A method and system for active temperature compensation of a MEMS oscillator based on A-f effect

Abstract

A MEMS oscillator active temperature compensation method and system based on A-f effect, which is composed of a closed loop oscillation circuit and a frequency drift compensation control circuit; a host computer in the frequency drift compensation control circuit calculates the error between the actual frequency and the initial set frequency according to the real-time collected frequency of the MEMS oscillator in the closed loop oscillation circuit, and converts the frequency difference into an alternating excitation voltage through the built-in compensation control algorithm to control the response amplitude of the MEMS oscillator in the closed loop oscillation circuit in real time; the oscillation frequency of the MEMS oscillator changes due to the A-f effect, so that the oscillation frequency is always stable near the set frequency, thereby realizing the compensation of the frequency drift; the amplitude-frequency dependence in the nonlinear MEMS oscillator is utilized to realize the fast, high-precision and low-power compensation for the temperature drift of the MEMS oscillator.

Description

Technical Field

[0001] This invention belongs to the field of MEMS oscillator technology, specifically relating to an active temperature compensation method and system for MEMS oscillators based on the Af effect. Background Technology

[0002] MEMS oscillators are widely used in high-precision clocks and sensors due to their advantages such as integration, miniaturization, and high quality factor. The frequency stability of MEMS oscillators plays a decisive role, directly determining the performance of electronic systems. However, the large temperature frequency coefficient (25ppm / ℃ to 60ppm / ℃) of silicon-based materials causes the output frequency of MEMS oscillators to drift drastically in varying temperature environments, thus degrading the oscillator's frequency stability. To suppress frequency drift in MEMS oscillators, temperature compensation is typically performed using both active and passive compensation methods.

[0003] Passive compensation typically reduces the temperature frequency coefficient of MEMS oscillators through device structure design, ion doping, and composite structures to achieve temperature compensation. However, this approach increases the difficulty of device fabrication and has limited compensation effect, usually only achieving frequency stability at the ppm level. Active compensation methods, such as constant temperature control scheme ([1]Kwon HK, Ortiz LC, Vukasin GD, et al. An Oven-Controlled Mems Oscillator (Ocmo) with Sub 10mw, + / -1.5Ppb Stability over Temperature[J]. 201920th International Conference on Solid-State Sensors, Actuators and Microsystems&Eurosensors Xxxiii(Transducers&Eurosensors Xxxiii), 2019:2072-2075; [2]Salvia JC, Melamud R, Chandorkar SA, et al.Real-Time Temperature Compensation of MEMS OscillatorsUsing an Integrated Micro-Oven and a Phase-Locked Loop[J].Journal ofMicroelectromechanical Systems,2010,19(1):192-201;[3]Liu CS,Tabrizian R,Ayazi F.A+ / -0.3ppm Oven-Controlled MEMS Oscillator Using StructuralResistance-Based Temperature Sensing[J].IEEE Trans Ultrason Ferroelectr FreqControl,2018,65(8):1492-1499;[4]Xiao Y,Han J,Zhu K,et al.AMicro-OvenControlled Dual-Mode Piezoelectric MEMS Resonator With±190ppb StabilityOver-40to 105℃ Temperature Range[J]. IEEE Electron Device Letters, 2023, 44(8):1340-1343.), by maintaining the constant operating temperature of the MEMS oscillator, active control of frequency drift is achieved. However, the constant temperature control scheme has problems such as temperature field uncertainty and non-uniformity, and large temperature gradient, which limits its temperature control accuracy. In addition, the constant temperature control scheme has high power consumption and long preheating time, which is not suitable for occasions with strict requirements for power consumption and preheating time. On the other hand, the active control scheme based on electrostatic softening effect ([5] Lee HK, Melmud R, Kim B, et al. Journal of Microelectromechanical Systems, 2011, 20(6): 1355-1365; [6] Chen D, Wang Y, Chen X, et al. Temperature-frequency drift suppression via electrostatic stiffnesssoftening in MEMS resonator with weakened duffing nonlinearity[J]. Applied Physics Letters, 2019, 114(2); [7] Liu JR, Li WC. Temperature-compensated CMOS-MEMS resonators via electrical stiffness frequency Pulling [J]. Journal of Micromechanics and Microengineering, 2020, 30(1).), compensation is achieved by adjusting the bias voltage, but the adjustable range is small. Therefore, developing a MEMS oscillator temperature compensation system that can achieve fast, high precision, and low power consumption is an urgent problem to be solved in this field.

