Electrostatic force balanced MEMS accelerometer and closed loop control method thereof

Abstract

The application provides a static force balance MEMS accelerometer and a closed loop control method thereof, and belongs to the field of instruments and meters.The method is as follows: converting an acceleration signal into a displacement signal; moving a parallel-plate capacitor dynamic electrode plate and forming a differential capacitor with two corresponding parallel-plate capacitor static electrode plates; applying a bias voltage to the parallel-plate capacitor dynamic electrode plate to convert the differential capacitor into a voltage signal; modulating the differential capacitor with a carrier wave, multiplying the voltage signal, sequentially passing through a low-pass filter and a PID control to form a feedback control signal; adding the feedback control signal and a carrier signal to obtain a static electrode plate application signal; and applying the static electrode plate application signal to the parallel-plate capacitor static electrode plate, and combining the bias voltage applied to the parallel-plate capacitor dynamic electrode plate to obtain a static feedback force, so that the position of the parallel-plate capacitor dynamic electrode plate returns to the initial position.The application has significant advantages in cost, processing difficulty and reliability compared with the existing force balance closed loop scheme.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of instruments and meters, more particularly, to a static force balanced MEMS accelerometer and a closed-loop control method thereof. BACKGROUND

[0002] MEMS accelerometers are widely used in consumer electronics, inertial navigation and autonomous driving fields due to their low power consumption, small size and low cost. With the improvement of resolution, accelerometers are gradually applied in the fields of seismic monitoring, gravity measurement, tide monitoring, etc.

[0003] An accelerometer converts acceleration changes into displacement changes through a proof mass, and then converts the displacement changes into electrical signals through different sensing methods. For high-performance capacitive accelerometers, a structure with a low intrinsic frequency is usually selected to reduce the noise of the capacitive detection circuit. The lower the mechanical stiffness of the accelerometer and the larger the detection mass, the lower the intrinsic frequency. Therefore, many accelerometers are designed to have quasi-zero stiffness structures, which are complex in stress and have a small displacement interval in the extremely low stiffness range. After the detection mass deviates from the balance position in an open-loop system, the stiffness changes immediately, and the output thus exhibits nonlinearity, with a small linear range. At the same time, the low intrinsic frequency in the open-loop limits the detection bandwidth. In order to meet the demand for expanding the range, expanding the bandwidth and improving the linearity, a force balanced closed-loop system becomes an inevitable choice for accelerometers.

[0004] There are mainly two types of existing force balanced closed-loop accelerometers. The first type is a force balanced closed-loop MEMS accelerometer based on Lorentz force. The feedback force of the actuator is provided by a current coil in a magnetic field. The current coil is processed on the detection mass, and the magnetic field is provided by an external permanent magnet. However, the volume of the permanent magnet is large, which conflicts with the technical advantage of small volume of MEMS, and it is difficult to integrate them. In addition, the magnetic field strength provided by the permanent magnet is easily affected by temperature, thereby affecting the linearity of the scale factor of the closed-loop accelerometer. The coil has a certain resistance, and when it is in dynamic operation, it will heat up due to the current passing through, further affecting its performance. The second type is an electrostatic force balanced closed-loop MEMS accelerometer based on variable gap comb capacitors. Its main structure is two groups of comb capacitors designed based on SOI technology, one group of variable area capacitors as a sensor and one group of variable gap capacitors as an actuator. The two groups of comb capacitors increase the difficulty of processing technology. In addition, the device layer based on SOI technology is thin, which reduces the thickness of the comb capacitor plate and the mass of the spring oscillator structure, resulting in a large noise of the accelerometer. The variable gap comb capacitor provides electrostatic force, which needs to consider the pull-in effect, and the application range and scene in harsh dynamic environment are limited. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide an electrostatic force balance type MEMS accelerometer and a closed-loop control method thereof, aiming at solving the problems of the existing force balance type closed-loop control accelerometer, such as being easily affected by temperature, low precision, low integration and high cost.

