Chip atomic clock temperature compensation method and device based on multivariate nonlinear regression

Abstract

The invention discloses a chip atomic clock temperature compensation method and device based on multivariate nonlinear regression. The method comprises the steps that nine observed quantities in a chip atomic clock are determined; determining the output frequency accuracy of the chip atomic clock; according to the nine observed quantities in the chip atomic clock and the accuracy of the output frequency of the chip atomic clock, determining a correlation coefficient between each observed quantity and the accuracy of the output frequency, and then screening characteristic variables strongly correlated with temperature change; determining that the laser temperature control quantity is used as the characteristic quantity of a chip atomic clock temperature compensation model, and then establishing a multivariate nonlinear regression model; and according to the multivariate nonlinear regression model, determining a model frequency compensation amount and an actual control amount in the single-chip microcomputer. According to the method, frequency drift can be effectively suppressed under various working conditions such as natural temperature fluctuation, temperature gradient change and abnormal temperature change, and the environmental adaptability of the chip atomic clock is remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of temperature compensation technology, and in particular to a chip atomic clock temperature compensation method and device based on multivariate nonlinear regression. Background Art

[0002] Chip-based atomic clocks eliminate the microwave resonant cavity and complex vacuum systems of traditional atomic clocks, allowing them to be shrunk to the chip level. They hold broad application prospects in satellite navigation, mobile communications, and defense and military fields. However, due to limitations in cost, size, and power consumption, they lack sophisticated temperature control measures, making them sensitive to external temperature fluctuations and severely impacting the stability of their output frequency.

[0003] The internal physical system of a chip atomic clock is highly sensitive to temperature changes, which is mainly reflected in the following two aspects: First, the output frequency and light intensity of the vertical cavity surface emitting laser (VCSEL) will change significantly with temperature fluctuations. This change will directly affect the frequency stability of the coherent population trapped (CPT) atomic frequency standard; second, the change of the absorption bubble temperature will cause the signal-to-noise ratio and collision frequency shift of the CPT frequency discrimination signal to change. These effects will eventually couple into the output frequency, causing frequency drift. At present, the traditional temperature compensation method mainly relies on the solution of external temperature sensors, which has obvious technical limitations. Specifically: (1) The system implementation complexity is high. This method requires the use of a high-precision temperature sensor array for distributed temperature monitoring. For the pursuit of miniaturization of chip atomic clock systems, it not only adds additional hardware complexity, but also affects the spatial layout and integration density of internal components, which is not conducive to the miniaturization design of the equipment. (2) The compensation accuracy is limited. Due to the difference in heat conduction paths between the temperature sensor and key sensitive components (such as VCSEL and absorption bubble), the temperature measurement value deviates from the actual temperature of the sensitive component, affecting the compensation effect. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a chip atomic clock temperature compensation method and system based on multivariate nonlinear regression to solve the output frequency drift problem of existing chip atomic clocks caused by ambient temperature fluctuations.

[0005] According to a first aspect of an embodiment of the present application, a chip atomic clock temperature compensation method based on multivariate nonlinear regression is provided, comprising: The chip atomic clock serial port monitors the host computer to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control value and microwave demodulation value, and determine nine observation quantities; Obtain the output frequency of the chip atomic clock and the reference frequency output by the standard clock source to determine the output frequency accuracy of the chip atomic clock; Determine the correlation coefficient between each observation value and the output frequency accuracy of the chip atomic clock using a Pearson correlation analysis method based on the nine observation values ​​and the output frequency accuracy of the chip atomic clock; According to the correlation coefficient, characteristic variables that are strongly correlated with temperature changes are screened, and the laser temperature control amount is determined to be the characteristic amount of the chip atomic clock temperature compensation model; Based on the characteristic quantities, a multivariate nonlinear regression model is established, and the model coefficients are determined by testing and evaluating the model under multiple environmental conditions, thereby completing the model construction; According to the multivariate nonlinear regression model and in combination with the actual control process, the relationship between the model frequency compensation amount and the actual control amount in the single chip microcomputer, that is, the frequency control word, is determined.

[0006] Furthermore, the multivariate nonlinear regression model is expressed as follows:

[0007] Where, is the compensation amount, is a constant term, is the laser temperature control quantity, is the laser temperature control variable change rate, and are the polynomial coefficients, is a random error, and The highest order of laser temperature control amount and laser temperature control amount change rate respectively.