[0004] As oscillator size decreases, scaling effects inevitably lead to nonlinear phenomena. The Af effect is a common dynamic phenomenon in nonlinear oscillators, where A corresponds to the oscillator's amplitude and f is the output frequency. Specifically, the Af effect manifests as the oscillator's frequency changing with its amplitude. This frequency-amplitude dependence causes amplitude noise to be converted into frequency fluctuations, thus the Af effect is generally considered to severely impact oscillator performance. Based on this, conventional MEMS oscillators typically operate in the linear range. However, recent studies have shown that driving MEMS oscillators into the nonlinear range can significantly suppress their phase noise; furthermore, by utilizing the nonlinear dependence of the MEMS oscillator's frequency on its amplitude within the nonlinear range, rapid and active frequency control can be achieved by adjusting its vibration amplitude. Currently, there is no published literature utilizing the nonlinear characteristics of MEMS oscillators for temperature compensation. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide an active temperature compensation method and system for MEMS oscillators based on the Af effect. By calculating the excitation intensity required to compensate for frequency drift through a control algorithm, the magnitude of the response amplitude of the MEMS oscillator is adjusted, and active control of the resonant frequency is achieved by means of the Af effect, thereby compensating for frequency drift caused by temperature changes.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An active temperature compensation method for MEMS oscillators based on the Af effect includes:

[0008] When the frequency of a MEMS oscillator drifts due to changes in external temperature, the frequency drift compensation control circuit converts the frequency offset into an AC excitation voltage (AC) at the excitation terminal of the MEMS oscillator. Utilizing the Af effect, the nonlinear resonant frequency corresponding to the peak point is adjusted by changing the amplitude of the MEMS oscillator response. The nonlinear resonant frequency of the MEMS oscillator is changed by the AC excitation voltage, compensating for the frequency drift caused by temperature changes, thereby achieving frequency stability.

[0009] An active temperature compensation method for MEMS oscillators based on the Af effect includes the following steps:

[0010] Step 1: Power on the MEMS resonator and select the control parameters of the MEMS resonator, including the operating phase and excitation intensity. The excitation intensity of the MEMS resonator is selected to exceed the dynamic range of the MEMS resonator, thereby causing the MEMS resonator to generate a nonlinear amplitude-frequency response.

[0011] Step 2: Under the action of the closed-loop oscillation circuit, the MEMS resonator generates a stable closed-loop oscillation. The MEMS resonator and the closed-loop oscillation circuit together constitute the MEMS oscillator.

[0012] Step 3: Based on the frequency of the closed-loop oscillation signal of the MEMS oscillator in Step 2, calculate the difference between the frequency value and the set frequency, and use the control algorithm to calculate the AC excitation voltage required to compensate for the frequency difference.

[0013] Step 4: Transmit the AC excitation voltage AC required for the compensation frequency in Step 3 to the closed-loop oscillation circuit and regulate the AC excitation voltage AC applied to the excitation electrode of the MEMS resonator.

[0014] Step 5: The AC excitation voltage changes the vibration amplitude of the MEMS oscillator. Under the action of nonlinear stiffness, the oscillation frequency of the MEMS oscillator moves along the nonlinear spine line, compensating for the frequency drift caused by external disturbances to the MEMS oscillator, achieving frequency stabilization, and completing one compensation.

[0015] Step 6: Return to step 3 and continue to acquire the frequency of the MEMS oscillator for the next compensation. Repeat this process until the output frequency of the MEMS oscillator is maintained within the set range.

[0016] In step 1, an AC excitation signal is given to the MEMS resonator through the excitation electrode of the MEMS resonator. The phase value corresponding to the peak point of the MEMS resonator response is determined by the amplitude-frequency response curve obtained by open-loop frequency sweep, and this phase value is used as the control parameter of the MEMS resonator.

