A crystal oscillator frequency deviation correction device and method based on GNSS system

Abstract

The present invention discloses a crystal oscillator frequency deviation correction device and method based on a GNSS system, which overcomes the limitations of satellite frequency granting devices in the prior art. The correction device includes: a satellite receiving module for receiving satellite signals and calculating the frequency deviation of a voltage-controlled crystal oscillator, and outputting the decoded frequency deviation data; a frequency deviation processing module for processing the frequency deviation data and positioning information output by the satellite receiving module and outputting a digital voltage; a digital-to-analog converter for converting the digital voltage output by the frequency deviation processing module into an analog voltage and sending the converted analog voltage to the voltage control terminal of the voltage-controlled crystal oscillator; and a voltage-controlled crystal oscillator for providing a frequency. The device can control the crystal oscillator frequency deviation and generate high-precision clocks and second pulses.

Description

Technical Field

[0001] The present invention relates to the field of satellite clock technology, and in particular to a crystal oscillator frequency deviation correction device and method based on a GNSS system. Background Art

[0002] The rapid development of information technology is placing increasingly high demands on clock accuracy. High-precision clocks play a vital role in power systems, traffic dispatching, measurement and control instrumentation, and other fields. High-precision clock sources, such as rubidium and cesium clocks, offer excellent long-term and short-term stability, but are costly and have strict environmental requirements. Consequently, they are primarily used in laboratories and other applications requiring extremely high precision. With the continuous improvement of satellite systems, satellite signal receivers can receive satellite signals through antennas and decode the pulse-per-second (1PPS) signal, which exhibits excellent long-term stability. By correcting for the frequency deviation of crystal oscillators, which exhibit good short-term stability but poor long-term stability, they can generate high-precision, stable clocks at low cost.

[0003] Existing technologies mainly implement high-precision frequency offset correction from two aspects:

[0004] (1) Frequency offset correction device: The frequency offset correction device is composed of a satellite signal receiving module, a field programmable gate array (FPGA), a microcontroller unit (MCU), etc.

[0005] (2) Frequency deviation correction method: Use unbiased FIR, wavelet transform, neural network and other methods to filter the frequency deviation, and use traditional PI or PID to control the frequency deviation.

[0006] Existing solutions have the following technical problems:

[0007] (1) Frequency offset correction device: Satellite receiving modules, FPGAs, MCUs and other devices use different crystal oscillators to provide clock sources, which introduces errors and increases costs;

[0008] (2) Frequency offset correction methods: Unbiased FIR, wavelet transform, and neural network models are complex and require large amounts of computation, which increases the burden on the system. Traditional PI and PID parameters are fixed, resulting in large overshoot, poor interference response, and long correction times. Summary of the Invention

[0009] The purpose of the present invention is to overcome the limitations of satellite frequency granting devices in the prior art and to provide a crystal oscillator frequency deviation correction device and method based on a GNSS system, which can control the crystal oscillator frequency deviation and enable the GNSS system to generate high-precision clocks and second pulses.

[0010] In order to achieve the above object, the present invention adopts the following technical solution: a crystal oscillator frequency deviation correction device based on a GNSS system, comprising:

[0011] Satellite receiving module, used to receive satellite signals and calculate the frequency deviation of the voltage-controlled crystal oscillator, and output the decoded frequency deviation data;

[0012] The frequency deviation processing module is used to process the frequency deviation and positioning information output by the satellite receiving module and output a digital voltage;

[0013] A digital-to-analog converter, used to convert the voltage digital quantity output by the frequency deviation processing module into a voltage analog quantity, and send the converted voltage analog quantity to the voltage control terminal of the voltage-controlled crystal oscillator;

[0014] Voltage-controlled crystal oscillator, used to provide frequency.

[0015] The input end of the satellite receiving module is connected to the antenna and the output end of the voltage-controlled crystal oscillator. The output end of the satellite receiving module is connected to the input end of the frequency deviation processing module. The output end of the frequency deviation processing module is connected to the digital-to-analog converter. The digital-to-analog converter is connected to the voltage control input end of the voltage-controlled crystal oscillator.

