CN115825478A - MEMS closed-loop micro-accelerometer capable of adaptively adjusting balance position - Google Patents
MEMS closed-loop micro-accelerometer capable of adaptively adjusting balance position Download PDFInfo
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Abstract
The invention discloses a MEMS closed loop micro-accelerometer for self-adaptively adjusting balance position, which also comprises: the first demodulation module is used for detecting a capacitance difference value between the first capacitor and the second capacitor and outputting a first differential signal; the second demodulation module is used for detecting a capacitance difference value between the first parasitic capacitance and the second parasitic capacitance and outputting a second differential signal; the control module outputs a first feedback voltage to the upper polar plate and outputs a second feedback voltage to the lower polar plate according to the first differential signal and the second differential signal; wherein the first feedback voltage and the second feedback voltage are symmetrical to each other; the balance position of the middle pole plate is controlled in the middle position in a self-adaptive mode, the problem that the balance position of a traditional closed-loop MEMS accelerometer is not in the middle position is solved, the linearity of the accelerometer is improved, the influence of environmental factors on the balance position is compensated in a self-adaptive mode, the drift of a model is restrained, and the detection precision is improved.
Description
Technical Field
The invention relates to the technical field of sensors, in particular to an MEMS closed-loop micro-accelerometer capable of adaptively adjusting a balance position.
Background
MEMS (Micro E electronic Mechanical Systems) accelerometers are accelerometers manufactured using MEMS technology. A conventional MEMS accelerometer includes an upper plate, a lower plate, and a middle plate. The middle pole plate is movably arranged between the upper pole plate and the lower pole plate, the middle pole plate and the upper pole plate form a first capacitor, and the middle pole plate and the lower pole plate form a second capacitor. When the accelerometer has no acceleration, the middle pole plate is in an equilibrium position, and the capacitance difference value of the first capacitor and the second capacitor is 0. When inertial force is applied to the accelerometer, the middle plate can displace towards the direction departing from the acceleration direction, and a difference value is generated between the first capacitor and the second capacitor.
Currently, a difference value between a first capacitor and a second capacitor needs to be detected, and then an acceleration value is calculated; and applying feedback voltage to the upper and lower polar plates to generate electrostatic force in the direction of acceleration to prevent the middle polar plate from deviating from the balance position. However, due to structural stress strain, parasitic capacitance change, detection circuit drift and the like, the balance position between the upper polar plate and the lower polar plate can be deviated, so that the measured acceleration is inaccurate.
Therefore, how to cause low measurement accuracy due to the balance position deviation becomes a problem that needs to be improved in the prior art.
Disclosure of Invention
The application aims to provide a MEMS closed-loop micro-accelerometer capable of adaptively adjusting a balance position so as to solve the problem of low measurement precision caused by balance position deviation.
In a first aspect, the present application provides an MEMS closed-loop micro accelerometer capable of adaptively adjusting a balance position, including an upper plate, a lower plate and a middle plate, wherein the middle plate forms a first capacitor and a first parasitic capacitor with the upper plate, the middle plate forms a second capacitor and a second parasitic capacitor with the lower plate, and the micro accelerometer further includes:
the first demodulation module is used for detecting a capacitance difference value between the first capacitor and the second capacitor and outputting a first differential signal;
the second demodulation module is used for detecting a capacitance difference value between the first parasitic capacitance and the second parasitic capacitance and outputting a second differential signal;
the control module outputs a first feedback voltage to the upper polar plate and outputs a second feedback voltage to the lower polar plate according to the first differential signal and the second differential signal;
wherein the first feedback voltage and the second feedback voltage are symmetrical to each other.
In some embodiments of the present application, the micro-accelerometer includes a standard power supply, the standard power supply is connected to the middle plate and is used for inputting a standard voltage to the middle plate; the first demodulation module includes a charge amplifier connected between a standard power supply and the middle plate.
In some embodiments of the present application, the charge amplifier is configured to detect a capacitance difference between the first capacitor and the second capacitor and output an amplified signal; the first demodulation module further includes a first demodulator for outputting the first differential signal in response to the amplified signal.