[0017] Step 3, which involves calculating the AC excitation voltage AC required to compensate for the frequency difference using a control algorithm, specifically involves: the vibration signal of the MEMS oscillator being transmitted to the frequency reading module via a phase-locked loop; the frequency reading module converting the vibration signal from analog to digital, reading the real-time frequency of the vibration signal, and transmitting it to the host computer; the host computer using the difference between the real-time frequency and the set frequency value as a basis to calculate the AC excitation voltage control signal required to compensate for the frequency difference, and controlling the AC output module to transmit the AC excitation voltage control signal to the phase-locked loop after digital-to-analog conversion, so as to regulate the AC excitation voltage AC applied to the excitation end of the MEMS resonator.

[0018] A system for implementing an active temperature compensation method for MEMS oscillators based on the Af effect includes:

[0019] Closed-loop oscillation circuit: used to make the MEMS resonator generate stable closed-loop oscillation at a set phase value, thereby forming a MEMS oscillator; the closed-loop oscillation circuit consists of a MEMS resonator, a differential amplifier and a phase-locked loop.

[0020] Frequency drift compensation control circuit: connected to the closed-loop oscillation circuit, used to monitor and control the output frequency of the MEMS oscillator; the frequency drift compensation control circuit consists of a host computer, a frequency reading module, and an AC output module. The frequency drift compensation control circuit reads the frequency value of the oscillation signal in the closed-loop oscillation circuit through the built-in analog-to-digital converter in the frequency reading module and transmits it to the host computer. The host computer calculates the magnitude of the AC excitation signal required to compensate for the frequency drift through the built-in control compensation algorithm, and compensates for the frequency drift caused by external disturbances.

[0021] The MEMS resonator in the closed-loop oscillation circuit has the following structural forms: disc type, double-ended fixed tuning fork type, cantilever beam type, thin film type, or ring type; the electromechanical transduction method is capacitive type, piezoelectric type, magnetic type, optical type, or thermodynamic type; and the nonlinear stiffness is derived from geometric nonlinearity, electrostatic nonlinearity, material nonlinearity, or inertial nonlinearity.

[0022] In the closed-loop oscillation circuit, an AC excitation signal is given to the MEMS resonator through the excitation electrode. By applying different AC excitation voltages, the amplitude of the MEMS oscillator is changed, and the resonant frequency of the MEMS oscillator changes along the spine line through the Af effect.

[0023] The phase-locked loop in the closed-loop oscillation circuit demodulates the motion signal amplified by the differential amplifier. The demodulated motion signal then uses the phase-locked loop, composed of a phase detector, a PID controller, and a numerically controlled oscillator (NCO), to perform closed-loop control of the excitation signal frequency of the MEMS oscillator.

[0024] The phase detector in the phase-locked loop uses the standard signal output by the numerically controlled oscillator (NCO) to perform phase detection on the amplified and demodulated motion signal. The phase detector outputs a phase difference signal, and the PID controller controls the output frequency of the NCO based on the phase difference signal, so that the MEMS oscillator always operates at the phase point corresponding to the highest amplitude point.

[0025] The frequency drift compensation control circuit is used to control the AC excitation magnitude of the MEMS oscillator in the closed-loop oscillation circuit, thereby suppressing frequency drift through the Af effect.

[0026] The frequency drift compensation control circuit includes:

[0027] Frequency reading module: used to read the real-time oscillation frequency of the MEMS oscillator;

[0028] Host computer: Used to respond to frequency drift and convert the frequency difference into an AC excitation voltage value;

[0029] AC output module: Used to transmit the adjusted AC excitation voltage control signal to the closed-loop oscillation circuit.

[0030] The frequency reading module reads the oscillation frequency of the MEMS oscillator through analog-to-digital conversion; the host computer calculates the difference between the read frequency value and the set value, and uses the frequency difference as the error quantity through the built-in control compensation algorithm to calculate the AC excitation voltage AC required to compensate for the frequency difference; the AC output module inputs the AC excitation voltage AC to the closed-loop oscillation circuit through digital-to-analog conversion, and adjusts the AC excitation voltage value output by the phase-locked loop in real time, using the Af effect to control the frequency of the MEMS oscillator to achieve frequency compensation.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] Step 1 of this invention uses an excitation intensity exceeding the dynamic range of the MEMS resonator to drive the MEMS resonator, which can increase the signal-to-noise ratio of the MEMS resonator response signal and has the characteristic of reducing the output frequency fluctuation of the MEMS resonator.

