A modal separated MEMS gyroscope frequency difference automatic tuning system

Abstract

The application discloses a modal separation type MEMS gyroscope frequency difference automatic tuning system. An excitation signal generation module converts drive detection current generated by a drive detection electrode into drive voltage and applies the drive voltage to the drive detection electrode, realizes extraction, storage and generation of a drive frequency, generates a sinusoidal excitation signal with the same frequency as the drive frequency, and makes the detection resonator vibrate forcibly. A frequency difference self-tuning module represents forced motion amplitude of the detection resonator through amplitude-frequency response of the excitation signal, generates a tuning voltage through automatic gain control after difference with an adjustable reference value, feeds back the tuning voltage to the moving mass electrode, and tunes the frequency difference through electrostatic negative stiffness effect. The stable tuning feedback voltage is stored in a tuning voltage generation module, a fixed tuning feedback voltage is generated by a time sequence control unit to act on the moving mass electrode, and the frequency difference self-tuning module is disconnected, so that the frequency difference automatic tuning is completed. The frequency difference dispersion of the MEMS gyroscope in batch production is overcome.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems and microinertial measurement technology, and in particular, it is a mode-separated MEMS gyroscope frequency difference automatic tuning system. Background Technology

[0002] A silicon micro gyroscope is a chip-based angular rate sensor designed using MEMS technology. Compared to traditional inertial gyroscopes, it features small size, light weight, low cost, low power consumption, ease of integration and mass production, high reliability, and a large measurement range. This makes it valuable for military applications and promising for broad development prospects in the civilian sector.

[0003] Currently, MEMS gyroscopes operating in the 50–100Hz small frequency difference mode have achieved zero bias instability of 0.1° / h, initially meeting the north-finding orientation requirements of 5G base stations, unmanned platforms, and other applications. However, due to the non-ideal constraints of MEMS fabrication technology, the frequency difference between individual MEMS gyroscopes produced in batches inevitably exhibits dispersion, requiring individual calibration. This has become a technical bottleneck restricting their cost and mass application.

[0004] The mechanical sensitivity of a mode-separated MEMS gyroscope is inversely proportional to the frequency difference between its driving and sensing modes. Reducing this frequency difference can effectively improve the mechanical sensitivity, suppress interface circuit noise, increase the signal-to-noise ratio (SNR) and angle random walk (ARW), and enhance the noise performance of the MEMS gyroscope. For typical mode-separated MEMS gyroscopes, when the frequency difference is within the small frequency range of 50–100 Hz, the mechanical sensitivity can reach above 0.1 fF / dps, suppressing interface circuit noise to below the mechanical thermal noise level, achieving zero-bias instability of ~0.1° / h, and initially possessing north-finding capability. However, sub-μm etching mismatch errors and stress bonding errors in the MEMS batch manufacturing process can lead to a frequency difference of ±100 Hz between individual MEMS gyroscopes within the same batch, resulting in a mechanical sensitivity difference of more than three times, causing insufficient MEMS gyroscope yield. To improve the yield of wafers, it is necessary to perform frequency difference tuning on the batch-produced MEMS gyroscopes so that the frequency difference of the MEMS gyroscopes all fall within the range of 50 to 100 Hz.

[0005] Current methods for frequency difference tuning leverage the electrostatic negative stiffness of MEMS gyroscopes. To maintain frequency difference consistency, the resonant frequency of the sensing mass is altered by changing the DC voltage on it, thus tuning the frequency difference. However, in mode separation mode, the sensing frequency of a MEMS gyroscope cannot be directly obtained. It requires manually changing the electrode voltage of each moving mass individually, performing scaling measurements, and conducting power spectrum analysis of the noise to indirectly deduce the actual frequency difference and determine the required tuning voltage for each gyroscope. This manual testing is cumbersome and increases costs. Automatic tuning, on the other hand, can achieve lower costs. Therefore, researching automatic frequency difference tuning methods for MEMS gyroscopes is significant for reducing calibration testing and labor costs.

