Signal processing method and system of micro electro mechanical system capacitive accelerometer

Abstract

The embodiment of the invention provides a signal processing method and system for a capacitive accelerometer of a micro electro mechanical system, and the method comprises the steps: detecting a capacitance change caused by acceleration through a differential capacitance structure, and obtaining a differential capacitance variation; inputting the differential capacitance variable quantity into a trans-impedance amplifier, converting the differential capacitance variable quantity into voltage change data, and superposing the voltage change data with a direct current bias voltage to generate a baseband modulation signal; a square wave carrier generation unit generates a square wave carrier signal, and modulates the baseband modulation signal and the square wave carrier signal to generate a modulation signal; synchronously demodulating the modulation signal through an annular diode demodulation circuit and outputting two paths of signals; performing low-pass filtering on the two paths of signals to filter out high-frequency carrier components and reserve low-frequency acceleration signals; and carrying out differential operation on the two paths of filtered signals, outputting a target voltage signal which is in a linear relation with the acceleration, and carrying out constant gain conversion by maintaining the signal processing link.

Description

Technical Field

[0001] This application relates to the technical field of micro-electro-mechanical systems (MEMS), specifically to a signal processing method and system for a capacitive accelerometer in a MEMS. Background Technology

[0002] MEMS capacitive accelerometers measure acceleration by detecting changes in differential capacitance caused by the displacement of an inertial mass. The basic principle is that when acceleration acts on the mass, the mass displaces relative to fixed electrodes, causing a change in differential capacitance. The acceleration value can be deduced by detecting this change in capacitance. However, in the manufacturing process of MEMS devices, deviations in the etching process inevitably lead to deviations in critical dimensional parameters from their design values. For example, a deviation of the electrode spacing y from the design value y0 may result in a deviation of ±20nm or even greater; the initial capacitance C0 may vary significantly between different chips.

[0003] Existing technologies typically employ three solutions to address the aforementioned problems: Solution 1: Traditional CV conversion circuits use switched-capacitor circuits or continuous-time integrators to convert capacitance changes into voltage. The main problem with Solution 1 is that the conversion gain is highly dependent on the reference capacitor and the parasitic parameters of the operational amplifier; process deviations directly lead to gain variations, requiring chip-by-chip calibration. Solution 2: Sine wave carrier modulation and demodulation uses a sine wave as the carrier and extracts the signal through synchronous demodulation. Solution 2 has the advantage of mature theory, but the sine wave generator circuit is complex, consumes more power, and has strict requirements for phase-locked loop design. Solution 3: Sigma-Delta modulation (also known as Σ-Δ modulation) employs oversampling and noise shaping techniques. While Solution 3 offers high accuracy, it has high circuit complexity, requires significant digital circuit resources, and is unsuitable for low-cost applications.

[0004] The scaling factor of the aforementioned existing technologies is significantly affected by process deviations, resulting in poor product consistency and necessitating expensive individual calibration processes. This restricts the large-scale application and cost advantages of the products. Therefore, a solution to these problems is urgently needed. Summary of the Invention

[0005] This application proposes a signal processing method and system for a microelectromechanical system capacitive accelerometer to address the deficiencies of the prior art.

[0006] According to a first aspect of the embodiments of this application, a signal processing method for a microelectromechanical system (MEMS) capacitive accelerometer is provided, comprising: The change in capacitance caused by acceleration is detected using a differential capacitor structure, and the amount of differential capacitance change is obtained. ; The change in the differential capacitance Input to transimpedance amplifier and converted into voltage change data and the voltage change data The baseband modulation signal is generated by superimposing it with a DC bias voltage, and the DC bias voltage is used to boost the signal level. A square wave carrier signal is generated by a square wave carrier generation unit, and the baseband modulation signal is modulated with the square wave carrier signal to generate a modulation signal; The modulation signal is synchronously demodulated by a ring diode demodulation circuit and two signals are output. The synchronous demodulation responds to the phase switching of the square wave carrier signal and achieves demodulation by periodically switching the transmission path and polarity of the modulation signal. The two signals are low-pass filtered to remove high-frequency carrier components and retain low-frequency acceleration signals; The two filtered signals are differentially processed, and a target voltage signal that is linearly related to the acceleration is output. By maintaining the constant gain conversion of the signal processing link, the scaling factor is kept in a stable target state under process deviation.

[0007] In some embodiments, detecting the capacitance change caused by acceleration through a differential capacitor structure includes: The initial capacitance of the differential capacitor structure is determined based on the nominal plate spacing. Detect the change in nominal electrode spacing caused by the displacement of the mass block due to acceleration; The capacitance change of the differential capacitor is calculated based on the change in the nominal plate spacing.

[0008] In some embodiments, the method further includes: By detecting the zero-point voltage when there is no acceleration input, the initial capacitance difference caused by process deviations is analyzed, which is used to evaluate the process deviations.

[0009] In some embodiments, the differential capacitance change The following formula is used to calculate:

[0010] in, Indicates the displacement capacitance conversion factor. This indicates the displacement of the mass block. Indicates the nominal electrode spacing.

[0011] In some implementations, the conversion factor of the transimpedance amplifier is kept constant to offset the effects of process variations; The feedback resistor of the transimpedance amplifier is used to set the conversion gain so that the voltage change is linearly related to the capacitance change, and to decouple the conversion coefficient from the initial capacitance.

[0012] In some implementations, the voltage change data The following formula is used to calculate:

[0013] in, This represents the capacitor voltage conversion factor.

[0014] In some implementations, the voltage change data is... The baseband modulation signal, generated by superimposing it with the DC bias voltage, is calculated using the following formula:

[0015] in, This represents the voltage value of the baseband modulation signal; This indicates the voltage change data. The sum of the DC bias voltage; This indicates the DC bias voltage value.

