Quartz beam accelerometer noise suppression circuit

Abstract

This invention discloses a noise suppression circuit for a quartz vibrating beam accelerometer. It employs a chopper-AGC closed-loop oscillation circuit to achieve stable driving of the quartz vibrating beam. The circuit includes a chopper amplifier, an AGC automatic control gain module, and a follower amplifier. The electrical signal generated during beam vibration is amplified by the chopper amplifier and low-frequency noise is filtered out, resulting in a noise-reduced signal. This noise-reduced signal is then stabilized by the AGC automatic control gain module and amplified and phase-compensated by the follower amplifier before being fed back to the quartz vibrating beam accelerometer head, forming a stable closed-loop drive. This invention uses chopper modulation technology to modulate the noise signal and input signal to different frequency bands, and uses filtering to separate the noise signal and input signal. This method effectively improves the zero-bias stability and noise performance of the QVBA system.

Description

Technical Field

[0001] The invention relates to closed-loop drive technology for MEMS quartz beam accelerometers, specifically to a noise suppression circuit for quartz beam accelerometers. Background Technology

[0002] The Quartz Vibrating Beam Accelerometer (QVBA) is a resonant accelerometer based on the piezoelectric effect of quartz. When there is no acceleration input, the excitation circuit causes the vibrating beam to operate at its natural frequency, which is related to the structure, cut, and dimensions of the quartz crystal. When acceleration input is present, the mass block, under the influence of force, transforms this into deformation of the vibrating beam, thus changing its vibration frequency. Currently, the Quartz Vibrating Beam Accelerometer has significant demand and applications in military, civilian, and aerospace fields. With future advancements in miniaturization, cost reduction, and high precision, it is poised for a broad market expansion.

[0003] In recent years, with the continuous development of MEMS technology, the structure and performance of accelerometers have been further improved, and noise performance has become an important indicator affecting the accuracy of accelerometers. Circuit noise introduced by factors such as changes in the external environment and power supply stability will directly affect the stability, resolution and other indicators of quartz beam accelerometers. When noise affects the carrier signal, especially when the noise signal is weak, this effect will cause the noise signal to overwhelm the carrier signal and make it impossible to process. At present, the main methods for noise suppression of beam accelerometers are: (1) improving the mechanical thermal noise of QVBA through process structure design; (2) reducing the complexity of the circuit through circuit simplification; (3) filtering out circuit noise through various filtering methods and some harmonic suppression circuit designs; (4) reducing the driving voltage through amplitude modulation circuit design; (5) solving the interference of low-frequency noise that traditional solutions cannot filter out through noise processing schemes such as chopper modulation technology and sampling technology.

[0004] Currently, three types of closed-loop drive circuits are widely used in driving circuits: those based on CD4069 inverters, those based on AGC (Automatic Gain Control), and those based on phase-locked loops (PLLs). All three are series-type drive circuits. Due to their simplicity, the CD4069 inverter-based closed-loop drive circuit is the most commonly used in laboratories. However, due to the output requirements of the CD4069 inverter, the drive voltage must be higher than 3.3V, and low-frequency noise interference cannot be handled, resulting in poor stability. AGC-based closed-loop drive circuits are widely used in applications with low precision requirements due to their low-voltage drive advantage. However, their structure is relatively complex, introducing additional thermal noise, and they still cannot filter out the impact of low-frequency noise on system frequency stability. PLL-based closed-loop drive circuits have been widely used in recent years due to their simpler circuit principle and better stability. However, they still cannot handle the impact of low-frequency noise on the system, and the matching process between the PLL and the preceding drive circuit introduces other external interference. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a noise suppression circuit for a quartz beam accelerometer, which solves the problem of the unbalanced gain and noise of traditional series-type (closed-loop series oscillation circuit based on CD4069 inverter) quartz beam accelerometers, and improves the zero-bias performance and noise performance of QVBA at the lowest cost.

[0006] Technical Solution: The noise suppression circuit of the quartz vibrating beam accelerometer described in this invention uses a chopper-AGC closed-loop oscillation circuit to achieve stable driving of the quartz vibrating beam. It includes a chopper amplifier, an AGC automatic control gain module, and a follower amplifier. The electrical signal generated when the vibrating beam vibrates is amplified by the chopper amplifier and low-frequency noise is filtered out. The output signal is then denoised. The denoised signal is stabilized by the AGC automatic control gain module and then amplified and phase-compensated by the follower amplifier. Finally, it is fed back to the quartz vibrating beam accelerometer head to form a stable closed-loop drive.

