CN107483051B - Precision Frequency Corrector Based on Direct Digital Measurement and Processing - Google Patents
Precision Frequency Corrector Based on Direct Digital Measurement and Processing Download PDFInfo
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- CN107483051B CN107483051B CN201710675629.XA CN201710675629A CN107483051B CN 107483051 B CN107483051 B CN 107483051B CN 201710675629 A CN201710675629 A CN 201710675629A CN 107483051 B CN107483051 B CN 107483051B
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- 238000005259 measurement Methods 0.000 title claims abstract description 30
- 238000012545 processing Methods 0.000 title claims abstract description 9
- 239000013078 crystal Substances 0.000 claims abstract description 26
- 238000012937 correction Methods 0.000 claims abstract description 15
- 238000013139 quantization Methods 0.000 claims abstract description 12
- 230000000694 effects Effects 0.000 claims abstract description 10
- 238000005070 sampling Methods 0.000 claims abstract description 7
- 230000001629 suppression Effects 0.000 claims abstract description 6
- 238000005516 engineering process Methods 0.000 claims abstract description 5
- 230000032683 aging Effects 0.000 abstract description 5
- 239000010453 quartz Substances 0.000 abstract description 2
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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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Abstract
本发明公开了一种基于直接数字化测量和处理的精密频率改正器，用于解决工程应用类原子钟、精密石英晶体振荡器老化和自身频率准确度变化的调整和补偿。本发明基于先进的直接数字测量原理，即在数字化的背景下，采用双路ADC测量结构，借助于采样时钟和输入信号之间的时钟游标效应以及模数转换器的量化误差抑制技术。此发明相比传统的频率改正器宽范围频率调节，其不同之处在于采用晶体振荡器作为公用时钟，通过频率改正功能实现设定的目标频率输出，其输出信号的频率范围明显要窄的多，如从0.1mHz到10Hz，同时可以实现秒级稳定度小于3*10‑12，以及10‑12量级的微小频率改正。相比传统的频率改正器该改正器为连续改正，并且性价比更高。The invention discloses a precise frequency corrector based on direct digital measurement and processing, which is used for adjusting and compensating for engineering application-like atomic clocks, precise quartz crystal oscillator aging and self-frequency accuracy changes. The invention is based on the advanced direct digital measurement principle, that is, in the background of digitization, a dual-channel ADC measurement structure is adopted, with the help of clock vernier effect between the sampling clock and the input signal and the quantization error suppression technology of the analog-to-digital converter. Compared with the wide-range frequency adjustment of the traditional frequency corrector, the difference of this invention is that the crystal oscillator is used as the common clock, and the set target frequency output is realized through the frequency correction function, and the frequency range of the output signal is obviously much narrower. , such as from 0.1mHz to 10Hz, at the same time, it can achieve a stability of less than 3*10 ‑12 in seconds, and a small frequency correction of the order of 10 ‑12 . Compared with the traditional frequency corrector, the corrector is continuous correction, and it is more cost-effective.
Description
Technical Field
The invention belongs to the technical field of satellite navigation, communication, precise measurement instruments and precise clock sources, and is used for adjusting and compensating aging of engineering application atomic clocks and precise quartz crystal oscillators and self frequency accuracy change.
Background
In order to have a wide frequency adjustment range, a frequency synthesizer often has difficulty in having a fine frequency adjustment step value, and although an atomic clock and a crystal oscillator have excellent performance, aging drift occurs to change a frequency nominal value, so that in order to use the crystal oscillator as a precise frequency source, an instrument or a device is required to finely correct the frequency of an output signal of the atomic clock and the crystal oscillator, thereby maintaining high accuracy of the atomic clock and the crystal oscillator. The prior art has complex structure, high cost and inconvenient use, so a frequency corrector with high precision, wide range and low cost is needed to solve the aging drift problem of atomic clocks and the like.
Disclosure of Invention
The invention discloses a precise frequency corrector based on direct digital measurement and processing, which has the characteristics of high precision, wide range and low cost.
The technical scheme of the invention is as follows: a precise frequency corrector based on direct digital measurement and processing is characterized by comprising a double-path ADC, an FPGA, an MCU, a DAC and a voltage-controlled crystal oscillator VCXO, wherein the MCU is provided with an external USB interface, an external high-stability crystal oscillator is adopted as a common clock signal, and a frequency source input signal f is measured by means of clock vernier effect and quantization error suppression technology0And the actual output signal fxThe frequency difference between the two signals is compared with a set frequency difference delta f to realize the set target frequency output, the frequency correction range is from 0.1mHz to 10Hz, and meanwhile, the micro frequency correction with the second-level stability of less than 3 x 10-12 and the 10-12-level can be realized.
