| Currently,the fields of navigation,communications,aerospace,and other fields are developing rapidly.As one of the most important components in these fields,frequency sources have increasingly higher requirements for frequency stability indicators.Phase noise is the main characteristic parameter of frequency stability.To better suppress the magnitude of phase noise,it is first necessary to achieve accurate measurement.As phase noise continues to decrease,the problems with traditional measurement methods become increasingly prominent,such as complex structures,significant background noise,and inability to eliminate reference source noise,which cannot meet new measurement requirements.Aiming at the above problems,this paper designs a dual reference source dual channel all digital phase noise measurement system based on cross correlation theory and linear zone phase discrimination principle.The specific research content is as follows:1.In response to the problems of complex structure and other issues in traditional measurement systems where phase detection modules mostly adopt phase-locked loop circuits,this article studies the variation law of phase difference between periodic signals and finds that when the frequency is a multiple and has a small frequency difference,the phase difference will monotonically change in an arithmetic sequence within the least common multiple period.Utilizing this characteristic and combining it with quantization error analysis of sine signals,this article selects digital devices to complete the acquisition of linear phase information of the measured signal without normalization,achieving high-precision phase detection between asynchronous signals.2.Aiming at the problem of high requirements for reference source noise in traditional measurement systems and the inability to eliminate reference source noise.This paper improves the current digital measurement system by designing a symmetrical phase detection structure with dual reference sources,using multiple cross correlation algorithms to eliminate non correlated noise in the channel,including reference source noise,thereby reducing the requirements on the performance of the reference source and obtaining pure and more accurate phase noise measurement results.While completing the software and hardware design of the measurement system,the national production substitution and overall design of the system components were carried out,and the performance of each part was theoretically demonstrated,providing theoretical and programmatic support for the physical implementation of the localized system.3.Simulation of cross-correlation algorithm and power spectral estimation algorithm was conducted using MATLAB.Based on theoretical derivation results,multiple sets of simulation results,and considerations of computational complexity,a suitable spectral estimation algorithm was selected for phase noise calculation in this system.In addition,to address the issue of fixed near-far carrier frequency resolution during spectral estimation,which can lead to resource waste,the FPGA’s phase comparison time was flexibly set according to the resolution requirements of different frequency bands,and the spectrum was calculated in segments before being spliced together to obtain a multi-resolution spectrum curve.This approach not only saves computational resources,but also effectively displays phase noise parameters.4.Perform performance testing on the measurement system.Under self-calibration conditions,the second-level stability of the OCXO 8607 can reach 3.11×10-13,and the background noise can reach-164 d Bc/Hz@>100k Hz.Under mutual calibration conditions,the TR2001 atomic clock was measured and compared with the measurement results of the 3120A and PN8010.The trends were basically the same,and the background noise did not differ by more than 5d B.Compared with a single-channel al-digital measurement system,the average background noise was reduced by about 6d B,proving the advanced nature of the system. |
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