[0016] In some implementations, the generated modulation signal is calculated based on the following formula:

[0017] in, This represents the voltage value of the modulated signal; The frequency value of the square wave carrier signal is higher than the mechanical resonant frequency value of the accelerometer; t represents time. This represents a square wave function.

[0018] In some embodiments, the ring diode demodulation circuit is a bridge structure composed of four diodes: a first diode, a second diode, a third diode, and a fourth diode. The characteristic feature is that the synchronous demodulation of the modulated signal and the output of two signals via the ring diode demodulation circuit includes: The ring diode demodulation circuit is powered by the first and third diodes during the positive half-cycle of the square wave carrier, and by the second and fourth diodes during the negative half-cycle of the square wave carrier.

[0019] According to a second aspect of this application, a signal processing system for a microelectromechanical system (MEMS) capacitive accelerometer is provided, comprising: The capacitance change acquisition module is used to detect the capacitance change caused by acceleration through a differential capacitor structure and obtain the amount of differential capacitance change. ; The baseband modulation signal generation module is used to generate the differential capacitance change. Input to transimpedance amplifier and converted into voltage change data and the voltage change data The baseband modulation signal is generated by superimposing it with a DC bias voltage, and the DC bias voltage is used to boost the signal level. The modulation signal generation module is used to generate a square wave carrier signal from the square wave carrier generation unit and modulate the baseband modulation signal with the square wave carrier signal to generate a modulation signal; A two-channel signal generation module is used to synchronously demodulate the modulated signal through a ring diode demodulation circuit and output two signals. The synchronous demodulation responds to the phase switching of the square wave carrier signal and achieves demodulation by periodically switching the transmission path and polarity of the modulated signal. The low-pass filter module is used to perform low-pass filtering on the two signals to filter out the high-frequency carrier components and retain the low-frequency acceleration signal; The target voltage signal generation module is used to perform differential operation on the filtered two signals and output a target voltage signal that is linearly related to acceleration. By maintaining the constant gain conversion of the signal processing link, the scaling factor is kept in a target stable state under process deviation.

[0020] The beneficial effects of the signal processing method and system for the microelectromechanical system capacitive accelerometer of the embodiments of this application include at least the following: This application embodiment utilizes a symmetrical differential capacitor structure for detection, effectively suppressing common-mode noise such as ambient temperature changes and electromagnetic interference, thereby improving the signal-to-noise ratio of signal detection. Simultaneously, this structure converts the single-ended capacitance change caused by acceleration into a differential signal, doubling the effective signal amplitude and significantly improving detection sensitivity. By employing a transimpedance amplifier for conversion, a direct, linear conversion path from capacitance to voltage is provided, helping to maintain the gain stability of the signal link. The introduction of a DC bias voltage raises the signal level, effectively preventing weak signal truncation distortion caused by device conduction voltage in subsequent demodulation stages, ensuring signal integrity. Using a square wave as the carrier signal simplifies the generation circuit compared to traditional sine wave generators, eliminating the need for complex oscillation circuits or phase-locked loops, directly reducing the overall system complexity and power consumption. Modulating the low-frequency baseband signal onto a high-frequency carrier creates conditions for subsequent synchronous demodulation, facilitating the accurate extraction of useful acceleration information from the modulated signal. By utilizing a ring diode circuit to control the signal path through phase switching of a square wave carrier, an analog multiplier function is implemented, thereby achieving synchronous demodulation. This scheme replaces the complex analog multiplier chip with a simple switching circuit, which helps reduce costs and improve reliability. The synchronous demodulation mechanism can accurately restore the modulated baseband signal while greatly suppressing interference signals that are out of sync with the carrier, enhancing the system's anti-interference capability. Low-pass filtering effectively removes residual high-frequency carrier components and their harmonics from the demodulated signal, purifying the signal and ensuring the signal-to-noise ratio of the output signal. By setting an appropriate filter bandwidth, effective low-frequency acceleration signals can be ensured to pass through without distortion, while suppressing out-of-band noise and optimizing the system's signal quality. Final differential operation on the two signals further suppresses potential common-mode interference, improving the purity of the output signal. The entire signal processing chain is designed to maintain a constant gain conversion, decoupling the core performance indicator scaling factor from initial parameters susceptible to process deviations. This ensures that the sensor maintains excellent product consistency and stability even with manufacturing deviations, reducing reliance on individual calibrations. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the signal processing method for a capacitive accelerometer in a microelectromechanical system according to an embodiment of this application. Figure 2 This is a schematic diagram of the differential capacitor structure according to an embodiment of this application; Figure 3 This is a model framework diagram of a capacitive accelerometer for a microelectromechanical system according to an embodiment of this application; Figure 4-5 This is a graph showing the input acceleration-output voltage experimental data under different process deviations in the embodiments of this application; Figure 6This is a simulation waveform diagram of the 500Hz bandwidth characteristics of an embodiment of this application; Figure 7 This is a simulation waveform diagram of the 1000Hz bandwidth characteristics of an embodiment of this application; Figure 8 This is a simulation waveform diagram of the 5000Hz bandwidth characteristics of an embodiment of this application; Figure 9 This is a schematic diagram of the signal processing system of the microelectromechanical system capacitive accelerometer according to an embodiment of this application; Figure 10 This is a schematic diagram of the modulation and demodulation circuit according to an embodiment of this application; Figure 11 This is a schematic diagram of the ring diode demodulation circuit according to an embodiment of this application; Figure 12 This is a model block diagram of the signal processing system of the microelectromechanical system capacitive accelerometer according to an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the signal processing method and system for a microelectromechanical system capacitive accelerometer will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only some embodiments of the 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.

[0023] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are all within the scope of protection of the embodiments of the present application.

[0024] It can 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 will not be further defined and explained in subsequent figures according to the embodiments of this application.