The invention adopts a double-path ADC measurement structure, wherein one path is used for collecting a frequency source input signal f0One path is used for collecting VCXO output signals to form feedback, the two paths of ADCs and the FPGA adopt a unified clock, the MCU obtains frequency counting of reference signals and input signals through the FPGA, so that frequency difference between the reference signals and actual output signals is calculated and compared with set frequency difference, an error signal epsilon is generated to drive the VCXO, the output frequency is kept at a target frequency, and thus a closed loop feedback loop is formed to achieve the purpose of automatic adjustment; the DAC converts the digital signal output by the MCU into an analog signal to drive the crystal oscillator VCXO.
By clock vernier effect is meant the sampling clock signal frAnd an input signal f0Clock vernier effect between, sampling clock signal f in the present inventionrAnd an input signal f0The method belongs to the relationship that the same frequency has a small frequency difference, and the movement of the sampling clock signal covers the holding and changing states of all quantized values converted by the ADC.
The invention uses quantization error suppression technology in digital measurement, selects a certain fixed zero crossing point as a measurement reference point, greatly suppresses quantization error and ensures high-precision frequency measurement.
Compared with the traditional frequency corrector for adjusting the frequency in a wide range, the frequency corrector has the advantages that the crystal oscillator is used as a common clock, the set target frequency output is realized through the frequency correction function, the frequency range of an output signal is obviously narrow, such as from 0.1mHz to 10Hz, and the second-level stability of less than 3 x 10 can be realized-12And 10 are-12A slight frequency correction of magnitude. Compared with the traditional frequency corrector, the corrector is used for continuous correction and has higher cost performance.
Drawings
FIG. 1 is a block diagram of a principle implementation of the present invention.
FIG. 2 is a schematic diagram of a prototype.
Detailed Description
As shown in fig. 1, a precision frequency corrector based on direct digital measurement and processing consists of two parts, namely precision frequency measurement and feedback correction.
The USB interface is further composed of a double-channel ADC, an FPGA, an MCU, a DAC and a voltage-controlled crystal oscillator VCXO, and the MCU is provided with an external USB interface.
The further fine frequency measurement section uses the clock vernier effect. In the digital measurement of the periodic signal, when the clock signal and the measured signal have a small frequency difference Δ f on the basis of the same frequency or a multiple relation, the acquisition point will periodically and sequentially move on the waveform of the measured signal along with the time extension, i.e. the clock vernier effect.
In the invention, the reference clock signal and the control signal to be tested belong to the relationship of same frequency and small deviation, and the movement of the clock signal covers the keeping and changing states of all quantized values converted by the ADC, wherein the keeping and changing states comprise the acquired strict and jump synchronous voltage-time information. Therefore, the clock vernier effect can be utilized, namely, the acquired digital voltage is in a monotonous change relationship, the influence of quantization errors is greatly reduced, and the quantization errors can be eliminated in an ideal state.
The further fine frequency measurement section uses a quantization error suppression technique. Due to quantization errors in the ADC, the sampled data transitions are followed by a "flat region" where the ideal phase coincidence point is "hidden", which is very difficult to capture. The invention selects a certain fixed jump point, namely a zero crossing point, as a gate opening and closing mark. Since the positional relationship of these points to the full coincidence point is fixed, i.e., there is a fixed offset in time, it is understood that the gate moves synchronously forward or backward, but the overall length of the gate does not change. The reference point is used as a measurement reference point, so that the quantization error is greatly inhibited, and the high-precision frequency measurement is ensured.