In some embodiments of the present application, the control module includes a compensation unit and a first PID control unit, where the compensation unit is configured to receive the first differential signal and the second differential signal and output a detection signal; the first PID control unit responds to the detection signal and outputs the first feedback voltage and the second feedback voltage.
In some embodiments of the present application, a symmetric output unit is disposed between the first PI D control unit and the lower plate, and the symmetric output unit is configured to enable the second feedback voltage and the first feedback voltage to be opposite numbers.
In some embodiments of the present application, the second demodulation module includes an excitation signal unit and a second demodulator, where the excitation signal unit is connected between the upper plate and the lower plate, and is configured to detect the first parasitic capacitance and the second parasitic capacitance, and output an excitation signal to trigger the second demodulator to output the second differential signal.
In some embodiments of the present application, a carrier amplitude modulation unit is further disposed between the excitation signal unit and the second demodulator, the carrier amplitude modulation unit receives the excitation signal and outputs a modulated signal at the same frequency, and the second demodulator outputs the second differential signal in response to the modulated signal at the same frequency.
In some embodiments of the present application, the second demodulator is further connected to the control module, and configured to receive an output signal of the control module and output the second differential signal in response to the output signal and the co-frequency modulation signal.
In some embodiments of the present application, the second demodulation module includes a second PID control unit, and the second PID control unit is configured to correct the second differential signal and output the corrected second differential signal to the control module.
In some embodiments of the present application, the micro accelerometer further includes a frame, and the frame is used to connect the upper plate, the lower plate and the middle plate, so that a first parasitic capacitance is generated between the frame and the upper plate, and a second parasitic capacitance is generated between the frame and the lower plate.
The utility model provides a little accelerometer of MEMS closed loop of self-adaptation regulation balanced position, including last polar plate, bottom plate and middle polar plate, middle polar plate and last polar plate form first electric capacity and first parasitic capacitance, and middle polar plate and bottom plate form second electric capacity and second parasitic capacitance, and this little accelerometer still includes: the first demodulation module is used for detecting a capacitance difference value between the first capacitor and the second capacitor and outputting a first differential signal; the second demodulation module is used for detecting a capacitance difference value between the first parasitic capacitance and the second parasitic capacitance and outputting a second differential signal; the control module outputs a first feedback voltage to the upper polar plate and outputs a second feedback voltage to the lower polar plate according to the first differential signal and the second differential signal; wherein the first feedback voltage and the second feedback voltage are symmetrical to each other; the balance position of the middle pole plate is controlled in the middle position in a self-adaptive mode, the problem that the balance position of a traditional closed-loop MEMS accelerometer is not in the middle position is solved, the linearity of the accelerometer is improved, the influence of environmental factors on the balance position is compensated in a self-adaptive mode, the drift of a model is restrained, and the detection precision is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is an idealized model of a prior art MEMS accelerometer closed-loop system of the present invention;
FIG. 2 is a cross-sectional view of a sensing structure of a sandwich accelerometer according to an embodiment of the invention;
FIG. 3 is a diagram of a capacitance structure of a micro accelerometer according to an embodiment of the invention;
FIG. 4 is a circuit diagram of a prior art micro accelerometer of the present invention;
FIG. 5 is a circuit diagram of a micro accelerometer according to an embodiment of the invention;
FIG. 6 is a diagram of a model of a micro accelerometer, according to an embodiment of the invention;
fig. 7 is a circuit diagram of a micro accelerometer according to another embodiment of the invention.
Description of the symbols of the main elements:
100-sensitive structure, 110-upper plate, 120-middle movable structure, 121-cantilever beam, 122-movable mass block, 123-first silicon dioxide, 124-frame, 125-second silicon dioxide, 130-lower plate, 200-capacitor structure, 210-first parasitic capacitor, 220-second parasitic capacitor, 240-first capacitor and 250-second capacitor.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In the description of the present invention, "a plurality" includes two or more unless specifically defined otherwise.
