Self-excited AGC closed-loop detection system of MEMS electric field sensor

Abstract

The invention discloses a self-excited AGC closed-loop detection system of an MEMS electric field sensor, and the system comprises an MEMS sensitive structure which comprises a shielding electrode, an induction electrode and a driving structure, the driving structure receives a voltage driving signal, generates mechanical deformation, drives the shielding electrode to generate displacement, couples a to-be-detected electric field signal with a displacement signal of the shielding electrode, and outputs a to-be-detected electric field signal and a to-be-detected electric field signal; outputting a differential mode current signal; the driving circuit is connected with the excitation end and the output end of the MEMS sensitive structure and is used for adjusting gain according to the displacement signal and adjusting a voltage driving signal according to the gain so as to form AGC closed-loop feedback and maintain stable resonance of the MEMS sensitive structure; and the signal demodulation circuit is connected with the output end of the MEMS sensitive structure and is used for receiving and demodulating the differential mode current signal. The beneficial effects of the invention are that the stability of the vibration amplitude of the sensor is guaranteed, the anti-interference capability and the electric field induction sensitivity of the sensor are improved, and the high-precision detection of the to-be-detected electric field signal is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro electric field sensor, in particular to a self-excitation AGC closed-loop detection system of MEMS electric field sensor. BACKGROUND

[0002] The resonant torsional MEMS electric field sensor has the problems of large spatial coupling interference and weak effective signal due to small device size, and is easily affected by noise and external interference.

[0003] At present, the sensor mainly adopts an open-loop driving mode, that is, a sinusoidal alternating signal generated by a signal source is directly driven to vibrate after being amplified. However, the sensor adopting the driving mode has poor anti-interference ability and low stability, and the driving signal frequency and the sensor resonant frequency are difficult to accurately match, and environmental changes will cause the sensor resonant frequency to drift, so that the sensor cannot work in the resonant state continuously, and it is difficult to play the maximum electric field sensing sensitivity. In addition, the waveform of the driving voltage is also easy to be distorted by the waveform generator, thereby affecting the vibration mode of the sensor vibration structure. SUMMARY

[0004] To solve the above problems, the purpose of the present application is to provide a self-excitation AGC closed-loop detection system of MEMS electric field sensor.

[0005] The present application provides a self-excitation AGC closed-loop detection system of MEMS electric field sensor, comprising:

[0006] A MEMS sensitive structure, comprising a shielding electrode, an induction electrode and a driving structure, the driving structure receives a voltage driving signal and generates a mechanical deformation, the shielding electrode generates a displacement under the driving of the driving structure, the induction electrode couples a to-be-measured electric field signal with a displacement signal of the shielding electrode and outputs a differential mode current signal;

[0007] A driving circuit connected with an excitation end and an output end of the MEMS sensitive structure, adjusts a gain according to the displacement signal, and adjusts the voltage driving signal according to the gain to form an AGC closed-loop feedback;

[0008] A signal demodulation circuit connected with the output end of the MEMS sensitive structure, receives and demodulates the differential mode current signal.

[0009] As a further improvement of the present application, the driving circuit comprises:

[0010] A self-excitation oscillation circuit, an input end of which is connected with the output end of the MEMS sensitive structure, receives and processes the displacement signal, and outputs a first voltage signal;

[0011] An AGC circuit, an input end of which is connected with an output end of the self-oscillation circuit, and an output end of the AGC circuit is connected with an excitation end of the MEMS sensitive structure, the AGC circuit adjusts gain according to the first voltage signal, generates a stable voltage drive signal, and feeds back the voltage drive signal to the excitation end of the MEMS sensitive structure.

[0012] As a further improvement of the application, the self-oscillation circuit comprises:

[0013] A driving displacement detection module is configured to receive the displacement signal and convert the displacement signal into a current signal.

[0014] An I / V conversion module is configured to convert the current signal into the first voltage signal.

[0015] A phase compensation module is configured to adjust the phase of the first voltage signal to meet the phase condition of self-oscillation.