[0006] Current research on automatic frequency difference tuning for MEMS gyroscopes mainly focuses on mode-matched MEMS gyroscopes. This involves using modal frequency self-matching technology to ensure the gyroscope's driving natural frequency and detection natural frequency are equal and maintained, thereby improving the gyroscope's mechanical sensitivity. There are no inventions regarding automatic frequency difference tuning for mode-separated gyroscopes. Chinese patent CN115452001A discloses a frequency difference tuning system for mode-matched gyroscopes. This system applies a bilateral frequency-doubled excitation signal to the detection mode excitation electrode of the MEMS gyroscope. The detection electrode senses the output signal of the detection mode excitation electrode and the angular velocity input signal, jointly calculating the modal frequency difference signal. Whether the modal frequency difference signal equals zero is used to determine if the MEMS gyroscope has reached a mode-matched state. However, this type of method is only applicable to mode-matched MEMS gyroscopes. When the MEMS gyroscope is in a mode-separated state, the symmetry of the bilateral excitation signal output sensing no longer exists, and the frequency difference value of the MEMS gyroscope cannot be determined from the modal frequency difference signal.

[0007] Existing frequency offset tuning primarily aims to achieve mode matching, which leads to a sharp decrease in the operating bandwidth of MEMS gyroscopes, making them susceptible to external interference and unable to meet the requirements for long-term operation in complex environments. Therefore, it is necessary to automatically control the frequency offset of MEMS gyroscopes within a target range, ensuring both high sensitivity and a certain operating bandwidth. Automatic tuning can effectively reduce calibration testing and manpower costs. Summary of the Invention

[0008] The purpose of this invention is to provide an automatic frequency difference tuning system for a mode-separated MEMS gyroscope. Based on the electrostatic negative stiffness effect of the MEMS gyroscope and the amplitude-frequency response of the sinusoidal excitation signal, the frequency difference of the MEMS gyroscope is automatically tuned by electrostatic tuning, so that the frequency difference of MEMS gyroscopes with relatively discrete frequency differences in the same batch is automatically tuned to a set target.

[0009] The technical solution to achieve the purpose of this invention is as follows:

[0010] A mode-separation MEMS gyroscope frequency difference automatic tuning system includes:

[0011] The excitation signal generation module is used to convert the driving detection current generated on the driving detection electrode into a driving voltage and apply it to the driving electrode of the MEMS gyroscope. It extracts and stores the driving frequency and generates a sinusoidal excitation signal with the same frequency as the driving frequency. The timing control unit controls the driving voltage to act on the force feedback electrode or the positive electrode of the detection electrode, so that the detection resonator in the MEMS gyroscope undergoes forced vibration.

[0012] The frequency difference self-tuning module characterizes the forced motion amplitude of the resonator by the amplitude-frequency response of the sinusoidal excitation signal generated by the excitation signal generation module. After subtracting from the adjustable reference value, it generates a tuning feedback voltage using automatic gain control, which is fed back to the moving mass block electrode. The frequency difference is then tuned using the electrostatic negative stiffness effect.

[0013] The tuning voltage generation module is used to convert the tuning feedback voltage after the frequency difference self-tuning module is stabilized into a digital signal and store it. The timing control unit controls the generation of a fixed analog feedback voltage to act on the moving mass block electrode and disconnect the frequency difference self-tuning module to complete the automatic frequency difference tuning.

[0014] The significant advantages of this invention compared to existing technologies are:

[0015] (1) Compared with the traditional manual frequency difference tuning method, the MEMS gyroscope frequency difference automatic tuning system of the present invention can automatically control the frequency difference of the MEMS gyroscope to the set target, which greatly saves the time cost of manual testing, shortens the testing time, and makes the testing process convenient and fast.

[0016] (2) The present invention adds a delay switch to control the driving voltage. After the driving frequency of the MEMS gyroscope is extracted, the connection between the driving voltage and the driving electrode is disconnected. This can effectively prevent the quadrature signal output of the MEMS gyroscope from interfering with the sinusoidal excitation signal output, making subsequent processing of the detection voltage output more convenient and more accurate in controlling the frequency difference within the set value.