In this application, the word "exemplary" is used to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. The following description is presented to enable any person skilled in the art to make and use the invention. In the following description, details are set forth for the purpose of explanation. It will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and processes are not shown in detail to avoid obscuring the description of the invention with unnecessary detail. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles disclosed herein.
An ideal model of the current MEMS accelerometer closed-loop system is shown in fig. 1, in which the acceleration sensitive part is divided into a fixed electrode (upper plate 110 and lower plate 130) and a movable electrode (middle plate), and the capacitance between the upper plate 110 and the middle plate is C1, and the capacitance between the lower plate 130 and the middle plate is C2. When the gauge outfit has no acceleration, the middle polar plate is in a balance position, C1 and C2 are equal, and the capacitance difference is 0. When inertial force is applied to the gauge head, the middle plate will move in the direction away from the acceleration, and differential capacitance is generated.
The circuit part implements the detection of the differential capacitance and applies a feedback voltage to the upper and lower plates 130, generating an electrostatic force in accordance with the direction of acceleration, hindering the middle plate from deviating from the equilibrium position. Because the proportional amplification factor of the PI D control link is the open-loop gain of the operational amplifier, and the ideal condition is infinity, when the closed-loop works, the differential capacitor is infinitesimal, and the middle polar plate is always approximately positioned at the central position.
The detection of the differential capacitor is realized by switch phase-sensitive demodulation, and the noise influence can be effectively reduced. The upper and lower plates 130 apply high frequency square wave carrier signals having the same amplitude and frequency and 180 ° phase difference. When subjected to inertial forces, the proof mass changes position, causing a change in differential capacitance. After the capacitance differential signal is subjected to charge amplification, phase-sensitive demodulation and PID (proportional-integral-derivative) correction, symmetrical feedback voltage is output and applied to the upper and lower electrode plates 130 to form electrostatic force feedback, and the feedback action keeps the detection quality at a middle balance position. Ideally, the distance between the middle plate and the upper and lower plates 130 is equal, and is d0, and the relationship between the force applied to the middle plate and the feedback voltage VF is linear as shown in formula (1).
When the balance position deviates from the middle position x, the relationship between the force applied to the middle plate and the feedback voltage VF is as shown in equation (2). Once the center plate equilibrium position deviates from the center position, the relationship between the electrostatic force and the feedback voltage VF will exhibit non-linearity. A change in the offset x will result in a change in the relationship of force to feedback voltage, manifested as a drift in the accelerometer detection model, resulting in a test error.
d On the upper part ＝d 0 +x
d Lower part ＝d 0 -x
Fig. 2 is a cross-sectional view of a conventional sandwich-structure accelerometer sensor 100. The upper electrode plate 110110, the middle movable structure 120120 and the lower electrode plate 130130 in the sensitive structure 100100 are made of heavily doped silicon materials, and the three layers of silicon are insulated and isolated by silicon dioxide and form a self-sealing system through fusion bonding.
Both the top plate 110110 and the bottom plate 130130 are flat silicon and the intermediate movable structure 120120 is relatively complex. The movable mass 122122 of the sensing structure 100 forms a middle movable electrode that forms an effective differential capacitance pair with the upper plate 110110, the lower plate 130130 and the acceleration sensing. Cantilever beams 121121 suspend the movable mass 122 from the frame 124124. The middle movable structure 120 has a first silicon dioxide 123 and a second silicon dioxide 125 formed on a frame 124 thereof to insulate the upper plate 110, the middle movable mass 122 and the lower plate 130 from each other. Due to the presence of silicon dioxide and air, stray capacitances are generated between the bezel 124 and the upper and lower plates 110, 130 and are connected in parallel to the first and second capacitors 240, 250, respectively.