[0016] This application uses a single voltage-controlled crystal oscillator (VCO) to provide a frequency source for the device. The satellite receiver module calculates and outputs the VCO's frequency deviation, eliminating the need for additional components to measure the frequency deviation. An input terminal of the satellite receiver module receives satellite signals via an antenna, while an input terminal of the frequency deviation processing module receives the frequency deviation and positioning information output by the satellite receiver module. An output terminal of the frequency deviation processing module transmits a voltage analog value to the VCO's voltage control input terminal via a digital-to-analog converter to implement frequency deviation correction.

[0017] Preferably, the frequency offset processing module includes:

[0018] The data pre-processing unit is used to receive and analyze the frequency deviation and positioning satellite number output by the satellite receiving module, determine whether the frequency deviation is abnormal, eliminate the abnormal frequency deviation, and obtain the effective frequency deviation;

[0019] A frequency deviation filtering unit, used to remove noise and errors of the effective frequency deviation sent by the data pre-processing unit;

[0020] A parameter analysis unit is used to analyze the distribution range of the natural frequency deviation variation of the voltage-controlled crystal oscillator over a period of time and calculate the conversion relationship between the voltage digital value of the voltage-controlled crystal oscillator and the frequency deviation of the voltage-controlled crystal oscillator;

[0021] The frequency deviation control unit is used to adjust and control the frequency deviation to obtain a voltage digital value.

[0022] The data preprocessing unit receives and analyzes the frequency deviation and the number of positioning satellites from the satellite receiving module through the serial port, and decides whether to pass the data to the frequency deviation filtering unit based on the number of positioning satellites. When the positioning signal is lost, the frequency deviation value still exists but is abnormal; when the voltage digital quantity adjustment amplitude is too large, the number of satellites fluctuates in the short term, and the frequency deviation is abnormal at this time. The abnormal frequency deviation is judged by the number of positioning satellites, and the abnormal frequency deviation is eliminated through delay processing to avoid the abnormal frequency deviation collected in the above situation from being passed to the frequency deviation filtering unit. The frequency deviation filtering unit is mainly an adaptive window sliding median filter to filter out the errors caused by frequency deviation measurement and reception. Considering that when the sliding median filter window is set too large, the GNSS system will have a large lag, and when the window is set too small, the filtering effect is not obvious; this application dynamically adjusts the window size by analyzing the fluctuation of the frequency deviation value over a period of time. The frequency deviation control unit converts the frequency deviation into a voltage digital quantity.

[0023] Preferably, the frequency deviation control unit includes:

[0024] A coarse adjustment control unit, used to quickly reduce a larger frequency deviation by fixing a proportional coefficient or to amplify a smaller frequency deviation by increasing the proportional coefficient;

[0025] The fine adjustment control unit is used to control the frequency deviation, calculate the voltage digital quantity, judge the relationship between the voltage digital quantity and the set value, and calculate the adjusted voltage digital quantity based on the judgment result.

[0026] The system can be divided into two functional stages: coarse frequency deviation adjustment and fine frequency deviation adjustment. The coarse frequency deviation adjustment stage employs an adaptive proportional control strategy. Initially, a fixed proportional coefficient is used to rapidly reduce the frequency deviation. Later, when the frequency deviation decreases to near zero, the proportional coefficient is increased to reverse the frequency deviation. When the frequency deviation reverses, the fine frequency deviation adjustment stage begins. Fuzzy PID control is used to convert the frequency deviation into a digital voltage value. Because a large digital value can cause significant overshoot and deviate from a stable state, when the digital voltage value exceeds the set range, the set upper and lower limits are used as the digital voltage value. However, this can also cause significant interference (such as sudden temperature changes or wind speed fluctuations) to occur, preventing the system from responding promptly. Therefore, an additional anti-interference measure is implemented. If the frequency deviation continuously exceeds the preset value, interference is considered present. The upper and lower limits of the digital voltage value are ignored, allowing for rapid response.

[0027] Preferably, the data loading unit is used to store the crystal oscillator frequency deviation change over a period of time, the voltage digital value and the frequency deviation conversion relationship value, and the voltage digital value when the device enters the frequency deviation control fine adjustment stage.