[0008] According to a second aspect of an embodiment of the present application, a chip atomic clock temperature compensation device based on multivariate nonlinear regression is provided, comprising: The observation quantity acquisition module is used to monitor the host computer through the chip atomic clock serial port to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control value and microwave demodulation value, and determine nine observation quantities; The accuracy determination module is used to obtain the output frequency of the chip atomic clock and the reference frequency output by the standard clock source to determine the output frequency accuracy of the chip atomic clock; A correlation coefficient determination module is used to determine the correlation coefficient between each observation quantity and the output frequency accuracy of the chip atomic clock by using a Pearson correlation analysis method based on the nine observation quantities and the output frequency accuracy of the chip atomic clock; A control quantity determination module is used to screen characteristic variables that are strongly correlated with temperature changes based on the correlation coefficient, and determine the laser temperature control quantity as the characteristic quantity of the chip atomic clock temperature compensation model; A model building module is used to establish a multivariate nonlinear regression model based on the characteristic quantities, determine the model coefficients by testing and evaluating the model under multiple environmental conditions, and thus complete the model building; The compensation amount determination module is used to determine the relationship between the model frequency compensation amount and the actual control amount in the single chip microcomputer, that is, the frequency control word, based on the multivariate nonlinear regression model and the actual control process.

[0009] According to a third aspect of the embodiments of the present application, there is provided an electronic device, including: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0010] According to a fourth aspect of an embodiment of the present application, a computer-readable storage medium is provided, on which computer instructions are stored. When the instructions are executed by a processor, the steps of the method described in the second aspect are implemented.

[0011] The technical solutions provided by the embodiments of the present application may have the following beneficial effects: As can be seen from the above embodiments, this application adopts temperature compensation technology to analyze the correlation between each internal variable and frequency accuracy through experiments. Unlike the traditional method that requires an external temperature sensor to increase hardware costs, this solution innovatively uses the existing monitoring and control quantities inside the chip atomic clock to screen out characteristic variables that are strongly correlated with temperature changes to build a compensation model. Specifically, this solution establishes a quantitative relationship between these internal variables and the output frequency through experimental data, and finally constructs a temperature compensation model based on the internal monitoring signal. This method not only avoids the introduction of additional hardware, but also achieves a more direct frequency compensation effect.

[0012] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0014] Figure 1 The present invention is a flowchart showing a method for temperature compensation of a chip atomic clock based on multivariate nonlinear regression according to an exemplary embodiment.

[0015] Figure 2 The figure is a block diagram of a temperature compensation structure of a chip atomic clock according to an exemplary embodiment.

[0016] Figure 3 FIG. 4 is a characteristic curve of correlation coefficients of key variables according to an exemplary embodiment.

[0017] Figure 4 The original frequency accuracy of the chip atomic clock and the different orders are shown according to an exemplary embodiment. i The compensation curve below.

[0018] Figure 5 The present invention is a block diagram of a chip atomic clock temperature compensation device based on multivariate nonlinear regression according to an exemplary embodiment. DETAILED DESCRIPTION

[0019] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0020] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this application and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0021] It should be understood that although the terms first, second, third, etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0022] like Figure 1 and Figure 2 As shown, a chip atomic clock temperature compensation method based on multivariate nonlinear regression provided by an embodiment of the present invention may include the following steps: S1: The chip atomic clock serial port monitors the host computer to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control value and microwave demodulation value, and determine the nine observation quantities; Specifically, this embodiment uses a CPT atomic clock prototype developed by Peking University as the compensation target. The chip atomic clock is connected to a host computer via an RS-232 / USB serial port, with the baud rate and data frame format configured to ensure real-time transmission stability. The microcontroller's own ADC module digitally samples analog signals (such as light intensity, laser temperature, and absorber bubble temperature) at a sampling rate of at least 1 kHz to prevent signal aliasing.

[0023] S2: Get the chip atomic clock output frequency Reference frequency output from a standard clock source , determine the output frequency accuracy of the chip atomic clock; Specifically, a high-stability reference clock source (such as a cesium atomic clock, a rubidium atomic clock, or a GPS disciplined crystal oscillator) with a frequency stability better than 1×10⁻¹² (1 second average) is used to ensure the reliability of the reference benchmark; a high-resolution frequency counter is used to measure the output frequency of the chip atomic clock. With reference frequency The instantaneous deviation of the frequency is obtained.

