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

Abstract

The invention relates to an A-f effect-based MEMS oscillator active temperature compensation method and system, the system is composed of a closed-loop oscillation circuit and a frequency drift compensation control circuit, an upper computer in the frequency drift compensation control circuit calculates an error between an actual frequency and an initial set frequency according to the frequency, collected in real time, of an MEMS oscillator in the closed-loop oscillation circuit, and the error is calculated according to the frequency of the MEMS oscillator in the closed-loop oscillation circuit. The frequency difference is converted into alternating-current excitation voltage through a built-in compensation control algorithm, the response amplitude of an MEMS oscillator in the closed-loop oscillation circuit is controlled in real time, the oscillation frequency of the MEMS oscillator changes along with the A-f effect, the oscillation frequency is stabilized near the set frequency all the time, and therefore compensation of frequency drift is achieved; according to the invention, the amplitude-frequency dependency relationship in the nonlinear MEMS oscillator is utilized to realize rapid, high-precision and low-power-consumption compensation of the temperature drift of the MEMS oscillator.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS oscillators, and in particular relates to a method and system for active temperature compensation of a MEMS oscillator based on the Af effect. Background Art

[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, and their quality directly determines the performance of electronic systems. However, the large temperature frequency coefficient of silicon-based materials (25ppm / ℃ to 60ppm / ℃) will cause the output frequency of the MEMS oscillator to drift dramatically in a variable temperature environment, thereby degrading the frequency stability of the oscillator. In order to suppress the frequency drift of the MEMS oscillator, active and passive compensation methods are usually used to temperature compensate the oscillator.

[0003] Passive compensation usually achieves temperature compensation by reducing the temperature frequency coefficient of the MEMS oscillator through device structure design, ion doping, composite structure, etc.; this solution increases the difficulty of device processing and has limited compensation effect, usually only achieving frequency stability of 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 to achieve active control of frequency drift, but the constant temperature control scheme has problems such as temperature field uncertainty and non-uniformity, large temperature gradient, etc., which limits its temperature control accuracy. In addition, the constant temperature control scheme has high power consumption and long warm-up time, and is not suitable for occasions with strict requirements on power consumption and warm-up time; while the active control scheme based on electrostatic softening effect ([5]Lee HK,Melamud R,Kim B,et al.Journal ofMicroelectromechanical Systems,2011,20(6):1355-1365; [6]Chen D,Wang Y,Chen X,et al.Temperature-frequency drift suppression via electrostatic stiffness softening in MEMS resonator with weakened duffing nonlinearity[J].AppliedPhysics 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 performed by adjusting the bias voltage, and 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 the size of the oscillator decreases, the scale effect leading to nonlinear phenomena is inevitable. The Af effect is a common dynamic phenomenon in nonlinear oscillators, where A corresponds to the amplitude of the oscillator and f is the output frequency of the oscillator; the Af effect is specifically manifested as the frequency of the oscillator changing accordingly with the change of its amplitude; this frequency dependence on amplitude will cause the amplitude noise to be converted into frequency fluctuations, so the Af effect is generally considered to seriously affect the performance of the oscillator. Based on this, conventional MEMS oscillators usually operate in the linear range. However, research in recent years has shown that by driving the MEMS oscillator to the nonlinear range, its phase noise can be significantly suppressed; and by utilizing the nonlinear dependence of the frequency of the MEMS oscillator on the amplitude in the nonlinear range, by regulating its vibration amplitude, the oscillation frequency can be rapidly and actively regulated. At present, there is no literature published on the use of the nonlinear characteristics of MEMS oscillators to achieve temperature compensation of MEMS oscillators. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method and system for active temperature compensation of a MEMS oscillator based on the Af effect, which calculates the excitation intensity required to compensate for the frequency drift through a control algorithm, regulates the magnitude of the MEMS oscillator response amplitude, and uses the Af effect to achieve active control of the resonant frequency, thereby compensating for the frequency drift caused by temperature changes.

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

[0007] A method for active temperature compensation of a MEMS oscillator based on the Af effect, comprising:

[0008] When the frequency of the 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 end of the MEMS oscillator, and utilizes the Af effect to change the nonlinear resonant frequency corresponding to the peak point by changing the response amplitude of the MEMS oscillator. The nonlinear resonant frequency of the MEMS oscillator is changed by the AC excitation voltage to compensate for the frequency drift caused by the temperature change of the MEMS oscillator, thereby achieving frequency stability.