[0006] To achieve the above-mentioned purpose, in one aspect, the present application provides an electrostatic force balance type MEMS accelerometer, comprising: a capacitance detection circuit, a bias voltage power supply, a carrier generator, a feedback control circuit and a MEMS system;

[0007] The input end of the capacitance detection circuit and the bias voltage power supply is connected to the output end of the MEMS system, and the output end of the capacitance detection circuit is connected to the input end of the feedback control circuit; the output end of the feedback control circuit is connected to the MEMS system; the carrier generator is connected to the feedback control circuit;

[0008] The MEMS system comprises a glass cover, a spring oscillator, a plurality of sets of parallel plate capacitance fixed plates and a plurality of parallel plate capacitance moving plates; the glass cover is provided with the parallel plate capacitance fixed plates near the side of the spring oscillator; the spring oscillator is provided with the parallel plate capacitance moving plates near one side of the glass cover; every two parallel plate capacitance fixed plates serve as a set and correspond to one parallel plate capacitance moving plate; the parallel plate capacitance fixed plates and the parallel plate capacitance moving plates are placed in parallel, and the parallel plate capacitance moving plate is initially placed in the middle of the two parallel plate capacitance fixed plates; the output end of the parallel plate capacitance moving plate is connected to the bias voltage power supply and the capacitance detection circuit;

[0009] The spring oscillator is used for converting the acceleration signal from the outside into a displacement signal; the parallel plate capacitance moving plate is used for moving under the movement of the spring oscillator, and the corresponding areas of the two corresponding parallel plate capacitance fixed plates increase and decrease respectively, forming a differential capacitance structure; the parallel plate capacitance fixed plate is used for, under the action of the fixed plate signal, jointly acting with the bias voltage applied on the parallel plate capacitance moving plate to obtain an electrostatic feedback force; the electrostatic feedback force is used for restoring the position of the parallel plate capacitance moving plate to the middle of the two parallel plate capacitance fixed plates;

[0010] The capacitance detection circuit is used for converting the modulation current into a modulation voltage signal;

[0011] The bias voltage power supply is used for applying a bias voltage on the parallel plate capacitance moving plate;

[0012] The carrier generator is used for generating a carrier to modulate the differential capacitance and output a modulation current signal; the feedback control circuit is used for multiplying the modulation voltage signal with the carrier after demodulation, and then performing low-pass filtering, PID control to generate a feedback control signal, adding the feedback control signal with the carrier signal to obtain the fixed plate signal.

[0013] Further preferably, the feedback control circuit comprises a multiplier, a carrier generator, a PID (proportion integral derivative) controller, a LPF (Low Pass Filter), a gain amplifier and an adder;

[0014] The gain amplifier comprises a first gain amplifier, a second gain amplifier, a third gain amplifier and a fourth gain amplifier; the adder comprises a first adder and a second adder;

[0015] The input end of the multiplier is connected to the output end of the capacitance detection circuit and the first output end of the carrier generator, and the output end thereof is connected to the input end of the LPF; the output end of the LPF is connected to the PID controller; the output end of the PID controller is connected to the third gain amplifier and the fourth gain amplifier; the second output end of the carrier generator is connected to the first gain amplifier and the second gain amplifier; the output ends of the first gain amplifier and the third gain amplifier are connected to the first adder; the output ends of the second gain amplifier and the fourth gain amplifier are connected to the second adder; the first adder and the second adder are respectively connected to two parallel-plate capacitance fixed electrodes in a group of parallel-plate capacitance fixed electrodes;

[0016] The multiplier is used for multiplying and demodulating the voltage modulation signal output by the capacitance detection circuit with the carrier; the LPF is used for low-pass filtering the demodulated signal; the PID controller is used for PID control of the low-pass filtered signal to generate a feedback control signal; the gain amplifier comprises a first gain amplifier, a second gain amplifier, a third gain amplifier and a fourth gain amplifier; the first gain amplifier is used for same-direction amplification of the carrier signal, and the second gain amplifier is used for reverse amplification of the carrier signal; the third gain amplifier is used for same-direction amplification of the feedback control signal; the fourth gain amplifier is used for reverse amplification of the feedback control signal; the adder comprises a first adder and a second adder; the first adder is used for adding the same-direction amplified carrier signal and the same-direction amplified feedback control signal to obtain a first fixed electrode application signal; the second adder is used for adding the reverse amplified carrier signal and the reverse amplified feedback control signal to obtain a second fixed electrode application signal.

