitude of the MEMS sensor can be determined based on the parameters under this state.

[0065] Furthermore, the amplitude of the MEMS sensor satisfies the formula:

[0066] Wherein, Vp is the voltage amplitude output by the differential amplifier 160, which is an electrical signal that is actually measured and can be digitized by the analog-to-digital converter 170; Let be the amplitude of the MEMS sensor to be solved, which is the maximum displacement of the mass block relative to the equilibrium position. The conversion coefficient between displacement and capacitance change is the normalized capacitance change caused by a unit displacement, which is uniquely determined by the aforementioned geometric parameters. This represents the relationship between capacitance change and output voltage amplitude. Its physical meaning is the output voltage amplitude generated by a unit capacitance change under the current circuit configuration. It is determined by the gain of the differential amplifier 160, the value of the feedback capacitor, and the circuit topology. These parameters have been introduced in the aforementioned formula and will not be repeated here.

[0067] As can be seen, this application, in determining the amplitude of the MEMS sensor, is based on a strict algebraic relationship derived from the fundamental physical laws of parallel plate capacitors (capacitance is inversely proportional to the distance between plates), the linear response characteristics of charge amplifiers, the 160 ratio operation principle of differential amplifiers, and the calibration logic of analog-to-digital conversion systems. It completely maps the originally invisible and difficult-to-measure microscopic mechanical vibrations into repeatable and software-analyzable digital voltage values, thereby eliminating the dependence on high-cost optical equipment (such as laser interferometers and high-speed camera systems) or harsh testing environments (such as cleanroom vacuum chambers). At the same time, since the entire calculation process does not involve weak ratio calculations (such as single-sideband voltage ratios), it also avoids the problem of accuracy degradation under noise dominance.

[0068] Based on the above implementation, this application also provides a MEMS sensor amplitude measurement circuit for performing the above method. Please refer to [link to relevant documentation]. Figure 1 The MEMS sensor amplitude measurement circuit includes a MEMS sensing chip 110, a first self-compensation module 120, a second self-compensation module 130, a first charge amplification module 140, a second charge amplification module 150, a differential amplifier 160, an analog-to-digital converter 170, and a PI controller 180. The MEMS sensing chip 110 includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode. The input terminal of the first self-compensation module 120 is connected to the output terminal of the PI controller 180 and the detection positive electrode, respectively. The output terminal of 20 is connected to the excitation positive electrode; the input terminal of the second self-compensation module 130 is connected to the output terminal of the PI controller 180 and the detection negative electrode respectively, and the output terminal of the second self-compensation module 130 is connected to the excitation negative electrode; the detection positive electrode is connected to the first charge amplification module 140, and the detection negative electrode is connected to the second charge amplification module 150; the first charge amplification module 140 and the second charge amplification module 150 are also connected to the input terminal of the differential amplifier 160 respectively; the differential amplifier 160, the analog-to-digital converter 170 and the PI controller 180 are connected in sequence.

[0069] By constructing a dedicated electrical measurement circuit with closed-loop self-calibration capability, the minute mechanical vibration amplitude of the sensitive structure of the MEMS sensor in the resonant state is converted into a stable, repeatable, and interference-resistant digital voltage signal. Relying on the deterministic connection relationship and collaborative working logic between the functional modules, the vibration amplitude can be directly calculated with high precision, non-destructively, and without optical assistance.

[0070] The self-compensation module has its input connected to the detection electrode of the MEMS sensor's sensing chip and the PI controller 180, and its output connected to the corresponding excitation electrode, used to compensate for the electrical feedthrough error between the excitation electrode and the detection electrode. The charge amplifier circuit has its input connected to the detection electrode and its output connected to the differential amplifier 160. The differential amplifier 160's input is connected to the first charge amplifier module 140 and the second charge amplifier module 150, respectively, used to suppress the common interference component (i.e., common-mode error) between the positive and negative detection electrodes, and its output is connected to the analog-to-digital converter 170 (ADC). The ADC 170 converts the input analog voltage signal into a digital signal and connects it to the PI controller 180. The PI controller 180's output is connected to the self-compensation circuit, and by adjusting the gain of the variable gain amplifier within the self-compensation circuit, automatic compensation for the electrical feedthrough error is achieved. A switch is connected at one end to the PI controller 180 and at the other end to the self-compensation circuit. This switch is used to switch between positive and negative compensation in a time-division manner, ensuring that feedthrough errors in both directions can be eliminated independently and accurately.

[0071] It should be understood that the core sensitive component of a MEMS sensor (microelectromechanical system sensor) is a micrometer-scale mass that undergoes high-frequency resonant motion along a specific direction under the action of a driving voltage; the amplitude of this motion is the vibration amplitude, which is a key physical quantity that determines the sensor's sensitivity, linearity, and signal-to-noise ratio. However, this amplitude is usually only tens to hundreds of nanometers, which cannot be observed with the naked eye or conventional instruments. Traditional methods either rely on expensive and precise optical equipment (such as laser interferometers) or on the calculation of weak electrical signal ratios that are susceptible to noise interference (such as the single-sideband voltage ratio method), resulting in high testing costs, strict environmental requirements, and poor repeatability of results.