[0025] This application discloses a signal processing method and system for a microelectromechanical system (MEMS) capacitive accelerometer. The signal processing method is based on a signal processing system for a MEMS capacitive accelerometer. The purpose of this method and system is to address the problem that the scaling factor in existing MEMS capacitive accelerometer systems is significantly affected by process deviations. It solves the problem of maintaining the stability of the scaling factor when the initial capacitance C0 changes due to etching process deviations, while simultaneously assessing the impact of process deviations, avoiding expensive wafer-by-wafer calibration processes, and simplifying the circuit to reduce power consumption and cost. This signal processing method and system for MEMS capacitive accelerometers can be used to analyze semiconductor process deviations and is robust to manufacturing process deviations.

[0026] Process deviation refers to the difference between the actual processed dimensions and the design dimensions during semiconductor manufacturing. For MEMS devices, deviations in the etching process can cause the electrode spacing to deviate from the design value by ±20nm or even more.

[0027] See attached document Figure 1 As shown, the signal processing method of the microelectromechanical system capacitive accelerometer includes steps S10-S60.

[0028] Step S10: Detect the capacitance change caused by acceleration using a differential capacitor structure to obtain the amount of differential capacitance change. .

[0029] Microelectromechanical systems (MEMS) are technologies that integrate microelectronics and mechanical engineering, and their dimensions are typically in the range of micrometers to millimeters.

[0030] In some implementations, detecting capacitance changes caused by acceleration through a differential capacitor structure includes: determining the initial capacitance of the differential capacitor structure based on the nominal plate spacing; detecting the change in nominal plate spacing caused by the displacement of the mass block due to acceleration; and calculating the capacitance change of the differential capacitor based on the change in nominal plate spacing.

[0031] Step S10 can also be understood as the differential capacitance detection step. The differential capacitance is a core detection structure in microelectromechanical system (MEMS) sensors, specifically referring to a detection unit composed of two symmetrically distributed capacitors (first capacitor C1 and second capacitor C2). Essentially, it's a sensing mechanism that detects physical quantities (such as acceleration) by measuring the change in the difference between the two capacitors (C1-C2). Compared to single-ended capacitors, differential capacitance can suppress common-mode interference and improve sensitivity.

[0032] For example, see Appendix Figure 2As shown, in the MEMS accelerometer of this embodiment, the differential capacitor forms a symmetrical structure with a movable mass block and fixed electrodes on both sides. When the acceleration a is zero, the mass block is in the equilibrium position, C1=C2, and the differential output is zero; when the acceleration a is applied, the mass block is displaced and moves a distance d to one side, causing the capacitor gap on one side to increase, and the second capacitor C2=C0- The gap decreases on the other side, and the first capacitor C1 = C0 + Increase; simultaneously generate a differential signal, representing the amount of differential capacitance change. The calculation expression is shown below:

[0033] in, This indicates the change in capacitance on one side; Indicates the initial capacitance. The relationship between the electrode spacing and the electrode spacing is expressed as follows:

[0034] Where ε represents the dielectric constant, A represents the effective area of ​​the plates, and d represents the distance between the plates. This represents the displacement capacitance conversion coefficient.

[0035] For example, the change in differential capacitance The following formula is used to calculate:

[0036] in, Indicates the displacement capacitance conversion factor. This indicates the displacement of the mass block. Indicates the nominal electrode spacing.

[0037] For example, see Appendix Figure 3 As shown, the calculation of mechanical displacement includes, for example, calculating the displacement based on Newton's second law and the characteristics of the mechanical system when a 1g acceleration signal 100 acts on the movable mass 200 of the MEMS differential capacitance sensor. The core associated module is the second-order dynamic model 101 of the MEMS accelerometer. The expression for calculating the displacement d is shown below:

[0038] The calculation of differential displacement includes, for example, the calculation of the total relative displacement due to the symmetry of the first capacitor 201 and the second capacitor 202 in the differential capacitor structure, where the gap on one side increases by d and the gap on the other side decreases by d. The expression is shown below:

[0039] The calculation of the differential capacitance change includes, for example, the change in capacitance value of differential capacitor 103 caused by displacement, wherein, in the absence of acceleration, the initial differential capacitance... The gap between the two electrode plates 203 204 (caused by etching deviation) The decision is made to calculate the total relative displacement. The expression is as follows:

[0040] in, The gap between the two electrodes depends on the etching error 102. 203 A minute difference of 204. Based on this, the change in differential capacitance after the application of an acceleration signal is calculated. Change, when << hour:

[0041]

[0042]

[0043] The differential detection in this application doubles the effective signal amplitude, which is significantly better than single-ended detection.

[0044] In some implementations, the method further includes analyzing the initial capacitance difference caused by process deviations by detecting the zero-offset voltage when there is no applied acceleration input, in order to evaluate the process deviations. Here, zero offset refers to the sensor's output voltage value when there is no applied acceleration input. Ideally, it should be 0V, but process deviations can cause zero-offset shifts.

[0045] Step S20, the change in differential capacitance Input to transimpedance amplifier and converted into voltage change data and the voltage change data When superimposed with a DC bias voltage, a baseband modulation signal is generated, which is used to boost the signal level.

[0046] In some implementations, the conversion factor of the transimpedance amplifier is kept constant to offset the effects of process variations; the feedback resistor of the transimpedance amplifier is used to set the conversion gain so that the voltage change is linearly related to the capacitance change, and to decouple the conversion factor from the initial capacitance.

[0047] In some implementations, this voltage change data The following formula is used to calculate:

[0048] in, This represents the capacitor-to-voltage (CV) conversion factor. Capacitor-to-voltage conversion is a circuit technique used to convert changes in capacitance into a voltage signal.