[0017] Further preferably, the preparation method of the variable-area parallel-plate capacitance is as follows:

[0018] A parallel-plate capacitance fixed electrode is obtained by performing photolithography and then evaporation on a glass cover; a parallel-plate capacitance moving electrode is obtained by performing photolithography and then evaporation on a silicon wafer; a free-vibration spring oscillator structure is obtained by deep silicon etching; the glass cover and the spring oscillator are bonded, and the parallel-plate capacitance fixed electrode and the parallel-plate capacitance moving electrode are combined to obtain the variable-area parallel-plate capacitance.

[0019] Further preferably, the differential capacitance is as follows:

[0020]

[0021] Wherein, ΔC is the differential capacitance; Δx is the displacement in the sensitive direction; n is the number of parallel-plate capacitor fixed electrode plates; the length of the parallel-plate capacitor moving electrode plate and the length of the parallel-plate capacitor fixed electrode plate are equal; l is the length of the electrode plate; and d is the distance between the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor moving electrode plate.

[0022] Further preferably, the electrostatic feedback force is:

[0023]

[0024] Wherein, V b is the bias voltage; V f is the feedback control signal.

[0025] In another aspect, the present application provides a closed-loop control method of an electrostatic force balanced MEMS accelerometer, comprising the following steps:

[0026] The spring oscillator is used to convert the external acceleration signal into a displacement signal;

[0027] The parallel-plate capacitor moving electrode plate is driven by the spring oscillator to move, and the corresponding areas of the two parallel-plate capacitor fixed electrode plates increase and decrease respectively, forming a differential capacitance structure;

[0028] A load wave is applied to the parallel-plate capacitor fixed electrode plate, and the differential capacitance is converted into a modulated current signal;

[0029] The modulated current signal is converted into a modulated voltage signal by using a capacitance detection circuit, and after being multiplied with the carrier wave and demodulated, low-pass filtering is performed;

[0030] The low-pass filtered signal is subjected to PID control to form a feedback control signal;

[0031] The feedback control signal is added to the carrier signal to obtain a fixed electrode plate applied signal;

[0032] The electrostatic feedback force is obtained under the joint action of the fixed electrode plate applied signal applied to the parallel-plate capacitor fixed electrode plate and the bias voltage applied to the parallel-plate capacitor moving electrode plate;

[0033] The electrostatic feedback force is applied to the parallel-plate capacitor moving electrode plate, so that the position of the parallel-plate capacitor moving electrode plate returns to the middle of the two parallel-plate capacitor fixed electrode plates.

[0034] Further preferably, the preparation method of the variable-area parallel-plate capacitor is:

[0035] The parallel-plate capacitor fixed electrode plate is obtained by evaporation after photolithography on a glass cover; the parallel-plate capacitor movable electrode plate is obtained by evaporation after photolithography on a silicon wafer; the free-vibration spring-mass structure is obtained by deep silicon etching; the glass cover is bonded with the spring-mass, and the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor movable electrode plate are combined to obtain the variable-area parallel-plate capacitor.

[0036] Further preferably, the differential capacitance is:

[0037]

[0038] wherein, Delta C is the differential capacitance; Delta x is the displacement in the sensitive direction; n is the number of parallel-plate capacitor fixed electrode plates; the lengths of the parallel-plate capacitor movable electrode plate and the parallel-plate capacitor fixed electrode plate are equal, and l is the length of the electrode plate; and d is the distance between the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor movable electrode plate.

[0039] Further preferably, the electrostatic feedback force is:

[0040]

[0041] wherein, V b is the bias voltage; and V f is the feedback control signal.