[0007] Optionally, the chopper amplifier includes a modulation circuit, a two-stage operational amplifier, a high-pass filter circuit, a demodulation circuit, and a first low-pass filter circuit. The electrical signal generated when the vibrating beam vibrates is processed by the modulation circuit to modulate the electrical signal to the high-frequency band. The modulated high-frequency signal is amplified by the two-stage operational amplifier and then filtered by the high-pass filter circuit to remove the low-frequency noise of the system. The filtered signal is demodulated back to the oscillation frequency by the demodulation circuit and then passed through the first low-pass filter circuit to achieve noise reduction processing of the entire process.

[0008] Optionally, the modulation and demodulation circuits use the ADG1413 four-channel analog switch chip U12, which controls the on / off state of the analog switches through a chopping signal to modulate the low-frequency input signal to a high frequency. When the chopping signal is greater than 1.5V, the four-channel analog switches are forward-biased and reverse-biased; when the chopping signal is less than 1.5V, the four-channel analog switches are reverse-biased and forward-biased.

[0009] Optionally, the signal modulated in the first half-cycle of the chopping signal is taken as the input signal, and the signal modulated in the second half-cycle of the chopping signal is taken as the inverse signal of the input signal; the demodulated signal is a noisy sine wave signal, which is further filtered by the first low-pass filter to obtain the denoised signal.

[0010] Optionally, the chopping signal is a square wave signal generated by STM32.

[0011] Optionally, the two-stage operational amplifier includes a C / V conversion circuit and an inverting amplifier circuit. The C / V conversion circuit performs preliminary amplification of the modulated high-frequency signal and provides a 180° phase shift; the inverting amplifier circuit performs secondary amplification of the output signal of the C / V conversion circuit and compensates its phase shift by 180° to meet the loop oscillation condition.

[0012] Optionally, the high-pass filter circuit adopts a second-order Butterworth high-pass filter circuit.

[0013] Optionally, the first low-pass filter circuit adopts a second-order Butterworth low-pass filter circuit.

[0014] Optionally, the AGC automatic control gain module includes a variable gain amplifier, a full-wave rectifier circuit, a second low-pass filter circuit, and a PI control circuit. The noise-reduced signal output from the chopper amplifier is input to the variable gain amplifier and the full-wave rectifier circuit, respectively. The output signal of the full-wave rectifier circuit is input to the PI control circuit after passing through the second low-pass filter circuit. The output signal of the PI control circuit and the output signal of the variable gain amplifier are input together to the subsequent amplifier.

[0015] Optionally, the closed-loop oscillation circuit adopts a sinusoidal self-excited oscillation method, so that the quartz vibrating beam accelerometer can achieve stable sinusoidal oscillation under the oscillation circuit.

[0016] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: (1) By adjusting the QVBA measurement circuit under low voltage through the AGC amplitude stabilization circuit, the circuit noise is effectively reduced; (2) By designing the chopper amplifier, the problem of low-frequency noise (1 / f noise) is solved compared with the traditional filter circuit; (3) In terms of noise reduction scheme, the low-frequency noise is filtered more thoroughly and no additional thermal noise is introduced compared with self-zeroing and other noise reduction schemes; (4) Compared with wavelet threshold denoising algorithms and other methods, the hardware denoising method is more effective in reducing the zero bias and noise performance of the QVBA system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the circuit structure of the present invention;

[0018] Figure 2 This is a schematic diagram of the chopper amplifier of the present invention;

[0019] Figure 3 This is a schematic diagram of the modulation circuit of the present invention;

[0020] Figure 4 This is a schematic diagram of the two-stage amplifier circuit of the present invention;

[0021] Figure 5 This is a schematic diagram of the high-pass filter circuit of the present invention;

[0022] Figure 6 This is a schematic diagram of the demodulation circuit of the present invention;

[0023] Figure 7 This is a schematic diagram of the low-pass filter circuit of the present invention;

[0024] Figure 8 This is a schematic diagram of the AGC automatic gain control module of the present invention;

[0025] Figure 9 This is a schematic diagram of the follower amplifier circuit of the present invention;

[0026] Figure 10 This is a zero-bias test diagram for measuring one hour according to the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0028] The noise suppression circuit of the quartz vibrating beam accelerometer of the present invention is based on the chopper-AGC automatic gain control drive circuit. The chopper stabilization technology reduces the problem of low-frequency noise affecting frequency stability due to nonlinear coupling to the oscillation frequency, which is difficult to solve in the three driving methods of the prior art. At the same time, the AGC automatic gain control drive method is used to achieve low-voltage drive and further improve the noise reduction effect.

