CN116045938A

CN116045938A - MEMS gyroscope

Info

Publication number: CN116045938A
Application number: CN202211717826.0A
Authority: CN
Inventors: 黄莉; 孟雨馨; 金羊华; 蒋乐跃
Original assignee: Meixin Semiconductor Tianjin Co ltd
Current assignee: Meixin Semiconductor Tianjin Co ltd
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2023-05-02

Abstract

The present invention provides a MEMS gyroscope comprising: a MEMS inertial sensing portion, comprising: a drive capacitor bank, a drive sense capacitor bank, one or more axes of sense capacitor banks; a gyroscopic interface circuit, comprising: the device comprises a driving circuit, one or more shaft detection circuits, one or more shaft correction capacitor groups and a digital processing circuit; the driving circuit comprises a driving charge amplifier, the detecting circuit comprises one or more shafts of detecting charge amplifiers, one end of a first correcting capacitor in each shaft of correcting capacitor groups is connected to a first output end of the driving charge amplifier, the other end of the first correcting capacitor is connected to a first input end of the detecting charge amplifier of the corresponding shaft, one end of a second correcting capacitor in each shaft of correcting capacitor groups is connected to a second output end of the driving charge amplifier, and the other end of the second correcting capacitor is connected to a second input end of the detecting charge amplifier of the corresponding shaft. Thus, the quadrature error can be eliminated, and the zero bias stability and the noise level of the gyroscope are improved.

Description

MEMS gyroscope

[ field of technology ]

The invention relates to the technical field of gyroscopes, in particular to a MEMS (Micro-Electro-Mechanical System, micro Electro mechanical system) gyroscope.

[ background Art ]

The gyroscope is an angular velocity sensor based on the Golgi force effect, has the advantages of low power consumption, small volume, low cost, easy integration and the like, and is widely applied to the fields of aerospace, automotive electronics, robots and the like.

The gyro interface circuit is implemented with a highly integrated ASIC (Application Specific Integrated Circuit ). The ASIC circuit has the advantages of high precision, small volume, low cost, strong environmental adaptability and the like, is easy to meet the practical requirements of batch measurement and adjustment of the MEMS gyroscope and the like, and can realize the integration of the MEMS gyroscope interface circuit to become the bottleneck for restricting the high performance, miniaturization and low cost of the device.

The gyro interface circuit is divided into a driving circuit and a detecting circuit. The driving circuit is an important measurement and control circuit in the MEMS gyroscope. The driving signal is generated to control the gyroscope mass block to vibrate and stably vibrate, and meanwhile demodulation reference signals are provided for the detection circuit. The stability of the silicon gyroscope self-excitation driving circuit is one of the difficulties of the current driving circuit. Amplitude stability and frequency stability due to gyro drive signal phase noise directly affect angular velocity stability. The traditional analog driving circuit has poor stability and environmental adaptability due to the fact that the reliability of an analog device is poor, the precision is low, performance parameters are easily affected by factors such as temperature and aging, and the analog circuit is not easy to realize an advanced control algorithm. The detection circuit is used for reading out the output signal of the sensor. The high-precision gyroscope has high requirements on the capabilities of weak signal detection, noise suppression, error elimination, environmental adaptability, temperature compensation and the like of a detection circuit.

Furthermore, silicon micro-gyroscopes are manufactured based on silicon micro-machining processes. Because of non-ideal factors such as machining errors, other coupling mechanisms exist between the motion in the driving direction and the motion in the detection direction, and most remarkable is elastic coupling, detection vibration caused by the elastic coupling is 90 degrees different from detection vibration caused by the Golgi effect in phase, so that the detection vibration is called quadrature error. The quadrature error directly affects the key performances of the gyroscope such as zero bias stability, zero bias temperature stability and the like.

Therefore, a new solution is needed to solve the above problems.

[ invention ]

One of the purposes of the present invention is to provide a MEMS gyroscope with synchronous compensation to eliminate quadrature errors and improve the zero bias stability and noise level of the gyroscope.