[0024] S3: Determine the correlation coefficient between each observation value and the output frequency accuracy of the chip atomic clock by using a Pearson correlation analysis method based on the nine observation values ​​and the output frequency accuracy of the chip atomic clock; Specifically, the Pearson correlation coefficient is calculated as follows:

[0025] Where, is the sample size, and They are variables and No. In this application, and Specifically, they are manifested as observation quantity and frequency accuracy. and They are variables and The numerator measures the covariance of the two variables, reflecting their common variation trend; the denominator is the product of the standard deviations of the two variables, which is used to standardize the covariance, keeping the correlation coefficient fixed in the range [-1, 1]. Table 1 shows the Pearson correlation coefficients between the nine observations and the frequency accuracy of four differently numbered chip atomic clocks.

[0026] Table 1:

[0027] As shown in Table 1, although the correlation coefficients between the laser temperature control variable and the absorption bubble temperature control variable and the frequency accuracy on different atomic clocks are different, they all show a large correlation. The other variables have a small correlation with the final output frequency of the chip atomic clock.

[0028] S4: screening characteristic variables that are strongly correlated with temperature changes based on the correlation coefficient, and determining to use the laser temperature control amount as a characteristic amount of the chip atomic clock temperature compensation model; Specifically, screening The observed variables are strongly correlated (such as laser temperature control variables), and visual verification is performed at the same time.

[0029] In order to further analyze the relationship between the laser temperature control amount and the output frequency of the chip atomic clock, taking the #1 atomic clock as an example, it runs freely for 36 hours in the test environment. The relationship curve between the laser temperature control amount and the frequency accuracy is as follows: Figure 3 As shown in (a) and (b), the drift characteristics of the two curves are removed and normalized, and the laser temperature control amount is inverted to obtain Figure 3 (c). Figure 3 It shows that the reverse laser temperature control amount of the chip atomic clock after drift removal is highly consistent with the frequency accuracy change trend, and the two show a strong correlation.

[0030] While similar results can be achieved with the absorber temperature control loop, its temperature control loop differs somewhat from the laser temperature control loop. Both loops clamp the output voltage to a set voltage and then perform a PID loop lock on the differentially amplified voltage. However, the differential amplification factors of the two loops differ: the laser temperature control loop has a differential amplification factor of 501, while the absorber temperature control loop has a differential amplification factor of only 101. This means that the laser temperature control loop requires higher loop lock accuracy and is more sensitive to environmental changes, while the absorber temperature control requirements are relatively low.

[0031] Based on this, the laser temperature control quantity is taken into consideration to construct a temperature compensation model, which is the subsequent multivariate nonlinear regression model.

[0032] S5: Determine a multivariate nonlinear regression model based on the characteristic quantities, determine the model coefficients by testing and evaluating the model under multiple environmental conditions, and thus complete the construction of the model; Specifically, from the correlation analysis between the observed quantity and the frequency accuracy, we can try to establish a multivariate nonlinear regression model based on the laser temperature control quantity and the change quantity and the frequency compensation quantity. The multivariate nonlinear regression model has the advantage of reducing the prediction error by fitting a more complex function form, while more realistically reflecting the complex relationship between the laser temperature and the frequency accuracy, taking into account both the prediction accuracy and the physical interpretability. Thus, the multivariate nonlinear regression model is constructed:

[0033] Where, is the compensation amount, is a constant term, is the laser temperature control quantity, is the laser temperature control variable change rate, and are the polynomial coefficients, is a random error, and The highest order of laser temperature control amount and laser temperature control amount change rate respectively.

[0034] make , that is, only the first-order term of the temperature change rate is retained. In order to determine The order of gradually changing The value of , compares the model effects under different orders, and and It can be estimated by the least squares method.

[0035] When the model order When the model is simplified to include the laser temperature control The quadratic term and the rate of change of the control variable The second-order multiple nonlinear regression model equation is expressed as:

[0036] Where, and Laser temperature control The first-order and second-order coefficients of is the first-order coefficient of the change rate of the laser temperature control variable.