[0028] When the system is just powered on, in order to maintain the initial frequency deviation of the crystal oscillator within a smaller range, the frequency deviation processing module loads the voltage digital value when the system enters the fine adjustment stage from the coarse adjustment stage before power failure, as the initial value of the crystal oscillator voltage control end. If this value does not exist, the median of the crystal oscillator control voltage digital value is taken as the initial value of the voltage control end.

[0029] Preferably, abnormal frequency deviation includes: when the positioning signal is lost, the frequency deviation value persists but is abnormal; when the voltage digital value is adjusted too much, the number of satellites fluctuates briefly, in which case the frequency deviation is abnormal. For example, when the satellite signal is lost, the satellite positioning number is used to determine that the frequency deviation is unusable, and the data is discarded. When the voltage digital value is changed significantly, the number of satellites fluctuates briefly, in which case the frequency deviation is abnormal, and the frequency deviation is discarded through delay processing and satellite count determination.

[0030] A method for correcting crystal oscillator frequency deviation based on a GNSS system, comprising the following steps:

[0031] S1: The device is powered on and the voltage digital value saved before the last power failure is determined to be present.

[0032] S2: If the voltage digital value saved before the device was powered off last time exists, convert it into voltage analog value and adjust the initial frequency deviation of the crystal oscillator to keep the initial frequency deviation within a smaller range;

[0033] S3: Receive satellite signals and decode them to obtain the number of positioning satellites;

[0034] S4: Determine whether the frequency deviation is abnormal based on the number of positioning satellites;

[0035] S5: Adjust and control the frequency deviation to obtain the current digital value of the crystal oscillator voltage;

[0036] S6: Convert the voltage digital quantity into voltage analog quantity and adjust the crystal oscillator frequency deviation.

[0037] This invention uses an adaptive window sliding median to eliminate frequency deviation errors. It also employs adaptive proportional control and fuzzy PID control strategies to control frequency deviation, enabling the system to generate high-precision clock and pulse-per-second signals. The resulting digital voltage is converted into an analog voltage and fed into the voltage control terminal of a voltage-controlled crystal oscillator to achieve frequency deviation correction.

[0038] Preferably, the step S2 further comprises:

[0039] If the voltage digital value saved before the last power failure does not exist, take the median of the crystal oscillator control voltage digital value as the initial value of the crystal oscillator voltage control terminal, and convert it into a voltage analog value to adjust the initial frequency deviation of the crystal oscillator.

[0040] Preferably, the step S2 further includes measuring the natural change of the crystal oscillator frequency deviation and the conversion relationship between the voltage digital value and the frequency deviation if the voltage digital value saved before the last power failure does not exist:

[0041] A: Maintain the voltage digital value constant for a period of time, record the frequency deviation and analyze the value range of the frequency deviation change;

[0042] B: Adjust the voltage digital value and record the current frequency deviation;

[0043] C: Narrow the voltage digital value adjustment range and repeat step B to obtain the conversion relationship between the voltage digital value and the frequency deviation;

[0044] D: Store the conversion relationship obtained in step C.

[0045] First, adjust the voltage digital value significantly and record the current frequency deviation. Then reduce the range and repeat several times to obtain a more stable conversion relationship between the voltage digital value and the frequency deviation.

[0046] Preferably, the specific method for determining whether there is abnormal frequency deviation is:

[0047] If the number of positioning satellites is greater than the preset value, the current frequency offset is retained; if the number of positioning satellites is less than the preset value, the current frequency offset is eliminated to obtain the effective frequency offset, and then the adaptive window sliding median algorithm is used to filter the effective frequency offset. The size of the adaptive window is dynamically adjusted according to the fluctuation of the frequency offset value over a period of time.

[0048] First, the received satellite signal is analyzed and the number of positioning satellites and frequency deviation are separated. Then, the presence of abnormal frequency deviation is determined based on the number of positioning satellites.