[0017] (3) Compared with the frequency of traditional mode-matched MEMS gyroscopes, the mode-separated MEMS gyroscope frequency difference automatic tuning system of the present invention can adjust the frequency difference of the MEMS gyroscope to any value within the set range, which can improve the working bandwidth of the MEMS gyroscope and reduce the impact of external interference on the output of the MEMS gyroscope. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the MEMS gyroscope used in this invention;

[0019] Figure 2 This is a schematic diagram of the overall process of the present invention;

[0020] Figure 3 This is a schematic diagram of the disassembled MEMS gyroscope detection electrode of the present invention;

[0021] Figure 4 This is a flowchart of the excitation signal generation module of the present invention;

[0022] Figure 5 This is a schematic diagram of the frequency difference self-tuning module of the present invention;

[0023] Figure 6 This is a schematic diagram of the tuning voltage generation module of the present invention;

[0024] Figure 7 This is a timing flowchart of the timing control unit of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] Figure 1 This is a schematic diagram of the MEMS gyroscope structure used in this embodiment, consisting of two symmetrical parts. The drive detection electrode E1, detection electrode E2, force feedback electrode E3, drive electrode E4, and moving mass electrode E5 are distributed as follows: Figure 1 As shown.

[0027] Figure 2 This is a schematic diagram of the overall process of a mode-separated MEMS gyroscope frequency difference automatic tuning system, which consists of an excitation signal generation module 1, a frequency difference self-tuning module 2, a tuning voltage generation module 3, and a timing control unit 4.

[0028] The excitation signal generation module 1 converts the drive detection current generated on the drive detection electrode E1 into a drive voltage and applies it to the MEMS gyroscope drive electrode E4. It can also extract and store the drive detection current frequency (i.e., the drive frequency) and generate a sinusoidal excitation signal with the same frequency as the drive frequency, controlled by the timing control unit 4. Figure 2 The middle triangle indicates that the enable control is applied to the force feedback electrode E3 or, as shown, Figure 3 The positive electrode E6 shown causes the detection resonator in the MEMS gyroscope to undergo forced vibration.

[0029] The frequency difference self-tuning module 2 characterizes the forced motion amplitude of the detection resonator by the amplitude-frequency response of the sinusoidal excitation signal generated by the excitation signal generation module 1. After subtracting from the adjustable reference value, it generates a tuning feedback voltage Vp using automatic gain control, which is fed back to the moving mass block electrode E5. Frequency difference tuning is performed using the electrostatic negative stiffness effect.

[0030] The tuning voltage generating module 3 converts the tuning feedback voltage Vp stabilized by the frequency difference self-tuning module 2 into a digital signal and stores it (since the frequency difference self-tuning module 2 needs to be disconnected later, the digital signal needs to be stored). The timing control unit 4 controls the generation of a fixed analog feedback voltage Vpm to act on the active mass block electrode E5 and disconnects the frequency difference self-tuning module 2 to complete the automatic frequency difference tuning.

[0031] Figure 4 This is a flowchart of the excitation signal generation module 1. As shown in the figure, the sinusoidal excitation signal generation module includes a drive detection interface circuit 5, a drive closed-loop circuit 6, an ADC analog-to-digital converter 7A, a frequency extraction circuit 8, a register A9A, a signal generation circuit 10, and delay switches A, B, and C.

[0032] The drive detection interface circuit 5 converts the drive detection current Ids generated by the drive detection electrode E1 into a drive detection voltage Vds. The drive detection interface circuit 5 adopts a transimpedance interface circuit.

[0033] The drive closed-loop circuit 6 converts the drive detection voltage signal Vds into a stable drive voltage Vd, which is then applied to the drive electrode E4 via delay switch A or delay switch C. The delay switches A and C are controlled by the timing control unit 4 to switch on and off.