[0042] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following advantages:

[0043] Beneficial effects:

[0044] The present application provides an electrostatic force balance type MEMS accelerometer and a closed-loop control method thereof, wherein every two parallel-plate capacitor fixed electrode plates are taken as a group, corresponding to one parallel-plate capacitor movable electrode plate; the parallel-plate capacitor fixed electrode plates and the parallel-plate capacitor movable electrode plate are placed in parallel, and the parallel-plate capacitor movable electrode plate is initially placed in the middle of the two parallel-plate capacitor fixed electrode plates; when there is an acceleration signal in the outside world, the parallel-plate capacitor movable electrode plate and the parallel-plate capacitor fixed electrode plate will form a differential variable-area capacitor, and the variable-area parallel-plate capacitor is taken as an executor; compared with the variable-distance parallel-plate comb capacitor, the linear moving range is large, the requirement for the distance between the capacitor electrode plates is more relaxed, the probability of electrostatic attraction is greatly reduced, and the cost, processing difficulty and reliability are significantly superior to those of the prior art force balance type closed-loop scheme.

[0045] The electrostatic force balance type MEMS accelerometer and the closed-loop control method thereof provided by the present application, wherein the variable-area parallel-plate capacitor can be taken as a sensor or an executor, the multiplexing mode avoids the device size occupied by the separately designed electrostatic comb capacitor executor or electromagnetic feedback coil, more parallel-plate capacitor numbers can be arranged, the detection sensitivity is improved, the design complexity is reduced, and the yield of the product is improved.

[0046] The electrostatic force balance type MEMS accelerometer and the closed loop control method thereof provided by the application, wherein the variable-area parallel-plate capacitor is used as an execution machine, which provides more space for the processing size of the spring-mass structure, and compared with the SOI technology, the spring-mass structure can be designed to be thicker and larger in area, so as to reduce the mechanical thermal noise of the device and improve the performance of the device.

[0047] The electrostatic force balance type MEMS accelerometer and the closed loop control method thereof provided by the application, wherein the spring-mass structure is controlled at the balance position by the electrostatic force balance type MEMS accelerometer, and the closed loop scale factor is determined by the bias voltage applied to the moving electrode plate. The scale factor is less affected by temperature fluctuation during the operation, and compared with the electromagnetic force balance closed loop, the scale factor is less prone to produce heat, and is easy to integrate with the temperature control system in the working state. The scale factor can be modified by adjusting the bias voltage. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a schematic diagram of the electrostatic force balance type MEMS accelerometer based on the variable-area parallel-plate capacitor provided by the embodiment of the application;

[0049] Figure 2 is a local schematic diagram of the variable-area parallel-plate capacitor provided by the embodiment of the application;

[0050] Figure 3 is a schematic diagram of the MEMS accelerometer structure provided by the embodiment of the application;

[0051] MARK DESCRIPTION:

[0052] 1-glass cover; 2-spring-mass structure; 3-parallel-plate capacitor fixed electrode plate A group; 4-parallel-plate capacitor fixed electrode plate B group; 5-parallel-plate capacitor moving electrode plate. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the application more clear and understandable, the application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and are not used to limit the application.

[0054] After the photolithography is performed on the silicon wafer and the glass cover respectively, the parallel-plate capacitor electrode plates are obtained by evaporation, the parallel-plate capacitor moving electrode plate and the parallel-plate capacitor fixed electrode plate are obtained, the spring-mass structure which can freely vibrate is obtained by deep silicon etching (DRIE), the glass cover and the spring-mass structure are bonded, and the parallel-plate capacitor electrode plate groups on the glass cover and the spring-mass structure are combined to obtain the variable-area parallel-plate capacitor; as shown in Figure 1As shown, the electrostatic force balance type MEMS accelerometer based on variable-area parallel-plate capacitor includes a capacitor detection circuit, a bias voltage power supply, a carrier generator, a feedback control circuit and a MEMS system; the MEMS chip includes a glass cover 1, a spring vibrator 2, a parallel-plate capacitor fixed electrode plate A group 3, a parallel-plate capacitor fixed electrode plate B group 4 and a parallel-plate capacitor movable electrode plate 5; the variable-area parallel-plate capacitor composed of the parallel-plate capacitor fixed electrode plate A group 3, the parallel-plate capacitor fixed electrode plate B group 4 and the parallel-plate capacitor movable electrode plate 5 acts as a sensor and an executor, and the placement position of the spring vibrator 2 is as shown in Figure 3 As shown, the variable-area parallel-plate capacitor is connected with the capacitor detection circuit through wire bonding;