[0033] The closed-loop oscillation circuit of this invention adopts a phase-locked loop scheme, which enables the MEMS resonator to generate stable closed-loop oscillation at any phase point, and has the characteristics of flexible use and strong stability.

[0034] The frequency drift compensation control circuit of this invention adopts a frequency drift compensation scheme based on the Af effect. It can actively adjust the amplitude of the MEMS oscillator according to the frequency deviation value of the MEMS oscillator, thereby making the oscillation frequency of the MEMS oscillator move along the nonlinear spine to quickly compensate for the frequency drift caused by temperature changes. It does not require an auxiliary heat source to heat the MEMS resonator and has the characteristics of low power consumption, fast response and wide control range.

[0035] In summary, this invention utilizes the Af effect of the MEMS resonator and compensates for frequency drift caused by temperature changes by altering the nonlinear resonant frequency (hysteresis range), thereby improving the long-term frequency stability of the MEMS oscillator. On one hand, this invention directly controls the peak resonant frequency of the MEMS oscillator through the AC excitation voltage (AC), improving the short-term frequency stability of the MEMS oscillator while avoiding the hysteresis of traditional isothermal control temperature compensation systems, significantly reducing the preheating time of the MEMS oscillator. On the other hand, by controlling the AC excitation voltage rather than the heating power to achieve temperature compensation, the power consumption of the temperature compensation system is significantly reduced. Attached Figure Description

[0036] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0037] Figure 2 This is a block diagram of the system according to an embodiment of the present invention.

[0038] Figure 3The graph shows the amplitude-frequency response curves of the MEMS resonator under different AC excitation voltages according to an embodiment of the present invention.

[0039] Figure 4 This is an Allan variance curve of the MEMS oscillator under different AC excitation voltages according to an embodiment of the present invention.

[0040] Figure 5 The following are test results of the system in the embodiment of the present invention: (a) is a comparison of frequency drift over 2 hours with and without compensation for Af effect; (b) is a comparison of frequency drift over 2 hours with compensation for Af effect; (c) is a comparison of Allan variance of MEMS oscillator output frequency with and without compensation for Af effect; and (d) is a comparison of frequency step change when the AC excitation voltage AC is changed.

[0041] In the diagram: 2-1. Differential amplifier; 2-2. Phase-locked loop; 2-3. Phase detector; 2-4. PID controller; 2-5. Numerically controlled oscillator (NCO); 2-6. Inverter; 2-7. Frequency reading module; 2-8. Analog-to-digital converter; 2-9. Host computer; 2-10. Control compensation algorithm; 2-11. AC output module; 2-12. Digital-to-analog converter; 3-1. MEMS resonator; 3-2. Excitation electrode; 3-3. Inverting excitation electrode; 3-4. Detection electrode; 3-5. Inverting detection electrode; 3-6. Body electrode. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0043] This invention provides an active temperature compensation method and system for MEMS oscillators based on the Af effect. An AC excitation signal is applied to the excitation electrode of the MEMS oscillator, exciting the MEMS oscillator to generate a resonant frequency signal. The detection electrode collects the resonant signal of the MEMS oscillator and transmits it to the closed-loop control circuit through a differential amplifier circuit. The resonant signal is transmitted sequentially between the phase detector, PID controller, and NCO. The closed-loop control circuit maintains the operating state of the MEMS oscillator at the phase corresponding to the highest amplitude point, forming a stable closed-loop oscillation. The host computer reads the frequency value generated by the NCO in the phase-locked loop of the closed-loop oscillation circuit through a frequency reading module. The host computer converts the error value between the read frequency and the initial set frequency into an AC excitation voltage AC at the excitation end through a control compensation algorithm. The host computer transmits the AC excitation voltage AC to the excitation end through an AC output module. By adjusting the AC signal voltage at the excitation end, the amplitude of the response peak is changed, thereby changing the frequency value corresponding to the response peak, so that the oscillation frequency is always stable near the set frequency, thereby achieving frequency drift compensation.