[0016] As a further improvement of the application, the phase condition of self-oscillation is that the total phase shift of the circuit is an integer multiple of 360°.

[0017] As a further improvement of the application, the AGC circuit comprises:

[0018] A gain comparison subunit is configured to receive the first voltage signal and compare the first voltage signal with a preset reference voltage, and output a gain deviation signal.

[0019] A gain adjustment subunit is configured to dynamically adjust gain according to the gain deviation signal to output a stable voltage drive signal.

[0020] As a further improvement of the application, the distribution mode of the shielding electrode and the sensing electrode is a comb or interdigital structure.

[0021] As a further improvement of the application, the driving structure adopts electrostatic driving, piezoelectric driving or thermal driving mode.

[0022] As a further improvement of the application, the signal demodulation circuit comprises an amplification module and a demodulation module.

[0023] As a further improvement of the application, the amplification module comprises:

[0024] A transimpedance amplifier is configured to amplify the differential mode current signal and convert the differential mode current signal into a second voltage signal.

[0025] A differential amplifier is configured to suppress common mode noise of the second voltage signal.

[0026] As a further improvement of the application, the demodulation module comprises:

[0027] The demodulation unit demodulates the amplified second voltage signal using a reference signal and outputs two quadrature signals.

[0028] The filtering unit performs low-pass filtering and sum-of-squares calculation on the two orthogonal signals to output an electric field signal.

[0029] The beneficial effects of this invention are as follows: by dynamically adjusting the gain to stabilize the signal amplitude through AGC technology, and then by compensating for the resonant frequency drift caused by temperature in real time through closed-loop feedback, the stability of the sensor vibration amplitude is ensured, and the resonant working state is accurately locked, which effectively improves the sensor's anti-interference ability and electric field sensing sensitivity, and realizes high-precision detection of the electric field signal to be measured. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a structural block diagram of a self-excited AGC closed-loop detection system for a MEMS electric field sensor according to an exemplary embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of a bridge capacitor detection circuit with a turns ratio arm in a self-excited AGC closed-loop detection system for a MEMS electric field sensor, as described in an exemplary embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of a Simulink simulation model of a MEMS electric field sensor.

[0034] Figure 4 The simulation results are shown when the driving frequency of the voltage driving signal is the same as the resonant frequency of the MEMS electric field sensor.

[0035] Figure 5 The simulation results show the resonant frequency drift of the MEMS electric field sensor by +0.5%. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0038] Furthermore, the terminology used in the description of this invention is for illustrative purposes only and is not intended to limit the scope of the invention. The terms "comprising" and / or "including" are used to specify the presence of said elements, steps, operations, and / or components, but do not exclude the presence or addition of one or more other elements, steps, operations, and / or components. The terms "first," "second," etc., may be used to describe various elements, do not represent an order, and do not limit these elements. Moreover, in the description of this invention, unless otherwise stated, "a plurality of" means two or more. These terms are used only to distinguish one element from another. These and / or other aspects become apparent in conjunction with the following drawings, and those skilled in the art will more readily understand the description of the embodiments of the invention. The drawings are used for illustrative purposes only to depict the embodiments of the invention. Those skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods shown in the invention can be employed without departing from the principles of the invention.

[0039] like Figure 1 As shown in the embodiment of the present invention, a self-excited AGC closed-loop detection system for a MEMS electric field sensor includes:

[0040] The MEMS sensing structure includes a shielding electrode, a sensing electrode, and a driving structure. The driving structure receives a voltage driving signal and generates mechanical deformation. The shielding electrode is displaced under the drive of the driving structure. The sensing electrode couples the electric field signal to be measured with the displacement signal of the shielding electrode and outputs a differential mode current signal.

[0041] A driving circuit is connected to the excitation terminal and the output terminal of the MEMS sensitive structure. It adjusts the gain according to the displacement signal and adjusts the voltage driving signal according to the gain to form an AGC closed-loop feedback and maintain the stable resonance of the MEMS sensitive structure.

