A voltage-controlled rebalancing quartz resonant accelerometer based on atomic clock frequency locking

Abstract

A voltage-controlled rebalanced quartz resonator accelerometer based on atomic clock frequency locking, comprising an atomic clock, a frequency divider, a frequency discriminator and phase detector, a loop controller, an analog-to-digital converter, a voltage-controlled capacitor, an automatic amplitude controller, and a quartz resonator with an acceleration-sensitive structure; the quartz resonator, the voltage-controlled capacitor, and the automatic amplitude controller are connected in sequence to form an oscillation loop, the frequency discriminator and phase detector, the loop controller, and the oscillation loop are connected in sequence to form a phase-locked loop, the atomic clock signal is connected to the reference input terminal of the frequency discriminator and phase detector through the frequency divider, the input port of the quartz resonator is connected to the feedback input terminal of the frequency discriminator and phase detector, and the analog-to-digital converter quantifies the output voltage control signal of the loop controller of the phase-locked loop as a digital representation of the sensitive acceleration; the present invention achieves a higher acceleration resolution, realizes digital output, and reduces the system integration cost and precision loss.

Description

Technical Field

[0001] The present invention belongs to the technical field of quartz resonant accelerometers, which are inertial sensor devices in microelectromechanical systems (MEMS). Specifically, it relates to a voltage-controlled rebalancing quartz resonant accelerometer based on atomic clock frequency locking. Background Art

[0002] Quartz resonant accelerometers belong to a type of inertial sensor device used to measure low-frequency acceleration signals and are widely used in various inertial navigation and control systems (IMUs). In such applications, quartz resonant accelerometers have the advantages of simple structure, high precision, high stability, and high resolution due to the piezoelectric properties of their materials and the stability of their crystal lattices. They play a dominant role in fields with extremely high requirements for acceleration measurement, such as missile guidance, rocket attitude control, and weapon platform stabilization. Quartz resonant accelerometers based on acceleration modulation frequency output square-wave quasi-digital signals. The frequency of the square-wave analog signal needs to be demodulated to represent the input acceleration. The accuracy loss in the frequency digital conversion process restricts the development of the high-precision acceleration measurement potential of quartz resonant accelerometers. Therefore, it is of great significance to develop quartz resonant accelerometers that meet higher-precision application requirements. At the same time, the simplification and integration of measurement and control systems are also of great importance.

[0003] For a thin-film sensitive accelerometer (Yang X M, Zhang W, Zhao W. Design and Analysis of a Piezoresistive Accelerometer with the Film-Island Structure[C]. Advanced Materials Research. Trans Tech Publications Ltd, 2012.), the acceleration-sensitive thin film deforms under the input of external acceleration. Due to the piezoresistive properties of the material, the strain causes a change in the resistance value of the resistance layer, which is reflected as a change in the output voltage through a bridge structure. An analog-to-digital converter is used to quantize the analog voltage signal into a digital signal that can be directly processed by a computer to achieve digital acceleration measurement. The accelerometer implemented in this way has the advantages of simple structure, high processing accuracy, and good environmental adaptability due to its thin-film structure only, but it is easily affected by thermal stress, and its temperature stability is difficult to meet the requirements of high-precision acceleration measurement.