Fig. 4 shows a specific structure of a capacitance structure 200 between the upper plate 110, the middle movable mass 122 (movable plate), and the lower plate 130 of the sensitive structure 100 of the micro-electromechanical accelerometer of fig. 3. The first parasitic capacitance 210 and the second parasitic capacitance 220 are the parasitic capacitances C between the middle movable plate and the upper plate 110, and between the lower plate 130 and the lower plate 110, respectively ft1 And C ft2 . The capacitance is created by the movable structural frame 124 and the upper plate 110, lower plate 130. The first parasitic capacitor 210 and the second parasitic capacitor 220 are an effective differential capacitor pair C between the middle movable mass 122 and the upper and lower plates 130 On the upper part And C Lower part . Parasitic capacitance C due to the non-uniform width and silicon dioxide on the frame 124 and the movable structure frame 124 during the manufacturing process ft1 And C ft2 Are not equal and there is a greater dispersion.
Since the PID input is 0, the total capacitance of the middle electrode and the upper and lower electrodes is required to be equal. When the parasitic capacitances in fig. 4 are not equal, the middle plate equilibrium position will be shifted from the middle position (x changes) to change above and below C to compensate for the asymmetry of the parasitic capacitances.
The present embodiment provides a MEMS closed-loop micro accelerometer capable of adaptively adjusting an equilibrium position, please refer to fig. 4 and fig. 5, including an upper plate 110, a lower plate 130, and a middle plate, where the middle plate and the upper plate 110 form a first capacitor 240 and a first parasitic capacitor 210, and the middle plate and the lower plate 130 form a second capacitor 250 and a second parasitic capacitor 220, and the micro accelerometer further includes: a first demodulation module, configured to detect a capacitance difference between the first capacitor 240 and the second capacitor 250, and output a first differential signal; a second demodulation module, configured to detect a capacitance difference between the first parasitic capacitor 210 and the second parasitic capacitor 220, and output a second differential signal; the control module outputs a first feedback voltage to the upper plate 110 and outputs a second feedback voltage to the lower plate 130 according to the first differential signal and the second differential signal; wherein the first feedback voltage and the second feedback voltage are symmetrical to each other.
In some embodiments of the present application, the micro-accelerometer includes a standard power supply, the standard power supply is connected to the middle plate and is used for inputting a standard voltage to the middle plate; the first demodulation module includes a charge amplifier connected between a standard power supply and the middle plate.
In some embodiments of the present application, the charge amplifier is configured to detect a capacitance difference between the first capacitor 240 and the second capacitor 250 and output an amplified signal; the first demodulation module further includes a first demodulator for outputting the first differential signal in response to the amplified signal.
In some embodiments of the present application, the control module includes a compensation unit and a first PID control unit, where the compensation unit is configured to receive the first differential signal and the second differential signal and output a detection signal; the first PID control unit responds to the detection signal and outputs the first feedback voltage and the second feedback voltage.
In some embodiments of the present application, a symmetric output unit is disposed between the first PID control unit and the lower plate 130, and the symmetric output unit is configured to enable the second feedback voltage and the first feedback voltage to be opposite numbers.
In some embodiments of the present application, the second demodulation module includes a driving signal unit and a second demodulator, the driving signal unit is connected between the upper plate 110 and the lower plate 130, and is configured to detect the first parasitic capacitor 210 and the second parasitic capacitor 220, and output a driving signal to trigger the second demodulator to output the second differential signal.
In some embodiments of the present application, a carrier amplitude modulation unit is further disposed between the excitation signal unit and the second demodulator, the carrier amplitude modulation unit receives the excitation signal and outputs a modulated signal at the same frequency, and the second demodulator outputs the second differential signal in response to the modulated signal at the same frequency.
In some embodiments of the present application, the second demodulator is further connected to the control module, and configured to receive an output signal of the control module and output the second differential signal in response to the output signal and the co-frequency modulation signal.
In some embodiments of the present application, the second demodulation module includes a second PID control unit, and the second PID control unit is configured to correct the second differential signal and output the corrected second differential signal to the control module.