[0055] The MEMS accelerometer detects the acceleration size by using the capacitor change; when the external acceleration signal is input, the spring vibrator structure 2 converts the acceleration signal into a displacement signal, as shown in Figure 2 As shown, the parallel-plate capacitor movable electrode plate 5 in the X direction will generate a displacement of Δx from the middle position, and the areas corresponding to the upper and lower capacitor electrode plates are increased and decreased respectively, forming a differential capacitor structure; the relationship between the differential capacitor output and the displacement is as follows:

[0056]

[0057] Wherein, ε is the dielectric constant of the capacitor medium; Δx is the displacement in the sensitive direction; n is the logarithm of the parallel-plate capacitor; l is the length of the electrode plate; and d is the distance between the fixed electrode plate and the movable electrode plate.

[0058] The carrier V c The capacitor change is modulated, converted into a modulated voltage signal through the C / V capacitor detection circuit, demodulated through a multiplier, filtered through an LPF low-pass filter, and a feedback control signal V f is obtained through a PID link. c The feedback control signal and the carrier signal are added (V f + V c , -V f ) to the parallel-plate capacitor fixed electrode plate A group 3 and the parallel-plate capacitor fixed electrode plate B group 4, which together with the bias voltage V b applied to the parallel-plate capacitor movable electrode plate 5 obtains an electrostatic feedback force:

[0059]

[0060] The electrostatic feedback force and the inertial force form an electrostatic force balance to make the mass always be in the geometric center position; when the system enters deep negative feedback, the feedback control signal V f is output, and the scale factor is:

[0061]

[0062] Wherein, m is the mass of the spring oscillator structure, when the bias voltage V b The scale factor also changes when the time scale factor changes, the bias voltage V b Increases, the scale factor decreases as the range increases.

[0063] In another aspect, the present application provides a closed-loop control method of an electrostatic force balanced MEMS accelerometer, comprising the following steps:

[0064] The spring oscillator is used to convert the external acceleration signal into a displacement signal;

[0065] The parallel-plate capacitor moving electrode plate moves under the driving of the spring oscillator, and the areas corresponding to the corresponding two parallel-plate capacitor fixed electrode plates increase and decrease respectively, forming a differential capacitor structure;

[0066] A carrier wave is applied to the parallel-plate capacitor fixed electrode plate, and the differential capacitor is converted into a modulated current signal;

[0067] The modulated current signal is converted into a modulated voltage signal by using a capacitor detection circuit, multiplied with the carrier wave, and then low-pass filtered;

[0068] The low-pass filtered signal is subjected to PID control to form a feedback control signal;

[0069] The feedback control signal is added to the carrier wave signal to obtain a fixed electrode plate applied signal;

[0070] The parallel-plate capacitor fixed electrode plate, under the action of the fixed electrode plate applied signal, together with the bias voltage applied to the parallel-plate capacitor moving electrode plate, obtains an electrostatic feedback force;

[0071] The parallel-plate capacitor moving electrode plate returns to the middle of the two parallel-plate capacitor fixed electrode plates under the action of the electrostatic feedback force.

[0072] Further preferably, the parallel-plate capacitor fixed electrode plate is obtained by evaporation after photolithography on the glass cover; the parallel-plate capacitor moving electrode plate is obtained by evaporation after photolithography on the silicon wafer; the free-vibration spring oscillator structure is obtained by deep silicon etching; the glass cover is bonded to the spring oscillator, and the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor moving electrode plate are combined to obtain a variable-area parallel-plate capacitor.

[0073] Further preferably, the differential capacitor is:

[0074]

[0075] Wherein, ΔC is the differential capacitor; Δx is the displacement in the sensitive direction; n is the number of parallel-plate capacitor fixed electrode plates; the lengths of the parallel-plate capacitor moving electrode plate and the parallel-plate capacitor fixed electrode plate are equal, l is the length of the electrode plate; d is the distance between the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor moving electrode plate.