[0004] The traditional quartz resonant accelerometer (Han C, Li C, Zhao Y, et al. High-Stability Quartz Resonant Accelerometer With Micro-Leverages[J]. Journal of Microelectromechanical Systems, 2021.) converts the inertial force into the deformation of the flexible hinge when sensing the input acceleration, thereby changing the axial force of the quartz double-ended clamped tuning fork. Due to the force-frequency characteristic of the tuning fork structure, the resonant frequency of the quartz tuning fork changes. Usually, the quartz resonator is in the resonant state through the double-inverter transimpedance connection method, and the loop is externally connected with a frequency digital converter to demodulate the acceleration modulation frequency signal and output the digital acceleration representation. Due to the high stability and large elastic modulus of the single-crystal quartz material, the quartz resonant accelerometer has the characteristics of large measurement range, high precision, and excellent stability, and the output quasi-digital signal is not easily interfered during the transmission process, and it is gradually accepted by the field of high-precision acceleration measurement. However, the oscillation loop composed of the transimpedance inverter does not have the function of automatically controlling the amplitude, and there is a contradiction when pursuing high signal-to-noise ratio and low zero-bias instability performance. Moreover, the traditional frequency digital converter counts the rising edge of the reference clock within one period of the signal to be measured based on the reset counter to obtain the frequency to be measured, and it is difficult to suppress the quantization noise and requires a higher reference clock, increasing the burden and cost of the backend digital system. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a voltage-controlled rebalancing quartz resonant accelerometer based on atomic clock frequency locking, which can achieve a higher acceleration resolution, realize digital output, and reduce the system integration cost and precision loss.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A voltage-controlled rebalancing quartz resonant accelerometer based on atomic clock frequency locking, comprising an atomic clock, a frequency divider, a frequency discriminator and phase detector, a loop controller, an analog-to-digital converter, a voltage-controlled varactor, an automatic amplitude controller, and a quartz resonator with an acceleration-sensitive structure; the quartz resonator, the voltage-controlled varactor, and the automatic amplitude controller are connected in sequence to form an oscillation loop, the frequency discriminator and phase detector, the loop controller, and the oscillation loop are connected in sequence to form a phase-locked loop, the atomic clock signal is connected to the reference input terminal of the frequency discriminator and phase detector through the frequency divider, the input port of the quartz resonator is connected to the feedback input port of the frequency discriminator and phase detector, and the analog-to-digital converter quantifies the output voltage signal of the loop controller of the phase-locked loop as the digital representation of the sensitive acceleration.

[0008] When working stably, the oscillation loop composed of the quartz resonator, voltage-controlled varactor and automatic amplitude controller keeps the quartz resonator in a resonant state; the clock signal output by the atomic clock is input to the reference input end of the frequency detector and phase detector through the frequency divider, and after frequency and phase detection with the feedback oscillation loop signal, the control voltage is generated by the loop controller and acts on the voltage-controlled varactor to achieve frequency locking;

[0009] When the quartz resonator's sensitive input acceleration changes, the resonant frequency changes, and the resonant frequency of the oscillation loop changes accordingly; the frequency and phase detector detects the frequency and phase difference between the feedback signal and the reference signal, and adjusts the control voltage of the voltage-controlled varactor through the loop controller to return the oscillation loop operating frequency to the reference frequency; the loop controller outputs a control voltage whose quantized value represents the input acceleration, thereby realizing digital acceleration measurement.

[0010] The automatic amplitude controller is formed by connecting an amplitude detector, a first subtractor, a PID controller, and a mixer in sequence. The input end of the amplitude detector is connected to the driving end of the quartz resonator to form a feedback control system; wherein the amplitude detector is formed by connecting a rectifier and a low-pass filter.

[0011] The rectifier and low-pass filter are implemented in two ways: active and passive devices.

[0012] The voltage-controlled varactor is realized by using a voltage-controlled varactor diode, or by designing a varactor structure on a quartz resonator.

[0013] The frequency and phase detector is formed by connecting two D triggers, a delay device, an AND gate and a second subtractor.

[0014] The frequency detector and phase detector can also be realized by an XOR phase detector and an analog multiplier. The analog multiplier and the XOR phase detector need auxiliary circuits to complete phase capture and synchronization.

[0015] The loop controller is implemented with active or passive devices and can be replaced by a higher order controller.

[0016] The frequency divider is an odd number or fractional number frequency divider.

[0017] The accelerometer circuit is implemented by discrete device analog circuit chips or through integrated circuit technology.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The quartz resonator oscillation loop controls the phase error through an atomic clock, and the automatic amplitude controller controls the resonator vibration amplitude. In the large amplitude working mode of the resonator, the amplitude modulation noise is suppressed to ensure the high resolution and low zero-bias instability characteristics of the design.

[0020] (2) The atomic clock realizes the digital output of frequency while controlling the phase error of the control loop, achieving the integration of the measurement and control system. At the same time, the loop controller can effectively suppress quantization noise, greatly improving the demodulation accuracy of the acceleration modulation frequency signal.