[0049] Preferably, the specific steps of step S5 are:

[0050] S5.1: From the start of frequency deviation control to the moment the frequency deviation decreases to zero, based on the adaptive proportional control strategy, the digital voltage is obtained by multiplying the frequency deviation by the set proportional coefficient. As the frequency deviation approaches zero, the proportional coefficient multiplied by the frequency deviation is increased.

[0051] S5.2: When the frequency deviation changes in the opposite direction, the proportional coefficient P, integral coefficient I, and differential coefficient D corresponding to the current frequency deviation and the frequency deviation change are calculated using a pre-set set of rules based on the fuzzy PID control strategy;

[0052] S5.3: Multiply the three parameters in step S5.2 by the frequency deviation, the accumulated frequency deviation, and the frequency deviation change, and sum them to obtain a digital voltage value;

[0053] S5.4: When the voltage digital value obtained in step S5.3 exceeds the voltage digital value setting value, the setting value is taken as the current voltage digital value;

[0054] S5.5: When the frequency deviation exceeds the expected value twice in a row, the voltage setting value limit is ignored, and the corresponding voltage digital value when the frequency deviation changes in the opposite direction is stored as the initial voltage digital value of the crystal oscillator after the device is powered on next time.

[0055] The device enters frequency deviation control mode, which is divided into two phases: coarse adjustment and fine adjustment, depending on the time period and deviation value of the frequency deviation. The coarse adjustment phase corresponds to the start of frequency deviation control until the frequency deviation decreases to 0. When the frequency deviation changes in the opposite direction, the system enters the fine adjustment phase. The digital voltage corresponding to the device entering the fine adjustment control phase is stored and used as the initial crystal oscillator voltage digital value after the device is next powered on. The digital voltage obtained in step S5.3 = proportional coefficient * frequency deviation + integral coefficient * accumulated frequency deviation + differential coefficient * frequency deviation change.

[0056] Therefore, the present invention has the following beneficial effects: 1. The same voltage-controlled crystal oscillator is used to provide a frequency source for the entire system device, and the satellite receiving module calculates and outputs the frequency deviation of the local voltage-controlled crystal oscillator, without the need for additional devices to measure the frequency deviation; 2. The error in the frequency deviation is eliminated by using an adaptive window sliding median, and the frequency deviation is controlled by using adaptive proportional control and fuzzy PID control algorithms, so that the system generates high-precision clocks and second pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram of the system structure of the correction device in the present invention.

[0058] Figure 2 It is a flow chart of the steps of the correction method in the present invention.

[0059] In the figure: 1. Satellite receiving module; 2. Frequency deviation processing module; 3. Digital-to-analog converter; 4. Voltage-controlled crystal oscillator; 5. Data preprocessing unit; 6. Frequency deviation filtering unit; 7. Parameter analysis unit; 8. Frequency deviation control unit; 9. Coarse adjustment control unit; 10. Fine adjustment control unit; 11. Data loading unit. DETAILED DESCRIPTION

[0060] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0061] Example 1:

[0062] This embodiment is a crystal oscillator frequency deviation correction device based on the GNSS system. Figure 1As shown, the system comprises: a satellite receiving module 1, a frequency deviation processing module 2, a digital-to-analog converter 3, and a voltage-controlled crystal oscillator 4, which are connected in sequence. The frequency deviation processing module comprises a data preprocessing unit 5, a frequency deviation filtering unit 6, and a parameter analysis unit 7, which are connected in sequence. The data preprocessing unit is also connected to the satellite receiving module. The frequency deviation filtering unit and the parameter analysis unit are also connected to a data loading unit 11. The data loading unit is also connected to a frequency deviation control unit 8, which is also connected to the digital-to-analog converter. The frequency deviation control unit comprises a coarse adjustment control unit 9 and a fine adjustment control unit 10.

