CN112152618B - Crystal oscillator calibration method based on TDMA communication system reference pulse - Google Patents
Crystal oscillator calibration method based on TDMA communication system reference pulse Download PDFInfo
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- 238000004891 communication Methods 0.000 title claims abstract description 53
- 239000013078 crystal Substances 0.000 title claims abstract description 48
- 238000000034 method Methods 0.000 title claims abstract description 17
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- 238000006243 chemical reaction Methods 0.000 claims description 4
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- 229910052701 rubidium Inorganic materials 0.000 description 3
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/26—Automatic control of frequency or phase; Synchronisation using energy levels of molecules, atoms, or subatomic particles as a frequency reference
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/0805—Details of the phase-locked loop the loop being adapted to provide an additional control signal for use outside the loop
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/099—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop
- H03L7/0991—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider
- H03L7/0992—Details of the phase-locked loop concerning mainly the controlled oscillator of the loop the oscillator being a digital oscillator, e.g. composed of a fixed oscillator followed by a variable frequency divider comprising a counter or a frequency divider
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Abstract
The invention discloses a crystal oscillator calibration method based on a TDMA communication system reference pulse, and belongs to the technical field of crystal oscillator calibration. The invention relates to a constant temperature crystal oscillator based on the communication characteristics of a ground TDMA satellite communication system terminal, which develops a TDMA satellite communication system to be used for TDMA burst reference pulses of equipment synchronous timing to tame the constant temperature crystal oscillator, thereby utilizing a master station of the TDMA communication system to send out burst reference pulses with fixed intervals, extracting errors after analog and digital frequency multiplication of reference frequencies, and utilizing the reference pulses with different time intervals to tame, thereby calibrating a radio frequency reference frequency source crystal oscillator in the TDMA satellite communication terminal receiving the burst reference pulses. The method is novel, has better frequency accuracy and stability, can simplify the circuit complexity of the terminal equipment, and reduces the platform cost.
Description
Technical Field
The invention relates to the technical field of crystal oscillator calibration, in particular to a crystal oscillator calibration method based on a TDMA communication system reference pulse.
Background
In recent years, with the increasing development and popularization of the application field of broadband satellite communication, the number of satellite communication services is rapidly increased, the channel capacity is rapidly increased, the radio frequency spectrum is increasingly crowded, and the mutual interference between communication channels becomes a prominent problem. Therefore, the international telecommunications union has made strict regulations on satellite communication adjacent channel interference. In the field of terrestrial satellite communication systems, the requirement on the precision of the occupied position of a communication signal is higher and higher, namely, the requirement on the accuracy of a reference frequency source (crystal oscillator) of a radio frequency part of a terminal of a terrestrial satellite communication system is higher and higher. Particularly, the terminal takes an internal crystal oscillator as a frequency source and feeds a clock to an external power module, the frequency source is subjected to frequency multiplication to a radio frequency band (3-6 GHz) by a radio frequency chip and then is subjected to frequency up-conversion to a high frequency Ku/Ka (10-40 GHz) or even a higher frequency band by the external power module, the frequency source is subjected to frequency multiplication by thousands to tens of thousands of times at most, and if the frequency source has an error, the radio frequency point error sent by the radio frequency module after the frequency multiplication is rapidly amplified. At present, the output accuracy of crystal oscillators of portable stations and miniaturized terminal systems of ground satellite communication equipment is manually calibrated once when the equipment leaves a factory, and along with the fact that the earth station equipment runs for a long time in uncertain severe environments such as vibration, temperature change and the like, the accuracy of the crystal oscillators is inevitably different from the accuracy of the crystal oscillators after the equipment leaves the factory, so that errors exist between a radio frequency band sent by the ground satellite communication equipment and a theoretical emission frequency band, and finally mutual crosstalk between channels can be caused due to the fact that the frequency spectrum interval of adjacent frequency band signals is too small, and therefore communication quality is affected. Therefore, a very high requirement is provided for the accuracy of a crystal oscillator serving as a reference frequency source in a satellite communication system, and the crystal oscillator serving as the frequency source of the ground satellite communication system is required to have high accuracy and still maintain high stability after the ground satellite communication system runs for a long time in uncertain severe environments such as vibration, temperature change and the like. The accuracy of the existing crystal oscillator product is good in short-time stability, but a large accumulated error exists after the crystal oscillator product works for a long time, and in addition, due to process problems, the accuracy of the output of the crystal oscillators in different batches also has small difference, and even if the crystal oscillator is constant in temperature and high in temperature, the accumulated error also exists.
At present, the frequency accuracy of the existing frequency source is better than that of a 5e-12 cesium atomic clock, a calibrated rubidium atomic clock and a common GPS/Beidou positioning system calibrated constant-temperature crystal oscillator. The cesium atomic clock and the rubidium atomic clock are expensive to calibrate, and are generally applied to a central station and a satellite, the accuracy of calibrating the constant-temperature crystal oscillator by using a GPS/Beidou positioning system of the current general system is superior to 1e-12, but for a ground satellite communication system terminal, when the GPS/Beidou calibration module is applied, an antenna receiving module, a navigation information processing module and a calibration module of the GPS/Beidou positioning system are required to be added on the existing equipment, and the cost and the complexity of a ground satellite communication system fixed station, a portable station and miniaturized terminal equipment can be increased.