[0044] This invention utilizes the Af effect to significantly improve the long-term stability of MEMS oscillators while enhancing their short-term frequency stability. It avoids the control delay in traditional temperature drift compensation and has great application value in fields such as solid-state clocks.

[0045] Reference Figure 1 An active temperature compensation method for MEMS oscillators based on the Af effect is proposed. When the frequency of the MEMS oscillator changes, the frequency drift compensation system converts the frequency shift into the magnitude of the AC excitation signal at the excitation end. Utilizing the Af effect of the MEMS oscillator, i.e., the dependence of the nonlinear resonant frequency on the response amplitude, compensation for frequency drift in variable temperature environments is achieved. The specific steps are as follows:

[0046] Step 1: Power on the MEMS resonator and select the control parameters of the MEMS resonator, including but not limited to the operating phase and excitation intensity. The excitation intensity of the MEMS resonator is selected to exceed the dynamic range of the MEMS resonator, thereby causing the MEMS resonator to generate a nonlinear amplitude-frequency response.

[0047] In step 1, an AC excitation signal is given to the MEMS resonator through the excitation electrode of the MEMS resonator. The phase value corresponding to the peak point of the MEMS resonator response is determined by the amplitude-frequency response curve obtained by open-loop frequency sweep, and the phase value is used as the control parameter of the MEMS resonator.

[0048] Step 2: Under the action of the closed-loop oscillation circuit, the MEMS resonator generates a stable closed-loop oscillation. The MEMS resonator and the closed-loop oscillation circuit together constitute the MEMS oscillator.

[0049] Step 3: The host computer reads the frequency of the NCO in the closed loop through the frequency reading module and collects the frequency of the closed loop oscillation of the MEMS oscillator in Step 2. Based on the difference between the collected frequency value and the set frequency, the host computer uses the control algorithm to calculate the AC excitation voltage required to compensate for the frequency drift.

[0050] The method of calculating the AC excitation voltage AC required to compensate for the frequency difference using the control algorithm is as follows: the vibration signal of the MEMS oscillator is transmitted to the frequency reading module via a phase-locked loop. The frequency reading module performs analog-to-digital conversion on the vibration signal, reads the real-time frequency of the vibration signal and transmits it to the host computer. The host computer calculates the AC excitation voltage control signal required to compensate for the frequency difference based on the difference between the real-time frequency and the frequency set value, and controls the AC output module to send the AC excitation voltage control signal to the phase-locked loop after digital-to-analog conversion, so as to regulate the AC excitation voltage AC applied to the excitation end of the MEMS resonator.

[0051] Step 4: Transmit the AC excitation voltage AC required for the compensation frequency in Step 3 to the closed-loop oscillation circuit and regulate the AC excitation voltage AC applied to the excitation electrode of the MEMS resonator.

[0052] Step 5: The AC excitation voltage changes the vibration amplitude of the MEMS oscillator. Under the action of nonlinear stiffness, the oscillation frequency of the MEMS oscillator moves along the nonlinear spine line, compensating for the frequency drift caused by external disturbances to the MEMS oscillator, achieving frequency stabilization, and completing one compensation.

[0053] Step 6: Return to step 3 and continue to collect the vibration frequency of the MEMS oscillator for the next compensation. Repeat this process until the output frequency of the MEMS oscillator is maintained within the set range.

[0054] Reference Figure 2 A system for implementing an active temperature compensation method for MEMS oscillators based on the Af effect includes:

[0055] Closed-loop oscillation circuit: used to make the MEMS resonator generate stable closed-loop oscillation at a set phase value, thereby forming a MEMS oscillator; the closed-loop oscillation circuit consists of a MEMS resonator, a differential amplifier and a phase-locked loop.