[0029] Quartz resonant beam accelerometers (QVBAs) are designed based on quartz resonant beams. Due to the requirements for the driving electrode area and measurement accuracy of quartz resonant beams, they have higher dynamic resistance (typically in the megaohm range). Because of the existence of the equivalent dynamic resistance, the driving circuit needs to provide higher gain (greater than the equivalent resistance) and energy during the design process.

[0030] To address the high impedance characteristic of quartz resonant beams, a high-gain driving circuit needs to be designed. This driving circuit typically needs to meet the following two conditions:

[0031] Amplitude conditions: in, To amplify the amplification factor of the network, For the feedback coefficients of the feedback network;

[0032] Phase condition: in, To amplify the phase shift of the network, The phase shift of the feedback network is given by n, which is a constant, and Z is an integer.

[0033] Currently, quartz crystal accelerometer oscillation circuits are divided into two types: series and parallel. Parallel quartz crystal oscillation circuits are further classified into three types based on their grounding method: Pierce, Clapp, and Colpitts circuits. Generally speaking, parallel crystal oscillation circuits are well-developed and are more commonly used in oscillation circuits with frequencies above 10MHz; series crystal oscillation circuits are more often used in low-to-medium frequency oscillation circuits. In terms of frequency, the fundamental frequency of a QVBA is in the tens of kHz range, making a series crystal oscillation circuit more suitable. Regarding circuit stability, due to its resistive nature, it consumes less power and generates relatively less heat, resulting in less temperature drift in the resonant sensor. Therefore, the series oscillation circuit is more stable. The resonant frequency of a parallel oscillation circuit is affected by external conditions such as external capacitors, leading to relatively poor stability. In terms of dynamic impedance, the dynamic resistance of this invention reaches the MΩ level, requiring higher gain from the drive circuit; therefore, a series oscillation circuit is chosen for the subsequent closed-loop drive circuit.

[0034] In this embodiment, a chopper-AGC closed-loop oscillation circuit is used to achieve stable driving of the quartz vibrating beam. The entire noise suppression circuit of the quartz vibrating beam accelerometer is implemented by amplifying a weak signal through a chopper amplifier, stabilizing it through an AGC automatic control gain module, and then amplifying it again through a subsequent amplifier and phase compensation to form a stable closed-loop drive. The noise signal is applied to the closed-loop drive circuit along with the carrier signal. The closed-loop oscillation circuit adopts a sinusoidal self-excited oscillation method, so that the QVBA performs constant amplitude frequency-locked oscillation at its oscillation frequency to achieve stable sinusoidal oscillation. The chopper amplifier uses a C / V conversion circuit and an inverting amplifier circuit as amplifier modules. The C / V conversion circuit initially amplifies the electrical signal generated by the vibration of the vibrating beam and provides a 180° phase shift. The inverting amplifier circuit amplifies the output signal of the C / V conversion circuit a second time and applies a 180° phase shift to it. Phase compensation is provided to meet the loop oscillation conditions; the high gain required by the vibrating beam and the amplitude and phase conditions required for oscillation are provided through the C / V conversion circuit and the inverting amplifier module; the input signal and noise signal are separated by modulation and demodulation in the chopper amplifier module. The modulation circuit modulates the input signal and noise signal to a higher frequency through the chopper signal. After amplification by the amplifier, the low-frequency noise is filtered out by the high-pass filter circuit. The demodulation circuit demodulates the modulated signal back to the original frequency and then filters out the high-frequency noise components through the low-pass filter. The signal after noise reduction by the chopper amplifier is stabilized by the AGC module and then forms a stable closed-loop system with the QVBA meter to improve the stability of the system.