[0042] The signal demodulation circuit is connected to the output terminal of the MEMS sensitive structure to receive and demodulate the differential mode current signal.

[0043] Automatic gain control (AGC) is an electronic control method that automatically adjusts the amplifier gain through a closed-loop negative feedback system. Its core function is to maintain a relatively stable output signal level when the amplitude of the input signal changes significantly.

[0044] After receiving the voltage drive signal from the drive circuit, the drive structure generates mechanical deformation through electrostatic / piezoelectric / thermal drive, causing the shielding electrode to displace. When the electric field to be measured is applied, the displacement of the shielding electrode blocks the induction electrode, causing a change in the surface charge of the induction electrode. This couples the electric field signal to be measured with the displacement signal, ultimately outputting a differential mode current signal in the nA range that is proportional to the intensity of the electric field to be measured, thus achieving the initial conversion of the electric field signal to an electrical signal.

[0045] Furthermore, the shielding electrode and the sensing electrode are distributed in a comb-like or interdigital structure.

[0046] In the comb-tooth structure, the shielding electrode and the sensing electrode are arranged in an alternating, parallel comb-like pattern. The comb teeth of the shielding electrode are embedded in the gaps between the teeth of the sensing electrode, with no contact and uniform gaps between them. In the interdigital structure, the finger-like structures of the shielding electrode and the sensing electrode interweave to form a coupling region covering a surface area. When the shielding electrode undergoes periodic displacement with the driving structure, the effective sensing area of ​​the sensing electrode can be changed by altering the shielding area of ​​the tooth / finger structure, thereby coupling the measured electric field signal with the displacement signal.

[0047] Furthermore, the driving structure adopts electrostatic driving, piezoelectric driving, or thermal driving methods.

[0048] Electrostatic drive uses electric field force as its core power source, and the drive structure typically consists of a fixed induction electrode and a movable shielding electrode. When a DC bias voltage and an AC drive voltage are applied to the two electrodes, a periodically changing electrostatic force is generated between the electrodes, driving the movable shielding electrode to reciprocate. The main advantages of this method are low drive voltage, low power consumption, and fast response speed.

[0049] Piezoelectric actuation achieves driving through the inverse piezoelectric effect of piezoelectric materials. The actuation structure is typically integrated from piezoelectric ceramic sheets or piezoelectric thin films. When an alternating voltage is applied to the piezoelectric material, it undergoes periodic expansion and contraction, directly causing the shielding electrode to resonate and displace. The main advantages of this method are high driving force, stable displacement output, and strong resistance to electromagnetic interference.

[0050] Thermal actuation works based on the principle of thermal expansion and contraction. The driving structure typically consists of a built-in miniature heating resistor and a flexible support beam. When an alternating current is applied to the heating resistor, it periodically generates heat. The support beam expands and contracts due to temperature changes, which in turn drives the shielding electrode to vibrate reciprocally. The main advantages of this method are its simple structure, low manufacturing difficulty, and large output displacement.

[0051] It is understood that the distribution of the shielding electrode and the sensing electrode, as well as the driving method of the driving structure, can be selected according to the actual situation, and this application does not make specific limitations in this regard.

[0052] The MEMS sensing structure is fabricated using silicon micromachining technology. Its shielding electrode is made of polycrystalline silicon, 3 μm thick and 80 μm long, exhibiting high elasticity and stability. The sensing electrode consists of two symmetrically distributed differential electrodes, spaced 10 μm apart, effectively suppressing common-mode noise. The driving structure comprises two sets of symmetrical excitation combs (20 teeth per set) and a folded beam support (8 μm wide and 80 μm long). An initial DC bias voltage is applied to the excitation combs, driving the shielding electrode to initially vibrate horizontally. When a target physical quantity (such as the atmospheric electric field E) acts on the MEMS sensing structure, the shielding electrode periodically blocks the sensing electrode, causing a periodic change in the surface charge of the sensing electrode, outputting two differential-mode current signals proportional to E.

[0053]

[0054] Where ε0 is the dielectric constant, A e Let Q be the effective area of ​​the electric field induction, and Q be the charge on the induction electrode.