[0072] In this application, to eliminate electrical feedthrough error, the functional positioning, connection relationship, and signal flow of each module are specifically designed. Specifically, the first self-compensation module 120 and the second self-compensation module 130 correspond to the spatial layout of the excitation positive / negative electrodes and the detection positive / negative electrodes, respectively, forming a mirror-symmetrical dual-channel compensation structure. The first charge amplification module 140 and the second charge amplification module 150 process the original charge signals of the positive / negative detection channels, respectively. The differential amplifier 160 utilizes the difference between their outputs to naturally suppress residual common-mode interference that has not been fully compensated. The PI controller 180 and the analog-to-digital converter 170 form a closed-loop feedback loop, enabling the entire system to have dynamic tracking and adaptive adjustment capabilities. This structural design allows the electrical feedthrough error to be pre-zeroed before the sensor starts oscillating, thus laying a pure electrical signal foundation for accurate amplitude measurement.

[0073] Therefore, this application constructs a dedicated measurement system with both feedforward compensation and feedback calibration mechanisms by interconnecting the self-compensation module, charge amplification module, differential amplifier 160, analog-to-digital converter 170 and PI controller 180 according to a specific topology. This significantly improves the accuracy, robustness and engineering feasibility of amplitude measurement without changing the physical structure of the MEMS chip, adding external optical equipment, or requiring a vacuum clean environment.

[0074] Please refer to Figure 3 The first self-compensation module includes: The first resistor R1 has one end connected to the positive detection electrode and the other end connected to the inverting output of the variable gain amplifier; the feedback resistor R2 has its two ends connected to the inverting input and output of the variable gain amplifier, respectively; the variable gain amplifier VGA has its non-inverting input grounded and its output connected to a capacitor; the output of capacitor C1 is connected to the positive detection electrode; the variable gain amplifier automatically adjusts its gain according to the output signal of the PI controller 180.

[0075] As one implementation method, please refer to Figure 4 Both the first and second charge amplification modules include an operational amplifier (OPA); feedback resistor R f Its two ends are connected to the inverting input and output terminals of the operational amplifier; feedback capacitor C f Its two ends are connected to the inverting input and output terminals of the operational amplifier; the non-inverting input terminal of the operational amplifier OPA is connected to the common-mode voltage V. ref The output terminal is used to output the voltage amplitude corresponding to the change in capacitance of the MEMS sensitive chip 110.

[0076] Furthermore, the MEMS sensor amplitude measurement circuit also includes a first switching switch 190 and a second switching switch 200. The first self-compensation module 120 is connected to the output terminal of the PI controller 180 through the first switching switch 190, and the second self-compensation module 130 is connected to the output terminal of the PI controller 180 through the second switching switch 200.

[0077] In summary, this application presents a MEMS sensor amplitude measurement circuit and method. By compensating for the electrical feedthrough error between the excitation and detection electrodes through a self-compensating circuit, it effectively suppresses parasitic coupling interference and improves measurement accuracy. Furthermore, by combining physical and electrical measurements, the amplitude is directly calculated, avoiding the problem of noise-dependent indirect ratio measurements, thus achieving high measurement accuracy. Secondly, the measurement circuit does not include a high-frequency carrier wave, omitting carrier generation, demodulation, and filtering modules. Compared to traditional carrier-based CV detection circuits, its circuit structure is simpler, easier to integrate, and lowers the bandwidth requirements of the operational amplifier, facilitating on-chip integration design of the measurement and control circuit. Thirdly, this method can be tested directly after packaging, without exposing the sensitive structure or requiring a cleanroom vacuum chamber, significantly reducing the requirements for the testing environment and equipment, allowing for more flexible testing conditions and greater environmental adaptability. Finally, the self-compensation of the electrical feedthrough error is achieved by automatically adjusting the variable gain amplifier through a PI controller, eliminating the need for manual intervention and improving testing efficiency.

[0078] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0079] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for measuring the amplitude of a MEMS sensor, characterized in that, An amplitude measurement circuit for a MEMS sensor is provided, comprising a MEMS sensing chip, a first self-compensation module, a second self-compensation module, a first charge amplification module, a second charge amplification module, a differential amplifier, an analog-to-digital converter, and a PI controller. The MEMS sensing chip includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode. The input terminal of the first self-compensation module is connected to the output terminal of the PI controller and the detection positive electrode, respectively, and the output terminal of the first self-compensation module is connected to the excitation positive electrode. The input terminal of the second self-compensation module is connected to the output terminal of the PI controller and the detection negative electrode, respectively, and the output terminal of the second self-compensation module is connected to the excitation negative electrode. The detection positive electrode is connected to the first charge amplification module, and the detection negative electrode is connected to the second charge amplification module. The first charge amplification module and the second charge amplification module are also connected to the input terminal of the differential amplifier. The differential amplifier, the analog-to-digital converter, and the PI controller are connected in sequence; the method includes: The gap between the excitation electrode and the mass block, the length of the excitation electrode, the height of the excitation electrode, and the number of excitation electrodes are obtained, and the conversion coefficient between displacement and capacitance change is determined based on the obtained parameters. The positive terminal coupling voltage self-compensation and the negative terminal coupling voltage self-compensation are performed sequentially. After the MEMS sensor driving circuit is connected and the MEMS sensing chip starts to oscillate and the amplitude stabilizes, the gain of the differential amplifier is adjusted until the voltage amplitude output by the differential amplifier reaches the preset circuit upper limit value, and the correspondence between the capacitance change and the output voltage amplitude is determined. The amplitude of the MEMS sensor is obtained based on the voltage amplitude output by the differential amplifier, the conversion coefficient between the displacement and the capacitance change, and the correspondence between the capacitance change and the output voltage amplitude.