[0063] During operation, the voltage-controlled crystal oscillator (VCO) provides a frequency source to the satellite receiving module and the frequency deviation processing module. The satellite receiving module receives satellite signals via an antenna at one input. The frequency deviation measurement unit within the module calculates the VCO's frequency deviation relative to the 1PPS signal and outputs the frequency deviation along with other decoded data. The data preprocessing unit in the frequency deviation processing module analyzes and processes the signal to obtain the effective frequency deviation. The result is then fed into the frequency deviation filtering unit to remove noise and errors. The data loading unit then retrieves the crystal oscillator's parameters. If the required parameters do not exist, the parameter analysis unit calculates them before frequency deviation control can be performed. The frequency deviation control unit consists of two stages: a coarse adjustment control unit and a fine adjustment control unit. The coarse adjustment stage utilizes an adaptive pure proportional control strategy, while the fine adjustment stage employs a fuzzy PID control strategy. The data obtained by the frequency deviation control unit is applied to the voltage control terminal of the VCO via a digital-to-analog converter to implement the crystal oscillator's frequency deviation correction function.

[0064] The frequency deviation processing module is specifically characterized as follows:

[0065] The data preprocessing unit receives and analyzes the frequency offset and positioning satellite count from the satellite receiving module via the serial port. Based on the positioning satellite count, the data is then passed to the frequency offset filtering unit. When the positioning signal is lost, the frequency offset value remains abnormal, albeit with an abnormal value. When the voltage digital adjustment amplitude is excessive, the satellite count fluctuates briefly, resulting in abnormal frequency offset. This design uses the positioning satellite count to identify abnormal frequency offset data and eliminates this data through delay processing, preventing any such abnormal frequency offset from being passed to the frequency offset filtering unit.

[0066] The frequency offset filter unit primarily employs an adaptive sliding median filter to remove errors introduced by frequency offset measurement and reception. Considering that excessively large sliding median filter windows can lead to significant lag in the GNSS system, while excessively small windows can lead to ineffective filtering, this design dynamically adjusts the window size by analyzing frequency offset fluctuations over time.

[0067] The parameter analysis unit analyzes the distribution of the VCC's frequency deviation over time, providing a reference for setting fuzzy PID parameters for subsequent frequency deviation correction. Furthermore, the crystal oscillator parameter analysis unit analyzes and calculates the conversion relationship between the VCC voltage and frequency deviation. By significantly varying the crystal oscillator control voltage and recording the current digital voltage and corresponding frequency deviation, the unit analyzes and determines the conversion relationship between the digital voltage and the VCC frequency deviation.

[0068] The frequency deviation control unit converts the frequency deviation into a digital voltage value. Functionally, it can be divided into two phases: coarse frequency deviation adjustment and fine frequency deviation adjustment. The coarse frequency deviation adjustment phase employs an adaptive proportional control strategy. Initially, a fixed proportional coefficient is used to rapidly reduce the frequency deviation. Later, when the frequency deviation decreases to near zero, the proportional coefficient is increased to reverse the frequency deviation. When the frequency deviation reverses, the system enters the fine frequency deviation adjustment phase, where a fuzzy PID control strategy is used to convert the frequency deviation into a digital voltage value. Because excessive digital values ​​can cause significant overshoot and deviate from a stable state, when the digital voltage value exceeds the set range, the set upper and lower limits are used as the digital voltage value. However, this can also cause the system to be unable to respond promptly to large disturbances (such as sudden temperature changes or wind speed fluctuations). Therefore, an additional anti-interference measure is implemented. If the frequency deviation continuously exceeds a preset value, interference is considered present and the upper and lower limits of the digital voltage value are ignored, allowing for rapid response.

[0069] The data loading unit stores the distribution range of the natural frequency deviation variation of the current voltage-controlled crystal oscillator, the conversion relationship between the voltage digital quantity and the frequency deviation, and the voltage digital quantity when the system enters the frequency deviation control fine adjustment stage.

[0070] This device uses the same voltage-controlled crystal oscillator to provide a frequency source to the device. The satellite receiving module calculates and outputs the frequency deviation of the voltage-controlled crystal oscillator. No additional devices are required to measure the frequency deviation. An adaptive window sliding median is used to eliminate the error in the frequency deviation. Adaptive proportional control and fuzzy PID control strategies are used to control the frequency deviation, enabling the GNSS system to generate high-precision clocks and second pulses.

