基于高速ADC的数字双混频时差测量系统  

Digital dual mixer time difference measurement system based on high-speed ADC

作　　者：冷杰兴 刘军良[1] 刘倩 王莹 徐超[1] 胡永辉[1] LENG Jie-xing;LIU Jun-liang;LIU Qian;WANG Ying;XU Chao;HU Yong-hui(National Time Service Center,Chinese Academy of Sciences,Xi’an 710600,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院国家授时中心,西安710600 [2]中国科学院大学,北京100049

出　　处：《时间频率学报》2024年第1期34-45,共12页Journal of Time and Frequency

基　　金：中国科学院国家授时中心“青年创新人才”项目(NTSC青创201901)。

摘　　要：使用双混频时差法进行时间和频率测量时,模拟部分引入的噪声会干扰信号过零点的判断,降低测量精度,而使用数字信号处理技术后不再需要判断过零点,量化噪声成为系统内的主要噪声来源,可以通过数字滤波器对其进行抑制。同时有利于设计结构紧凑的系统,更易于小型化,测量速度也可以进行灵活配置。通过引入高速模数转换器、数控振荡器、低通抽取滤波器、数字鉴相器等,设计了数字双混频时差测量系统,并研制了4通道的原理样机。测试结果表明,当频率源为10 MHz的信号时,原理样机中属于同片ADC(analog-to-digital converter)的两个通道间的本底噪声约为5×10^(-14)@1 s,属于不同片ADC的两个通道间的本底噪声约为8×10^(-14)@1 s,满足原子振荡器的测量要求。并以主动型氢钟VCH-1003M为参考,使用原理样机分别对Microchip的5071A铯原子钟和SRS的FS725铷原子钟的稳定度进行测量,测量结果与Microchip的相噪分析仪53100A和5120A无显著差异。In the dual mixer time difference(DMTD)method used for time and frequency measurement,the noise introduced by the analog components will interfere with the determination of the zero-crossing point of signal,reducing the measurement accuracy.By utilizing digital signal processing techniques,it is no needs to determine the zero-crossing point,and quantization noise becomes the primary source of noise in the system,which can be suppressed through the digital filtering.Additionally,it is conducive to the design of a compact system and easier to miniaturize,and the measurement speed can be flexibly configured.By introducing high-speed analog-to-digital converter(ADC),numerically controlled oscillators,low pass decimation filters,digital phase detectors,etc.,a digital DMTD measurement system is designed,and a prototype with four measurement channels is developed.Test results demonstrate that when the frequency source is 10 MHz signal,in the prototype,the noise floor between the two channels belonging to the same ADC is about 5×10^(-14)@1 s,and the noise floor between the two channels belonging to differentADCs is about 8×10^(-14)@1 s,satisfying measurement requirements for atomic oscillators.Using the active hydrogen maser VCH-1003M as a reference,the stability of Microchip’s 5071A cesium atomic clock and SRS’s FS725 rubidium atomic clock is measured using the prototype,with measurement results being almost identical to Microchip’s phase noise analyzer 53100Aand 5120A.

关 键 词：双混频时差 模数转换器 低通抽取滤波器 本底噪声 

分 类 号：TN792[电子电信—电路与系统] TN752