2. The MEMS sensor amplitude measurement method according to claim 1, characterized in that, The conversion coefficient between displacement and capacitance change satisfies the formula: in, This is the conversion coefficient between displacement and capacitance change. The gap between the excitation electrode and the mass block. For the length of the excitation electrode, Where is the height of the excitation electrode, N is the number of excitation electrodes, and ε0 is the vacuum permittivity.

3. The MEMS sensor amplitude measurement method according to claim 1, characterized in that, The MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch. The first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch. The steps to complete positive terminal coupling voltage self-compensation include: The first switching switch is closed and the second switching switch is opened. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the mass block to the excitation positive electrode until the output of the first charge amplification module is 0, so as to achieve self-compensation of the positive terminal coupling voltage.

4. The MEMS sensor amplitude measurement method according to claim 1, characterized in that, The MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch. The first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch. The steps to complete negative terminal coupling voltage self-compensation include: The first switching switch is controlled to open, and the second switching switch is controlled to close. A sinusoidal voltage with an amplitude of Vac is applied at a frequency 1 kHz apart from the natural frequency of the mass block to the excitation negative electrode until the output of the second charge amplification module is 0, so as to achieve self-compensation of the negative terminal coupling voltage.

5. The MEMS sensor amplitude measurement method according to claim 1, characterized in that, The relationship between the change in capacitance and the magnitude of the output voltage satisfies the following formula: in, This represents the relationship between the change in capacitance and the amplitude of the output voltage. For the gain of the differential amplifier, This represents the voltage difference between the common-mode voltage of the mass block and the detection electrode. This is the capacitance value of the feedback capacitor.

6. The MEMS sensor amplitude measurement method according to claim 1, characterized in that, The amplitude of a MEMS sensor satisfies the formula: Where Vp is the voltage amplitude output by the differential amplifier. The amplitude of the MEMS sensor. This is the conversion coefficient between displacement and capacitance change. This represents the relationship between the change in capacitance and the amplitude of the output voltage.

7. A MEMS sensor amplitude measurement circuit, characterized in that, The MEMS sensor amplitude measurement circuit is used to perform the method as described in any one of claims 1 to 6. The MEMS sensor amplitude measurement circuit includes a MEMS sensing chip, a first self-compensation module, a second self-compensation module, a first charge amplification module, a second charge amplification module, a differential amplifier, an analog-to-digital converter, and a PI controller. The MEMS sensing chip includes an excitation positive electrode, an excitation negative electrode, a mass block, a detection positive electrode, and a detection negative electrode. The input terminal of the first self-compensation module is connected to the output terminal of the PI controller and the detection positive electrode, respectively, and the output terminal of the first self-compensation module is connected to the excitation positive electrode. The input terminal of the second self-compensation module is connected to the output terminal of the PI controller and the detection negative electrode, respectively, and the output terminal of the second self-compensation module is connected to the excitation negative electrode. The detection positive electrode is connected to the first charge amplification module, and the detection negative electrode is connected to the second charge amplification module. The first charge amplification module and the second charge amplification module are also connected to the input terminal of the differential amplifier, respectively. The differential amplifier, the analog-to-digital converter, and the PI controller are connected in sequence.

8. The MEMS sensor amplitude measurement circuit according to claim 7, characterized in that, The first self-compensation module includes: The first resistor has one end connected to the positive detection electrode and the other end connected to the inverting output of the variable gain amplifier. The feedback resistor is connected at both ends to the inverting input and output terminals of the variable gain amplifier, respectively. A variable gain amplifier with its non-inverting input grounded and its output connected to a capacitor; the output of the capacitor is connected to the positive detection electrode. The variable gain amplifier automatically adjusts its gain based on the output signal of the PI controller.

9. The MEMS sensor amplitude measurement circuit according to claim 7, characterized in that, The first charge amplification module includes: Operational amplifier; The feedback resistor is connected at both ends to the inverting input and output terminals of the operational amplifier. The feedback capacitor has its two ends connected to the inverting input and output terminals of the operational amplifier; The non-inverting input of the operational amplifier is connected to a common-mode voltage, and the output is used to output the voltage amplitude corresponding to the change in capacitance of the MEMS sensitive chip.

10. The MEMS sensor amplitude measurement circuit according to claim 7, characterized in that, The MEMS sensor amplitude measurement circuit further includes a first switching switch and a second switching switch. The first self-compensation module is connected to the output terminal of the PI controller through the first switching switch, and the second self-compensation module is connected to the output terminal of the PI controller through the second switching switch.

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