用于红外气体检测的高稳定性DFB激光器驱动电源

为了满足红外气体检测对高性能激光器驱动电源的要求,文中采用PID控制算法,设计并研制了一款高稳定的DFB激光器驱动电源。其硬件主要包括信号产生模块、压控恒流源模块、电路保护模块,具备输出电流保护功能。信号产生模块主要通过DDS产生正弦波,再通过比较器产生方波,同时采用DA转换技术实现直流波、三角波、锯齿波的输出。控制方案上采用PID算法,通过深度负反馈控制,实现高稳定电流输出。利用此驱动电源对中心波长为1 563.09 nm的DFB激光器进行驱动实验。结果表明,所研制的驱动电源具有输出波形类型、幅度和频率三者数控可调的功能,电流幅度范围为0~1 A;正弦、方波频率范围为1 Hz~1 MHz,三角、锯齿、直流波频率范围为1 Hz~100 Hz,频率分辨率为1 Hz;输出电流线性度为99.93%,长时间输出电流稳定度为0.019 7%。     

带电压前馈的固定充放电时间锯齿波振荡器

设计了一种用于降压型DC-DC开关电源转换器的锯齿波振荡器。利用电压前馈方法和固定充放电时间方法,实现了锯齿波幅度随电源电压线性变化且频率固定的锯齿波振荡器,抑制了电源电压突变时的输出电压过冲。基于0.18 μm BCD工艺进行设计和仿真。仿真结果表明,该锯齿波振荡器产生的锯齿波频率为2.73 MHz。在2.7~5.5 V电源电压、-55 ℃~125 ℃温度范围内,频率偏移在±6%以内。振荡幅度在0.576~1.470 V范围内随电源电压线性变化。     

简易多种波形发生器

通常的方波-三角波振荡器,都使用正负对称的双向电源供电,其输出波形的不对称度是固定不变的,两种波形同步调幅困难.此外,调节三角波幅值的同时,也改变了三角波和方波的频率.这里介绍一种采用单电源供电的方波-三角波发生器,其电原理图如图1所     

基于Howland电流源产生更优线性度三角波的设计

针对三角波发生器性能的改善,按照对方波电流进行积分的拓扑结构,设计了一种基于方波电压控制的Howland电流源积分电路。理论分析验证了设计的正确性,证明了产生波形为线性对称三角波。实验结果表明,Howland电流源恒流误差小于微安级,产生三角波较常用发生器在测试频段内具有最小二乘评价法下更优的线性度和对称性,且频率和幅值均可灵活地进行调节。实现方法结构简单、硬件开销小、产生波形标准、具有很好的应用价值。     

线性三角波发生器

在这种Ｄ类音频放大器中，三角波用来调节开关频率，并产生一个脉宽调制（ＰＷＭ）信号来控制高频全桥驱动器（ＨＩＰ４０８０Ａ）的栅极输出，以驱动一对半桥（ＨＩＰ２０６０）ＦＥＴ（参见附图）。目标是要引出一种位于Ｖ-和地电源总线之间中心点上的高度线性的三角波。这可通过使用一种定时器电路（ＩＣＭ７５５）来实现。ＩＣＭ７５５５在最高达１．０ＭＨｚ的可变频率范围上产生一个１２Ｖｐ－ｐ方波，然后通过集成电路变换成三角波输出。该电路由运算放大器（ＨＡ５２２１）和电阻器电容器网络组成。该发生器产生高频线性三角波，用…     

压电陶瓷驱动器三角波频率特性

给出了三角波驱动信号下d31悬臂梁式驱动器的工作特性和频率特性。由于三角波包含了许多频率为基频奇数倍的谐波分量,当某一信号的谐波频率接近驱动器的共振频率时,该频率的三角波就会引起驱动器的谐振。因此,可以通过采用对扫描反馈电压的波形进行快速傅里叶分析法(FFT)来获得压电陶瓷驱动器的共振频率,而且,可以获得避开驱动器谐振点的驱动器设计原则,即:fr<0.6fk。此外,本试验压电陶瓷驱动器输出波形的延迟和非线性度与其驱动三角波频率的关系为:随频率增加,延迟不断增大;频率较低时,非线性度很大,而且随频率增大而增大,当频率在80～120Hz时,非线性度出现极大值,此后,非线性度随频率增大而减小。     

一种温度不敏感频率范围宽的三角波振荡器

本文介绍了一种由双比较器型施密特触发器构成的三角波振荡器电路,它通过对电容恒流充放电产生对称三角波;此电路的优点是其产生的三角波的频率稳定且具有很高的精度,并对温度和电源的变化不敏感;文章最后给出了电路的Hspice仿真结果。     