According to one aspect of the present invention, there is provided a MEMS gyroscope comprising: a MEMS inertial sensing portion, comprising: a drive capacitor bank, a drive sense capacitor bank, one or more axes of sense capacitor banks; a gyroscopic interface circuit, comprising: the device comprises a driving circuit, one or more shaft detection circuits, one or more shaft correction capacitor groups and a digital processing circuit; the driving circuit comprises a driving charge amplifier, a first input end of the driving charge amplifier is connected with one end of a first driving detection capacitor in the driving detection capacitor group, a second input end of the driving charge amplifier is connected with one end of a second driving detection capacitor in the driving detection capacitor group, the driving circuit comprises one or more shafts of detection charge amplifiers, a first input end of each shaft of detection charge amplifier is connected with one end of a first detection capacitor in the detection capacitor group of the corresponding shaft, a second input end of each shaft of detection charge amplifier is connected with one end of a second detection capacitor in the detection capacitor group of the corresponding shaft, one end of the first correction capacitor in each shaft of correction capacitor groups is connected to the first output end of the driving charge amplifier, the other end of the second correction capacitor in each shaft of correction capacitor groups is connected to the second output end of the driving charge amplifier, and the other end of the second correction capacitor in each shaft of correction capacitor groups is connected to the second input end of the detection charge amplifier of the corresponding shaft of correction capacitor.

Compared with the prior art, the invention compensates the input current of the detection charge amplifier (SCSA) in the detection circuit by utilizing the characteristic that the useful signal of the output current of the drive charge amplifier (DCSA) in the drive circuit is in the same frequency and in phase, thereby eliminating the quadrature signal which is 90 degrees different from the useful signal in the detection charge amplifier (SCSA) in the detection circuit, and improving the zero offset stability and the noise level of the gyroscope.

[ description of the drawings ]

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:

FIG. 1 is a schematic diagram of a MEMS gyroscope of the present invention in one embodiment;

[ detailed description ] of the invention

In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Unless specifically stated otherwise, the terms connected, or connected herein denote an electrical connection, either directly or indirectly.

In the present invention, unless specifically stated and limited otherwise, the terms "connected," "coupled," and the like should be construed broadly; for example, they may be directly connected or indirectly connected through an intermediate medium. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

The invention compensates the input current of the detection charge amplifier (SCSA) in the detection circuit by utilizing the characteristic that the useful signal of the output current of the driving charge amplifier (DCSA) in the driving circuit is in the same frequency and in phase, thereby eliminating the quadrature signal which is 90 degrees different from the useful signal in the detection charge amplifier (SCSA) in the detection circuit, and improving the zero offset stability and noise level of the gyroscope.

FIG. 1 is a schematic diagram of a MEMS gyroscope 100 in one embodiment of the present invention. As shown in fig. 1, the MEMS gyroscope 100 includes a MEMS inertial sensing portion 110 and a gyroscope interface circuit. The MEMS inertial sensing portion 110 is a sensing device of the MEMS gyroscope 100 that operates on the principle of converting acceleration of the reference frame into capacitance changes in the sensor capacitance.

As shown in fig. 1, the MEMS inertial sensing part 110 includes: drive capacitor sets d_p and d_n, drive sense capacitor sets d_sense_p and d_sense_n, sense capacitor sets for one or more axes.

The gyro interface circuit includes: a drive circuit, one or more axis detection circuits, one or more axis correction capacitance sets QDAC, and a digital processing circuit 121.

The driving circuit comprises a driving charge amplifier DSCA, a first input terminal of the driving charge amplifier DSCA is connected to one terminal of a first driving detection capacitor d_sense_p of the driving detection capacitor groups d_sense_p and d_sense_n, and a second input terminal of the driving charge amplifier DSCA is connected to one terminal of a second driving detection capacitor d_sense_n of the driving detection capacitor groups d_sense_p and d_sense_n. The detection circuit comprises one or more shaft detection charge amplifiers SCSA, wherein a first input end of each shaft detection charge amplifier SCSA is connected with one end of a first detection capacitor in the corresponding shaft detection capacitor group, and a second input end of each shaft detection charge amplifier is connected with one end of a second detection capacitor in the corresponding shaft detection capacitor group. One end of a first correction capacitor in each correction capacitor group QDAC of the shaft is connected to the first output terminal of the driving charge amplifier DCSA, the other end is connected to the first input terminal of the detection charge amplifier SCSA of the corresponding shaft, one end of a second correction capacitor in each correction capacitor group QDAC of the shaft is connected to the second output terminal of the driving charge amplifier DCSA, and the other end is connected to the second input terminal of the detection charge amplifier SCSA of the corresponding shaft.