[0076] Further preferably, the electrostatic feedback force is:

[0077]

[0078] wherein V b is the bias voltage; V f is the feedback control signal.

[0079] In summary, the present application has the following advantages compared with the prior art:

[0080] The present application provides an electrostatic force balance MEMS accelerometer and a closed-loop control method thereof, wherein every two parallel-plate capacitor fixed electrodes form a group, and correspond to one parallel-plate capacitor moving electrode; the parallel-plate capacitor fixed electrodes and the parallel-plate capacitor moving electrode are placed in parallel, and the parallel-plate capacitor moving electrode is initially placed in the middle of the two parallel-plate capacitor fixed electrodes; when there is an acceleration signal in the external environment, the parallel-plate capacitor moving electrode and the parallel-plate capacitor fixed electrode will form a differential variable-area capacitor, and the variable-area parallel-plate capacitor is used as an actuator; compared with a variable-distance parallel-plate comb capacitor, the linear moving range of the variable-area parallel-plate capacitor is large, the requirement for the distance between the capacitor electrodes is more relaxed, and therefore the probability of electrostatic attraction is greatly reduced; compared with the existing force balance closed-loop scheme, the present application has significant advantages in cost, processing difficulty and reliability.

[0081] The present application provides an electrostatic force balance MEMS accelerometer and a closed-loop control method thereof, wherein the variable-area parallel-plate capacitor can be used as a sensor or an actuator, and the multiplexing mode avoids the device size occupied by the separately designed electrostatic comb capacitor actuator or electromagnetic feedback coil; more parallel-plate capacitor pairs can be arranged, the detection sensitivity is improved, the design complexity is reduced, and the yield of the product is improved.

[0082] The present application provides an electrostatic force balance MEMS accelerometer and a closed-loop control method thereof, wherein the variable-area parallel-plate capacitor is used as an actuator, which provides more space for the processing size of the spring-mass structure; compared with the SOI technology, a thicker and larger spring-mass structure can be designed, the mechanical thermal noise of the device is reduced, and the performance of the device is improved.

[0083] The present application provides an electrostatic force balance MEMS accelerometer and a closed-loop control method thereof, wherein the spring-mass structure of the electrostatic force balance MEMS accelerometer is controlled at a balance position, and the closed-loop scale factor is determined by the bias voltage applied to the moving electrode; the scale factor is less affected by temperature fluctuations during operation, the heat generation is less compared with the electromagnetic force balance closed loop, and the temperature control system is easily integrated in the working state. The scale factor can be modified by adjusting the bias voltage.

[0084] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrostatically force-balanced MEMS accelerometer, characterized by, The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof.

2. The electrostatically force-balanced MEMS accelerometer of claim 1, wherein, The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. 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The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system and a feedback control method thereof. The application relates to a MEMS system The output end of the PID controller is connected with a third gain amplifier and a fourth gain amplifier; the second output end of the carrier generator is connected with a first gain amplifier and a second gain amplifier; the output ends of the first gain amplifier and the third gain amplifier are connected with a first adder; the output ends of the second gain amplifier and the fourth gain amplifier are connected with a second adder; the first adder and the second adder are respectively connected with two parallel-plate capacitor fixed electrodes in a group of parallel-plate capacitor fixed electrodes; The multiplier is used for multiplying and demodulating the voltage modulation signal output by the capacitance detection circuit with the carrier; the LPF is used for low-pass filtering the demodulated signal; the PID controller is used for PID control of the low-pass filtered signal to generate a feedback control signal; the gain amplifier comprises a first gain amplifier, a second gain amplifier, a third gain amplifier and a fourth gain amplifier; the first gain amplifier is used for same-direction amplification of the carrier signal; the second gain amplifier is used for reverse amplification of the carrier signal; the third gain amplifier is used for same-direction amplification of the feedback control signal; the fourth gain amplifier is used for reverse amplification of the feedback control signal; the adder comprises a first adder and a second adder; the first adder is used for adding the same-direction amplified carrier signal and the same-direction amplified feedback control signal to obtain a first fixed electrode application signal; the second adder is used for adding the reverse amplified carrier signal and the reverse amplified feedback control signal to obtain a second fixed electrode application signal.