[0056] This embodiment of the closed-loop oscillation circuit includes a MEMS resonator 3-1. The MEMS resonator 3-1 is provided with an excitation electrode 3-2, an inverting excitation electrode 3-3, a detection electrode 3-4, an inverting detection electrode 3-5, and a body electrode 3-6. The detection electrode 3-4 and the inverting detection electrode 3-5 are connected to the input of the differential amplifier 2-1. The output of the differential amplifier 2-1 is connected to the input of the phase detector 2-3. The output of the phase detector 2-3 is connected to the input of the PID controller 2-4. The output of the PID controller 2-4 is connected to the input of the numerically controlled oscillator NCO 2-5. The first output of the numerically controlled oscillator NCO 2-5 is connected to the input of the inverter 2-6. The output of the inverter 2-6 is connected to the inverting excitation electrode 3-3. The second output of the numerically controlled oscillator NCO 2-5 is connected to the excitation electrode 3-2. The phase detector 2-3, the PID controller 2-4, and the numerically controlled oscillator NCO 2-5 constitute a phase-locked loop 2-2.

[0057] Frequency drift compensation control circuit: connected to the closed-loop oscillation circuit, used to monitor and control the output frequency of the MEMS oscillator; the frequency drift compensation control circuit consists of a host computer, a frequency reading module and an AC output module. The frequency drift compensation control circuit reads the frequency value of the oscillation signal in the closed-loop oscillation circuit and transmits it to the host computer. The host computer calculates the AC excitation magnitude required to compensate for the frequency drift through the control compensation algorithm, and compensates for the frequency drift of the MEMS oscillator under the influence of external disturbances.

[0058] In this embodiment, the frequency drift compensation control circuit includes a host computer 2-9, which is equipped with a control compensation algorithm 2-10. The host computer 2-9 is connected to the output of the frequency reading module 2-7 and the phase-locked loop 2-2. The frequency reading module 2-7 has a built-in analog-to-digital converter 2-8. The host computer 2-9 is connected to the input of the phase-locked loop 2-2 through the AC output module 2-11. The AC output module 2-11 has a built-in digital-to-analog converter 2-12.

[0059] To remove the feedthrough parasitic signal from MEMS resonator 3-1, two in-phase, same-frequency excitation signals are needed to excite MEMS resonator 3-1. The MEMS resonator generates two in-phase, same-frequency detection signals. These two detection signals are sent to differential amplifier 2-1, which performs differential processing on the two detection signals. The processed signal is then transmitted to phase-locked loop 2-2. Phase-locked loop 2-2 includes phase detector 2-3, numerically controlled oscillator NCO2-5, and PID controller 2-4. Phase detector 2-3 uses the standard frequency signal generated by numerically controlled oscillator NCO2-5 to perform phase detection on the motion signal processed by differential amplifier 2-1. The detected phase signal serves as the error signal for PID controller 2-4, controlling the frequency of the AC excitation signal generated by numerically controlled oscillator NCO2-5. The AC excitation signal is transmitted to the excitation terminal of MEMS resonator 3-1, causing the oscillator to start oscillating.

[0060] The excitation signal generated by the phase-locked loop 2-2 is directly transmitted to the excitation electrode 3-2 and the inverter 2-6. After the phase of the excitation signal is shifted by 180° by the inverter 2-6, it is transmitted to the excitation electrode 3-3 for excitation.

[0061] The frequency drift compensation control circuit is as follows: The host computer 2-9 reads the output frequency of the numerically controlled oscillator NCO2-5 in the phase-locked loop 2-2 through the frequency reading module 2-7. This output frequency is first converted into a digital quantity by the analog-to-digital converter 2-8 to read the oscillation frequency of the MEMS oscillator. The frequency reading module 2-7 transmits the frequency signal to the host computer 2-9 in real time. The control compensation algorithm 2-10 converts the frequency error into an AC excitation voltage AC. The AC output module 2-11 transmits the regulated AC excitation voltage control signal to the phase-locked loop 2-2 through the digital-to-analog converter 2-12, thereby regulating the AC excitation signal output by the phase-locked loop 2-2 to the excitation terminal of the MEMS oscillator. The AC excitation voltage AC regulates the magnitude of the response amplitude. Due to the Af effect, the nonlinear resonant frequency corresponding to the peak point of the MEMS oscillator response changes accordingly, thereby compensating for the frequency drift of the MEMS oscillator under varying temperature conditions.