[0055] Let the longitudinal length of the shielding electrode be L, the vibration amplitude be X, and the shielding electrode undergo sinusoidal vibration, then:

[0056]

[0057] After receiving the displacement signal and converting it into a voltage signal, the drive circuit inputs the AGC to dynamically adjust the gain and stabilize the signal amplitude. At the same time, the drive circuit adjusts the corresponding drive voltage parameters according to the adjusted gain to form a stable voltage drive signal and feeds it back to the excitation end of the MEMS sensitive structure. The voltage drive signal assignment and drive frequency are optimized in real time to compensate for the resonant frequency drift caused by factors such as ambient temperature and electromagnetic interference, forming a complete closed-loop feedback to ensure that the MEMS sensitive structure always maintains a stable resonant state.

[0058] like Figure 1As shown, the driving circuit includes an I / V converter, an operational amplifier, and an AGC circuit. The I / V converter input is connected to the output of the electrode pair of the MEMS sensitive structure, and the I / V converter output is connected to the input of the operational amplifier, converting the displacement signal of the shielded electrode into a first voltage signal. The operational amplifier output is connected to the input of the AGC circuit and the input of the demodulation unit (multiplier) in the signal demodulation circuit, respectively, to initially amplify the first voltage signal and provide a basic signal (e.g., an amplitude-enhanced and phase-stable first voltage signal, a reference signal) for subsequent AGC adjustment and signal demodulation. The AGC circuit output is connected to the excitation terminal (electrode pair) of the MEMS sensitive structure to generate a stable voltage driving signal and maintain stable resonance of the MEMS sensitive structure.

[0059] The signal demodulation circuit receives the differential mode current signal under stable resonance state, and outputs it after amplification, noise reduction and demodulation processing to achieve high-precision detection of the electric field signal under test.

[0060] like Figure 1 As shown, the signal demodulation circuit includes an I / V converter, a differential amplifier, a multiplier, a phase shifter, a low-pass filter, and a sum-of-squares operation unit (multiplier). The I / V converter input is connected to the output of the MEMS sensing structure, and the output is connected to the input of the differential amplifier, converting the differential-mode current signal output by the MEMS sensing structure into a second voltage signal. The multiplier input is connected to the output of the differential amplifier and the output of the operational amplifier of the drive circuit (via the phase-shifting sub-unit), respectively. The multiplier output is connected to the input of the low-pass filter, which uses the differential input characteristics of the differential amplifier to suppress common-mode noise (such as environmental interference and power fluctuations) in the second voltage signal. The phase-shifting sub-unit converts the signal output by the drive circuit into a pair of reference signals with the same frequency as the drive frequency but a 90° phase difference. The low-pass filter output is connected to the input of the sum-of-squares unit (multiplier), which filters out harmonic interference and high-frequency noise, retaining only the effective signal related to the electric field signal to be measured. The sum-of-squares unit (multiplier) output is the final output of the signal demodulation circuit, which performs a sum-of-squares operation on the two filtered effective signals to generate a detection signal proportional to the electric field strength to be measured, ensuring detection accuracy.

[0061] The system in this application does not require an external oscillation source. By using the MEMS sensitive structure as part of the oscillation circuit, the signal generated by the MEMS sensitive structure is analyzed and processed, and then fed back to the MEMS sensitive structure, forming a stable oscillation system that can be spontaneously maintained and adjusted.

[0062] In one embodiment, the driving circuit includes:

[0063] The self-excited oscillation circuit has its input terminal connected to the output terminal of the MEMS sensitive structure, receives and processes the displacement signal, and outputs a first voltage signal;

[0064] Furthermore, the self-excited oscillation circuit includes:

[0065] A drive displacement detection module is used to receive the displacement signal and convert it into a current signal;

[0066] An I / V conversion module is used to convert the current signal into the first voltage signal;

[0067] The phase compensation module is used to adjust the phase of the first voltage signal to meet the phase conditions for self-excited oscillation.

