气体开关串级环形间隙放电相互影响机制研究

针对中空和非中空触发电极结构的两间隙开关，进行了触发击穿特性实验，对比两个间隙的击穿抖动和通道数，分析了串级两间隙的相互影响机制。实验结果表明：两只开关触发间隙击穿抖动和通道数变化规律基本一致；非中空开关自击穿间隙击穿抖动随工作系数的增大而减小，最小约3 ns，中空开关自击穿间隙击穿抖动始终约1 ns；非中空开关自击穿间隙难形成多通道放电，中空开关自击穿间隙通道数明显多于其他间隙。触发间隙首先放电产生紫外光，通过触发电极中空通孔预先照射自击穿间隙产生初始电子，是自击穿间隙击穿抖动减小、通道数增加的主要作用机制。     

基于FPGA的机载DME抖频信号产生器设计及实现

机载测距机系统是现代飞机上必不可少的重要导航设备,DME测距的核心是采取闪频原理来实现应答脉冲的识别,抖频信号产生器是实现闪频原理的关键电路。基于FPGA设计并实现了机载DME抖频信号产生器电路,该电路主要包括随机数发生器、可变分频器等模块。经测试表明,电路性能稳定,工作可靠。     

A novel DSP‐based PFC‐DPLL with fuzzy controlled acquisition aid to improve acquisition performance and noise immunity

This paper proposes a new digital signal processing (DSP)‐based phase frequency controlled digital phase locked loop. Here, a very simplistic form of fuzzy logic controller with the help of carrier phase and frequency error as input data is used to provide an acquisition aid. A frequency discriminator is employed to generate frequency error, and phase detector output is taken for phase error. This addition of an acquisition aid helps the loop to achieve the minimum acquisition time and maximum noise rejection simultaneously. An additional phase control in the digitally controlled oscillator makes the loop perform even better towards this goal. The implementation of the proposed loop is carried out on a reconfigurable logic platform using System Generator^®;, a tool from Xilinx^®; used to design real‐time DSP application. A significant improvement of time domain characteristics are observed as well as the performance in presence of additive white Gaussian noise is demonstrated in terms of the reduction in steady‐state phase jitter and enhancement in output signal to noise ratio in the proposed loop. Copyright © 2014 John Wiley & Sons, Ltd.     

基于锁相环电源噪声引起的周期抖动分析

针对电源噪声在时钟电路的锁相环中引起的抖动问题，通过分析周期抖动和相位抖动与电源噪声间的关系，提出了用于预测电源噪声引起的锁相环抖动峰峰值的计算公式。文中预测的抖动峰峰值与HSPICE的仿真结果间的误差最大为3%，说明了文中公式的有效性。     

Pinhole imaging to observe spatial jitters of a triple-pulse X-ray source on the Dragon-Ⅱ LIA

In high-energy flash radiography,scattered photons degrade the acquiring image,which limits the resolving power of interfaces and density of dense object.The application of large anti-scatter grid can reduce the scattered photons remarkably,but this requires a stable source position in order to reduce the loss of signal photons in the grid structure.The pinhole imaging technique is applied to observe spatial jitters of a triple-pulse radiographic source of a linear induction accelerator.Numerical simulations are conducted to analyze the imaging performance with the same or close parameters of the pinhole object and experimental alignment.Experiments are carried out to observe spatial jitters of the source between different measurements.Deviations of the source position between different pulses are measured in each experiment.     

低功率抽运光纤参量振荡器的时钟提取抖动性能

采用两次光调制技术将非归零(NRZ)码数据转换成归零(RZ)码光信号后,利用光纤参量振荡器(FOPO)结构实现了较低光功率抽运下的参量波长转换和时钟提取功能。实验表明,对于波长转换间隔为1.6nm的10Gbit/s时钟提取,优化的输入抽运光功率范围是8～14dBm;当输入信号的幅度抖动和相位抖动分别大于2.28mV和3.5ps时,该时钟提取系统可实现抖动抑制功能,其输入/输出抖动转移曲线斜率约为0.29和0.16。     

一种改进的定时误差检测算法

定时恢复环路是数字接收机同步模块的一个重要组成部分,Gardner算法以实现结构简单,不敏感于载波相位,独立于调制方式等优点作为定时误差检测算法广泛应用于数字接收机的定时恢复环路中。鉴于Gardner算法在数字接收机定时同步中的广泛应用,并通过比较Gardner算法及其改进算法的定时抖动和捕获性能,研究了一种改进的Gardner定时误差检测算法。仿真结果表明,该算法对于MPSK恒包络的调制信号定时抖动性能有很明显的改善,并且在小滚降因子下改善仍然成立,但是对于16QAM非恒包络的调制信号改善不理想。     

基于相关函数的超声图像方位跳变检测和校正

为了解决超声电视测井成像图像中出现的方位跳变问题,提出了一种利用相关特征来检测方位跳变测井图像的方法.该方法利用超声测井图像相邻行之间相关性来自动搜索图像出现方位跳变的深度位置和方位差,根据跳变深度位置和方位差来循环平移图像,最终实现校正图像的目标.实验结果证明,该方法能准确地自动校正方位跳变的图像.对实际测井资料的处...     

1.2V低功耗时钟发生器设计

基于整数分频锁相环结构实现的时钟发生器,该时钟发生器采用低功耗、低抖动技术,在SMIC 65 nm CMOS工艺上实现。电路使用1.2 V单一电源电压,并在片上集成了环路滤波器。其中,振荡器为电流控制、全差分结构的五级环形振荡器。该信号发生器可以产生的时钟频率范围为12.5～800MHz,工作在800 MHz时所需的功耗为1.54 mW,输出时钟的周期抖动为:pk-pk=75 ps,rms=8.6 ps;Cycle-to-Cycle抖动为:pk-pk=132 ps,rms=14.1 ps。电路的面积为84μm2。     

利用帧头消除测距时标整周期滑动的方法

在弹载扩频脉冲应答式测距系统中,应答机直接利用捕获脉冲作为时标信号进行测距。此法在高信噪比时测距精度较高,但在低信噪比时,伪码同步脉冲的抖动较大,同时捕获脉冲会产生整数个伪码周期地滑动,导致测距误差较大。为了提高测距精度,提出了一种利用帧头消除脉冲应答式测距时标整周期滑动并降低时钟抖动的方法。在获得伪码捕获脉冲并检测到帧头后,应答机才启动应答信号,可有效降低低信噪比时的测距误差。