[0049] In some implementations, the voltage change data will be... The baseband modulation signal, generated by superimposing it with the DC bias voltage, is calculated using the following formula:

[0050] in, This represents the voltage value of the baseband modulation signal; This indicates the voltage change data. The sum of the DC bias voltage; This indicates the DC bias voltage value.

[0051] For example, the change in differential capacitance Converted to change in current Then, it is converted into a voltage change by a transimpedance amplifier. The expression for its calculation is shown below;

[0052] in, This represents the feedback resistor of the transimpedance amplifier. This is the capacitor voltage conversion factor; this conversion factor It has the following characteristics: When manufacturing process deviations cause initial capacitance When changing, Keep it constant to ensure that the scaling factor is not affected by process deviations.

[0053] For example, refer again to the appendix Figure 3 As shown, the CV amplification module 105 amplifies the differential capacitance change. Converted to voltage change The core parameter is the capacitor voltage conversion factor. 300. Calculate the voltage change. The expression is shown below:

[0054]

[0055]

[0056] Wherein, initial voltage In the absence of acceleration, etching errors lead to There exists an initial voltage zero point. Taking the nominal process as an example, the calculation... The expression is shown below:

[0057] at this time, ≈3V ( (Due to variations in process deviations), calculate the total voltage. The expression is shown below: .

[0058] For example, the voltage change data The DC bias voltage is superimposed on the voltage change at the output of the transimpedance amplifier. DC bias voltage Superimpose, calculate and form the baseband modulation signal Its calculation expression is shown below;

[0059] Among them, the DC bias voltage Its function is to raise the signal level and prevent the effective signal from being masked by the forward voltage of the diodes in the subsequent demodulation circuit.

[0060] For example, see Appendix Figure 3 As shown, a DC bias of 104 is superimposed to prevent the signal from being masked by the diode's forward voltage during subsequent loop demodulation, and a 10V DC bias of 301 is superimposed. The baseband modulation signal is calculated and formed. Its calculation expression is shown below;

[0061] The signal at this time includes a DC component (13.3V, including a 10V bias + 3.3V effective signal) and an AC component (0V, with acceleration as DC or low-frequency signal).

[0062] Step S30: A square wave carrier signal is generated by the square wave carrier generation unit, and the baseband modulation signal is modulated with the square wave carrier signal to generate a modulation signal.

[0063] Carrier modulation is the process of shifting a low-frequency baseband signal onto a high-frequency carrier. The embodiments of this application use a square wave carrier with a frequency fc = 200 kHz, which is much higher than the frequency of the acceleration signal (typically fc < 1 kHz).

[0064] In some implementations, the generated modulated signal is calculated based on the following formula:

[0065] in, This represents the voltage value of the modulated signal; The frequency of the square wave carrier signal is higher than the mechanical resonant frequency of the accelerometer; t represents time. This represents a square wave function.

[0066] For example, a square wave carrier signal is generated by a square wave carrier generation unit, and the baseband modulation signal is modulated with the square wave carrier signal to generate a modulated signal, including: generating a frequency of... Amplitude The square wave carrier signal will modulate the baseband signal. A modulated signal is generated by multiplying a square wave carrier wave with a ring diode circuit. The expression is shown below;

[0067] Where t represents time, and the square wave carrier frequency is... Much higher than the mechanical resonant frequency of the accelerometer ,satisfy >> conditions.

[0068] For example, see Appendix Figure 3 As shown, a high-frequency square wave carrier is generated based on the square wave carrier generation unit 106, which converts the baseband signal... 302 modulation to a high-frequency carrier signal 303, carrier frequency kHz, carrier amplitude Generate a modulated signal. The expression is shown below;

[0069] Modulated signal amplitude The signal is a 200kHz square wave (304) with a voltage of 6.65V, whose envelope carries acceleration information. The amplitude of the modulated signal is... The expression is shown below:

[0070] Step S40: The modulated signal is synchronously demodulated by a ring diode demodulation circuit and two signals are output. The synchronous demodulation responds to the phase switching of the square wave carrier signal and demodulation is achieved by periodically switching the transmission path and polarity of the modulated signal.

[0071] The synchronous demodulation of the modulated signal and the output of two signals are achieved by using a ring diode demodulation circuit. The ring demodulator (also known as a ring modulator) consists of four diodes forming a bridge structure to perform signal multiplication.

[0072] In some embodiments, the ring diode demodulation circuit is a bridge structure composed of four diodes: a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4, used to implement an analog multiplier function and complete synchronous demodulation. The synchronous demodulation of the modulated signal and output of two signals via the ring diode demodulation circuit includes: the first diode D1 and the third diode D3 being turned on during the positive half-cycle of the square wave carrier, and the second diode D2 and the fourth diode D4 being turned on during the negative half-cycle of the square wave carrier.

[0073] For example, the synchronous demodulation of the modulated signal and output of two signals via a ring diode demodulation circuit includes: when the square wave carrier is in the positive half-cycle, diodes D1 and D3 are turned on, and the signal is transmitted in the forward direction; when the square wave carrier is in the negative half-cycle, diodes D2 and D4 are turned on, and the signal is transmitted in the reverse direction. Through the above switching action, the input signal is multiplied by the square wave carrier, and two signals are demodulated and output. The expression is shown below:

[0074] in, Indicates the differential amplifier gain. Indicates the forward voltage drop of the diode: For example, see Appendix Figure 3 As shown, the modulation signal is input to the ring diode demodulation circuit 107. Synchronous demodulation is achieved by switching the first diode D1 401, the second diode D2 402, the third diode D3 403, and the fourth diode D4 404 on / off. The forward voltage drop of the diodes is... V. During the positive half-cycle of the square wave: diodes D1 (401) and D3 (403) are turned on, and the signal is transmitted in the forward direction; during the negative half-cycle of the square wave: diodes D2 (402) and D4 (404) are turned on, and the signal is transmitted in the reverse direction; the above switching achieves the "input signal..." The analog multiplication function of the "square wave carrier" outputs a demodulated signal 305, and the voltage of the demodulated signal 305 is... The expression is shown below: ; Among them, when there is no acceleration (i.e.) When =0), the initial voltage of the ring diode The expression is shown below: ; Wherein, at an acceleration of 1g (i.e.) When =5.5fF): ; Calculating the single-channel gain The expression is shown as follows: .