[0009] A method for active temperature compensation of a MEMS oscillator based on the Af effect comprises the following steps:

[0010] Step 1, powering on the MEMS resonator, selecting control parameters of the MEMS resonator, the control parameters including working phase and excitation intensity; the excitation intensity 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;

[0011] Step 2, under the action of the closed-loop oscillation circuit, the MEMS resonator generates a stable closed-loop oscillation, and the MEMS resonator and the closed-loop oscillation circuit together constitute a MEMS oscillator;

[0012] 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 to compensate for the frequency difference is calculated using a control algorithm;

[0013] Step 4, transmitting the AC excitation voltage AC required for the compensation frequency in step 3 to the closed-loop oscillation circuit, and regulating the AC excitation voltage AC loaded to the excitation electrode of the MEMS resonator;

[0014] Step 5, the AC excitation voltage AC 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 on the MEMS oscillator, achieving frequency stability, and completing a compensation.

[0015] Step 6, return to step 3, continue to collect the frequency of the MEMS oscillator, and perform the next compensation, and repeat this cycle until the output frequency of the MEMS oscillator is maintained within the set range.

[0016] In the step 1, an AC excitation signal is given to the MEMS resonator through the excitation electrode of the MEMS resonator, and 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 sweeping, and the phase value is used as the control parameter of the MEMS resonator.

[0017] The use of a control algorithm to calculate the AC excitation voltage AC required to compensate for the frequency difference described in step 3 is specifically 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 / 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 setting value, and controls the AC output module to transmit the AC excitation voltage control signal to the phase-locked loop after digital / analog conversion, so as to regulate the AC excitation voltage AC loaded to the excitation end of the MEMS resonator.

[0018] A system for implementing an active temperature compensation method for a MEMS oscillator based on the Af effect, comprising:

[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 is composed 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 is composed of a host computer, a frequency reading module, and an AC output module. The frequency drift compensation control circuit reads the oscillation signal frequency value in the closed-loop oscillation circuit through the built-in analog / digital conversion in the frequency reading module and transmits it to the host computer. The host computer calculates the size 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 structure of the MEMS resonator in the closed-loop oscillation circuit is disk type, double-ended tuning fork type, cantilever beam type, film type or ring type; the electromechanical transduction method is capacitive type, piezoelectric type, magnetic type, optical type or thermal type; the source of nonlinear stiffness is 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, and the amplitude of the MEMS oscillator is changed by applying different AC excitation voltages AC, thereby causing the resonant frequency of the MEMS oscillator to change 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, and the demodulated motion signal performs closed-loop control on the excitation signal frequency of the MEMS oscillator through a phase-locked loop composed of a phase detector, a PID controller and a numerically controlled oscillator NCO in the phase-locked loop.

[0024] The phase detector in the phase-locked loop uses the standard signal output by the numerically controlled oscillator to perform phase detection on the amplified and demodulated motion signal, and the phase detector outputs a phase difference signal. 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 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 the frequency drift through the Af effect.

[0026] The frequency drift compensation control circuit comprises:

[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 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 / digital conversion; the host computer subtracts the read frequency value from the set value, and uses the frequency difference as the error amount through the built-in control compensation algorithm to calculate the AC excitation voltage AC required to compensate the frequency difference; the AC output module inputs the AC excitation voltage AC into the closed-loop oscillation circuit through digital / analog conversion, adjusts the AC excitation voltage value output by the phase-locked loop in real time, and uses the Af effect to adjust the frequency of the MEMS oscillator to achieve frequency compensation.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] Step 1 of the present invention drives the MEMS resonator with an excitation intensity exceeding the dynamic range of 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 the present invention adopts a phase-locked loop solution, which can enable 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 the present invention adopts a frequency drift compensation scheme based on the Af effect, which can actively adjust the amplitude of the MEMS oscillator according to the frequency deviation value of the MEMS oscillator, thereby causing the oscillation frequency of the MEMS oscillator to move along the nonlinear spine line to quickly compensate for the frequency drift caused by temperature changes. No auxiliary heat source is required to heat the MEMS resonator, and the circuit has the characteristics of low power consumption, rapid response and a large control range.

[0035] In summary, the present invention uses the Af effect of the MEMS resonator to change the nonlinear resonant frequency (hysteresis interval) to compensate for the frequency drift caused by temperature changes, thereby improving the long-term frequency stability of the MEMS oscillator. On the one hand, the present invention directly adjusts the peak resonant frequency of the MEMS oscillator through the AC excitation voltage AC, while improving the short-term frequency stability of the MEMS oscillator, avoiding the hysteresis of the traditional constant temperature control temperature compensation system, and significantly reducing the preheating time of the MEMS oscillator; on the other hand, temperature compensation is achieved by adjusting the AC excitation voltage instead of adjusting the heating power, which significantly reduces the power consumption of the temperature compensation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a flow chart of a method according to an embodiment of the present invention.