[0034] The ADC analog-to-digital converter 7A converts the analog drive detection voltage signal into a digital drive detection voltage signal.

[0035] The frequency extraction circuit 8 extracts the frequency of the digital drive detection voltage signal, i.e. the drive frequency of the MEMS gyroscope, and stores it in register A9A.

[0036] The signal generating circuit 10 generates an amplitude of V based on the frequency stored in register A9A. i The sinusoidal excitation signal with a frequency equal to the driving frequency is applied to the force feedback electrode E3 or the positive detection electrode E6 of the MEMS gyroscope after passing through the delay switch B.

[0037] Figure 5 This is a flowchart of the frequency difference self-tuning module 2. It includes a detection interface circuit 11, a low-pass filter circuit 12, a PI control circuit 13, a limiting circuit 14, a multiplier 101, and an error comparator 102.

[0038] When a sinusoidal excitation signal is applied to the force feedback electrode E3 or the positive electrode E6 of the detection electrode, the detection resonator undergoes forced vibration, generating a detection current Is on the detection electrode E2. The detection interface circuit 11 converts the detection current into a detection voltage Vs. According to the excitation signal response of the mode-separated MEMS gyroscope, Vs is as shown in equation (1):

[0039] Vs = V E sin(ω d t) (1)

[0040] Where V E ω is a constant related to the structural parameters of the detection resonator and the circuit parameters of the detection interface circuit 11. d The driving angular frequency is t, and time is t. The detection interface circuit 11 adopts a transimpedance interface circuit.

[0041] The multiplier 101 multiplies and demodulates the detected voltage signal and the sinusoidal excitation signal, and outputs the result as shown in equation (2):

[0042]

[0043] Where Vo is the demodulated output signal, V i It is the amplitude of the sinusoidal excitation signal generated by the signal generation circuit 10.

[0044] Furthermore, the output Vo after multiplication and demodulation is filtered out by the low-pass filter circuit 12 to remove the second harmonic signal, while retaining the DC signal.

[0045] The error comparator is used to compare the DC signal retained by the low-pass filter circuit with the reference voltage VREF through the error comparator 102, and then use the difference between the two signals through the PI control circuit 13 to adjust the DC signal to be equal to the reference voltage VREF, and output the DC voltage Vpi.

[0046] The limiting circuit 14 limits the voltage input to the limiting circuit to the range of ±VL and outputs a tuning feedback voltage Vp. The timing control unit 4 controls the delay switch B to act on the moving mass block electrode E5, thereby stabilizing the frequency difference of the MEMS gyroscope at the set value and completing the frequency difference tuning.

[0047] Figure 6 The flowchart of the tuning voltage generation module 3 is shown, which includes ADC analog-to-digital converter 7B, register B9B, DAC digital-to-analog converter 15, and delay switch C.

[0048] The ADC analog-to-digital converter 7B converts the stabilized tuning feedback voltage Vp of the frequency difference self-tuning module 2 into a digital feedback voltage signal and stores it in register B9B. Then, it is converted into an analog feedback voltage signal Vpm by the DAC digital-to-analog converter 15. The timing control unit 4 controls the delay switch C to apply the analog feedback voltage signal Vpm to the active mass block electrode E5. At the same time, the timing control unit 4 controls the delay switch B to open, so that the frequency difference self-tuning module 2 is disconnected.

[0049] Figure 7This is the timing flowchart for timing control unit 4. It includes the on / off times of delay switches A, B, and C.

[0050] The delay switch A controls whether the driving voltage signal is applied to the driving electrode E4 and whether the register A9A stores data. When the delay switch A9A is closed, the driving voltage signal is applied to the driving electrode E4, causing the driving resonator to vibrate under forced conditions, and the register A9A stores the frequency output by the frequency extraction circuit 8. When the delay switch A is open, the driving resonator stops vibrating and the data stored in the register A9A is no longer updated.