[0075] Step S50, perform low-pass filtering on the two signals to filter out the high-frequency carrier components and retain the low-frequency acceleration signals.

[0076] In some embodiments, performing low-pass filtering on the two signals includes: passing through a load resistor and a load capacitor to form an RC low-pass filter to filter out the high-frequency carrier components and retain the low-frequency acceleration signals. The filter bandwidth The expression is shown as follows;

[0077] where the bandwidth BW satisfies: acceleration signal frequency range < BW < carrier frequency .

[0078] For example, as shown in the attached Figure 3 Perform low-pass filtering on the two signals. Through the RC low-pass filter unit 108, filter out the 200 kHz high-frequency carrier and retain the low-frequency acceleration signals. The load resistor , the load capacitor 406. The filter parameter calculations are shown as follows respectively: Time constant: τ = RL × CL = 300 μs.

[0079] Cutoff frequency: BW = 1 / (2πτ) = 530.5 Hz.

[0080] Attenuation calculation: Based on the 200 kHz carrier: [[ID=第

[44] ]]]; where, based on the acceleration signal less than 500 Hz of the carrier and the attenuation less than 1 dB, it passes through almost without loss.

[0081] The two signals output after filtering , are respectively: .

[0082] Step S60, perform differential operation on the two filtered signals, and output a target voltage signal linearly related to the acceleration, and maintain the target stable state of the scale factor under process variations through constant gain conversion of the signal processing link.

[0083] It should be noted that there seems to be an error in the numbering in the original text for item

[44] . It is recommended to check and correct it for a more accurate translation. Also, the text contains some special tags like etc. which are preserved as per the instruction but their specific meaning and usage might need further context clarification.The scale factor (SF) is the ratio of the output voltage change to the input acceleration, measured in V / g. In this embodiment, the scale factor is 0.3V / g, meaning that every 1g of acceleration produces a 0.3V voltage change.

[0084] For example, refer to the appendix. Figure 3 As shown, the differential output unit 109 performs differential operations on the two filtered signals 407 and 408 to obtain the final output voltage. ,in, Differential gain : ; When there is no acceleration: ; At an acceleration of 1g: ; Scale factor 111 The ratio of the change in voltage signal to the change in acceleration signal is expressed as follows:

[0085] This result is consistent with the target steady state.

[0086] See attached document Figure 4-5 As shown, two sets of experimental data are presented regarding a signal processing method for a capacitive accelerometer in a microelectromechanical system according to an embodiment of this application. The first set (nominal process) shows the initial differential capacitance. =70.20 fF, voltage change ΔV=0.297 V when 1g input; second group (process deviation) initial differential capacitor =16.64 fF, voltage change ΔV=0.295 V at 1g input, scaling rate less than 0.1%. Based on this experiment, it can be concluded that even if the process etching error causes a change in the gap between the left and right sides of the capacitor, the initial capacitance remains constant. The change was 4.2 times. Even without changing the scaling factor, the same scaling factor can still be obtained. At the same time, the impact of process deviation can be analyzed by analyzing the zero point, which verifies the anti-process deviation and analyzable process deviation characteristics of the embodiments of this application.

[0087] See attached document Figure 6-8The diagram shows the demodulated output waveforms at different input frequencies. For a 500Hz input signal, the output waveform is a sine wave with good fidelity and distortion less than 1%, allowing the signal to pass completely. For a 1000Hz input signal, the output waveform is a sine wave with a slight amplitude attenuation of about 3dB, close to the cutoff frequency. For a 5000Hz input signal, the output waveform shows a significant attenuation of about 20dB, effectively filtering out signals exceeding the bandwidth. Based on this experiment, it can be concluded that the bandwidth design (BW = 530.5 Hz) is reasonable, effectively demodulating acceleration signals within the bandwidth while sufficiently suppressing the carrier component (200kHz).

[0088] This application embodiment utilizes a symmetrical differential capacitor structure for detection, effectively suppressing common-mode noise such as ambient temperature changes and electromagnetic interference, thereby improving the signal-to-noise ratio of signal detection. Simultaneously, this structure converts the single-ended capacitance change caused by acceleration into a differential signal, doubling the effective signal amplitude and significantly improving detection sensitivity. By employing a transimpedance amplifier for conversion, a direct, linear conversion path from capacitance to voltage is provided, helping to maintain the gain stability of the signal link. The introduction of a DC bias voltage raises the signal level, effectively preventing weak signal truncation distortion caused by device conduction voltage in subsequent demodulation stages, ensuring signal integrity. Using a square wave as the carrier signal simplifies the generation circuit compared to traditional sine wave generators, eliminating the need for complex oscillation circuits or phase-locked loops, directly reducing the overall system complexity and power consumption. Modulating the low-frequency baseband signal onto a high-frequency carrier creates conditions for subsequent synchronous demodulation, facilitating the accurate extraction of useful acceleration information from the modulated signal. By utilizing a ring diode circuit to control the signal path through phase switching of a square wave carrier, an analog multiplier function is implemented, thereby achieving synchronous demodulation. This scheme replaces the complex analog multiplier chip with a simple switching circuit, which helps reduce costs and improve reliability. The synchronous demodulation mechanism can accurately restore the modulated baseband signal while greatly suppressing interference signals that are out of sync with the carrier, enhancing the system's anti-interference capability. Low-pass filtering effectively removes residual high-frequency carrier components and their harmonics from the demodulated signal, purifying the signal and ensuring the signal-to-noise ratio of the output signal. By setting an appropriate filter bandwidth, effective low-frequency acceleration signals can be ensured to pass through without distortion, while suppressing out-of-band noise and optimizing the system's signal quality. Final differential operation on the two signals further suppresses potential common-mode interference, improving the purity of the output signal. The entire signal processing chain is designed to maintain a constant gain conversion, decoupling the core performance indicator scaling factor from initial parameters susceptible to process deviations. This ensures that the sensor maintains excellent product consistency and stability even with manufacturing deviations, reducing reliance on individual calibrations.