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

[0038] Figure 31 is a graph showing the amplitude-frequency characteristics of the MEMS resonator under different AC excitation voltages AC according to an embodiment of the present invention.

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

[0040] Figure 5 The test result diagrams of the system of the embodiment of the present invention, wherein (a) is a comparison diagram of the frequency drift in 2 hours without compensation and with Af effect compensation; (b) is a comparison diagram of the frequency drift in 2 hours with Af effect compensation; (c) is a comparison diagram of the Allan variance of the MEMS oscillator output frequency in the cases without compensation and with Af effect compensation; (d) is a diagram of the frequency step change when the AC excitation voltage AC is changed.

[0041] In the figure: 2-1. Differential amplifier; 2-2. Phase-locked loop; 2-3. Phase detector; 2-4. PID controller; 2-5. Numerical control oscillator NCO; 2-6 Inverter; 2-7. Frequency reading module; 2-8. Analog / digital conversion; 2-9. Host computer; 2-10. Control compensation algorithm; 2-11. AC output module; 2-12. Digital / analog conversion; 3-1. MEMS resonator; 3-2. Excitation electrode; 3-3. Anti-phase excitation electrode; 3-4. Detection electrode; 3-5. Anti-phase detection electrode; 3-6. Body electrode. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with embodiments and drawings.

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

[0044] The present invention utilizes the Af effect to improve the short-term frequency stability of the MEMS oscillator while significantly improving the long-term stability of the MEMS oscillator, avoiding the control delay during traditional temperature drift compensation, and has great application value in the fields of solid-state clocks and the like.

[0045] Reference Figure 1 , an active temperature compensation method for MEMS oscillators based on the Af effect. When the frequency of the MEMS oscillator changes, the frequency drift compensation system converts the frequency offset into the AC excitation signal size at the excitation end, and utilizes the Af effect of the MEMS oscillator, that is, the dependence of the nonlinear resonant frequency on the response amplitude, to achieve compensation for the frequency drift in a variable temperature environment. The specific steps are as follows:

[0046] Step 1, powering on the MEMS resonator, selecting control parameters of the MEMS resonator, including but not limited to a working phase and an excitation intensity; the excitation intensity of the MEMS resonator is selected to be a value exceeding a dynamic range of the MEMS resonator, so that the MEMS resonator generates a nonlinear amplitude-frequency response;

[0047] In the step 1, an AC excitation signal is given to the MEMS resonator through the excitation electrode of the MEMS resonator, and a phase value corresponding to a peak point of the MEMS resonator response is determined by an amplitude-frequency response curve obtained through an open-loop frequency sweep, and the phase value is used as a 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, and the MEMS resonator and the closed-loop oscillation circuit together constitute a MEMS oscillator;

[0049] Step 3, the host computer reads the frequency of the NCO in the closed loop through the frequency reading module, collects the frequency of the closed loop oscillation of the MEMS oscillator in step 2, and the host computer calculates the AC excitation voltage AC required to compensate for the frequency drift based on the difference between the collected frequency value and the set frequency using the control algorithm;

[0050] The method of using the control algorithm to calculate the AC excitation voltage AC required to compensate for the frequency difference 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 / 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 setting value, and controls the AC output module to transmit the AC excitation voltage control signal to the phase-locked loop after digital / analog conversion, so as to regulate the AC excitation voltage AC loaded to the excitation end of the MEMS resonator;

[0051] Step 4, transmitting the AC excitation voltage AC required for the compensation frequency in step 3 to the closed-loop oscillation circuit, and regulating the AC excitation voltage AC loaded to the excitation electrode of the MEMS resonator;

[0052] Step 5, the AC excitation voltage AC 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 on the MEMS oscillator, achieving frequency stability, and completing a compensation.

[0053] Step 6, return to step 3, continue to collect the vibration frequency of the MEMS oscillator, and perform the next compensation, and repeat this cycle 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 a MEMS oscillator based on the Af effect, comprising:

[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 is composed of a MEMS resonator, a differential amplifier and a phase-locked loop;

[0056] The closed-loop oscillation circuit of this embodiment includes a MEMS resonator 3-1, on which an excitation electrode 3-2, an anti-phase excitation electrode 3-3, a detection electrode 3-4, an anti-phase detection electrode 3-5, and a body electrode 3-6 are provided, wherein the detection electrode 3-4 and the anti-phase 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 NCO2-5, the first output of the numerically controlled oscillator NCO2-5 is connected to the input of the inverter 2-6, the output of the inverter 2-6 is connected to the anti-phase excitation electrode 3-3, and the second output of the numerically controlled oscillator NCO2-5 is connected to the excitation electrode 3-2; the phase detector 2-3, the PID controller 2-4, and the numerically controlled oscillator NCO2-5 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 is composed 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 required to compensate for the frequency drift through a control compensation algorithm, and compensates for the frequency drift of the MEMS oscillator under external disturbance.