大功率超声电源的改进

将集成式D类全桥电路引入超声电源中,采用IR2110芯片驱动MOSFET构成全桥式逆变主电路,实现逆变降压和输出电压控制。驱动电路以脉宽调制电路为核心,运用555芯片产生三角波信号,并将产生的三角波信号转化为不同偏置的两路三角波信号;然后分别与相应端口输入的正弦波信号进行比较调制,得到两路PWM波,提高了电路的动态响应并实现频率的可调性。     

一种CMOS锯齿波振荡电路的设计

以比较器为核心电路,并采用恒流源充放电技术,设计了一种基于1.2 μmCMOS工艺的锯齿波振荡电路.并利用Cadence SpectreS仿真工具对电路进行了仿真模拟,结果表明,锯齿波信号的线性度较好,同时其信号振荡频率随电源电压的变化和温度的变化很小,性能良好,可广泛应用在PWM等各种电子电路中.     

LFMCW雷达干扰源分析

线性频率调制连续波(LFMCW)雷达具备测距精度高、无盲区等优点,有着广泛的应用。分析了典型的锯齿波和三角波LFMCW雷达的基本工作原理,并以锯齿波为例,分析了各种干扰源的情况。     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Alternative Schemes for Dynamic Secure VPN Deployment in UMTS

Three alternative schemes for secure Virtual Private Network (VPN) deployment over the Universal Mobile Telecommunication System (UMTS) are proposed and analyzed. The proposed schemes enable a mobile node to voluntarily establish an IPsec-based secure channel to a private network. The alternative schemes differ in the location where the IPsec functionality is placed within the UMTS network architecture (mobile node, access network, and UMTS network border), depending on the employed security model, and whether data in transit are ever in clear-text, or available to be tapped by outsiders. The provided levels of privacy in the deployed VPN schemes, as well as the employed authentication models are examined. An analysis in terms of cost, complexity, and performance overhead that each method imposes to the underlying network architecture, as well as to the mobile devices is presented. The level of system reliability and scalability in granting security services is presented. The VPN management, usability, and trusted relations, as well as their behavior when a mobile user moves are analyzed. The use of special applications that require access to encapsulated data traffic is explored. Finally, an overall comparison of the proposed schemes from the security and operation point of view summarizes their relative performance. Christos Xenakis received his B.Sc. degree in computer science in 1993 and his M.Sc. degree in telecommunication and computer networks in 1996, both from the Department of Informatics and Telecommunications, University of Athens, Greece. In 2004 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). From 1998–2000 was with the Greek telecoms system development firm Teletel S.A., where was involved in the design and development of advanced telecommunications subsystems for ISDN, ATM, GSM, and GPRS. Since 1996 he has been a member of the Communication Networks Laboratory of the University of Athens. He has participated in numerous projects realized in the context of EU Programs (ACTS, ESPRIT, IST). His research interests are in the field of mobile/wireless networks, security and distributed network management. He is the author of over 15 papers in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was on the faculty of Electrical Engineering and Computer Science at the University of Connecticut, Storrs. From 1986 to 1994 he was on the faculty of the Electrical and Computer Engineering Department at Northeastern University, Boston, MA. During the period 1993–1994 he served as Director of the Communications and Digital Processing Research Center at Northeastern University. During the summers of 1990 and 1991, he was a Visiting Scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a Professor in the Department of Informatics and Telecommunications, and Director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. His research interests are in the design and performance analysis of broadband networks, and wireless/mobile communication systems and services. He has authored more than 150 papers in the above areas. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies & Services (ACTS) and Information Society Technologies (IST) programmes funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE). He is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the Best Paper presented at the International Zurich Seminar on Mobile Communications.     

车辆状态信息显示处理系统的研究与设计

介绍了基于CAN总线的车辆状态信息显示处理系统,分析了CAN.总线的特点及在汽车中使用CAN总线的优点,并给出了其在国内外汽车中的应用现状.首重介绍了系统的总体设计方案,系统的主节点、固定节点及活动节点的硬件组成和工作原理,以及大屏幕液晶显示器的特点及其在系统中的应用.     