[0051] The delay switch B controls whether the sinusoidal excitation signal is applied to the force feedback electrode E3 or the positive electrode E6 of the detection electrode, whether the register B9B stores data, and whether the tuning feedback voltage Vp is applied to the moving mass electrode E5. When the delay switch B is closed, the sinusoidal excitation signal is applied to the force feedback electrode or the positive electrode E6 of the detection electrode, causing the detection resonator to vibrate under forced conditions. The register B9B stores the tuning feedback voltage Vp generated by the frequency difference self-tuning module 2 and causes Vp to be applied to the moving mass electrode E5 for frequency difference tuning. When the delay switch B is open, the detection resonator no longer vibrates, the data stored in the register B9B is no longer updated, and the tuning feedback voltage Vp is disconnected from the moving mass electrode E5.

[0052] The delay switch C controls whether the drive voltage signal is applied to the drive electrode E4 and whether the analog feedback voltage Vpm is applied to the moving mass electrode E5. When the delay switch C is closed, the drive voltage is applied to the drive electrode E4 again, causing the drive resonator of the MEMS gyroscope to vibrate under forced vibration, and causing the analog feedback voltage Vpm to act on the moving mass electrode E5. When the delay switch C is open, the drive resonator stops vibrating and the analog feedback voltage Vpm is disconnected from the moving mass electrode E5.

[0053] like Figure 7 As shown, the timing control unit controls the delay switch in the following specific timing sequence: the power-on time is denoted as T0, and T4>T3>T2>T1>T0.

[0054] During the time period T0 to T1, delay switch A is closed, while delay switches B and C are both open.

[0055] During the time period T1 to T2, delay switch A, delay switch B, and delay switch C are all disconnected;

[0056] During the time period T2 to T3, delay switch B is closed, while delay switches A and C are both open.

[0057] During the time period T3 to T4, delay switch A, delay switch B, and delay switch C are all turned off;

[0058] After time T4, delay switch C closes, and delay switches A and B open.

[0059] By controlling the timing of delay switches A, B, and C through the timing control unit 4, the excitation signal generation module 1, the frequency difference self-tuning module 2, and the tuning voltage generation module 3 work in coordination to complete the automatic tuning of the frequency difference of the mode-separated MEMS gyroscope. This allows the frequency difference of different MEMS gyroscopes in batch production to be controlled at a uniform set value, thus overcoming the frequency difference dispersion of MEMS gyroscopes in batch production in a quick and easy way.

[0060] The above description is only one embodiment of the present invention and is not intended to limit the design of this case. All equivalent changes made based on the key design of this case shall fall within the protection scope of this case.

Claims

1. A mode-separated MEMS gyroscope frequency difference automatic tuning system, capable of adjusting the frequency difference of a MEMS gyroscope to any value within a set range, characterized in that, include: The excitation signal generation module is used to convert the driving detection current generated on the driving detection electrode into a driving voltage and apply it to the driving electrode of the MEMS gyroscope. It extracts and stores the driving frequency and generates a sinusoidal excitation signal with the same frequency as the driving frequency. The timing control unit controls the driving voltage to act on the force feedback electrode or the positive electrode of the detection electrode, so that the detection resonator in the MEMS gyroscope undergoes forced vibration. The frequency difference self-tuning module characterizes the forced motion amplitude of the resonator by the amplitude-frequency response of the sinusoidal excitation signal generated by the excitation signal generation module. After subtracting from the adjustable reference value, it generates a tuning feedback voltage using automatic gain control, which is fed back to the moving mass block electrode. The frequency difference is then tuned using the electrostatic negative stiffness effect. The tuning voltage generation module is used to convert the tuning feedback voltage after the frequency difference self-tuning module is stabilized into a digital signal and store it. The timing control unit controls the generation of a fixed analog feedback voltage to act on the moving mass block electrode and disconnect the frequency difference self-tuning module to complete the automatic frequency difference tuning. The excitation signal generation module includes: The drive detection interface circuit is used to convert the drive detection current generated by the drive detection electrode into a drive detection voltage. The drive closed-loop circuit is used to convert the drive detection voltage signal into a stable drive voltage, which is then applied to the drive electrode via delay switch A or delay switch C. The timing control unit controls the on / off state of delay switches A and C. An ADC (Analog-to-Digital Converter) is used to convert analog drive detection voltage signals into digital drive detection voltage signals. The frequency extraction circuit is used to extract the frequency of the digital drive detection voltage signal and store it in register A; The signal generation circuit is used to generate a sinusoidal excitation signal based on the frequency stored in register A, which is then applied to the force feedback electrode or the positive electrode of the detection electrode of the MEMS gyroscope via the delay switch B. The timing control unit performs the following specific timing control on the delay switch: During the time period T0~T1, delay switch A is closed, and delay switches B and C are both open; During the time period T1~T2, delay switch A, delay switch B, and delay switch C are all turned off; During the time period T2 to T3, delay switch B is closed, while delay switches A and C are both open. During the time period T3 to T4, delay switch A, delay switch B, and delay switch C are all turned off; After time T4, delay switch C closes, and delay switches A and B open. Where T0 is the power-on time, and T4>T3>T2>T1>T0.