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

[0059] In order to remove the feedthrough parasitic signal of the MEMS resonator 3-1, two excitation signals of the same frequency and opposite phases are required to excite the MEMS resonator 3-1, and the MEMS resonator generates two detection signals of the same frequency and opposite phases; the two detection signals are transmitted to the differential amplifier 2-1, and the differential amplifier 2-1 performs differential processing on the two detection signals, and the processed signals are transmitted to the phase-locked loop 2-2; the phase-locked loop 2-2 part includes a phase detector 2-3, a numerically controlled oscillator NCO2-5 and a PID controller 2-4, and the phase detector 2-3 uses the standard frequency signal generated by the numerically controlled oscillator NCO2-5 to perform phase detection on the motion signal processed by the differential amplifier 2-1, and the detected phase signal is used as the error signal of the PID controller 2-4 to control the frequency of the AC excitation signal generated by the numerically controlled oscillator NCO2-5, and the AC excitation signal is transmitted to the excitation end of the MEMS resonator 3-1 to start the oscillator.

[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 inverter 2-6 shifts the phase of the excitation signal by 180°, it is transmitted to the excitation electrode 3-3 for excitation.

[0061] The frequency drift compensation control circuit is specifically 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. The output frequency is first converted into a digital quantity through the analog / digital conversion 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 / analog conversion 2-12, thereby regulating the AC excitation signal output by the phase-locked loop 2-2 to the excitation end 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 generated by the MEMS oscillator in a variable temperature environment.

[0062] Reference Figure 2The MEMS resonator 3-1 has three types of external connection electrodes, including a detection electrode 3-4, an inverted detection electrode 3-5, an excitation electrode 3-2, an inverted excitation electrode 3-3, and a body electrode 3-6, wherein the detection electrode 3-4 and the inverted detection electrode 3-5 are output terminals, and the excitation electrode 3-2, the inverted excitation electrode 3-3 and the body electrode 3-6 are input terminals; wherein the excitation electrode 3-2 and the inverted excitation electrode 3-3 are used to apply an AC excitation signal AC, and the body electrode 3-6 is used to apply a DC bias voltage, and a potential difference is formed between the body electrode and the excitation electrode, making the device easier to oscillate.

[0063] Reference Figure 3 The open-loop amplitude-frequency characteristic curve of the MEMS resonator in this embodiment under different AC excitation voltages AC exhibits 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 point of the amplitude of the amplitude-frequency characteristic curve increases with the increase of the nonlinear hysteresis range. This phenomenon that the peak frequency of the amplitude-frequency characteristic curve changes accordingly with the change of the vibration amplitude is called the Af effect.

[0064] Reference Figure 4 , Allan variance curve of the MEMS oscillator under different AC excitation voltages AC when the integration time is 0.02s. When different AC excitation voltages AC are applied to the MEMS oscillator, the short-time stability of the MEMS oscillator is different. The figure shows that the Allan variance at the integration time of 0.02s gradually decreases with the increase of AC. Therefore, the nonlinear effect can be used to improve the short-time frequency stability of the MEMS oscillator.

[0065] Reference Figure 5 , a 2h frequency drift comparison diagram of the MEMS oscillator without compensation and with frequency drift compensation based on the Af effect, a 2h frequency drift diagram with frequency drift compensation based on the Af effect, an Allan variance comparison diagram, and a schematic diagram of the frequency compensation range and regulation process of the frequency drift compensation system based on the Af effect; Figure 5 (a) shows that under frequency compensation, the long-term frequency drift of the MEMS oscillator can be controlled within 30 ppb, which is two orders of magnitude higher than 2 ppm without compensation. Figure 5 (b) is an enlarged view of the long-term frequency drift after the Af effect is compensated in (a); Figure 5 (c) is a comparison of the Allan variance of the oscillator with and without compensation. Under compensation conditions, the long-term stability of the MEMS oscillator is improved, and the Allan variance at 1600s can be improved from the ppm level to 0.039ppb; Figure 5(d) in the middle shows the step response diagram 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 controlled in the range of 0.2V to 2.5V, the frequency tuning range is 45Hz.