In some embodiments of the present application, the micro accelerometer further includes a frame 124, where the frame 124 is used to connect the upper plate 110, the lower plate 130 and the middle plate, so that a first parasitic capacitor 210 is generated between the frame 124 and the upper plate 110, and a second parasitic capacitor 220 is generated between the frame 124 and the lower plate 130.
In this embodiment, the modulation amount of the balance position deviation amount x is superimposed on the output VF by carrier amplitude modulation. And then carrying out related demodulation on the same-frequency modulation signal subjected to carrier amplitude modulation and the output VF to obtain the output representing x. The compensation voltage Vcom is generated by the PID controller 2. Because of Vcom, the output of the original switch demodulation is not 0 but-Vcom, namely the total capacitance of the middle pole plate and the upper and lower electrodes in the figure 4 is not equal any more, thereby realizing the adjustment of the balance position of the middle pole plate. The equilibrium position control loop is designed as a deep negative feedback, i.e. the input of the PID controller 2 is 0, i.e. the modem for x should be 0, so that x is 0. Finally, due to the action of the control loop, the middle plate balance position offset x is always 0 and is located at the middle position of the upper and lower plates 130.
In a more specific embodiment, referring to fig. 6, consider that the carrier is loaded into the upper and lower plates 130 in opposite phases, and the carrier is amplitude modulated, as shown in equation (3). Where VDsin (wt) is the amplitude modulation signal.
VS＝V D sin(wt) (3)
The first term in equation (4) is carrier independent, and the correlation between the carrier amplitude of term (3) and x is small. Further calculating the second term in equation (4)
The third term on the right side in the formula (5) shows that due to the action of the carrier amplitude modulation signal, due to the existence of the offset x of the balance position of the middle plate, a modulation force which is in direct proportion to the offset x and has the same frequency with the modulation signal is generated on the middle plate. Due to the presence of the modulation force, the output quantity Vt associated with the modulation force will be superimposed on the output detected feedback voltage VF.
Vt＝K·V D sin(wt)x (6)
By performing coherent demodulation on the output (feedback) voltage and the modulation signal, the component x in equation (6) will be solved:
after the equation (7) is subjected to low-pass filtering, a demodulation quantity can be obtained, and the demodulation quantity is in direct proportion to the balance position quantity x of the middle mass block.
In a more specific embodiment, referring to fig. 7, when the PID input is increased by a compensation voltage, since the total input of the PID must be 0 (virtual short), the output of the switch demodulation is required to be not 0, that is, the total capacitance difference between the middle plate and the upper and lower plates 130 changes, so that the balance position of the middle mass changes. The compensation voltage of the present invention is generated by the associated demodulated output, which is proportional to the equilibrium position offset x, via the PID controller 2. The carrier modulator, the adder, the PID controller, the relevant demodulation controller and the PID controller 2 form a balance position control loop, and the control loop is set to be in a negative feedback state. Due to the virtual short requirement input by the PID controller 2, the input is 0, that is, the offset x of the equilibrium position is 0, and finally the adaptive compensation of the equilibrium position is realized. The balance position of the middle pole plate is controlled at the middle position (x = 0) in a self-adaptive mode, the problem that the balance position of a traditional closed-loop MEMS accelerometer is not at the middle position is solved, the linearity of the accelerometer is improved, the influence of environmental factors (parasitic capacitance, drift of a detection circuit and the like) on the balance position is compensated in a self-adaptive mode, the drift of a model is restrained, and the detection precision is improved.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and parts that are not described in detail in a certain embodiment may refer to the above detailed descriptions of other embodiments, and are not described herein again.
Having thus described the basic concept, it will be apparent to those skilled in the art that the foregoing detailed disclosure is to be considered merely illustrative and not restrictive of the broad application. Various modifications, improvements and adaptations to the present application may occur to those skilled in the art, although not explicitly described herein. Such modifications, improvements and adaptations are proposed in the present application and thus fall within the spirit and scope of the exemplary embodiments of the present application.
Also, the present application uses specific words to describe embodiments of the application. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the present application is included in at least one embodiment of the present application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.
Similarly, it should be noted that in the preceding description of embodiments of the application, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.