[0068] Furthermore, the phase condition for the self-excited oscillation is: the total phase shift of the circuit is an integer multiple of 360°, to ensure that the first voltage signal processed by the self-excited oscillation circuit is in phase with the voltage drive signal of the MEMS sensitive structure, forming a positive feedback loop and maintaining the continuous stable resonance of the system.

[0069] Preferred, such as Figure 2 As shown, the drive displacement detection module adopts a variable ratio arm bridge-type capacitor detection circuit. This circuit has a differential structure, and the core of the variable ratio arm bridge circuit consists of the capacitor C to be measured. x The conductivity under test G x The detection branch and the reference capacitor C constitute r The reference branch is configured such that its input terminals are respectively connected to AC voltage source V. s With -V s The inverting input of the operational amplifier is connected to the output of the turns ratio arm bridge, the non-inverting input of the operational amplifier is grounded, and a capacitor C is connected in parallel to the feedback loop. f With resistance R f The operational amplifier output is connected to the AC amplifier input, and the output phase modulator input is connected to the AC amplifier. At the same time, the reference signal from the reference branch side of the ratio arm bridge is connected (via a phase shifter) to ensure that the phase of the first voltage signal meets the phase condition for self-excited oscillation.

[0070] When the circuit is working, an AC voltage source in the acoustic frequency domain is applied to the bridge capacitance detection circuit. When the shielding electrode of the MEMS sensitive structure is displaced, it will change the capacitance C under test in the detection branch. x The capacitance value disrupts the bridge circuit balance, thus converting the capacitance change corresponding to the displacement into a differential current signal. This differential current signal is further converted into a first voltage signal by a transimpedance amplifier (I / V conversion module). The differential current signal flowing into the transimpedance amplifier is:

[0071] I = V x [G x+jω(C x -C r )]

[0072] Transimpedance amplifiers can be improved by selecting an appropriate feedback resistor R. f and feedback capacitor C f This allows the amplification factor of the transimpedance amplifier to be determined by the feedback resistor R within the desired frequency range. f The decision is made simultaneously through the feedback capacitor C. f Most high-frequency noise is filtered out; then the first voltage signal is amplified by an AC amplifier, ultimately outputting a first voltage signal that precisely corresponds to the displacement of the MEMS sensitive structure. Finally, the phase of the first voltage signal is adjusted by a phase compensation module to ensure that the total phase shift of the circuit meets the phase condition of an integer multiple of 360°, allowing the system to operate stably at its inherent resonant frequency. This amplifies weak signal amplitudes to the mV or even V level, improving signal processability, and ultimately outputting a first voltage signal V with enhanced amplitude and stable phase. x .

[0073] The AGC circuit has its input terminal connected to the output terminal of the self-excited oscillation circuit, and its output terminal connected to the excitation terminal of the MEMS sensitive structure. The gain is adjusted according to the first voltage signal to generate a stable voltage drive signal, which is then fed back to the excitation terminal of the MEMS sensitive structure.

[0074] Furthermore, the AGC circuit includes:

[0075] A gain comparison subunit is used to receive the first voltage signal and compare it with a preset reference voltage, and output a gain deviation signal;

[0076] The gain adjustment subunit is used to dynamically adjust the gain according to the gain deviation signal in order to output a stable voltage drive signal.

[0077] The preset reference voltage can be set according to the actual requirements of the resonance amplitude of the MEMS sensitive structure, and this application does not make specific limitations on it.

[0078] When the circuit is working, the gain comparator subunit will receive the first voltage signal V x With preset reference voltage V ref Amplitude comparison is performed, and a gain deviation signal is output. For example, when the first voltage signal V... x The amplitude is higher than V ref When the first voltage signal V is output, a positive gain deviation signal is output; when the first voltage signal V is output, a positive gain deviation signal is output. x The amplitude is lower than V refWhen a positive gain deviation signal is output, the gain adjustment subunit dynamically adjusts the gain G0 based on the gain deviation signal, and outputs a stable voltage drive signal. For example, for a positive gain deviation signal, it outputs a gain reduction command; for a negative gain deviation signal, it outputs a gain increase command. The output voltage (voltage drive signal) V... G With the first voltage signal V x A linear relationship exists:

[0079] V G =G0(2-V x / V ref )

[0080] After the first voltage signal is adjusted by gain G0, a voltage drive signal with stable amplitude and drive frequency is output. Finally, the voltage drive signal is fed back to the excitation end of the MEMS sensitive structure in real time through a feedback link to compensate for the resonant frequency drift caused by factors such as ambient temperature fluctuations and external electromagnetic interference. This not only ensures that the MEMS sensitive structure always maintains the optimal resonant state, but also guarantees the stability and continuity of the signal amplification effect.

[0081] In one embodiment, the signal demodulation circuit includes an amplification module and a demodulation module.

[0082] Furthermore, the amplification module includes:

[0083] A transimpedance amplifier is used to amplify the differential-mode current signal and convert it into a second voltage signal. It can filter out high-frequency noise and parasitic interference and avoid signal distortion during the conversion process.

[0084] The differential amplifier is used to suppress the common-mode noise of the second voltage signal. It can significantly attenuate the interference components (such as environmental electromagnetic interference, power supply fluctuation noise, etc.) that are common in the two differential-mode current signals, and significantly improve the signal-to-noise ratio of the second voltage signal.

[0085] Furthermore, the demodulation module includes:

[0086] The demodulation unit demodulates the amplified second voltage signal using a reference signal and outputs two quadrature signals.

[0087] The reference signal is a pair of AC signals with the same frequency as the driving frequency but a 90° phase difference, derived from the driving circuit. During operation, a multiplier mixes and demodulates the second voltage signal with both AC signals, ultimately outputting two orthogonal mixed signals. Since the frequency of the effective electric field component in the second voltage signal is the same as the reference signal frequency, the mixing process generates a mixed signal containing a DC component (proportional to the electric field strength) and harmonic interference components. Irrelevant noise components, due to frequency mismatch, remain high-frequency interference after mixing.

[0088] The filtering unit performs low-pass filtering and sum-of-squares operation on the two orthogonal signals to output an electric field signal (the final output electric field signal is proportional to the electric field signal under test).

[0089] A low-pass filter can effectively filter out harmonic interference and high-frequency noise interference generated by mixing, retaining only the pure DC / low-frequency signal directly related to the electric field under test. Then, the sum of squares of the two pure signals can cancel out the phase deviation of the two orthogonal signals, thereby avoiding detection errors caused by phase fluctuations and ensuring detection accuracy.

[0090] The invention will be further illustrated using a Simulink simulation example:

[0091] like Figure 3 As shown, this is a Simulink simulation model of a MEMS electric field sensor built according to the system structure block diagram. In the figure, module 1 is the AGC automatic gain control circuit, and module 2 is the signal back-end amplification and demodulation circuit, whose reference signal comes from the driving circuit.

[0092] The EFS module represents the system transfer function of a MEMS electric field sensor:

[0093]

[0094] Where m is the effective mass of the vibration module, ω0 is the natural frequency of the sensor, ξ is the damping ratio of the sensor, and K x Let be the elastic coefficient in the horizontal direction of the vibrating structure, and c be the damping coefficient of the horizontal vibration.

[0095] Based on the sensor's transfer function, the sensor can be equivalently represented as a variable capacitor formed by the shielding electrode and the sensing electrode. The capacitance to voltage conversion is achieved through the xC, PSD, and Q-i3 modules. The random disturbance module r represents a random disturbance at the sensor's input terminal, enabling the sensor system to achieve self-excited oscillation.

[0096] Based on the structural characteristics of the sensor, and through calculation and approximation, the following parameters are taken as simulation parameters: ξ=0.005, ω0=2×10 5 rad / s, m=1×10 -9 kg, resonant frequency 31.83kHz, and the required amplitude of the vibration output signal is 2V.