[0089] The following is an experimental result shown in a first specific implementation of a signal processing method for a microelectromechanical system capacitive accelerometer according to an embodiment of this application, based on the mass production of consumer electronics products.

[0090] This embodiment is based on a smartphone manufacturer purchasing 10 million MEMS accelerometer sensors for a new phone, used for screen rotation and motion detection functions. The problem to be solved is that traditional accelerometer solutions suffer from the following drawbacks: large scaling factor differences (±15%) between batches of chips, leading to inconsistent motion detection sensitivity across different phones; sensor suppliers need to calibrate each chip, increasing costs by 3-5 yuan per chip; and the calibration process adds 2-3 days to the production cycle, impacting delivery time.

[0091] By using the above-described scheme of this application embodiment, at least the following four beneficial effects are achieved through parameter acquisition: Chip manufacturing stage: Through the design of the accelerometer in this application embodiment, a square wave carrier generation unit and a loop demodulation unit are integrated into the ASIC chip; Wafer testing stage: By testing the zero-point value V0, etching process deviations (such as electrode gap differences of ±18nm) are automatically identified, but no calibration is required; Post-packaging testing: The scaling factor is directly tested, and it is found that even under process deviations, the scaling factor of all chips is 0.30±0.0003V / g (change rate <0.1%); Mobile phone assembly stage: The accelerometer chip is directly soldered to the motherboard without additional calibration procedures, making it plug-and-play.

[0092] The following is an experimental result shown in a second specific implementation of a signal processing method for a microelectromechanical system capacitive accelerometer according to an embodiment of this application, based on the mass production of consumer electronics products.

[0093] The experimental steps for scaling factor-based stability testing include: batch sample testing, scaling factor measurement, statistical analysis, process deviation analysis, and judgment criteria. Batch sample testing involves purchasing 50-100 samples from the same batch of products; scaling factor measurement involves applying a standard acceleration of 1g using a precision vibration table, measuring the output voltage of each sample, and calculating the scaling factor SF = ΔV / 1g; statistical analysis includes calculating the standard deviation and coefficient of variation of the scaling factor; process deviation analysis includes measuring the zero-point voltage V0 (output voltage without acceleration) and analyzing the correlation between V0 and the scaling factor SF; the judgment criteria include a scaling factor coefficient of variation <0.2% (a characteristic of this embodiment, traditional methods typically >5%), meaning that even if V0 changes significantly (indicating process deviation), SF remains constant, and products that have not undergone piece-by-piece calibration still have a highly consistent scaling factor.

[0094] When using the null-point analysis method, the experimental steps include: null-point measurement, acceleration response testing, data analysis, process deviation inference, and judgment criteria. Null-point measurement involves measuring the output voltage V0 of each sample without acceleration input; acceleration response testing involves applying a standard acceleration (e.g., 1g) and measuring the output voltage change ΔV; data analysis includes plotting a scatter plot of V0 versus ΔV and calculating the correlation coefficient R²; process deviation inference involves inferring the difference in electrode gap based on the V0 value; and judgment criteria include: significant differences in V0 among different samples (±10-30%) indicate process deviation, but all samples have highly consistent ΔV (coefficient of variation <0.2%), which can be determined using the formula... The difference in electrode gap can be deduced by reverse deduction.

[0095] The core of this application's embodiments lies in converting the gap error caused by uneven etching load into a statistically regular displacement. By introducing this displacement deviation into the signal transmission process of the MEMS accelerometer system, it is possible to both evaluate MEMS process deviations and ensure that the sensor can still output according to the design scale when process deviations exist. Compared with previous technologies, the specific differences are as follows: 1. Process deviation handling logic: Traditional CV conversion circuits, sinusoidal carrier modulation, and Sigma-Delta modulation schemes lack specific mechanisms to address electrode spacing deviations and initial capacitance (C0) differences caused by etching processes. They passively accept scale factor drift due to process deviations, ultimately requiring piece-by-piece calibration to compensate for the deviations, without analyzing the process deviations themselves. This application's embodiment proactively converts the gap error caused by uneven etching load into a quantifiable displacement, integrating this displacement deviation into the MEMS accelerometer's signal transmission chain (the entire process from differential capacitance detection to differential output). The gap error magnitude can be inferred from the initial voltage zero-point value, enabling proactive assessment of process deviations rather than simply passively responding to measurement errors caused by these deviations.

[0096] 2. Scale factor stability: Previous technologies relied on components susceptible to process variations for scaling factor stability. For example, the conversion gain of traditional CV conversion circuits is highly dependent on the reference capacitor and operational amplifier parasitic parameters; the signal demodulated by a traditional sinusoidal carrier modulation loop is affected by the initial capacitance C0, causing the scaling factor to vary significantly with process variations, resulting in poor product consistency and requiring individual calibration to ensure accuracy. This application's embodiments, by combining a transimpedance circuit and a loop demodulation circuit design, employ a unique capacitance-voltage conversion relationship Kcv, decoupling it from the initial capacitance C0—Kcv remains constant even when the initial capacitance C0 changes due to etching variations. Even if C0 changes by a factor of 4.2 due to process variations, the scaling factor remains unchanged at 0.3V / g, with a change rate of <0.1%, eliminating the need for individual calibration.