[0062] Reference Figure 2The MEMS resonator 3-1 has three types of external connection electrodes, including detection electrode 3-4, inverting detection electrode 3-5, excitation electrode 3-2, inverting excitation electrode 3-3, and body electrode 3-6. Among them, detection electrode 3-4 and inverting detection electrode 3-5 are output terminals, while excitation electrode 3-2, inverting excitation electrode 3-3, and body electrode 3-6 are input terminals. Excitation electrode 3-2 and inverting excitation electrode 3-3 are used to apply AC excitation signal, while body electrode 3-6 is used to apply DC bias voltage. The potential difference between the body electrode and the excitation electrode makes the device easier to start oscillating.

[0063] Reference Figure 3 In this embodiment, the open-loop amplitude-frequency response curves of the MEMS resonator under different AC excitation voltages AC exhibit different amplitude-frequency response characteristics. The figure shows that as the AC excitation voltage AC increases, the hysteresis range of the MEMS resonator increases, and the nonlinear resonant frequency corresponding to the highest amplitude of the amplitude-frequency response curve increases with the increase of the nonlinear hysteresis range. This phenomenon in which the peak frequency of the amplitude-frequency response curve changes accordingly with the change of vibration amplitude is called the Af effect.

[0064] Reference Figure 4 In this embodiment, the Allan variance curves of the MEMS oscillator with an integration time of 0.02s under different AC excitation voltages AC are shown. When different AC excitation voltages AC are applied to the MEMS oscillator, the short-time stability of the MEMS oscillator is different. As shown in the figure, the Allan variance at the integration time of 0.02s gradually decreases with the increase of AC. Therefore, the short-time frequency stability of the MEMS oscillator can be improved by using nonlinear effects.

[0065] Reference Figure 5 This embodiment includes a comparison chart of the 2-hour frequency drift of the MEMS oscillator under uncompensated and Af-effect-based frequency drift compensation, a comparison chart of the Allan variance, and a schematic diagram of the frequency compensation range and control process of the Af-effect-based frequency drift compensation system. Figure 5 As shown in (a), with frequency compensation, the long-term frequency drift of the MEMS oscillator can be controlled within 30 ppb, which is two orders of magnitude better than the 2 ppm without compensation. Figure 5 (b) is an enlarged view of the long-term frequency drift after compensation for the Af effect in (a); Figure 5 (c) shows the comparison of the Allan variance of the oscillator with and without compensation. Under the condition of compensation, the long-term stability of the MEMS oscillator is improved, and the Allan variance at 1600s can be improved from the order of ppm to 0.039ppb. Figure 5Figure (d) shows the step response of the closed-loop oscillation frequency of the MEMS oscillator when the AC excitation voltage changes stepwise in the closed-loop oscillation circuit. When the AC excitation voltage is adjusted from 0.2V to 2.5V, the frequency tuning range is 45Hz.

[0066] The above description is merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Anyone skilled in MEMS oscillators and their temperature compensation techniques can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, any modifications made to the technical solution based on the technical concept proposed in this invention fall within the protection scope of the claims of this invention.

Claims

1. A MEMS oscillator active temperature compensation method based on A-f effect, characterized in that, The method comprises the following steps: Step 1, the MEMS resonator is powered on, and the control parameters of the MEMS resonator are selected, the control parameters including the working phase and the excitation strength; the excitation strength of the MEMS resonator is selected to be a value exceeding the dynamic range of the MEMS resonator, so that the MEMS resonator generates a nonlinear amplitude-frequency response; Step 2, under the action of the closed-loop oscillation circuit, the MEMS resonator generates stable closed-loop oscillation, and the MEMS resonator and the closed-loop oscillation circuit jointly constitute a MEMS oscillator; Step 3, according to the frequency of the closed-loop oscillation signal of the MEMS oscillator in step 2, the difference between the frequency value and the set frequency is calculated, and the AC excitation voltage AC required for compensating the frequency difference is calculated by using a control algorithm; The AC excitation voltage AC required for compensating the frequency difference calculated by using the control algorithm in step 3 is specifically: the vibration signal of the MEMS oscillator is transmitted to a frequency reading module through a phase-locked loop, the frequency reading module reads the real-time frequency of the vibration signal after the vibration signal is converted from analog to digital, and transmits the real-time frequency to an upper computer, the upper computer calculates the AC excitation voltage control signal required for compensating the frequency difference according to the difference between the real-time frequency and the set frequency, and controls an AC output module to transmit the AC excitation voltage control signal from digital to analog to the phase-locked loop, so as to control the AC excitation voltage AC loaded to the excitation electrode of the MEMS resonator; Step 4, the AC excitation voltage AC required for compensating the frequency in step 3 is transmitted to the closed-loop oscillation circuit to control the AC excitation voltage AC loaded to the excitation electrode of the MEMS resonator; Step 5, the AC excitation voltage AC changes the vibration amplitude of the MEMS oscillator, and under the action of the nonlinear stiffness, the oscillation frequency of the MEMS oscillator moves along the nonlinear spine line, compensates the frequency drift of the MEMS oscillator caused by external disturbance, realizes frequency stability, and completes one compensation; Step 6, return to step 3, continue to collect the vibration frequency of the MEMS oscillator, and perform the next compensation, so as to circulate until the output frequency of the MEMS oscillator is maintained within the set range.