[0071] This embodiment also provides a method for correcting crystal oscillator frequency deviation based on a GNSS system, such as Figure 2As shown, the following steps are included: first, powering on the device and determining whether a voltage digital value saved before the device was last powered off exists; second, if the voltage digital value saved before the device was last powered off exists, converting it into a voltage analog value, and adjusting the initial frequency deviation of the crystal oscillator; third, receiving and decoding satellite signals to obtain the number of positioning satellites; fourth, calculating the crystal oscillator frequency deviation, and determining whether an abnormal frequency deviation exists based on the relationship between the number of positioning satellites and the calculated frequency deviation; fifth, adjusting and controlling the frequency deviation to obtain a current crystal oscillator voltage digital value; and sixth, converting the voltage digital value into a voltage analog value, and adjusting the crystal oscillator frequency deviation.

[0072] This method can quickly respond to abnormal frequency deviation data. For example, when a satellite signal is lost, the satellite positioning count indicates that the frequency deviation is unusable, and the data is discarded. When the digital voltage is significantly altered, the satellite count fluctuates briefly, indicating an abnormal frequency deviation. This data is discarded through delay processing and satellite count determination. This allows the GNSS system to generate highly accurate clock and second pulses.

[0073] The compensation method of this application is further explained below:

[0074] Step 1: Power on the device and determine whether the voltage digital value saved before the device was powered off last time exists.

[0075] Step 2: If the voltage digital value saved before the device was powered off last time exists, convert it into voltage analog value and adjust the initial frequency deviation of the crystal oscillator.

[0076] When the system is just powered on, in order to maintain the initial frequency deviation of the crystal oscillator within a smaller range, the frequency deviation processing module loads the voltage digital value when the device enters the fine adjustment stage from the coarse adjustment before power failure as the initial value of the crystal oscillator voltage control terminal.

[0077] If the voltage digital value saved before the last power failure does not exist, take the median of the crystal oscillator control voltage digital value as the initial value of the crystal oscillator voltage control terminal, and convert it into a voltage analog value to adjust the initial frequency deviation of the crystal oscillator.

[0078] At the same time, if the voltage digital value saved before the last power failure does not exist, the natural change of the crystal oscillator frequency deviation and the conversion relationship between the voltage digital value and the frequency deviation are measured: first, the voltage digital value is maintained unchanged for a period of time, the frequency deviation is recorded and the value range of the frequency deviation change is analyzed; then, the voltage digital value is adjusted significantly and the current frequency deviation is recorded; then, the voltage digital value adjustment range is narrowed, the voltage digital value is adjusted and the current frequency deviation is recorded to obtain a relatively stable conversion relationship between the voltage digital value and the frequency deviation; and the above measurement results are stored.

[0079] Step 3: Receive satellite signals and decode them to obtain the number of positioning satellites.

[0080] The satellite signal receiving module receives satellite signals through an antenna and decodes them to obtain positioning information and 1PPS. The module's internal frequency deviation measurement unit calculates the frequency difference of the voltage-controlled crystal oscillator relative to the 1PPS and outputs the frequency deviation and positioning information. The data preprocessing unit in the frequency deviation processing module analyzes the data from the satellite signal receiving module and separates the number of positioning satellites and the frequency deviation.

[0081] Step 4: Determine whether the frequency deviation is abnormal based on the number of positioning satellites.

[0082] If the number of positioning satellites is greater than the preset value, the current frequency offset is retained; if the number of positioning satellites is less than the preset value, the current frequency offset is eliminated to obtain the effective frequency offset, and then the adaptive window sliding median algorithm is used to filter the effective frequency offset. The size of the adaptive window is dynamically adjusted according to the fluctuation of the frequency offset value over a period of time.

[0083] Step 5: Adjust and control the frequency deviation to obtain the current digital value of the crystal oscillator voltage.

