【作者】 孙伟；

【导师】 钟志；

【作者基本信息】 哈尔滨工程大学 ， 信息与通信工程， 2016， 硕士

【摘要】 时间作为国际上七个标准物理量之一,是基本计量单位中精度最高的一个量。时频测量水平的提高对整个科学技术发展水平的提高具有积极的促进作用。计时、工业控制、邮电通信以及人造卫星、航天飞机的导航定位控制都离不开时间频率技术和时间频率测量。随着经济、科技和国防的高速发展,人们对频率标准的精确度要求越来越高。目前,世界各国都致力于精密的时频测量设备及其相关产品开发。进一步提高时频基标准器的研究水平、提高频率源的技术工艺水平、摆脱大多数检测设备和仪器依赖进口的技术发展现状,是当今科学研究发展亟待解决的问题。本文围绕高精度数字化频率测量及噪声处理方法展开研究,在传统频率测量方法基础上,设计了一种将数字下变频理论与相位比对算法结合的新型数字化测量系统。该测量方法基于单频正(余)弦信号欠采样和最大似然相位估计原理,利用欠采样后等价的低频模拟信号仍保留采样前高频信号初始相位信息的特点,采用双通道ADC对参考信号和待测信号同时进行数据采集,采集的包含两路信号相位信息的数据送入SDRAM进行缓存,再通过FPGA读取及USB控制芯片以数据流的形式上传给上位机,后者借助MATLAB平台,运行相位比对算法对采集的数据进行运算分析,从而得出两路信号的相位差值,并计算相应的频率差值等信息。对数据整理分析,在取样时间τ为10ms的范围内,测量准确度优于10-10,本底噪声差异均在10-13量级,为数字化频率测量提供了技术基础。文章详细介绍了数字化频率测量系统的硬件组成及软件设计,首先在理论上验证了设计方案的可行性,综合分析了影响系统的各个因素,提出了相应的改进措施。其次,通过对模拟频率源重复性实验测试,标定了系统具体的性能指标。同时,本系统具有工作稳定、结构简单、高精度及高稳定度的特点,测试指标达到了国内先进水平,其重要性更在于提供了一种数字化频率测量思想,为今后基于传统频率测量法的改进方案提供依据。更多还原

【Abstract】 As one of the seven international standard physical quantities, time is of the highest measurement accuracy currently achievable. The advancement in time and frequency measurement has a positive role in improving the overall level of science and technology.Timing, telecommunication, navigation and positioning are inseparable from time and frequency measurement. With the rapid growth of economy, technology as well as national defense, the accuracy of frequency standards has become increasingly demanded. Enhancing the research level of frequency standards, improving the manufacturing level of frequency sources, getting rid of the situation that most testing equipments and instruments depend on import has become an urgent and key problem to be solved.Based on traditional frequency measurement methods, a new digital measurement system is designed which is the combination of digital down conversion and phase alignment algorithm. The method is built on two principles: ML phase estimation algorithm and signal subsampling. Utilizing the characteristic that the low-frequency analog signal after undersampling remains equivalent initial phase information of high-frequency signal before sampling. Reference signal and signal under test are simultaneously sampled by dual-channel ADC. The digital data which carries phase information of both signals is sent to SDRAM cache. Then it could be read by FPGA and be transmitted by USB controlling chip. As the form of data stream, the data is delivered to PC. The latter analyses the data acquired using ML estimation algorithm and calculates the corresponding frequency difference information.With the sampling interval in the range of 10ms, the measurement accuracy is better than 10-10, noise floor is in the order of 10-13.In this article,hardware and software design of digital frequency measurement system is described in detail. First of all, the feasibility of design is proven in theory and all factors which would affect the system are analyzed comprehensively. Secondly, through the repetitive tests of the system, the specified performance indexes are calibrated. Besides, the system has characters of high-stability, simple-structure and high-precision. Testing indicators have reached the competitive domestic level. More importantly, it provide a digital frequency measurement thinking and lay the foundation for future improvement based on traditional frequency measurement means.更多还原