2. The mode-separated MEMS gyroscope frequency difference automatic tuning system according to claim 1, characterized in that, The frequency difference self-tuning module includes: The detection interface circuit is used to convert the detection current into a detection voltage. The multiplier is used to multiply and demodulate the detected voltage signal and the sinusoidal excitation signal before outputting the result. The low-pass filter circuit is used to filter out the second harmonic signal from the output after multiplication and demodulation, and retain the DC signal; An error comparator is used to compare the DC signal retained by the low-pass filter circuit with the reference voltage, and then pass the difference between the two signals through a PI control circuit. A PI control circuit is used to adjust the DC signal to equal the reference voltage and output a DC voltage. The limiting circuit is used to limit the voltage input to the limiting circuit within a set range and output a tuning feedback voltage. The timing control unit controls the delay switch B to act on the moving mass electrode, thereby stabilizing the frequency difference of the MEMS gyroscope at the set value and completing the frequency difference tuning.

3. The mode-separated MEMS gyroscope frequency difference automatic tuning system according to claim 1, characterized in that, The tuning voltage generating module includes: The ADC analog-to-digital converter is used to convert the tuned feedback voltage after the frequency difference self-tuning module is stabilized into a digital feedback voltage signal and store it in register B. A DAC (Digital-to-Analog Converter) is used to convert digital feedback voltage signals into analog feedback voltage signals. The timing control unit controls the delay switch C to apply the analog feedback voltage signal to the active mass block electrode, while the timing control unit controls the delay switch B to open, thus disconnecting the frequency difference self-tuning module.

4. The mode-separated MEMS gyroscope frequency difference automatic tuning system according to claim 3, characterized in that, The timing control unit controls the on / off times of delay switches A, B, and C, including: When delay switch A is closed, the driving voltage signal is applied to the driving electrode, causing the driving resonator to vibrate under forced conditions, and register A stores the frequency output by the frequency extraction circuit; when delay switch A is open, the driving resonator stops vibrating and the data stored in register A is no longer updated. When the delay switch B is closed, the sinusoidal excitation signal acts on the force feedback electrode or the positive terminal of the detection electrode, causing the detection resonator to vibrate under forced conditions. Register B stores the tuning feedback voltage generated by the frequency difference self-tuning module and applies the tuning feedback voltage to the moving mass electrode for frequency difference tuning. When the delay switch B is open, the detection resonator stops vibrating, the data stored in register B is no longer updated, and the tuning feedback voltage is disconnected from the moving mass electrode. When the delay switch C is closed, the driving voltage is applied to the driving electrode again, causing the driving resonator of the MEMS gyroscope to vibrate under forced conditions, and causing the analog feedback voltage to act on the moving mass electrode; when the delay switch C is open, the driving resonator stops vibrating and the analog feedback voltage is disconnected from the moving mass electrode.

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