In summary, although the conventional crystal oscillator calibration method can achieve the purpose of calibrating the clock, there is still room for further improvement in the practical implementation of TDMA satellite communication system engineering.
Disclosure of Invention
The invention aims to solve the technical problem of making up the problems in the prior art, and provides a crystal oscillator calibration method based on the reference pulse of a TDMA communication system in a novel way by combining the characteristic of burst reference in ground TDMA satellite communication. The method utilizes the fixed interval burst reference pulse sent by the master station of the TDMA communication system, extracts errors after analog and digital frequency multiplication of the reference frequency, and utilizes the reference pulses with different time intervals, thereby calibrating the crystal oscillator of the radio frequency reference frequency source in the TDMA satellite communication terminal, and having better frequency accuracy and stability.
In order to achieve the purpose, the invention adopts the technical scheme that:
a crystal oscillator calibration method based on a TDMA communication system reference pulse is applied to a TDMA communication terminal, the TDMA communication terminal comprises a crystal oscillator module, a digital-to-analog converter module, a clock power divider, a frequency multiplier module, a comparator module, a radio frequency receiving module, a clock feeding module and an FPGA module, and the FPGA module comprises a burst capture logic module, an error extraction module, an average filter and a PID logic module; the method comprises the following steps:
the sine wave analog signal output by the crystal oscillator module enters a clock power divider, is converted into 3 paths of sine wave analog signals with equal power through the clock power divider, and is respectively output to a comparator module, a frequency multiplier module and a clock feed module;
the radio frequency receiving module receives the burst reference pulse radio frequency signal, and the burst reference pulse radio frequency signal is converted into a baseband signal in a down-conversion mode through the clock feed module and is input into the FPGA module;
a burst capture logic module in the FPGA module receives a signal sent by a TDMA communication system master station, and generates a reference pulse signal with fixed intervals as an input signal of an error extraction module through a burst reference pulse radio frequency signal forwarded by a satellite;
the error extraction module extracts an error value by comparing the count value of the fixed interval reference pulse with the frequency count value generated by the frequency for multiple times, and then the error value is output to the PID logic module by the mean filter;
the PID logic module controls the digital-to-analog converter module to output numerical control voltage and apply the numerical control voltage to the crystal oscillator module, so that a closed-loop control structure is realized, and the domestication of the crystal oscillator module is completed.
The invention has the beneficial effects that:
1. the TDMA satellite communication system terminal uses the existing GPS/Beidou crystal oscillator calibration technology, a GPS/Beidou navigation information receiving antenna and a navigation information processing module are additionally added, and the circuit complexity of the terminal system is increased. Compared with the prior art, the invention is based on the communication characteristic of the timing synchronization of the ground TDMA satellite communication system, and the burst reference pulse of the TDMA communication system is taken as the calibration standard of the frequency source to calibrate the crystal oscillator in a new way, only the software upgrading is needed to be carried out on the prior terminal, and part of logic and circuit resources can be shared.
2. The invention not only can achieve the same or even higher frequency accuracy and stability as the prior art, but also can be realized by combining the ground TDMA satellite communication system engineering, thereby simplifying the circuit complexity of the terminal equipment and reducing the platform cost.
3. The invention is suitable for terminals with an independent clock module as a radio frequency source in a ground TDMA satellite communication system, such as a fixed station, a portable station and a miniaturized terminal of the TDMA satellite communication system, and is particularly suitable for the ground TDMA satellite communication system with severe working environment, crowded channel frequency bands, externally-fed clock of the system and almost zero frequency offset of a transmitting frequency band.
Drawings
FIG. 1 is a diagram comparing a method for calibrating a crystal oscillator according to an embodiment of the present invention with a prior art.
Fig. 2 is a schematic diagram of a TDMA burst reference pulse used in an embodiment of the present invention.
FIG. 3 is a schematic diagram of a TDMA communication terminal taming related modules in an embodiment of the present invention.
FIG. 4 is a flowchart of a method for calibrating a crystal oscillator according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a TDMA communication terminal in an embodiment of the present invention.
Detailed Description
The following detailed description of specific embodiments of the present invention will be provided in conjunction with the accompanying drawings for better understanding of the present invention by those skilled in the art. It should be particularly reminded that while detailed descriptions of known functions and designs may obscure the subject matter of the present invention in the following description, such descriptions will be omitted here.
A Crystal Oscillator calibration method based on a TDMA communication system reference pulse is applied to a TDMA communication terminal, wherein the TDMA communication terminal comprises a Crystal Oscillator (CO), a Digital-to-Analog Converter (DAC), a frequency multiplier module, a comparator module, a radio frequency receiving module, a clock feeding module and a Field Programmable Gate Array (FPGA).