[0021] (3) The circuit of the present invention can be realized by integrated circuit technology, thereby further reducing the system power consumption and cost and realizing the miniaturization of the inertial navigation system. Description of the Drawings

[0022] Figure 1 It is a structural block diagram of an embodiment of the present invention.

[0023] Figure 2 It is a structural block diagram of the automatic amplitude controller in the embodiment.

[0024] Figure 3 It is a schematic diagram of the three-state frequency discriminator and phase discriminator in the embodiment.

[0025] Figure 4 They are several structural forms of the loop controller in the embodiment. Detailed Embodiment

[0026] The present invention will be described in detail below with reference to the drawings and embodiments.

[0027] As Figure 1 shown, a voltage-controlled rebalancing quartz resonator accelerometer based on atomic clock frequency locking includes an atomic clock 1, a frequency divider 2, a frequency discriminator and phase discriminator 3, a loop controller 4, an analog-to-digital converter 5, a voltage-controlled capacitor 6, an automatic amplitude controller 7, and a quartz resonator 8 with an acceleration-sensitive structure; the accelerometer is equivalent to using an acceleration-sensitive voltage-controlled oscillator composed of the quartz resonator 8, the voltage-controlled capacitor 6, and the automatic amplitude controller 7 that senses the acceleration input to replace the analog voltage-controlled oscillator in the phase-locked loop, and is sequentially connected to the frequency discriminator and phase discriminator 3 and the loop controller 4 to form a phase-locked loop; the signal of the atomic clock 1 is connected to the reference input terminal of the frequency discriminator and phase discriminator 3 through the frequency divider 2, the input port of the quartz resonator 8 is connected to the feedback input terminal of the frequency discriminator and phase discriminator 3, and the analog-to-digital converter 5 quantifies the voltage control signal output by the loop controller 4 as a digital representation of the sensed acceleration; adopting the solution of the present invention can achieve a higher acceleration resolution, realize digital output, and reduce the system integration cost and accuracy loss.

[0028] When working stably, the oscillation loop composed of the quartz resonator 8, the voltage-controlled capacitor 6, and the automatic amplitude controller 7 keeps the quartz resonator 8 in a resonant state; the clock signal output by the atomic clock 1 is input to the reference input terminal of the frequency discriminator and phase discriminator 3 through the frequency divider 2, and after frequency discrimination and phase discrimination with the feedback oscillation loop signal, a control voltage is generated through the loop controller 4 and acts on the voltage-controlled capacitor 6 to achieve frequency locking;

[0029] When the quartz resonator 8 senses a change in the input acceleration, its resonant frequency changes, and the resonant frequency of the oscillation loop follows suit. The frequency discriminator and phase detector 3 detects the frequency and phase difference between the feedback signal and the reference signal, and adjusts the control voltage of the voltage-controlled capacitor 6 through the loop controller 4, so that the operating frequency of the oscillation loop returns to the reference frequency again. The loop controller 4 outputs a quantization value of the control voltage to characterize the magnitude of the input acceleration, realizing digital measurement of acceleration.

[0030] In this embodiment, the accelerometer atomic clock 1 is a rubidium atomic clock, the frequency divider 2 is a 2N frequency divider, the frequency discriminator and phase detector 3 is a three-state frequency discriminator and phase detector, and the loop controller 4 is a third-order type-II loop controller.

[0031] The overall input signal of the accelerometer in this embodiment is the input acceleration signal, and the output signal is the output voltage of the loop controller 4 quantized by the analog-to-digital converter 5. This value is used as the digital measurement value of the input acceleration signal.