单相无刷直流电机的设计分析与建模仿真

文中针对单相无刷直流电机结构设计及驱动方式展开研究,推导出电机理想工况下的基本方程,根据工程实际需求并结合无刷直流电机的设计原则确定该电机的设计方案。利用设计方案设计一台额定功率38 W,额定转速750 rpm的单相无刷直流电机,并分析了渐变气隙对电机起动性能和齿槽转矩的影响,确定了最优气隙长度。通过对比单极性绕组和双极性绕组形式的优缺点确定绕组形式,结合传统电机设计公式确定绕组匝数。文中利用有限元法初步验证了设计方案的合理性。根据电机动态数学模型在Simulink环境中搭建了电机系统的模型,仿真得到电机的转速、转矩变化曲线,结果与理论分析吻合良好,验证了电机设计方案的合理性和电机模型的有效性。     

位屏蔽多叉树搜索射频识别防碰撞算法

针对RFID树型防碰撞算法中时隙数多、数据通行量大等问题,提出了一种改进的多叉树防碰撞算法,阅读器准确检测碰撞位并向标签反馈碰撞位信息,标签对阅读器已知的ID位进行屏蔽,把ID号转换成连续碰撞的序列号.阅读器利用屏蔽位信息和标签返回的碰撞位编码信息,对标签进行分层分类搜索.通过对标签ID进行屏蔽,阅读器和标签间仅发送对方不知道的碰撞位信息.该算法减少了碰撞时隙和识别时隙,避免了空闲时隙,减少了阅读器和标签间的数据通信量.理论分析和仿真结果表明,该算法减少了系统的时隙总数和数据通信量,提高了阅读器的识别效率.     

网络空间威胁狩猎的研究综述

近年来,随着网络的普及和信息化水平的不断提高,越来越多的公司把重要信息和机密文件存储在连接着网络的计算机上。但是,由于网络攻击的手段层出不穷,威胁狩猎的思想和理念孕育而生并且逐渐成熟。由此,首先对网络空间威胁的定义和攻击流程模型进行介绍,再阐述了威胁狩猎的定义和核心技术,然后描述了威胁狩猎使用的工具;最后,概括总结现有的主流威胁狩猎的框架,比较各个框架的优缺点,并阐明了下一步的发展方向。     

Progress in doping semiconductor nanowires during growth

The anisotropic growth of one-dimensional or filamental crystals in the form of microwires and nanowires constitutes a rich domain of epitaxy and newly enabled applications at different length and size scales. Significant progress has been accomplished in controlling the growth, morphology, and properties of semiconductor nanowires and consequently their device level performance. The objective of this review is two-fold: to highlight progress up to date in nanowire doping and to discuss the remaining fundamental challenges. We focus on the most common semiconductor nanowire growth mechanism, the vapor-liquid-solid growth, and the perturbation of its kinetic and thermodynamic aspects with the introduction of dopants. We survey the origins of dopant gradients in nanowire growth and summarize quantification techniques for dopants and free-carrier concentrations. We analyze the morphological changes due to dopants and the influence of growth droplet seeds on composition and morphology and review growth aspects and alternatives that can mitigate these effects. We then summarize some of the remaining issues pertaining to dopant control in nanowires.     

5-DOF混联雕刻机速度运动学分析及仿真

五自由度混联机器人因为兼有串联机器人和并联机器人的优点而成为重要的研究方向。在对五自由度并串联雕刻机控制的过程中,求解其输入与末端位置之间的速度及加速度的传递是研究的重点和难点。文中先通过机构拓扑理论对雕刻机的自由度进行分析,再运用矢量法对雕刻机末端运动学进行正向分析,然后采用求导法对雕刻机滑块运动学进行逆向分析,最终通过MATLAB和ADAMS仿真分析验证了雕刻机速度运动学分析的合理性以及算法的有效性。该结果为五自由度混联机器人的实际控制编程提供了参考。     

5G传输网络承载方案分析

5G时代3类典型场景的业务需求对承载网络在容量、时延和组网灵活性方面提出了更高的要求,同时针对无线网和核心网架构的变化提出了网络切片、增强路由转发功能等要求。首先分析5G的承载需求,重点考虑5G的3类典型业务场景、无线和核心网的架构变化;然后结合现网100GE PTN的实际应用情况,重点围绕容量、时延等维度完成需求与网络现状的对标;最后提出了网络回传、机房配套的演进方案。     

Instantaneous envelope and phase extraction from real signals: Theory,implementation, and an application to EEG analysis

This paper presents a unified treatment of various important signal processing techniques for the extraction of the instantaneous envelope and phase of a real signal. These techniques include Complex Demodulation, Hilbert Transformation, In-Phase and In-Quadrature Filtering, Phase-Locked Loop Demodulation, and Peak Amplitude and Zero-Crossing Detection. The salient points in the mathematical theory and implementation of these techniques are outlined, as well as their interrelationships via the theory of analytic signals. The advantages and limitations of each of these techniques are elaborated upon, and Complex Demodulation is shown to be the most effective and flexible method from an implementation point of view. The relation of the above techniques to Fourier spectrum analysis is elucidated, and an example is presented of applying Complex Demodulation for the quantification of time nonstationarities in the electrographic morphology of an EEG waveform.