3. The electrostatically force-balanced MEMS accelerometer according to claim 1 or 2, characterized in that, The preparation method of the variable-area parallel-plate capacitor is as follows: After photolithography on a glass cover, parallel-plate capacitor fixed electrodes are obtained by evaporation; after photolithography on a silicon wafer, parallel-plate capacitor moving electrodes are obtained by evaporation; a free-vibration spring oscillator structure is obtained by deep silicon etching; the glass cover and the spring oscillator are bonded, and the parallel-plate capacitor fixed electrodes and the parallel-plate capacitor moving electrodes are combined to obtain the variable-area parallel-plate capacitor.

4. The electrostatically force-balanced MEMS accelerometer of claim 3, wherein, The differential capacitance is as follows: wherein, ΔC is the differential capacitance; Δx is the displacement in the sensitive direction; n is the logarithm of the parallel-plate capacitor fixed electrodes; the lengths of the parallel-plate capacitor fixed electrodes and the parallel-plate capacitor moving electrodes are equal, and l is the electrode length; d is the distance between the parallel-plate capacitor fixed electrodes and the parallel-plate capacitor moving electrodes.

5. The electrostatically force-balanced MEMS accelerometer of claim 4, wherein, The electrostatic feedback force is as follows: wherein V b is a bias voltage; V f is a feedback control signal.

6. A closed loop control method for the electrostatically force balanced MEMS accelerometer according to claim 1 or 2, characterized by, The method comprises the following steps: The spring oscillator is used to convert the external acceleration signal into a displacement signal; The parallel-plate capacitor moving electrodes are moved under the driving of the spring oscillator, and the areas corresponding to the two parallel-plate capacitor fixed electrodes are increased and decreased respectively, so as to form a differential capacitance structure; A carrier is applied to the parallel-plate capacitor fixed electrodes, and the differential capacitance is converted into a modulation current signal; The capacitance detection circuit is used to convert the modulation current signal into a modulation voltage signal, and the modulation voltage signal is multiplied and demodulated with the carrier, and then low-pass filtered; The low-pass filtered signal is subjected to PID control to form a feedback control signal; The feedback control signal is added to the carrier signal to obtain a fixed electrode application signal; The fixed electrode application signal applied to the parallel-plate capacitor fixed electrodes and the bias voltage applied to the parallel-plate capacitor moving electrodes jointly form an electrostatic feedback force. The electrostatic feedback force is applied to the parallel-plate capacitor moving electrode plate, so that the position of the parallel-plate capacitor moving electrode plate is restored to the middle of the two parallel-plate capacitor fixed electrode plates.

7. The closed loop control method of claim 6, wherein, The preparation method of the variable-area parallel-plate capacitor is as follows: After photolithography on a glass cover, a parallel-plate capacitor fixed electrode plate is obtained by evaporation; after photolithography on a silicon wafer, a parallel-plate capacitor moving electrode plate is obtained by evaporation; a free-vibration spring-mass structure is obtained by deep silicon etching; the glass cover is bonded to the spring-mass structure, and the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor moving electrode plate are combined to obtain the variable-area parallel-plate capacitor.

8. The closed loop control method according to claim 6 or 7, characterized in that, The differential capacitance is: wherein ΔC is the differential capacitance; Δx is the displacement in the sensitive direction; n is the number of parallel-plate capacitor fixed electrode plates; the length of the parallel-plate capacitor moving electrode plate is equal to the length of the parallel-plate capacitor fixed electrode plate, and l is the length of the electrode plate; and d is the distance between the parallel-plate capacitor fixed electrode plate and the parallel-plate capacitor moving electrode plate.

9. The closed loop control method of claim 8, wherein, The electrostatic feedback force is: wherein V b is a bias voltage; V f is a feedback control signal.

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