[0032] As Figure 2 shown, the automatic amplitude controller 7 is formed by connecting a amplitude detector 71, a first subtractor 72, a PID controller 73, and a mixer 74 in sequence. The input end of the amplitude detector 71 is connected to the drive end of the quartz resonator 8, forming a feedback control system. Among them, the amplitude detector 71 is formed by connecting a rectifier 711 and a low-pass filter 712. The output signal of the quartz resonator 8 is feedback to the drive end of the quartz resonator 8 after CV conversion. The drive signal, as the input signal of the automatic amplitude controller 7, obtains a voltage signal proportional to the amplitude through the amplitude detector 71, and compares the error with the reference voltage in the first subtractor 72. The negative feedback signal is adjusted through the PID controller 73 and mixed with the modulation signal output by the quartz resonator 8. The mixed signal is used as the drive signal of the quartz resonator 8. The error between the drive signal of the quartz resonator 8 and the reference voltage is eliminated through negative feedback, realizing precise control of the vibration amplitude of the quartz resonator 8.

[0033] The rectifier 711 uses a full-wave rectifier, or a half-wave rectifier can also be used, but amplification is required at the back end to achieve the same effect as the full-wave rectifier. The rectifier 711 and the low-pass filter 712 can be implemented in two ways: active and passive devices.

[0034] The voltage-controlled capacitor 6 is realized by using a voltage-controlled varactor diode, or a varactor structure can also be designed on the quartz resonator 8. The quartz resonator 8 uses a quartz tuning fork resonator, which resonates in a specific eigenmode. The voltage-controlled varactor diode is connected in series in the oscillation loop, and the capacitance value is changed by controlling the control voltage of the voltage-controlled varactor diode, thereby realizing frequency pulling of the oscillation loop. The acceleration-sensitive voltage-controlled oscillator is composed of the quartz resonator 8, the voltage-controlled capacitor 6, and the automatic amplitude controller 7, simulating the behavior of the ring voltage-controlled oscillator or the LC voltage-controlled oscillator in the analog phase-locked loop.

[0035] The rubidium atomic clock generates a high-stability frequency signal as the constant reference input signal of the accelerometer, enabling the accelerometer reference to have the precision of atomic energy level transition. The 2N frequency divider tunes the high-frequency atomic clock signal to near the natural frequency of the quartz resonator, improving the loop capture and synchronization capabilities.

[0036] There is a lot of noise in the oscillation loop composed of the quartz resonator 8, the voltage-controlled varactor 6, and the automatic amplitude controller 7. In particular, the 1 / f noise has a great impact on the accelerometer zero-bias instability. The remaining noises all contribute to the white frequency noise, and when the quartz resonator is excited at a large amplitude to achieve a high signal-to-noise ratio, the amplitude-frequency effect is significant, deteriorating the stability and resolution of the accelerometer. The structure of the accelerometer in the present invention enables the key noises to be regulated by the phase-locked loop, especially being suppressed when passing through the loop controller 4 after the frequency discriminator and phase discriminator 3, and the quantization noise is effectively improved.

[0037] As Figure 3 shown, the three-state frequency discriminator and phase discriminator is formed by connecting two D flip-flops, a delay element, an AND gate, and a second subtractor; the reference input signal Ref(t) and the feedback signal Fb(t) are input to the clock terminals of the two D flip-flops of the three-state frequency discriminator and phase discriminator. When the phases of Ref(t) and Fb(t) are the same, the reset terminals of the D flip-flops are opened under the action of the AND gate and the delay element, and both the output terminals UP and DN of the three-state frequency discriminator and phase discriminator are at low level; when there is a deviation in the phases of Ref(t) and Fb(t), a high level at the UP terminal indicates that Ref(t) leads Fb(t), and a high level at the DN terminal indicates that the phase of Fb(t) leads Ref(t); the pulse widths of the high levels at the UP terminal and the DN terminal characterize the magnitude of the phase deviation, and the direction and magnitude of the frequency change of the oscillation loop are adjusted through the output voltage of the loop controller.

[0038] The frequency discriminator and phase discriminator 3 can also be implemented by an XOR phase discriminator and an analog multiplier. The analog multiplier and the XOR phase discriminator require additional auxiliary circuits to cooperate to complete phase capture and synchronization.

