Design And Simulation Of Dual Mixer Time Difference Measurement System

With the rapid development of aerospace,high-speed digital communications,satellite navigation and other scientific and technological fields,Many systems have a growing demand for high-quality frequency sources.Among them,atomic clocks have been widely used in various timing and punctual systems in China due to their extremely high frequency stability.With the continuous upgrading of the original timing and punctuality systems and the successive completion of new systems,the proportion of hydrogen atomic clocks in the system is increasing,and its stability in seconds is mostly better than 1.5E-13,so the frequency measurement for high precision more and more important.A technique using Dual-Mixer Time-Difference(DMTD)is one of the most common methods for high-precision frequency measurement.Based on this and the task of “One-Three-Five”Strategic Planning the development of high-performance time-frequency instruments by the National Time Service Center of the Chinese Academy of Sciences,the these designs and simulates the double-mixed time difference system.The design of the dual mixing time difference measurement system mainly includes the classical analog design method and the digital design method.In this thesis,an analog dual-mixing measurement system is designed and constructed,and the digital double-mixing time difference measurement system is analyzed and simulated.The main research work of this subject is divided into the following parts:(1)According to the principle of classical analog dual-mixing time difference measurement,an analog dual-mixing time difference measurement system scheme is designed.The key design realizes the mixing and zero-crossing detection module,introduces the principle of zero-crossing detection,and explains the main functions,circuit design and configuration of each circuit level in detail,and completes the circuit schematic diagram of the mixing and zero-crossing detection module.Drawing of the PCB(Printed Circuit Board).Finally,a complete analog dual-mixing time difference measurement system is constructed by using the existing modules in the laboratory and the designed mixing and zero-crossing detection modules.(2)The experimental platform was built to test and analyze the constructed analog dual-mixing time difference measurement system.First,the modules such as the time interval counter used are tested to verify that the module performance meets the system requirements.Secondly,the noise floor of the simulated doubl E-mixed time difference measurement system is tested.The experimental results show that the noise floor of the system is better than 1E-13.Finally,the effects of different common frequency sources on the system noise floor are analyzed and compared.The analysis results show that the noise floor performance is positively correlated with the short-term stability of the public frequency source.(3)According to the principle of Hilbert transform,the FIR-type Hilbert filter is designed by using the window function method and the equal-ripple Chebyshev method.The Hilbert filter designed by the two methods is compared.The simulation results show that the FIR Hilbert filter designed by the equal ripple Chebyshev method can achieve better performance with fewer orders than that by the window function method.(4)According to a digital dual-mixing time difference measurement method proposed by Masaharu Uchino et al,theoretical analysis and simulation experiments were carried out.Firstly,the digital double-mixing time difference measurement system without noise is simulated.The simulation results show that the better the stability of the frequency source,the better the noise floor of the system.Secondly,the influence of additional noise on the system after mixing is analyzed.The simulation results show that the beat signal after mixing has a large tolerance to additive noise.With the introduction of relatively large additive noise,the system's noise floor can also be maintained at a relatively high level.Finally,the influence of additive noise introduced by the common frequency source link before mixing on the system is analyzed.The greater the additive noise introduced before mixing,the more obvious the impact on the system.