[0035] like Figure 1As shown, the noise suppression circuit for the quartz beam accelerometer designed in this invention suppresses low-frequency noise based on chopper stabilization technology. It includes three parts connected in series: a chopper amplifier, an AGC automatic control gain module, and a follower amplifier. The chopper amplifier is used as the main noise reduction method. The input signal of the chopper amplifier is the electrical signal generated when the quartz beam vibrates. The output filtered signal is stabilized by the AGC automatic control gain module, and then amplified and phase-compensated by the follower amplifier to obtain a stabilized output signal that is fed back to the quartz beam, forming a closed-loop system. The chopper amplifier includes a modulation circuit, two operational amplifiers, a high-pass filter circuit, a demodulation circuit, and a first low-pass filter circuit connected in series. The electrical signal generated when the vibrating beam vibrates is processed by the modulation circuit to modulate the signal to the high-frequency band, then amplified by the amplifier, and then preliminarily processed by the high-pass filter circuit to remove low-frequency noise. After being demodulated back to the oscillation frequency by the demodulation circuit, the signal is then filtered by the low-pass filter to achieve noise reduction throughout the process. The two operational amplifiers include a C / V conversion circuit and an inverting amplifier circuit connected in series. The AGC automatic gain control module includes a full-wave rectifier, a second low-pass filter circuit, a PI control circuit, and a variable gain amplifier. The full-wave rectifier, low-pass filter circuit, and PI control circuit are connected in series. The inputs of the full-wave rectifier and the variable gain amplifier are connected to the output of the first low-pass filter circuit. The outputs of the PI control circuit and the variable gain amplifier are connected to the inputs of the subsequent amplifiers. The output of the subsequent amplifiers is connected to the QVBA meter, forming a stable closed-loop system. The noise suppression circuit of the entire quartz beam accelerometer is achieved by amplifying the weak signal (i.e. the electrical signal generated when the quartz beam vibrates) through a chopper amplifier, stabilizing the amplitude through an AGC automatic control gain module, and then amplifying it again by a subsequent amplifier and performing phase compensation to form a stable closed-loop drive.

[0036] This circuit meets the high gain requirements of QVBA through a two-stage amplifier circuit, an AGC module, and a follow-up amplifier.

[0037] The specific implementation is as follows:

[0038] like Figure 2 As shown, in this embodiment, the modulation and demodulation circuits are represented by multipliers. The chopper signal M1(t) is a square wave signal of 3V or higher provided by the STM32, with a frequency of approximately 356kHz; the frequency of the square wave can be adjusted according to actual needs. The modulation circuit multiplies the input signal Vin and the chopper signal M1(t) to modulate the input signal to a high frequency band. After being amplified by two stages of amplifier A, it is input to a high-pass filter circuit. The signal after filtering out low-frequency noise signals is then multiplied with the chopper signal in the demodulation circuit to demodulate the filtered signal back to its original frequency, outputting the denoised signal V. out .

[0039] like Figure 3As shown, the modulation circuit includes an ADG1413 four-channel analog switch chip U12, a 35th resistor R35, a 29th capacitor C29, and a 30th capacitor C30. The ADG1413 four-channel analog switch chip consists of two pairs of complementary MOSFETs, including a set of four-channel analog switches. Pins 2 (D1) and 3 (S1), 6 (S4) and 7 (D4), 10 (D3) and 11 (S3), and 14 (S2) and 15 (D2) represent four sets of analog switches. D1 and S1 are the two ends of the first analog switch, D2 and S2 are the two ends of the second analog switch, D3 and S3 are the two ends of the third analog switch, and D4 and S4 are the two ends of the fourth analog switch. Pins 1 (IN1), 8 (IN4), 9 (IN3), and 16 (IN2) are the signal control terminals for the four sets of analog switches, respectively. IN1 is the signal control terminal for the first analog switch, IN2 for the second, IN3 for the third, and IN4 for the fourth. Pin 4 (VSS) is connected to the negative power input, pin 5 (GND) is connected to digital ground, and pin 13 (VDD) is connected to the positive power input. When the chopper signal M1(t) is greater than 1.5V, the four sets of analog switches conduct in the forward direction and are disconnected in the reverse direction; when the chopper signal M1(t) is less than 1.5V, the four sets of analog switches conduct in the reverse direction and are disconnected in the forward direction. Capacitor C (29th capacitor) 29 and the thirtieth capacitor C 30 The resistor is 100nF and its function is to stabilize the power supply output; the thirty-fifth resistor R 35 The resistor is zero ohm, used to facilitate debugging of subsequent circuit connections. Signal modulation is achieved by controlling the on / off state of the analog switch using the chopper signal M1(t), thus modulating the low-frequency input signal to a high frequency. The input signal is modulated to a higher frequency range by the chopper signal; in practice, the input signal and the chopper signal M1(t) are multiplied. The output waveform, within one cycle, is the input signal modulated in the first half-cycle and the inverse signal modulated in the second half-cycle.