[0084] The device enters frequency deviation control mode, which is divided into a coarse adjustment phase and a fine adjustment phase based on the frequency deviation time period and deviation value. The coarse adjustment phase corresponds to the start of frequency deviation control until the frequency deviation decreases to zero. Based on the adaptive proportional control strategy, the frequency deviation is multiplied by a set proportional coefficient to obtain a digital voltage. As the frequency deviation approaches zero, the proportional coefficient multiplied by the frequency deviation is increased. When the frequency deviation changes in the opposite direction, the device enters the fine adjustment phase. Based on the fuzzy PID control strategy, a predefined set of rules is used to calculate the proportional coefficient P, integral coefficient I, and differential coefficient D corresponding to the current frequency deviation and the frequency deviation change. These three parameters are then multiplied by the frequency deviation, the accumulated frequency deviation, and the frequency deviation change, respectively, and the sum is calculated to obtain a digital voltage. If this digital voltage exceeds the set value, the set value is used as the current digital voltage. If the frequency deviation exceeds the expected value twice consecutively, the set voltage limit is ignored. The digital voltage corresponding to the system entering the fine adjustment control phase is stored in the data loading module and used as the initial digital voltage of the crystal oscillator after the system is powered on again.

[0085] Step 6: Convert the digital voltage into analog voltage and adjust the crystal oscillator frequency deviation.

[0086] The voltage digital quantity obtained in the fifth step is converted into a voltage analog quantity through a digital-to-analog converter and sent to the voltage control terminal of the voltage-controlled crystal oscillator to realize the frequency deviation correction function.

[0087] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A crystal oscillator frequency deviation correction device based on a GNSS system, characterized in that: include: Satellite receiving module, used to receive satellite signals and calculate the frequency deviation of the voltage-controlled crystal oscillator, and output the decoded frequency deviation data; The frequency deviation processing module is used to process the frequency deviation and positioning information output by the satellite receiving module and output a digital voltage. When processing the frequency deviation, an adaptive proportional control strategy is adopted. In the early stage, a fixed proportional coefficient proportional control is used to quickly reduce the frequency deviation. In the later stage, when the frequency deviation is reduced to close to 0, the proportional coefficient is increased to change the frequency deviation in the opposite direction. When the frequency deviation changes in the opposite direction, the frequency deviation fine adjustment stage is entered, and the frequency deviation is converted into a digital voltage through a fuzzy PID control strategy and anti-interference combination. A digital-to-analog converter, used to convert the voltage digital quantity output by the frequency deviation processing module into a voltage analog quantity, and send the converted voltage analog quantity to the voltage control terminal of the voltage-controlled crystal oscillator; A voltage-controlled crystal oscillator, wherein the output end of the voltage-controlled crystal oscillator is connected to the frequency input end of the satellite receiving module to provide frequency.

2. The crystal oscillator frequency deviation correction device based on the GNSS system according to claim 1, characterized in that: The frequency deviation processing module includes: The data pre-processing unit is used to receive and analyze the frequency deviation and positioning satellite number output by the satellite receiving module, determine whether the frequency deviation is abnormal, eliminate the abnormal frequency deviation, and obtain the effective frequency deviation; A frequency deviation filtering unit, used to remove noise and errors of the effective frequency deviation sent by the data pre-processing unit; The parameter analysis unit is used to analyze the frequency deviation variation of the voltage-controlled crystal oscillator over a period of time and calculate the conversion relationship between the voltage-controlled crystal oscillator voltage digital value and the voltage-controlled crystal oscillator frequency deviation; The frequency deviation control unit is used to adjust and control the frequency deviation to obtain a corresponding voltage digital value.

3. The crystal oscillator frequency deviation correction device based on the GNSS system according to claim 2, characterized in that: The frequency deviation control unit includes: A coarse adjustment control unit, used to quickly reduce a larger frequency deviation by fixing a proportional coefficient or to amplify a smaller frequency deviation by increasing the proportional coefficient; The fine adjustment control unit is used to fine-tune the frequency deviation, calculate the voltage digital value, judge the relationship between the voltage digital value and the set value, and calculate the adjusted voltage digital value based on the judgment result.

4. A crystal oscillator frequency deviation correction device based on a GNSS system according to claim 2 or 3, characterized in that: The frequency deviation processing module further includes: The data loading unit is used to save the crystal oscillator frequency deviation change within a period of time, the voltage digital value and frequency deviation conversion relationship value, and the voltage digital value when the device enters the frequency deviation control fine adjustment stage.