The crystal oscillator module can finely adjust the output frequency according to voltage-controlled voltage provided by the outside, and the module is used as a frequency source in a ground TDMA satellite communication system terminal and respectively provides a clock source for the radio frequency receiving module and the FPGA.
And the DAC is respectively connected with the FPGA and the crystal oscillator module. The FPGA controls the DAC output voltage, and the voltage output by the DAC controls the voltage control end of the crystal oscillator, so that the frequency control of the frequency source crystal oscillator output is realized.
The clock signal output by the crystal oscillator is divided into multiple clock signals which are respectively a first clock signal, a second clock signal and a third clock signal.
And the frequency multiplier module is used for multiplying the frequency of the first clock signal and then connecting the frequency multiplied frequency to the input end of the reference frequency end of the radio frequency module.
And the comparator module is used for connecting the second clock signal to the input end of the comparator module, and the output end of the comparator module outputs a square wave clock signal.
And a frequency multiplication clock signal output by the frequency multiplier is input to a reference clock input end of the radio frequency receiving module, and a configuration interface of the radio frequency receiving module is connected with the FPGA.
And the clock feeding module inputs the third path of clock signals and the radio frequency signals output by the radio frequency receiving module into the clock feeding module together and outputs the clock feeding module.
The square wave clock signal output by the comparator module is connected to a global clock network of the FPGA, and the FPGA respectively controls the DAC and the radio frequency chip.
The invention combines the burst reference characteristic of the ground TDMA satellite communication system and utilizes the TDMA burst reference pulse originally used for equipment synchronous timing of the TDMA satellite communication system to calibrate the constant temperature crystal oscillator.
The master station uses a cesium/rubidium atomic clock as a frequency source to send TDMA burst reference pulses at fixed intervals, the TDMA burst reference pulses are transparently forwarded to a Ka/Ku antenna system through a satellite, and the TDMA burst reference pulses are output to a radio frequency receiving end of a TDMA channel terminal system after down-conversion. Inside the terminal, a radio frequency chip down-converts a burst reference pulse radio frequency signal to a baseband signal and outputs the baseband signal to an FPGA logic module, then the burst reference pulse baseband signal is subjected to demodulation preprocessing modules such as matched filtering, a burst reference pulse capturing module of an FPGA demodulation part generates logic reference pulse signals with fixed intervals and outputs the logic reference pulse signals to a frequency error extraction module. The error extraction module extracts an error value by comparing the count value of the fixed interval reference pulse with the frequency count value generated by the frequency for many times, the error value is output to the PID logic module after passing through the mean filter, the PID module controls the voltage control end of the crystal oscillator through the DAC controller according to the error, so that the frequency output by the frequency source is changed to be close to a theoretical value, the error is gradually reduced through PID loop control and is finally stabilized to be almost error-free through repeated operation, and then the frequency source outputs the clock frequency with extremely high accuracy.
The above description is a detailed description of the present invention with reference to specific preferred embodiments, and it is not to be construed that the specific embodiments of the present invention are limited to the description. It will be apparent to those skilled in the art that other signal and interface extensions and substitutions may be made without departing from the spirit of the invention, and all such changes are within the scope of the invention as defined in the claims.
Claims (1)
1. A crystal oscillator calibration method based on a TDMA communication system reference pulse is characterized in that the method is applied to a TDMA communication terminal, the TDMA communication terminal comprises a crystal oscillator module, a digital-analog converter module, a clock power divider, a frequency multiplier module, a comparator module, a radio frequency receiving module, a clock feed module and an FPGA module, and the FPGA module comprises a burst capture logic module, an error extraction module, an average value filter and a PID logic module; the method comprises the following steps:
the sine wave analog signal output by the crystal oscillator module enters a clock power divider, is converted into 3 paths of sine wave analog signals with equal power through the clock power divider, and is respectively output to a comparator module, a frequency multiplier module and a clock feed module;
the radio frequency receiving module receives the burst reference pulse radio frequency signal, and the burst reference pulse radio frequency signal is converted into a baseband signal in a down-conversion mode through the clock feed module and is input into the FPGA module;
a burst capture logic module in the FPGA module receives a signal sent by a TDMA communication system master station, and generates a reference pulse signal with fixed intervals as an input signal of an error extraction module through a burst reference pulse radio frequency signal forwarded by a satellite;
the error extraction module extracts an error value by comparing the count value of the fixed interval reference pulse with the frequency count value generated by the frequency for multiple times, and then the error value is output to the PID logic module by the mean filter;
the PID logic module controls the digital-to-analog converter module to output numerical control voltage and apply the numerical control voltage to the crystal oscillator module, so that a closed-loop control structure is realized, and the domestication of the crystal oscillator module is completed.
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| CN113359191B (en) * | 2021-06-01 | 2022-04-19 | 中国科学院地质与地球物理研究所 | Real-time correction method of constant-temperature crystal oscillator and electromagnetic receiver |
| US11545933B2 (en) | 2021-06-01 | 2023-01-03 | Institute Of Geology And Geophysics, Chinese Academy Of Sciences | Real-time correction method for oven controlled crystal oscillator and electromagnetic receiver |
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