[0066] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Anyone familiar with MEMS oscillators and temperature compensation technologies can modify or change the above embodiments without violating the spirit and scope of the present application. Therefore, any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for active temperature compensation of a MEMS oscillator based on the Af effect, characterized in that: include: When the frequency of the MEMS oscillator drifts due to external temperature changes, the frequency drift compensation control circuit converts the frequency offset into an AC excitation voltage AC at the excitation end of the MEMS oscillator, and utilizes the Af effect to change the peak value of the MEMS oscillator response to adjust the nonlinear resonant frequency corresponding to the peak point; the nonlinear resonant frequency of the MEMS oscillator is changed by the AC excitation voltage, which compensates for the frequency drift of the MEMS oscillator caused by temperature changes, thereby achieving frequency stability.

2. A method for active temperature compensation of a MEMS oscillator based on the Af effect, characterized in that: The following steps are involved: Step 1, powering on the MEMS resonator, selecting control parameters of the MEMS resonator, the control parameters including working phase and excitation intensity; the excitation intensity of the MEMS resonator is selected to be a value exceeding the dynamic range of the MEMS resonator, so that the MEMS resonator produces a nonlinear amplitude-frequency response; Step 2, under the action of the closed-loop oscillation circuit, the MEMS resonator generates a stable closed-loop oscillation, and the MEMS resonator and the closed-loop oscillation circuit together 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 to compensate for the frequency difference is calculated using a control algorithm; Step 4, transmitting the AC excitation voltage AC required for the compensation frequency in step 3 to the closed-loop oscillation circuit, and regulating 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. 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 on the MEMS oscillator, achieving frequency stability, and completing a compensation. Step 6, return to step 3, continue to collect the vibration frequency of the MEMS oscillator, and perform the next compensation, and repeat this cycle until the output frequency of the MEMS oscillator is maintained within the set range.

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

4. The compensation method according to claim 2, characterized in that: The use of a control algorithm to calculate the AC excitation voltage AC required to compensate for the frequency difference described in step 3 is specifically 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 / 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 setting value, and controls the AC output module to transmit the AC excitation voltage control signal to the phase-locked loop after digital / analog conversion, so as to regulate the AC excitation voltage AC loaded to the excitation end of the MEMS resonator.

5. A system for implementing the active temperature compensation method for a MEMS oscillator based on the Af effect as described in any one of claims 1 to 4, characterized in that: include: 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 is composed of a MEMS resonator, a differential amplifier, and a phase-locked loop; 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 is composed of a host computer, a frequency reading module, and an AC output module. The frequency drift compensation control circuit reads the oscillation signal frequency value in the closed-loop oscillation circuit through the built-in analog / digital conversion in the frequency reading module and transmits it to the host computer. The host computer calculates the size 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.

6. The system according to claim 5, characterized in that: The phase-locked loop in the closed-loop oscillation circuit demodulates the motion signal amplified by the differential amplifier, and the demodulated motion signal performs closed-loop control on the excitation signal frequency of the MEMS oscillator through a phase-locked loop composed of a phase detector, a PID controller and a numerically controlled oscillator NCO in the phase-locked loop.

7. The system according to claim 5, characterized in that: The phase detector in the phase-locked loop uses the standard signal output by the numerically controlled oscillator to perform phase detection on the amplified and demodulated motion signal, and the phase detector outputs a phase difference signal. 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 operates at the phase point corresponding to the highest amplitude point.

8. The system according to claim 5, characterized in that: The frequency drift compensation control circuit is used to control the AC excitation magnitude of the MEMS resonator in the closed-loop oscillation circuit, change the peak amplitude magnitude of the amplitude-frequency characteristic curve of the MEMS oscillator, and then change the oscillation frequency of the MEMS oscillator along the spine line through the Af effect, thereby achieving suppression of frequency drift.

9. The system according to claim 5, characterized in that: The frequency drift compensation control circuit comprises: Frequency reading module: used to read the real-time oscillation frequency of the MEMS oscillator; Host computer: used to respond to frequency drift and convert the frequency difference into AC excitation voltage value; AC output module: used to transfer the adjusted AC excitation voltage to the closed-loop oscillation circuit.

10. The system according to claim 9, characterized in that: The frequency reading module reads the oscillation frequency of the MEMS oscillator through analog / digital conversion; the host computer subtracts the read frequency value from the set value, and uses the frequency difference as the error amount through the built-in control compensation algorithm to calculate the AC excitation voltage AC required to compensate the frequency difference; the AC output module inputs the AC excitation voltage AC into the closed-loop oscillation circuit through digital / analog conversion, adjusts the AC excitation voltage value output by the phase-locked loop in real time, and uses the Af effect to adjust the frequency of the MEMS oscillator to achieve frequency compensation.

Images