5. The crystal oscillator frequency deviation correction device based on the GNSS system according to claim 2 or 3, characterized in that: The abnormal frequency deviation includes: when the positioning signal is lost, the frequency deviation value still exists but is abnormal; when the voltage digital quantity adjustment amplitude is too large, the number of satellites fluctuates in the short term, and the frequency deviation is abnormal at this time.

6. A method for correcting crystal oscillator frequency deviation based on a GNSS system, applied to a device for correcting crystal oscillator frequency deviation based on a GNSS system as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1: The device is powered on and the voltage digital value saved before the device was powered off is determined to be present. S2: If the voltage digital value saved before the device was powered off last time exists, convert it into voltage analog value and adjust the initial frequency deviation of the crystal oscillator; S3: Receive satellite signals and decode them to obtain the number of positioning satellites and frequency deviation values; S4: Determine whether the frequency deviation is abnormal based on the number of positioning satellites; S5: Adjust and control the frequency deviation to obtain the current digital value of the crystal oscillator voltage; S6: Convert the voltage digital quantity into voltage analog quantity and adjust the crystal oscillator frequency deviation.

7. The method for correcting crystal oscillator frequency deviation based on a GNSS system according to claim 6, characterized in that: The step S2 further includes: If the voltage digital value saved before the last power failure does not exist, take the median of the crystal oscillator control voltage digital value as the initial value of the crystal oscillator voltage control terminal, and convert the initial value of the crystal oscillator voltage control terminal into a voltage analog value to adjust the initial frequency deviation of the crystal oscillator.

8. A method for correcting crystal oscillator frequency deviation based on a GNSS system according to claim 6 or 7, characterized in that: The step S2 further includes measuring the natural change of the crystal oscillator frequency deviation and the conversion relationship between the voltage digital value and the frequency deviation if the voltage digital value saved before the last power failure does not exist: A: Maintain the voltage digital value constant for a period of time, record the frequency deviation and analyze the value range of the frequency deviation change; B: Adjust the voltage digital value and record the current frequency deviation; C: Narrow the voltage digital value adjustment range and repeat step B to obtain the conversion relationship between the voltage digital value and the frequency deviation; D: Store the conversion relationship obtained in step C.

9. The method for correcting crystal oscillator frequency deviation based on a GNSS system according to claim 6, wherein: In step S4, the specific method of determining whether there is abnormal frequency deviation is: If the number of positioning satellites is greater than the preset value, the current frequency offset is retained; if the number of positioning satellites is less than the preset value, the current frequency offset is eliminated to obtain the effective frequency offset, and then the adaptive window sliding median algorithm is used to filter the effective frequency offset. The size of the adaptive window is dynamically adjusted according to the fluctuation of the frequency offset value over a period of time.

10. The method for correcting crystal oscillator frequency deviation based on a GNSS system according to claim 6, characterized in that: The specific steps of step S5 are: S5.1: From the start of frequency deviation control to the moment the frequency deviation decreases to zero, based on the adaptive proportional control strategy, the digital voltage is obtained by multiplying the frequency deviation by the set proportional coefficient. As the frequency deviation approaches zero, the proportional coefficient multiplied by the frequency deviation is increased. S5.2: When the frequency deviation changes in the opposite direction, the proportional coefficient P, integral coefficient I, and differential coefficient D corresponding to the current frequency deviation and the frequency deviation change are calculated using a pre-set set of rules based on the fuzzy PID control strategy; S5.3: Multiply the three parameters in step S5.2 by the frequency deviation, the accumulated frequency deviation, and the frequency deviation change, and sum them to obtain a digital voltage value; S5.4: When the voltage digital value obtained in step S5.3 exceeds the voltage digital value setting value, the setting value is taken as the current voltage digital value; S5.5: When the frequency deviation exceeds the expected value twice in a row, the voltage setting value limit is ignored, and the corresponding voltage digital value when the frequency deviation changes in the opposite direction is stored as the initial voltage digital value of the crystal oscillator after the device is powered on next time.

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