[0097] In summary, the system described in this application maintains a stable scaling factor even under process deviations, and transforms gap errors into statistically significant displacements through a model, thereby enabling the assessment of MEMS process deviations. It fully realizes the ability to transform gap errors into statistically significant displacements through a system model when electrode spacing changes due to process deviations, maintains the design scaling even with process deviations, and simplifies the circuitry to reduce power consumption and cost.

[0098] See attached document Figure 9 As shown, this application also discloses a signal processing system for a microelectromechanical system capacitive accelerometer, including: a capacitance change acquisition module 910, a baseband modulation signal generation module 920, a modulation signal generation module 930, a two-channel signal generation module 940, a low-pass filter module 950, and a target voltage signal generation module 960.

[0099] The capacitance change acquisition module 910 is used to detect the capacitance change caused by acceleration through a differential capacitor structure and obtain the amount of differential capacitance change. .

[0100] The baseband modulation signal generation module 920 is used to generate the differential capacitance change. Input to transimpedance amplifier and converted into voltage change data and the voltage change data When superimposed with a DC bias voltage, a baseband modulation signal is generated, which is used to boost the signal level.

[0101] The modulation signal generation module 930 is used to generate a square wave carrier signal by the square wave carrier generation unit, and modulate the baseband modulation signal with the square wave carrier signal to generate a modulation signal.

[0102] The two-channel signal generation module 940 is used to synchronously demodulate the modulated signal through a ring diode demodulation circuit and output two signals. The synchronous demodulation responds to the phase switching of the square wave carrier signal and achieves demodulation by periodically switching the transmission path and polarity of the modulated signal.

[0103] The low-pass filter module 950 is used to perform low-pass filtering on the two signals to filter out the high-frequency carrier components and retain the low-frequency acceleration signal.

[0104] The target voltage signal generation module 960 is used to perform differential operation on the two filtered signals and output a target voltage signal that is linearly related to the acceleration. By maintaining the constant gain conversion of the signal processing link, the scaling factor is kept in a target stable state under process deviation.

[0105] In some implementations, refer to the appendix. Figure 3 As shown, the signal processing system of this microelectromechanical system (MEMS) capacitive accelerometer further includes: a MEMS differential capacitance sensor unit (for detecting capacitance changes caused by acceleration), a process deviation injection unit (simulating etching errors), a CV unit (converting capacitance changes into voltage signals), a DC bias unit (adding DC bias to the signal), a square wave carrier generation unit (generating a 200kHz square wave carrier), a ring diode demodulation unit (achieving synchronous demodulation), an RC low-pass filter unit (filtering out high-frequency carrier components), and a differential output unit (outputting the final acceleration signal). The signal flow includes: MEMS accelerometer → CV amplification → bias superposition → carrier modulation → ring diode demodulation → low-pass filtering → differential output.

[0106] In some implementations, refer to the appendix. Figure 10 As shown, the circuit of the signal processing system of this microelectromechanical system capacitive accelerometer includes: a CV amplifier (converting the differential capacitance change into a voltage signal), and a DC bias source (providing...). =10V bias voltage), square wave carrier generator (generates a square wave with a carrier frequency of 200kHz and a voltage of 0.5V), ring diode bridge circuit (implements signal modulation and demodulation), RC low-pass filter (RL=100Ω, CL=3μF, BW=530.5Hz), differential amplifier (differential gain) =2). The signal processing flow fully demonstrates the entire process from capacitance detection to the final output.

[0107] In some implementations, refer to the appendix. Figure 11 The diagram shows the schematic of a ring diode demodulation circuit. The ring diode demodulation circuit includes: four diodes D1, D2, D3, and D4 (forming a bridge structure), an input terminal (receiving the baseband modulation signal), a carrier control terminal (receiving the square wave carrier signal), and an output terminal (connected to the load resistor RL and the load capacitor CL). Working principle: During the positive half-cycle of the square wave, D1 and D3 conduct, while D2 and D4 are cut off, and current flows forward through the load; during the negative half-cycle of the square wave, D2 and D4 conduct, while D1 and D3 are cut off, and current flows backward through the load. It achieves an analog multiplication function, where the output equals the input signal multiplied by the square wave carrier. Key parameters include: the diodes are Schottky diodes, and the forward voltage drop V0 is... d =0.2V, load parameters RL=100Ω, CL=3μF.

[0108] like Figure 12The diagram illustrates the complete implementation of the signal processing chain in the simulation model of this application embodiment, including: a MEMS mechanical model (including mass, spring, and damping system), a differential capacitance detection module (simulating displacement-capacitance conversion), a process deviation injection module (simulating etching error), a transimpedance amplification module (realizing CV conversion), a modulation and demodulation module (realizing square wave carrier modulation and loop demodulation), and a filtering output module (RC low-pass filtering and differential output). Simulation parameters: mechanical resonant frequency 8.7172 kHz, carrier frequency 200 kHz, filter bandwidth BW = 530.5 Hz, scaling factor SF = 0.3 V / g. This simulation verifies the correctness of the theoretical analysis and the feasibility of the system in the embodiments of this application.

[0109] Compared with existing technologies, the embodiments of this application have significant advantages. The system of this application has strong resistance to process deviations; when the initial capacitance C0 changes due to etching process deviations, the scaling factor remains unchanged at the design value of 0.3V / g, with a change rate of less than 0.1%. The system of this application can analyze process deviation values ​​and analyze the gap error value caused by uneven etching load based on the output zero-point value. The circuit implementation of the system of this application is simple, using a square wave as the carrier signal. The generation circuit only requires a digital oscillator, eliminating the need for complex circuits such as sine wave generators and phase-locked loops, thus reducing system complexity and power consumption. The system of this application has significant cost advantages, eliminating the need for expensive wafer-by-wafer calibration processes, improving product yield and consistency; and simplifying the circuit structure to reduce chip area and power consumption.