Specifically, the MEMS inertial sensing portion 110 has three sensing capacitor sets, which are the x-axis sensing capacitor sets sense_x_p and sense_x_n, and the y-axis sensing capacitor sets sense_y_p and sense_y_n and the z-axis sensing capacitor sets sense_z_p and sense_x_n, respectively. The gyro interface circuit comprises a three-axis detection circuit and a three-axis correction capacitor group. The three-axis detection circuits are respectively an x-axis detection circuit, a y-axis detection circuit and a z-axis detection circuit, and the three-axis correction capacitance sets are respectively an x-axis correction capacitance set QDAC_x, a y-axis correction capacitance set QDAC_y and a z-axis correction capacitance set QDAC_z. One end of a first correction capacitor in the x-axis correction capacitor group qdac_x is connected to the first output end of the driving charge amplifier DCSA, the other end is connected to the first input end of the x-axis detection charge amplifier scsa_x, one end of a second correction capacitor in the x-axis correction capacitor group qdac_x is connected to the second output end of the driving charge amplifier DCSA, and the other end is connected to the second input end of the x-axis detection charge amplifier scsa_x. One end of a first correction capacitor in the y-axis correction capacitor group qdac_y is connected to the first output end of the driving charge amplifier DCSA, the other end is connected to the first input end of the y-axis detection charge amplifier scsa_y, one end of a second correction capacitor in the y-axis correction capacitor group qdac_y is connected to the second output end of the driving charge amplifier DCSA, and the other end is connected to the second input end of the y-axis detection charge amplifier scsa_y. One end of a first correction capacitor in the z-axis correction capacitor group qdac_z is connected to the first output end of the driving charge amplifier DCSA, the other end is connected to the first input end of the z-axis detection charge amplifier scsa_z, one end of a second correction capacitor in the z-axis correction capacitor group qdac_z is connected to the second output end of the driving charge amplifier DCSA, and the other end is connected to the second input end of the z-axis detection charge amplifier scsa_z.

In one embodiment, the MEMS inertial sensor 110 may also be provided with one or two axis sensing capacitor sets, and similarly, the gyro interface circuit may also be provided with one or two axis sensing circuits and one or two axis correcting capacitor sets.

As shown in fig. 1, the detection circuit of each axis further includes detection mixers mixer_x, mixer_y, and mixer_z and detection analog-to-digital converters sadc_x, sadc_y, and sadc_z. The digital processing circuit 121 includes a Low Pass Filter (LPF) 1211 or a band pass filter. The two inputs of each of the shaft detection mixers mixer_x, mixer_y and mixer_z are connected to the two outputs of the corresponding shaft detection charge amplifiers scsa_x, scsa_y and scsa_z, the two outputs of each of the shaft detection mixers mixer_x, mixer_y and mixer_z are connected to the two inputs of the corresponding shaft detection analog-to-digital converters sadc_x, sadc_y and sadc_z, the detection analog-to-digital converter sadc_x of each shaft, the outputs of sadc_y and sadc_z are connected to a low pass filter 1211 or a band pass filter of the digital processing circuit 121, which digital processing circuit 121 supplies the detection mixers mixer_x, mixer_y and mixer_z with a detection mixing clock signal sen_mix_clk, which is in phase and in phase with the driving clock signal clk_gyro supplied to the driving mixer d_mixer. The low-pass filter 1211 or the band-pass filter low-pass filters or band-pass filters the digital detection signals bs_sadc_x, bs_sadc_y, and bs_sadc_z output from the detection analog-to-digital converters sadc_x, sadc_y, and sadc_z of each axis.

