新型全数字三相SPWM信号产生芯片的设计与实现

针对电力电子领域的需要,自行研制了一种新型三相正弦脉宽调制信号产生芯片.该芯片采用了改进的直接数字频率合成算法、流水线结构与ROM分时复用技术,保证了芯片的高性能和速度,节省了芯片面积.芯片系统时钟可达24MHz,输出信号的范围为DC到4kHz,精度为65536级,控制功能齐全.采用0.35μm COMS工艺流片,测试结果显示芯片达到设计指标.     

A novel frequency offset estimation method for OFDM systems with large estimation range

In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel.     

一种1V电压工作的高精度CMOS带隙基准源

基于标准1μmCMOS工艺,针对1V供电电压,设计了一种自偏置PTAT电流产生电路和低电源、高增益的运算放大器,最终实现了低电源工作的带隙基准电路.在1V电源电压下,采用1μm CMOS工艺进行仿真,温度系数在-20～120℃范围内达到13×10-6,低频电源抑制比达到-90dB.     

基于数据流方法的大规模网络异常发现

随着网络规模和速度的增加,大规模网络异常发现要求检测算法能够在无保留状态或者少保留状态下对G比特级的海量网络业务量数据进行实时在线分析。针对在高速骨干网上进行大规模网络异常发现的特点和要求,提出了一种基于数据流的大规模网络异常发现的方法,第一次将数据流模型用于大规模网络的异常发现。主要包括以下创新点:设计了一种面向异常发现的网络流量概要数据结构和突发高频事件检测算法;提出了一种基于安全监测策略定制的预查询方法来进行多数据流的关联监测并且对数据流查询进行了优化;在真实数据分析的基础上,对网络业务量进行了数据约减,使得监测部分特殊类型的数据流能最大程度地获得整体网络业务量的变化特征以提高异常发现的效率。通过真实网络环境下的实验和性能评价验证了数据流方法的有效性。     

Effect of Nickel Contamination on Formation of Denuded Zone in Czochralski Silicon

研究了过渡族金属镍在快速热处理作用下对直拉单晶硅中洁净区形成的影响.实验结果发现:硅中魔幻洁净区(MDZ)形成后,氧沉淀及其诱生缺陷能有效地吸杂金属镍;而沾污金属镍的硅中,随后的快速热处理工艺不能形成MDZ,硅片近表面出现大量沉淀.采用传统的内吸杂工艺,镍沾污的次序对洁净区的形成没有影响.实验表明由于硅片表面形成的镍硅化合物的晶格常数比硅小,所以在硅片近表面产生高浓度的空位,导致近表面的氧依然能够在MDZ工艺中形成沉淀.     

垂直腔面发射激光器的TO封装的耦合效率模拟分析

采用FRESNEL光学软件和MATLAB软件,详细分析了垂直腔面发射激光器的TO封装组件对耦合效率的影响.发现增加耦合透镜的折射率、减少管帽的高度和耦合透镜的尺寸可以提高耦合效率.     

目标基视频编码中的运动目标提取与跟踪新算法

自动、快速的视频目标提取与跟踪是目标基视频编码中的一项关键技术.本文提出一种运动目标提取与跟踪新算法.首先,根据多帧运动信息和高阶统计检测方法得到二值运动掩模图像,然后提出一种改进分水岭算法对运动区域及其周围部分进行分割.将二者所得结果进行投影运算,得到最终运动目标.最后提出一种运动目标跟踪新算法,能对目标进行有效的跟踪.实验结果说明了本文算法的有效性.     

再论Pedoe不等式的高维推广及应用

本文对欧氏空间E~n中的两个n维单形,给出了著名的Pedoe不等式的一个实质性推广,并讨论了它的应用.     

Effect of surface condition on liquid crystal photoalignment by light-induced azo dye adsorption phenomena

The effect of surface condition on the photoalignment of light-induced methyl red (MR) adsorption phenomena on various substrates based on azo dye-doped liquid crystals is investigated. The results show that the polar surface energy determines the initiation of MR adsorption phenomena. The surface polarity energy of different substrates, which are modulated by oxygen plasma treatment (OPT), is further examined using the sessile drop method. The results also indicate that the uniformity and efficiency of MR adsorption can be enhanced by OPT. Light intensity influences the MR adsorption rate. The uniformity of MR adsorption onto various substrates is analysed via polarised optical microscopy.