[0040] like Figure 4As shown, due to the high impedance of the QVBA in this invention, the selection of the amplifier is particularly crucial. Traditional single-stage amplifiers cannot meet the oscillation conditions due to insufficient gain and phase conditions. Therefore, this invention employs a two-stage amplifier. The first stage of the chopper two-stage amplifier uses a C / V conversion circuit to provide partial gain while adjusting the first resistor R1 and first capacitor C1 of the first stage with the dynamic resistance and dynamic capacitance of the quartz resonator to achieve a 180° phase difference between the input and output. The second stage uses an inverting amplifier circuit to amplify the signal and provide a 180° phase shift. The C / V conversion circuit includes a first amplifier A1, a first resistor R1, a first capacitor C1, and a third resistor R3. The inverting amplifier circuit includes a second amplifier A2, a first resistor R2, and a first capacitor C2. The input current signal I... s The first amplifier A1 is connected to its inverting input terminal. A first resistor R1 and a first capacitor C1 are connected in parallel, with one end connected to the inverting input terminal of the first amplifier A1 and the other end connected to the output terminal of the first amplifier A1. A third resistor R3 is connected with one end to the output terminal of the first amplifier A1 and the other end connected to the inverting input terminal of the second amplifier A2. A first resistor R2 and a first capacitor C2 are connected in parallel, with one end connected to the inverting input terminal of the second amplifier A2 and the other end connected to the output terminal of the second amplifier A2. The second amplifier A2 outputs a voltage signal V. o The non-inverting input terminals of both the first amplifier A1 and the second amplifier A2 are connected to GND. The two operational amplifier stages (i.e., the first amplifier A1 and the second amplifier A2) are selected using the AD8065 chip. The AD8065 is a high-speed, low-noise FET input amplifier. With a bandwidth of 145MHz and a low supply current of 0.6mA, this chip ensures a balance between gain, bandwidth, and phase, making it a suitable choice for interface circuit design. The modulated signal, after amplification, generates significant noise and interference.

[0041] The chopper amplifier employs a C / V conversion circuit and an inverting amplifier circuit as its amplifier modules. The C / V conversion circuit initially amplifies the electrical signal generated by the vibrating beam and provides a 180° phase shift. The inverting amplifier circuit amplifies the output signal from the C / V conversion circuit a second time and compensates for its phase shift by 180° to meet the loop oscillation conditions. This invention uses an AD8065 operational amplifier directly connected to the two ends of the feedback capacitor and feedback resistor.

[0042] like Figure 5As shown, the high-pass filter circuit is mainly used to separate the high-frequency modulated input signal from low-frequency noise. This invention uses a second-order Butterworth high-pass filter circuit. The input signal has already been modulated to a high frequency band. The high-pass filter circuit can separate the input signal from the DC bias voltage and low-frequency noise introduced by the two-stage amplifier circuit, thereby achieving the purpose of isolating low-frequency noise and amplifying the low-frequency input signal. Since the cutoff frequency of low-frequency noise is very low, much lower than the chopping frequency, in order to isolate low-frequency noise and transmit the signal while compensating for the signal attenuation caused by the high-pass filter circuit, the -3dB cutoff frequency is set to 200Hz, and the circuit gain is 1.1 times. This invention uses a second-order Butterworth high-pass filter circuit, including chip U11. The inverting input terminal -IN of U11 is connected to GND via resistor R32 (32nd resistor) and to the output terminal VOUT via resistor R33 (33rd resistor). The non-inverting input terminal +IN is connected to GND via resistor R34 (34th resistor) and to one end of resistor R31 (35th capacitor) and one end of capacitor C26 (26th capacitor) via capacitor C25 (25th capacitor). The other end of resistor R31 is connected to the output terminal VOUT, and the other end of capacitor C26 is connected to resistor R42 (42nd resistor). The negative power supply voltage V- is connected to power supply VEE and one end of capacitor C27 (27th capacitor). The other end of capacitor C27 is connected to GND. The positive power supply voltage V+ is connected to power supply VDD and one end of capacitor C28 (28th capacitor). The other end of capacitor C28 is connected to GND. In the figure, R... 31 R 34 C 25 and C 26 Used to adjust the cutoff frequency of the high-pass filter circuit; R 32 R 33 Used to adjust the gain of the high-pass filter circuit; C 27 and C 28 It is 100nF, used to stabilize the power output and reduce power ripple interference.