[0037] With A set of experimental data points can be constructed by and the observation vector :

[0038] The coefficient vector is:

[0039] Therefore, the model equation can be expressed as:

[0040] Establish the minimum residual sum of squares:

[0041] For each coefficient , , and Find the partial derivative, set its derivative to zero, and set the equation to matrix form:

[0042] in, is a 4×4 symmetric matrix with the following elements:

[0043] is a 4×1 vector with the following elements:

[0044] like is reversible, then the coefficient estimate is:

[0045] In this way, the model coefficients can be obtained and the construction of the multiple linear regression model can be completed.

[0046] S6: Determine the model frequency compensation amount based on the multivariate nonlinear regression model and the actual control process The relationship between the actual control quantity in the microcontroller, that is, the frequency control word.

[0047] Specifically, to obtain experimental data points, the CPT atomic clock was started at room temperature. After the CPT atomic clock locked, the incubator was started and the temperature was ramped as follows: the initial incubator temperature was maintained at 25°C. After 60 minutes, the temperature was increased at a rate of 0.1°C / min to 30°C. This temperature was maintained for 60 minutes, and then the temperature was increased at a rate of 0.1°C / min to 35°C. This process was repeated until the temperature reached 45°C, where the experiment was terminated. Frequency accuracy data for the chip atomic clock was obtained through temperature-variable experiments.

[0048] The frequency accuracy data obtained through the variable temperature experiment is used to obtain different orders using the multivariate nonlinear regression model. i The frequency compensation amount under Figure 4 As shown in the figure, different orders iThe results achieved by the following models are different. When the model order is 1, the fitting effect is not ideal and it cannot follow the changes of the output frequency well when the temperature range is different. Increasing the model order gradually matches the fitting effect. As can be seen from the thumbnail, there is little difference between the model under the conditions of 2nd and 3rd order. In order to save computing resources, the present invention selects the 2nd order multiple nonlinear regression model.

[0049] According to the working principle of CPT atomic clock, it is necessary to use a frequency synthesizer to multiply the 10MHz output of the crystal oscillator to 87 Half of the Rb hyperfine level transition frequency, that is, 3417.341307MHz. Taking LMX2572 as an example, it has a 32-bit fractional divider. When the phase detection frequency is 10MHz, in order to facilitate the adjustment of the frequency deviation, the denominator of the fractional divider needs to be adjusted. Let the denominator be , we can establish the equation:

[0050] get , that is, when the denominator is at this value, the output frequency deviation changes by ±1×10 -12 The corresponding frequency compensation is obtained through the conversion formula Finally, the compensation amount is converted into the frequency control word of the LMX2572 frequency synthesizer, thereby realizing the closed-loop calibration of the CPT atomic clock output frequency-temperature compensation system.

[0051] It can be seen from the above embodiments that the present application adopts a temperature compensation method based on a multivariate nonlinear regression model to improve the output frequency performance of the clock. By comparative experiments, the relationship between the internal observation quantities and the output frequency of the chip atomic clock is explored, and the strong correlation between the laser temperature control quantity and the frequency output is revealed. By constructing a second-order polynomial model including the laser temperature control quantity and its rate of change, the compensation algorithm is realized by modifying the microwave frequency control word in combination with the single-chip microcomputer. This scheme shows good environmental adaptability for chip atomic clocks in the case of natural temperature fluctuations, temperature gradient changes and abnormal temperature mutations, effectively suppresses the frequency drift caused by temperature changes, and provides a reliable compensation scheme for the engineering application of chip atomic clocks in a wide temperature range environment.

[0052] Corresponding to the aforementioned embodiment of the chip atomic clock temperature compensation method based on multivariate nonlinear regression, the present application also provides an embodiment of a chip atomic clock temperature compensation device based on multivariate nonlinear regression.