2. The compensation method of claim 1, wherein: In step 1, the AC excitation signal is given to the MEMS resonator through the excitation electrode of the MEMS resonator, the phase value corresponding to the peak value point of the MEMS resonator response is determined through the open-loop amplitude-frequency response curve, and the phase value is taken as the control parameter of the MEMS resonator.

3. A system implementing the method of active temperature compensation of a MEMS oscillator based on the A-f effect according to any one of claims 1-2, characterized in that, It comprises: A closed-loop oscillation circuit for making the MEMS resonator generate stable closed-loop oscillation at a set phase value, thereby constituting a MEMS oscillator; The closed-loop oscillation circuit is composed of a MEMS resonator, a differential amplifier and a phase-locked loop. The frequency drift compensation control circuit is connected with the closed loop oscillation circuit, and is used for monitoring and controlling the output frequency of the MEMS oscillator. The frequency drift compensation control circuit is composed of an upper computer, a frequency reading module and an AC output module. The frequency drift compensation control circuit reads the frequency value of the oscillation signal in the closed loop oscillation circuit through the built-in analog-to-digital conversion in the frequency reading module and transmits the frequency value to the upper computer. The upper computer calculates the size of the AC excitation signal required for compensating the frequency drift through the built-in control compensation algorithm, and compensates the frequency drift caused by external disturbances.

4. The system of claim 3, wherein: The phase-locked loop in the closed loop oscillation circuit demodulates the motion signal amplified by the differential amplifier, and the demodulated motion signal is used for closed loop control of the excitation signal frequency of the MEMS oscillator through the phase detector, PID controller and numerically controlled oscillator NCO in the phase-locked loop.

5. The system of claim 3, wherein: The phase detector in the phase-locked loop uses the standard signal output by the numerically controlled oscillator to detect the phase of the amplified and demodulated motion signal. The phase detector outputs a phase difference signal, and the PID controller controls the output frequency of the numerically controlled oscillator NCO according to the phase difference signal, so that the MEMS oscillator always works at the phase point corresponding to the highest amplitude point.

6. The system of claim 3, wherein: The frequency drift compensation control circuit is used for controlling the AC excitation size of the MEMS resonator in the closed loop oscillation circuit, changing the peak amplitude size of the amplitude-frequency characteristic curve of the MEMS oscillator, and then changing the oscillation frequency of the MEMS oscillator along the spine line through the A-f effect, so as to realize the suppression of the frequency drift.

7. The system of claim 3, wherein: The frequency drift compensation control circuit comprises: a frequency reading module for reading the real-time oscillation frequency of the MEMS oscillator; an upper computer for converting the frequency difference into an AC excitation voltage value in response to the frequency drift; an AC output module for transmitting the adjusted AC excitation voltage to the closed loop oscillation circuit.

8. The system of claim 7, wherein: The frequency reading module reads the oscillation frequency of the MEMS oscillator through analog-to-digital conversion. The upper computer calculates the AC excitation voltage AC required for compensating the frequency difference by taking the frequency difference as the error through the built-in control compensation algorithm. The AC output module inputs the AC excitation voltage AC to the closed loop oscillation circuit through digital-to-analog conversion, real-time regulates the AC excitation voltage value output by the phase-locked loop, regulates the frequency of the MEMS oscillator through the A-f effect, and realizes the frequency compensation.

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