Accordingly, in some embodiments, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameter should take into account the specified significant digits and employ a general digit preserving approach. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the range are approximations, in the specific examples, such numerical values are set forth as precisely as possible within the scope of the application.
For each patent, patent application publication, and other material cited in this application, such as articles, books, specifications, publications, documents, and the like, the entire contents of which are hereby incorporated by reference into this application, except for application history documents that are inconsistent with or conflict with the contents of this application, and except for documents that are currently or later become incorporated into this application as though fully set forth in the claims below. It is noted that the descriptions, definitions and/or use of terms in this application shall control if they are inconsistent or contrary to the present disclosure.
The technical solutions provided by the embodiments of the present application are described in detail above, and the principles and embodiments of the present invention are explained herein by using specific examples, and the descriptions of the above embodiments are only used to help understanding the method and the core ideas of the present invention; meanwhile, for those skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (10)
1. The utility model provides a little accelerometer of MEMS closed loop of self-adaptation regulation equilibrium position, includes top plate, bottom plate and middle plate, middle plate with top plate forms first electric capacity and first parasitic capacitance, middle plate with the bottom plate forms second electric capacity and second parasitic capacitance, its characterized in that, this little accelerometer still includes:
the first demodulation module is used for detecting a capacitance difference value between the first capacitor and the second capacitor and outputting a first differential signal;
the second demodulation module is used for detecting a capacitance difference value between the first parasitic capacitance and the second parasitic capacitance and outputting a second differential signal;
the control module outputs a first feedback voltage to the upper polar plate and outputs a second feedback voltage to the lower polar plate according to the first differential signal and the second differential signal;
wherein the first feedback voltage and the second feedback voltage are symmetrical to each other.
2. The micro accelerometer of claim 1, wherein said micro accelerometer includes a standard power supply connected to said intermediate plate and adapted to input a standard voltage to said intermediate plate; the first demodulation module includes a charge amplifier connected between a standard power supply and the middle plate.
3. A micro accelerometer according to claim 2, wherein the charge amplifier is configured to detect a capacitance difference between the first capacitance and the second capacitance and output an amplified signal; the first demodulation module further includes a first demodulator for outputting the first differential signal in response to the amplified signal.
4. The micro accelerometer according to claim 1, wherein the control module comprises a compensation unit and a first PID control unit, the compensation unit being configured to receive the first differential signal and the second differential signal and output a detection signal; the first PID control unit responds to the detection signal and outputs the first feedback voltage and the second feedback voltage.
5. The micro accelerometer according to claim 4, wherein a symmetrical output unit is disposed between the first PID control unit and the bottom plate, and the symmetrical output unit is configured to enable the second feedback voltage and the first feedback voltage to be opposite numbers.
6. The micro accelerometer according to claim 1, wherein the second demodulation module comprises an excitation signal unit and a second demodulator, the excitation signal unit is connected between the upper plate and the lower plate and is configured to detect the first parasitic capacitance and the second parasitic capacitance and output an excitation signal to trigger the second demodulator to output the second differential signal.
7. The micro accelerometer according to claim 6, wherein a carrier amplitude modulation unit is further disposed between the excitation signal unit and the second demodulator, the carrier amplitude modulation unit receives the excitation signal and outputs a modulated signal at a same frequency, and the second demodulator outputs the second differential signal in response to the modulated signal at the same frequency.
8. A micro accelerometer according to claim 7, wherein the second demodulator is further connected to the control module and is configured to receive the output signal from the control module and output the second differential signal in response to the output signal and the on-frequency modulated signal.
9. The micro accelerometer according to claim 6, wherein the second demodulation module comprises a second PID control unit, and the second PID control unit is configured to correct the second differential signal and output the second differential signal to the control module.
10. The micro accelerometer of claim 1, further comprising a frame connecting the upper plate, the lower plate, and the middle plate such that a first parasitic capacitance is generated between the frame and the upper plate and a second parasitic capacitance is generated between the frame and the lower plate.
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