[0097] like Figure 4 As shown in the simulation results obtained when the driving frequency is the resonant frequency, it can be seen that the sensor oscillates and the output eventually stabilizes at 2V. The resonant frequency is the sensor's natural frequency of 31.83kHz.

[0098] likeFigure 5 The simulation results shown are obtained when the resonant frequency drifts by +0.5%. It can be seen that the resonant frequency has a very small impact on the vibration output signal, and the AGC control strategy is effective.

[0099] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0100] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments.

[0101] Those skilled in the art will understand that although the invention has been described with reference to exemplary embodiments, various changes may be made and its elements may be substituted with equivalents without departing from the scope of the invention. Furthermore, many modifications may be made to adapt particular situations or materials to the teachings of the invention without departing from the essential scope of the invention.

Claims

1. A self-excited AGC closed-loop detection system for a MEMS electric field sensor, characterized in that, The application relates to a MEMS sensor, which comprises the following parts: a MEMS sensing structure, which comprises a shield electrode, an induction electrode and a driving structure, the driving structure receives a voltage driving signal and generates a mechanical deformation, the shield electrode generates a displacement under the driving of the driving structure, the induction electrode couples a to-be-measured electric field signal with a displacement signal of the shield electrode and outputs a differential mode current signal; a driving circuit, which is connected with an excitation end and an output end of the MEMS sensing structure, adjusts a gain according to the displacement signal and adjusts the voltage driving signal according to the gain to form an AGC closed loop feedback; a signal demodulation circuit, which is connected with the output end of the MEMS sensing structure and receives and demodulates the differential mode current signal.

2. The self-oscillating AGC closed loop detection system of claim 1, wherein, The driving circuit comprises: a self-oscillation circuit, which is connected with the output end of the MEMS sensing structure, receives and processes the displacement signal and outputs a first voltage signal; an AGC circuit, which is connected with the output end of the self-oscillation circuit, and the output end of the AGC circuit is connected with the excitation end of the MEMS sensing structure, adjusts a gain according to the first voltage signal, generates a stable voltage driving signal and feeds back the voltage driving signal to the excitation end of the MEMS sensing structure.

3. The self-oscillating AGC closed loop detection system of claim 2, wherein, The self-oscillation circuit comprises: a driving displacement detection module, which is used for receiving the displacement signal and converting the displacement signal into a current signal; an I / V conversion module, which is used for converting the current signal into the first voltage signal; a phase compensation module, which is used for adjusting the phase of the first voltage signal to meet a phase condition of self-oscillation.

4. The self-oscillating AGC closed loop detection system of claim 3, wherein, The phase condition of self-oscillation is that the total phase shift of the circuit is an integer multiple of 360 degrees.

5. The self-oscillating AGC closed loop detection system of claim 2, wherein, The AGC circuit comprises: a gain comparison subunit, which is used for receiving the first voltage signal and comparing the first voltage signal with a preset reference voltage and outputting a gain deviation signal; a gain adjustment subunit, which is used for dynamically adjusting a gain according to the gain deviation signal to output a stable voltage driving signal.

6. The self-oscillating AGC closed loop detection system of claim 1, wherein, The distribution mode of the shield electrode and the induction electrode is a comb or interdigital structure.

7. The self-oscillating AGC closed loop detection system of claim 1, wherein, The driving structure adopts electrostatic driving, piezoelectric driving or thermal driving mode.

8. The self-oscillating AGC closed loop detection system of claim 1, wherein, The signal demodulation circuit comprises an amplification module and a demodulation module.

9. The self-oscillating AGC closed loop detection system of claim 8, wherein, The amplification module comprises: a transimpedance amplifier, which is used for amplifying the differential mode current signal and converting the differential mode current signal into a second voltage signal; a differential amplifier, which is used for suppressing common mode noise of the second voltage signal.

10. The self-oscillating AGC closed loop detection system of claim 9, wherein, The demodulation module comprises: a demodulation unit, which demodulates the amplified second voltage signal by a reference signal and outputs two-way quadrature signals; a filter unit, which carries out low-pass filtering and square sum operation on the two-way quadrature signals and outputs an electric field signal.

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