As shown in fig. 1, the MEMS gyroscope further includes: a power supply circuit 130. The output end of the power circuit 130 is connected to the other end of each capacitor in the driving capacitor group, the driving detecting capacitor group and the detecting capacitor group. The power circuit 130 provides a voltage to the other end of each capacitor in the driving capacitor group, the driving detection capacitor group, and the detection capacitor group.

As shown in fig. 1, the driving circuit further comprises a comparator Comp, a phase locked loop PLL, a driving analog to digital converter DADC, an automatic gain control digital to analog converter agc_dac and a driving mixer d_mixer.

The digital processing circuit 121 includes an automatic gain control module (AGC) 1212.

The first input terminal of the comparator Comp is connected to the first output terminal of the driving charge amplifier DSCA, the second input terminal of the comparator Comp is connected to the second output terminal of the driving charge amplifier DSCA, the reference input terminal ref_pl of the phase-locked loop PLL is connected to the output terminal of the comparator Comp, the comparator Comp provides a reference clock to the phase-locked loop PLL, and the output terminal of the phase-locked loop PLL is connected to the digital processing circuit 121. The phase-locked loop PLL generates a phase-locked loop clock pll_clk based on the reference clock.

The digital processing circuit 121 generates a feedback clock pl_fb_clk having the same frequency and the same phase as the reference clock based on the phase-locked loop clock pl_clk and supplies the feedback clock pl_fb_clk to a feedback input terminal fb_pl of the phase-locked loop PLL, and the digital processing circuit 121 phase-shifts the feedback clock pl_fb_clk by-90 degrees and supplies the feedback clock clk_gyro to the driving mixer d_mixer through a driving clock port.

The two input ends of the driving analog-digital converter daccc are respectively connected with the first output end and the second output end of the driving charge amplifier DSCA, so as to convert the voltage signal output by the driving charge amplifier DSCA into a digital voltage signal, the automatic gain control module AGC performs low-pass filtering on the digital voltage signal through the driving low-pass filter DLPF, and then a digital gain control signal dac_da for controlling driving amplitude is given through the PID controller, and the digital gain control signal dac_da is converted into an analog gain control signal by the automatic gain control digital-analog converter agc_dac and is provided to the driving mixer d_mixer.

And the driving mixer d_mixer generates a driving signal according to the driving clock signal and the analog gain control signal so as to drive the mass blocks corresponding to the driving capacitor groups D_p and D_n to do simple harmonic motion. The capacitance of the drive sense capacitance sets d_sense_p and d_sense_n changes due to the simple harmonic motion of the masses.

The charge transfer caused by the change of the driving detection capacitance sets d_sense_p and d_sense_n is sensed and amplified by the driving charge amplifier DCSA to be converted into a voltage signal. The comparator Comp converts the output of the driving charge amplifier DCSA into a square wave signal, which is inverted at the zero crossing point of the output of the driving charge amplifier DCSA. The phase-locked loop PLL takes the output of the comparator Comp as its reference clock and outputs a multiplied high-frequency clock of the reference clock as the phase-locked loop clock pll_clk. The digital processing circuit 121 generates a feedback clock pll_fb_clk of the same frequency and phase as the reference clock based on the phase-locked loop clock pll_clk by frequency division. The phase-locked loop PLL loop can realize self-excitation starting of the MEMS gyroscope and lock the vibration frequency driven by the MEMS to be near the resonance frequency driven by the MEMS, so that stable operation of the gyroscope is ensured.

The first connection end of the driving mixer d_mixer is connected with one end of a first driving capacitor D_p in the driving capacitor group, and the second connection end of the driving mixer d_mixer is connected with one end of a second driving capacitor D_n in the driving capacitor group.