[0110] The product applications in this application include, but are not limited to, consumer electronics, automotive electronics, and industrial control products. Consumer electronics include, but are not limited to, applications such as screen rotation, pedometers, gesture recognition, and image stabilization for smartphones / tablets; motion-sensing gaming, posture control, and motion capture for game controllers; and attitude stabilization, flight control, and gimbal stabilization for drones. Automotive electronics include, but are not limited to, applications of active safety systems such as Electronic Stability Control (ESC), Anti-lock Braking System (ABS), and Traction Control System (TCS); applications of passive safety systems such as airbag triggering, collision detection, and rollover detection; and applications of vehicle body control such as suspension system adjustment and vehicle posture control. Industrial control products include, but are not limited to, applications such as robot posture detection, balance control, vibration monitoring, collision protection, equipment health monitoring, fault warning, and maintenance prediction for vibration monitoring systems, and applications of precision measuring instruments such as inclinometers, levels, and attitude measurement systems.

[0111] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. A signal processing method for a capacitive accelerometer in a microelectromechanical system, characterized in that, include: The change in capacitance caused by acceleration is detected using a differential capacitor structure, and the amount of differential capacitance change is obtained. ; The change in the differential capacitance Input to transimpedance amplifier and converted into voltage change data and the voltage change data The baseband modulation signal is generated by superimposing it with a DC bias voltage, and the DC bias voltage is used to boost the signal level. A square wave carrier signal is generated by a square wave carrier generation unit, and the baseband modulation signal is modulated with the square wave carrier signal to generate a modulation signal; The modulation signal is synchronously demodulated by a ring diode demodulation circuit and two signals are output. The synchronous demodulation responds to the phase switching of the square wave carrier signal and achieves demodulation by periodically switching the transmission path and polarity of the modulation signal. The two signals are low-pass filtered to remove high-frequency carrier components and retain low-frequency acceleration signals; The two filtered signals are differentially processed, and a target voltage signal that is linearly related to the acceleration is output. By maintaining the constant gain conversion of the signal processing link, the scaling factor is kept in a stable target state under process deviation.

2. The method according to claim 1, characterized in that, The detection of capacitance changes caused by acceleration using a differential capacitor structure includes: The initial capacitance of the differential capacitor structure is determined based on the nominal plate spacing. Detect the change in nominal electrode spacing caused by the displacement of the mass block due to acceleration; The capacitance change of the differential capacitor is calculated based on the change in the nominal plate spacing.

3. The method according to claim 2, characterized in that, The method further includes: By detecting the zero-point voltage when there is no acceleration input, the initial capacitance difference caused by process deviations is analyzed, which is used to evaluate the process deviations.

4. The method according to claim 1, characterized in that, The change in differential capacitance The following formula is used to calculate: in, Indicates the displacement capacitance conversion factor. This indicates the displacement of the mass block. Indicates the nominal electrode spacing.

5. The method according to claim 1, characterized in that, The conversion factor of the transimpedance amplifier remains constant to offset the effects of process deviations; The feedback resistor of the transimpedance amplifier is used to set the conversion gain so that the voltage change is linearly related to the capacitance change, and to decouple the conversion coefficient from the initial capacitance.

6. The method according to claim 1, characterized in that, The voltage change data The following formula is used to calculate: in, This represents the capacitor voltage conversion factor.

7. The method according to claim 1, characterized in that, The voltage change data The baseband modulation signal, generated by superimposing it with the DC bias voltage, is calculated using the following formula: in, This represents the voltage value of the baseband modulation signal; This indicates the voltage change data. The sum of the DC bias voltage; This indicates the DC bias voltage value.

8. The method according to claim 1, characterized in that, The generated modulation signal is calculated based on the following formula: in, This represents the voltage value of the modulated signal; The frequency value of the square wave carrier signal is higher than the mechanical resonant frequency value of the accelerometer; t represents time. This represents a square wave function.

9. The method according to claim 1, wherein the ring diode demodulation circuit is a bridge structure composed of four diodes: a first diode, a second diode, a third diode, and a fourth diode, characterized in that, The step of synchronously demodulating the modulated signal and outputting two signals through a ring diode demodulation circuit includes: The ring diode demodulation circuit is powered by the first and third diodes during the positive half-cycle of the square wave carrier, and by the second and fourth diodes during the negative half-cycle of the square wave carrier.

10. A signal processing system for a microelectromechanical system (MEMS) capacitive accelerometer, characterized in that, include: The capacitance change acquisition module is used to detect the capacitance change caused by acceleration through a differential capacitor structure and obtain the amount of differential capacitance change. ; The baseband modulation signal generation module is used to generate the differential capacitance change. Input to transimpedance amplifier and converted into voltage change data and the voltage change data The baseband modulation signal is generated by superimposing it with a DC bias voltage, and the DC bias voltage is used to boost the signal level. The modulation signal generation module is used to generate a square wave carrier signal from the square wave carrier generation unit and modulate the baseband modulation signal with the square wave carrier signal to generate a modulation signal; A two-channel signal generation module is used to synchronously demodulate the modulated signal through a ring diode demodulation circuit and output two signals. The synchronous demodulation responds to the phase switching of the square wave carrier signal and achieves demodulation by periodically switching the transmission path and polarity of the modulated signal. The low-pass filter module is used to perform low-pass filtering on the two signals to filter out the high-frequency carrier components and retain the low-frequency acceleration signal; The target voltage signal generation module is used to perform differential operation on the filtered two signals and output a target voltage signal that is linearly related to acceleration. By maintaining the constant gain conversion of the signal processing link, the scaling factor is kept in a target stable state under process deviation.

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