[0039] As Figure 4 shown, the loop controller 4 can be implemented with active or passive devices, or can be replaced by a higher-order controller; Figure 4 respectively show passive second-order type-I (TypeⅠ, order2), second-order type-II (TypeⅡ, order 2), third-order type-I (TypeⅠ, order 3), third-order type-II (TypeⅡ, order 3) loop controllers and their transfer functions, where I in is the current input, V outis the voltage output, s is the Laplace transform complex frequency, R, L, and C represent resistance, inductance, and capacitance respectively, and the subscript numbers represent different device parameters. Loop controllers of different orders and types have different response characteristics and have a key impact on system performance such as bandwidth, response, and error.

[0040] The described frequency divider 2 can also be an odd or fractional frequency divider.

[0041] The described quartz resonator 8 and the acceleration-sensitive structure are common existing forms and are interchangeable with the accelerometer system of the present invention.

[0042] The circuit of the present invention can be implemented by discrete device analog circuit chips or by application-specific integrated circuit technology.

Claims

1. A voltage-controlled rebalancing quartz resonator accelerometer based on atomic clock frequency locking, comprising an atomic clock, a frequency divider, a frequency discriminator and phase detector, a loop controller, an analog-to-digital converter, a voltage-controlled capacitor, an automatic amplitude controller, and a quartz resonator with an acceleration-sensitive structure; characterized in that: A quartz resonator, a voltage-controlled varactor, and an automatic amplitude controller are connected in sequence to form an oscillation loop. A frequency discriminator and phase detector, a loop controller, and the oscillation loop are connected in sequence to form a phase-locked loop. The atomic clock signal is connected to the reference input terminal of the frequency discriminator and phase detector through a frequency divider, and the input port of the quartz resonator is connected to the feedback input port of the frequency discriminator and phase detector. The analog-to-digital converter quantifies the output voltage signal of the loop controller of the phase-locked loop as a digital representation of the sensitive acceleration. When operating stably, the oscillation loop composed of the quartz resonator, the voltage-controlled varactor, and the automatic amplitude controller keeps the quartz resonator in a resonant state. The clock signal output by the atomic clock is input to the reference input terminal of the frequency discriminator and phase detector through the frequency divider. After frequency discrimination and phase detection with the feedback oscillation loop signal, a control voltage is generated through the loop controller and acts on the voltage-controlled varactor to achieve frequency locking. When the quartz resonator senses a change in the input acceleration, the resonant frequency changes, and the resonant frequency of the oscillation loop changes accordingly. The frequency discriminator and phase detector detects the frequency and phase difference between the feedback signal and the reference signal. Through the loop controller, the control voltage of the voltage-controlled varactor is adjusted to make the operating frequency of the oscillation loop return to the reference frequency again. The quantization value of the control voltage output by the loop controller represents the magnitude of the input acceleration, realizing digital measurement of acceleration.

2. The accelerometer according to claim 1, characterized in that: The automatic amplitude controller is formed by connecting an amplitude detector, a first subtractor, a PID controller, and a mixer in sequence. The input terminal of the amplitude detector is connected to the drive terminal of the quartz resonator, constituting a feedback control system. Among them, the amplitude detector is formed by connecting a rectifier and a low-pass filter.

3. The accelerometer according to claim 2, characterized in that: The rectifier and the low-pass filter are implemented in two ways: active and passive devices.

4. The accelerometer according to claim 1, characterized in that: The voltage-controlled varactor is realized by using a voltage-controlled varactor diode or by designing a varactor structure on the quartz resonator.

5. The accelerometer according to claim 1, characterized in that: The frequency discriminator and phase detector is formed by connecting two D flip-flops, a delay element, an AND gate, and a second subtractor.

6. The accelerometer according to claim 1, characterized in that: The frequency discriminator and phase detector is realized by an XOR phase detector, an analog multiplier, and a three-state frequency discriminator and phase detector. Among them, the analog multiplier and the XOR phase detector need an auxiliary circuit to cooperate to complete phase capture and synchronization.

7. The accelerometer according to claim 1, characterized in that: The loop controller is realized by active or passive devices and can be replaced by a higher-order controller.

8. The accelerometer according to claim 1, characterized in that: The frequency divider uses an integer, odd, or fractional frequency divider.

9. The accelerometer according to claim 1, characterized in that: The accelerometer circuit is realized by discrete device analog circuit chips or through integrated circuit technology.

Images