The further precision frequency measurement part adopts a crystal oscillator with a non-standard frequency as a reference signal. In practice, it is difficult to have a fine step value for frequency adjustment in order to have a wide frequency adjustment range in a conventional frequency synthesizer. Although the crystal oscillator has excellent performance, the aging drift causes the frequency nominal value to change, so in order to use the crystal oscillator as a precise frequency source, an instrument or a device is needed to finely correct the frequency of the output signal of the crystal oscillator, thereby maintaining the high accuracy of the crystal oscillator. The conventional frequency correction uses a standard frequency signal as a reference source, so that the overall performance depends on the performance of the reference source, and the measurement and control principles depend on the standard frequency standard. The working frequency point of the invention is designed aiming at a common precision crystal oscillator, such as 10MHz, but the input frequency standard adopts the crystal oscillator which has deviation with a standard frequency signal as a reference, the standard frequency signal output is realized through an internal measurement and control circuit, and simultaneously, the invention has high regulation precision, so that the output value is stabilized in an error range as small as possible, thereby ensuring the accurate and precise continuous operation of the equipment. Fig. 2 is a schematic diagram of a prototype of the invention.
Further, the feedback correction part adopts a two-way ADC measurement structure, one way is used for collecting a reference signal, the other way is used for collecting a feedback signal output by the VCXO, and the two-way ADC and the FPGA adopt a unified clock. The MCU calculates the deviation between the reference signal and the actual output through the counting value obtained by the FPGA, and compares the deviation with the set deviation to generate an error signal to drive the VCXO so as to keep the output frequency at the expected frequency, thus forming a closed-loop feedback loop and achieving the purpose of automatic adjustment.
Further, the software design of the MCU module is mainly to write the control program of the singlechip by C language. Secondly, the FPGA module is used for obtaining frequency counting of the reference signal and the input signal, strict requirements are required on the clock aspect, and the software design is mainly that Verilog language is used for programming the FPGA module. And finally, converting a voltage signal for driving the voltage-controlled crystal oscillator by the DAC, and converting a digital signal output by the MCU into an analog signal to drive the crystal oscillator.
In the invention, the frequency difference between the crystal oscillator input reference signal with the deviation and the actual output signal is obtained through measurement, and the final output signal is not only narrow in range but also high in second-level stability through the comparison of the frequency difference and the set frequency difference.
Further, a standard frequency output is realized by the frequency correction function, and the frequency range of the output signal is obviously narrow, such as 0.1mHz to 10 Hz. Meanwhile, the output signal is accurate standard frequency (the set frequency difference is zero) or the standard frequency has small deviation (the set frequency difference is not zero but far less than the standard frequency), and the second-level stability of less than 3 x 10 can be realized-12And 10 are-12A slight frequency correction of magnitude.
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| CN108572345B (en) * | 2017-12-29 | 2020-12-15 | 深圳市鼎阳科技股份有限公司 | Oscilloscope, and method and system for correcting frequency accuracy based on undersampling |
| CN110995250A (en) * | 2019-11-07 | 2020-04-10 | 西安电子科技大学 | A direct digital phase-locked circuit and method for high-resolution arbitrary frequency signal |
| CN111628764A (en) * | 2020-05-25 | 2020-09-04 | 河北远东通信系统工程有限公司 | Phase-locked loop based on digital direct linear phase comparison |
| CN113676199A (en) * | 2021-08-25 | 2021-11-19 | 福建科立讯通信有限公司 | Solution method for receiver reference frequency source frequency multiplication interference and receiver |
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|---|---|---|---|---|
| US5802123A (en) * | 1993-12-24 | 1998-09-01 | Sony Corporation | Clock signal reproduction circuit and data reproduction circuit |
| CN101873135A (en) * | 2006-03-31 | 2010-10-27 | 日本电波工业株式会社 | Frequency synthesizer |
| CN102122958A (en) * | 2011-02-21 | 2011-07-13 | 江汉大学 | device and method for automatically repairing rubidium atom frequency-standard frequency drift |
| CN105407528A (en) * | 2015-11-25 | 2016-03-16 | 四川省绵阳西南自动化研究所 | Wireless ranging communication module based on measurement of asynchronous response time |
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- 2017-08-09 CN CN201710675629.XA patent/CN107483051B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5802123A (en) * | 1993-12-24 | 1998-09-01 | Sony Corporation | Clock signal reproduction circuit and data reproduction circuit |
| CN101873135A (en) * | 2006-03-31 | 2010-10-27 | 日本电波工业株式会社 | Frequency synthesizer |
| CN102122958A (en) * | 2011-02-21 | 2011-07-13 | 江汉大学 | device and method for automatically repairing rubidium atom frequency-standard frequency drift |
| CN105407528A (en) * | 2015-11-25 | 2016-03-16 | 四川省绵阳西南自动化研究所 | Wireless ranging communication module based on measurement of asynchronous response time |
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