[0053] Figure 5 This is a block diagram of a chip atomic clock temperature compensation device based on multivariate nonlinear regression according to an exemplary embodiment. Figure 5 , the device comprises: Observation quantity acquisition module 1 is used to monitor the host computer through the chip atomic clock serial port to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control voltage value and microwave demodulation value, and determine nine observation quantities; Accuracy determination module 2, used to obtain the output frequency of the chip atomic clock and the reference frequency output by the standard clock source, and determine the output frequency accuracy of the chip atomic clock; Correlation coefficient determination module 3, used to determine the correlation coefficient between each observation quantity and the chip atomic clock output frequency accuracy through the Pearson correlation analysis method based on the nine observation quantities and the chip atomic clock output frequency accuracy; The control amount determination module 4 is used to screen the characteristic variables that are strongly correlated with the temperature change according to the correlation coefficient, and determine the laser temperature control amount as the characteristic amount of the chip atomic clock temperature compensation model; Model building module 5, used to establish a multivariate nonlinear regression model based on the characteristic quantities, determine the model coefficients by testing and evaluating the model under multiple environmental conditions, and thus complete the model construction; The compensation amount determination module 6 is used to determine the relationship between the model frequency compensation amount and the actual control amount in the single chip microcomputer, that is, the frequency control word, based on the multivariate nonlinear regression model and the actual control process.

[0054] Regarding the apparatus in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0055] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present application scheme. A person of ordinary skill in the art can understand and implement it without paying any creative work.

[0056] Correspondingly, the present application also provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the chip atomic clock temperature compensation method based on multivariate nonlinear regression as described above.

[0057] Correspondingly, the present application also provides a computer-readable storage medium on which computer instructions are stored. When the instructions are executed by a processor, the chip atomic clock temperature compensation method based on multivariate nonlinear regression as described above is implemented.

[0058] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope and spirit of the present application are indicated by the claims.

[0059] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A chip atomic clock temperature compensation method based on multivariate nonlinear regression, characterized in that: include: The chip atomic clock serial port monitors the host computer to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control value and microwave demodulation value, and determine nine observation quantities; Obtain the output frequency of the chip atomic clock and the reference frequency output by the standard clock source to determine the output frequency accuracy of the chip atomic clock; Determine the correlation coefficient between each observation value and the output frequency accuracy of the chip atomic clock using a Pearson correlation analysis method based on the nine observation values ​​and the output frequency accuracy of the chip atomic clock; According to the correlation coefficient, characteristic variables that are strongly correlated with temperature changes are screened, and the laser temperature control amount is determined to be the characteristic amount of the chip atomic clock temperature compensation model; Based on the characteristic quantities, a multivariate nonlinear regression model is established, and the model coefficients are determined by testing and evaluating the model under multiple environmental conditions, thereby completing the model construction; According to the multivariate nonlinear regression model and in combination with the actual control process, the relationship between the model frequency compensation amount and the actual control amount in the single chip microcomputer, that is, the frequency control word, is determined.

2. The method according to claim 1, characterized in that The multivariate nonlinear regression model expression is as follows: Where, is the compensation amount, is a constant term, is the laser temperature control quantity, is the laser temperature control variable change rate, and are the polynomial coefficients, is a random error, and The highest order of laser temperature control amount and laser temperature control amount change rate respectively.

3. A chip atomic clock temperature compensation device based on multivariate nonlinear regression, characterized in that: include: The observation quantity acquisition module is used to monitor the host computer through the chip atomic clock serial port to obtain the key physical quantities inside the chip atomic clock in real time, including light intensity, laser current control quantity, laser demodulation value, laser temperature control quantity, laser temperature value, absorption bubble temperature control quantity, absorption bubble temperature value, crystal oscillator voltage control value and microwave demodulation value, and determine nine observation quantities; The accuracy determination module is used to obtain the output frequency of the chip atomic clock and the reference frequency output by the standard clock source to determine the output frequency accuracy of the chip atomic clock; A correlation coefficient determination module is used to determine the correlation coefficient between each observation quantity and the output frequency accuracy of the chip atomic clock by using a Pearson correlation analysis method based on the nine observation quantities and the output frequency accuracy of the chip atomic clock; A control quantity determination module is used to screen characteristic variables that are strongly correlated with temperature changes based on the correlation coefficient, and determine the laser temperature control quantity as the characteristic quantity of the chip atomic clock temperature compensation model; A model building module is used to establish a multivariate nonlinear regression model based on the characteristic quantities, determine the model coefficients by testing and evaluating the model under multiple environmental conditions, and thus complete the model building; The compensation amount determination module is used to determine the relationship between the model frequency compensation amount and the actual control amount in the single chip microcomputer, that is, the frequency control word, based on the multivariate nonlinear regression model and the actual control process.

4. An electronic device, characterized in that: include: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 2.

5. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by a processor, the steps of the method according to any one of claims 1 to 2 are implemented.

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