When the driving mass moves in a simple harmonic manner in a certain direction, if the reference system of the driving mass has acceleration which is not parallel to the simple harmonic movement direction, the mass is also subjected to a Coriolis force perpendicular to the acceleration and the driving simple harmonic movement plane, and the Coriolis force phase is 90 degrees different from the driving displacement. The coriolis force causes the mass to simultaneously make a simple harmonic motion (sense acceleration and motion) in this vertical direction. The induced motion will cause the capacitance of the sense_p/sense_n Sense capacitor set on that axis to change. The charge transfer caused by this capacitance change is sensed and amplified by the sense charge amplifier SCSA to be converted into a voltage signal. This voltage signal is then demodulated by the detection mixer clock signal sen_mix_clk, which is-90 degrees from fb_pl, as mentioned above, leaving a low frequency acceleration voltage signal. The low frequency voltage signal is detected by SADC of the shaft and converted into a digital signal, which is filtered by LPF in the digital processing circuit 121 to become the final output of gyro inertial sensing.

In addition, due to non-ideal factors such as machining errors, other coupling mechanisms exist between the motion in the driving direction and the motion in the detection direction, and detection vibration caused by the coupling mechanisms is 90 degrees different from detection vibration caused by the Goldng effect in phase. Due to the different design parameters of MEMS actuation and sensing, quadrature errors tend to be much larger than the amplitude of the acceleration signal actually to be detected, which can lead to saturation of scsa_x/y/z. Saturation of SCSA results in true acceleration not being measured. In order to eliminate the signal coupling the driving direction to the detecting direction, the quadrature error correction capacitor set qdac_x/y/z (quadrature error correction capacitor set of x/y/z axis) is used to introduce the current signal in-phase with the driving signal to scsa_x/y/z to eliminate the quadrature error coupling the MEMS driving.

In the invention, the digital driving closed-loop circuit can enable the gyroscope to start vibrating rapidly and can effectively improve the performances of control precision, stability, environmental adaptability and the like. The detection circuit has very high performance for weak signal amplification and detection, noise suppression, environmental adaptability, temperature compensation and the like. The quadrature error compensation circuit effectively eliminates quadrature errors in the useful signal and largely avoids saturation of the SCSA. Further, quadrature error compensation reduces the noise level of the coupling noise due to large amplitude quadrature errors and clock jitter. The detection circuit and the quadrature error compensation ensure the accuracy of the gyroscope output signal measurement.

In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Further, one skilled in the art may combine and combine the different embodiments or examples described in this specification.

While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications and alternatives to the above embodiments may be made by those skilled in the art within the scope of the invention.

Claims

1. A MEMS gyroscope, comprising:

a MEMS inertial sensing portion, comprising: a drive capacitor bank, a drive sense capacitor bank, one or more axes of sense capacitor banks;

a gyroscopic interface circuit, comprising: the device comprises a driving circuit, one or more shaft detection circuits, one or more shaft correction capacitor groups and a digital processing circuit;

the driving circuit comprises a driving charge amplifier, a first input end of the driving charge amplifier is connected with one end of a first driving detection capacitor in the driving detection capacitor group, a second input end of the driving charge amplifier is connected with one end of a second driving detection capacitor in the driving detection capacitor group,

the detection circuit comprises one or more shaft detection charge amplifiers, a first input end of each shaft detection charge amplifier is connected with one end of a first detection capacitor in the corresponding shaft detection capacitor group, a second input end of each shaft detection charge amplifier is connected with one end of a second detection capacitor in the corresponding shaft detection capacitor group,

one end of a first correction capacitor in each correction capacitor group of the shaft is connected to the first output end of the driving charge amplifier, the other end of the first correction capacitor is connected to the first input end of the detection charge amplifier of the corresponding shaft, one end of a second correction capacitor in each correction capacitor group of the shaft is connected to the second output end of the driving charge amplifier, and the other end of the second correction capacitor is connected to the second input end of the detection charge amplifier of the corresponding shaft.