[0043] like Figure 6 As shown, the demodulation circuit mainly demodulates the high-frequency input signal back to the base frequency. The demodulation principle is similar to that of modulation, implemented through analog switches. The demodulation circuit includes an ADG1413 four-channel analog switch chip U13. The pins of U13 are the same as those of U12 in the figure, and will not be described again here. Among them, the 37th resistor R... 37 The thirty-eighth resistor R 38 And the thirty-third capacitor C 33 This low-pass passive filter structure serves as a preliminary filter. In the diagram, the thirty-sixth resistor, R... 36 A zero-ohm resistor is used to test circuit performance before and after adjustments; the thirty-second capacitor C 32 and the thirty-third capacitor C 33The voltage is 100nF, used to stabilize the power output and reduce power supply ripple interference. The demodulated signal is a sinusoidal signal with noise, requiring further filtering.

[0044] like Figure 7 As shown, the low-pass filter circuit uses a second-order Butterworth low-pass filter circuit, mainly to process the high-order harmonics and high-frequency noise in the demodulated signal. Since the fundamental frequency of QVBA is approximately 62kHz, and the frequency of the modulated signal is in the hundreds of kHz range, the cutoff frequency of the low-pass filter is set to 100kHz. The low-pass filter circuit includes chip U10. The inverting input terminal -IN of U10 is connected to GND via resistor 27, and to the output terminal VOUT via resistor 30. The non-inverting input terminal +IN is connected to GND via resistor 21, resistor C21, resistor R28 via resistor 29, and to the output terminal VOUT via capacitor C22. The negative power supply voltage V- is connected to power supply VEE via capacitor 24, and to GND via capacitor C24. The positive power supply voltage V+ is connected to power supply VDD via capacitor C24, and to GND via capacitor C24. In the figure, R... 28 R 29 C 21 and C 22 Used to adjust the cutoff frequency of the high-pass filter circuit; C 23 and C 24 It is 100nF, used to stabilize the power output and reduce power supply ripple interference. R 27 R 30 It is used to adjust the gain of the high-pass filter circuit. After passing through the second-order Butterworth low-pass filter circuit, a standard sine wave signal is obtained.

[0045] The output signal provided by the chopper amplifier is stabilized by the AGC (Automatic Gain Control) module. When the driving frequency and oscillation frequency of the resonator are close, the output voltage amplitude of the AGC module is at its maximum and the same as the amplitude at the resonant frequency. At this point, the circuit achieves amplitude stabilization, allowing the resonator to operate at its resonant frequency. The AGC module uses negative feedback to stabilize the QVBA (Variable Gain Array) output voltage. In this system, an amplitude detection circuit detects the amplitude of the QVBA output signal, and the detected voltage and reference voltage are used as the gain control voltage for the variable gain amplifier. Negative feedback stabilizes the output voltage amplitude of the QVBA. Unlike traditional solutions, this invention uses the AGC module to achieve stable oscillation of the QVBA at low driving voltages. Furthermore, the subsequent amplifier provides a certain gain while compensating for the 90° phase shift generated by the AGC module, alleviating the need for the chopper amplifier to provide the primary gain requirement.

[0046] like Figure 8As shown, the variable gain amplifier U1 in the AGC automatic control gain module uses a VCA810. The inverting input terminal -in of U1 is connected to the first resistor R41, and the non-inverting input terminal +in is connected to GND. The negative power supply voltage -VS is connected to power supply VEE on one side and to GND via the first capacitor C41 on the other. The positive power supply voltage +VS is connected to power supply VDD on one side and to GND via the third capacitor C42 on the other. The output terminal VOUT is connected to the positive input terminal of operational amplifier OPA690 via the fifth resistor R5. The negative input terminal of operational amplifier OPA690 is connected to the output terminal of operational amplifier on one side via the fifteenth capacitor C15, and on the other side via the thirteenth resistor R13, one side via the ninth capacitor C9 to GND. The other side is split into two paths: one via the sixth resistor R6 to power supply VDD, and the other via the twelfth resistor R1. Pin 2 and the sixteenth resistor R16 are connected to GND; the amplifier output is divided into five paths after passing through diode D1 and the eleventh resistor R11. One path is connected to GND via the thirteenth capacitor C13, another via the twelfth capacitor C12, another via the fifteenth resistor R15, and yet another via the fourteenth resistor R14 to the power supply VEE. The fourth path is connected to the gain control terminal GainControlVC of U1; pin 2 of the operational amplifier is the negative power supply voltage terminal. One path is connected to the negative power supply voltage VEE, and the other is connected to GND through the sixth capacitor C6. Pin 5 is the amplifier selection terminal, connected to the positive power supply voltage VDD to ensure normal operation of the amplifier. Pin 6 is the positive power supply voltage terminal, directly connected to the positive power supply voltage VDD. One path is connected to the positive power supply voltage VDD, and the other is connected to GND through the fourteenth capacitor C14.