2. The MEMS gyroscope of claim 1, wherein,

the MEMS inertial sensing part is provided with three detection capacitance groups which are respectively an x-axis detection capacitance group, a y-axis detection capacitance group and a z-axis detection capacitance group,

the gyro interface circuit comprises three-axis detection circuits and three-axis correction capacitance groups, wherein the three-axis detection circuits are respectively an x-axis detection circuit, a y-axis detection circuit and a z-axis detection circuit, the three-axis correction capacitance groups are respectively an x-axis correction capacitance group, a y-axis correction capacitance group and a z-axis correction capacitance group,

one end of a first correction capacitor in the x-axis correction capacitor group is connected to the first output end of the driving charge amplifier, the other end of the first correction capacitor is connected to the first input end of the x-axis detection charge amplifier, one end of a second correction capacitor in the x-axis correction capacitor group is connected to the second output end of the driving charge amplifier, the other end of the second correction capacitor is connected to the second input end of the x-axis detection charge amplifier,

one end of a first correction capacitor in the y-axis correction capacitor group is connected to the first output end of the driving charge amplifier, the other end of the first correction capacitor is connected to the first input end of the y-axis detection charge amplifier, one end of a second correction capacitor in the y-axis correction capacitor group is connected to the second output end of the driving charge amplifier, the other end of the second correction capacitor is connected to the second input end of the y-axis detection charge amplifier,

one end of a first correction capacitor in the correction capacitor group of the z axis is connected to the first output end of the driving charge amplifier, the other end of the first correction capacitor is connected to the first input end of the detection charge amplifier of the z axis, one end of a second correction capacitor in the correction capacitor group of the z axis is connected to the second output end of the driving charge amplifier, and the other end of the second correction capacitor is connected to the second input end of the detection charge amplifier of the z axis.

3. The MEMS gyroscope of claim 1, wherein the detection circuitry for each axis further comprises a detection mixer and a detection analog-to-digital converter,

the digital processing circuit comprises a low pass filter or a band pass filter,

the two input ends of the detection mixer of each shaft are connected with the two output ends of the detection charge amplifier of the corresponding shaft, the two output ends of the detection mixer of each shaft are connected with the two input ends of the detection analog-to-digital converter of the corresponding shaft, the output end of the detection analog-to-digital converter of each shaft is connected with a low-pass filter or a band-pass filter of the digital processing circuit, the digital processing circuit provides detection mixing clock signals for the detection mixer, the detection mixing clock signals and the driving clock signals provided for the driving mixer are in the same frequency and phase,

the low-pass filter or the band-pass filter performs low-pass filtering or band-pass filtering on the digital detection signal output by the detection analog-to-digital converter of each axis.

4. The MEMS gyroscope of claim 1, further comprising:

and the output end of the power supply circuit is connected with the other end of each capacitor in the driving capacitor group, the driving detection capacitor group and the detection capacitor group.

5. The MEMS gyroscope of claim 1, wherein,

the driving circuit further comprises a comparator, a phase-locked loop, a driving analog-to-digital converter, an automatic gain control digital-to-analog converter and a driving mixer,

the digital processing circuit includes an automatic gain control module,

a first input end of the comparator is connected with a first output end of the driving charge amplifier, a second input end of the comparator is connected with a second output end of the driving charge amplifier, a reference input end of the phase-locked loop is connected with an output end of the comparator, the comparator provides a reference clock for the phase-locked loop, an output end of the phase-locked loop is connected with the digital processing circuit,

the digital processing circuit generates a feedback clock with the same frequency and phase as the reference clock based on the phase-locked loop clock and provides the feedback clock to a feedback input end of the phase-locked loop, the digital processing circuit phase-shifts the feedback clock by-90 degrees and provides the feedback clock as a driving clock signal to the driving mixer through a driving clock port,

the two input ends of the driving analog-digital converter are respectively connected with the first output end and the second output end of the driving charge amplifier so as to convert the voltage signal output by the driving charge amplifier into a digital voltage signal, the automatic gain control module carries out low-pass filtering on the digital voltage signal, then a digital gain control signal for controlling driving amplitude is given out through a PID controller, the digital gain control signal is converted into an analog gain control signal by the automatic gain control digital-analog converter and is provided for the driving mixer,

the driving mixer generates a driving signal according to the driving clock signal and the analog gain control signal to drive the mass block corresponding to the driving capacitor group to do simple harmonic motion,

the first connecting end of the driving mixer is connected with one end of a first driving capacitor in the driving capacitor group, and the second connecting end of the driving mixer is connected with one end of a second driving capacitor in the driving capacitor group.