[0047] The VCA810 variable gain amplifier is the core component of the AGC automatic control gain module. Its gain control is achieved by voltage divider resistors R6 and R7. 12 and R 16 The system consists of a reference signal that is divided and applied to the inverting input of an operational amplifier. After amplification, the amplifier's output signal is applied to the gain control terminal of a variable gain amplifier, and after amplitude adjustment, the system's output signal is obtained. In the diagram, diode D1, operational amplifier OPA690, and their peripheral circuitry constitute a peak detector circuit and a low-pass filter circuit. VCA810 is the variable gain amplifier. The entire process uses voltage divider resistors to adjust the system gain, achieving a relatively stable output voltage. C1, C3, C9, and C... 14 The voltage is 100nF, used to stabilize the power output and reduce power ripple interference. After passing through the AGC automatic control gain module, a stable sinusoidal signal is obtained.

[0048] like Figure 9As shown, the follower amplifier is used to alleviate the gain provided by the variable gain amplifier VGA in the AGC automatic control gain module. Here, the follower amplifier further amplifies the output voltage signal from VGA and effectively solves the problem of the large equivalent impedance of the QVBA itself, which makes it difficult for the drive circuit design to start oscillation. The output voltage signal obtained from the follower amplifier is fed back to the QVBA, realizing the design of the QVBA closed-loop drive circuit. The follower amplifier includes chip U2. The non-inverting input terminal +IN of U2 is connected to GND. The inverting input terminal -IN is connected to the output terminal VOUT through the fourth resistor R4, and the other is connected to the seventh capacitor C7 through the eighth resistor R8. The positive power supply voltage terminal V+ is connected to the power supply VDD through the eighth capacitor C8, and the other is connected to GND through the tenth capacitor C10. The voltage signal from VGA is amplified by a certain factor through the feedback resistor R4 in the figure. The follower amplifier provides phase compensation and further amplification of the output of the AGC automatic control gain module, resulting in a standard sine wave signal. The subsequent amplifier uses a traditional integrating circuit to provide 90° of phase shift, satisfying the phase condition for system oscillation. In the diagram, amplifier U2 uses the AD8675, which consists of a set of amplifiers. The AD8675 is a high-gain, low-noise operational amplifier. Pins 2 and 3 on the chip are the inverting and non-inverting inputs of the amplifier, respectively, and pin 6 is the output. The gain provided by the amplifier is adjusted by changing the ratio of R4 and R8, and C8 and C... 10 It is 100nF, used to stabilize the power output and reduce power ripple interference.

[0049] This invention employs a closed-loop self-excited oscillation method to achieve stable series resonance in a quartz vibrating beam. Noise signals are mixed in with the input signal and, after amplification by the drive circuit, affect the entire QVBA system. This invention utilizes a chopper-AGC-based closed-loop oscillation circuit to achieve stable drive of the quartz vibrating beam. The entire quartz vibrating beam accelerometer noise suppression circuit is implemented by amplifying a weak signal through a chopper amplifier, stabilizing it through an AGC automatic control gain module, and then amplifying it again with subsequent amplifiers and phase compensation to form a stable closed-loop drive. The circuit primarily filters out noise signals through hardware methods, isolating the input and noise signals. Chopper modulation technology modulates the noise and input signals to different frequency bands, and filtering achieves separation of the noise and input signals. This method effectively improves the zero-bias stability and noise performance of the QVBA system.

[0050] The working principle of the noise suppression circuit for the aforementioned quartz vibrating beam accelerometer is as follows: a chopper-AGC closed-loop oscillation circuit is used to achieve stable driving of the quartz vibrating beam. The electrical signal generated during beam vibration is amplified by a chopper amplifier and low-frequency noise is filtered out, resulting in a noise-reduced signal. This noise-reduced signal is then stabilized by an AGC automatic control gain module, amplified and phase-compensated by a subsequent amplifier, and then fed back to the quartz vibrating beam accelerometer head, forming a stable closed-loop drive. This invention uses chopper modulation technology to modulate the noise signal and input signal to different frequency bands, and uses filtering to separate the noise signal and input signal. This method can effectively improve the zero-bias stability and noise performance of the QVBA system.

[0051] like Figure 10 As shown, the noise suppression circuit of the quartz vibrating beam accelerometer of the present invention, under the action of the chopping signal M1(t), after the system has been preheated and stabilized, obtains its frequency data for one hour through a frequency meter, wherein the sampling time is 1 second. According to the measurement data, the zero-bias stability of the noise suppression circuit of the quartz vibrating beam accelerometer of the present invention is 189.34 μg, and the frequency change within one hour is less than 0.03 Hz.

Claims

1. A noise suppression circuit for a quartz vibrating beam accelerometer, characterized in that, A chopper-AGC closed-loop oscillation circuit is used to achieve stable driving of the quartz vibrating beam. The circuit includes a chopper amplifier, an AGC automatic control gain module, and a follower amplifier. The electrical signal generated when the vibrating beam vibrates is amplified by the chopper amplifier and low-frequency noise is filtered out. The output signal is then denoised. The denoised signal is stabilized by the AGC automatic control gain module and then amplified and phase-compensated by the follower amplifier. Finally, it is fed back to the quartz vibrating beam accelerometer head to form a stable closed-loop drive. The chopper amplifier includes a modulation circuit, a two-stage operational amplifier, a high-pass filter circuit, a demodulation circuit, and a first low-pass filter circuit. The electrical signal generated when the vibrating beam vibrates is processed by the modulation circuit to modulate the electrical signal to the high-frequency band. The modulated high-frequency signal is amplified by the two-stage operational amplifier and then filtered by the high-pass filter circuit to remove the low-frequency noise of the system. The filtered signal is demodulated back to the oscillation frequency by the demodulation circuit and then passed through the first low-pass filter circuit to achieve noise reduction processing of the entire process. The AGC automatic gain control module includes a variable gain amplifier, a full-wave rectifier circuit, a second low-pass filter circuit, and a PI control circuit. The noise-reduced signal output from the chopper amplifier is input to the variable gain amplifier and the full-wave rectifier circuit, respectively. The output signal of the full-wave rectifier circuit is input to the PI control circuit after passing through the second low-pass filter circuit. The output signal of the PI control circuit and the output signal of the variable gain amplifier are input together to the subsequent amplifier.

2. The noise suppression circuit for the quartz vibrating beam accelerometer according to claim 1, characterized in that, The modulation and demodulation circuits use the ADG1413 four-channel analog switch chip U12. The low-frequency input signal is modulated to a high frequency by controlling the on / off state of the analog switches through a chopping signal. When the chopping signal is greater than 1.5V, the four-channel analog switches are forward-biased and reverse-biased; when the chopping signal is less than 1.5V, the four-channel analog switches are reverse-biased and forward-biased.

3. The noise suppression circuit for the quartz vibrating beam accelerometer according to claim 2, characterized in that, The signal modulated in the first half-cycle of the chopping signal is taken as the input signal, and the signal modulated in the second half-cycle of the chopping signal is taken as the inverse signal of the input signal. The demodulated signal is a sinusoidal signal with noise, which is further filtered by the first low-pass filter to obtain the denoised signal.

4. The noise suppression circuit for a quartz vibrating beam accelerometer according to claim 2, characterized in that, The chopping signal is a square wave signal generated by STM32.

5. The noise suppression circuit for a quartz vibrating beam accelerometer according to claim 1, characterized in that, The two-stage operational amplifier includes a C / V conversion circuit and an inverting amplifier circuit. The C / V conversion circuit performs preliminary amplification of the modulated high-frequency signal and provides a 180° phase shift. The inverting amplifier circuit performs secondary amplification of the output signal of the C / V conversion circuit and performs 180° phase compensation on its phase shift to meet the loop oscillation condition.

6. The noise suppression circuit for a quartz vibrating beam accelerometer according to claim 1, characterized in that, The high-pass filter circuit adopts a second-order Butterworth high-pass filter circuit.

7. The noise suppression circuit for a quartz vibrating beam accelerometer according to claim 1, characterized in that, The first low-pass filter circuit adopts a second-order Butterworth low-pass filter circuit.

8. The noise suppression circuit for a quartz vibrating beam accelerometer according to claim 1, characterized in that, The closed-loop oscillation circuit adopts a sinusoidal self-excited oscillation method, which enables the quartz vibrating beam accelerometer to achieve stable sinusoidal oscillation under the oscillation circuit.

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