一种低电压无死区鉴频鉴相器

提出了一种高性能低电压无死区鉴频鉴相器（PFD）电路，并通过时钟分析优化其设计参数。阐述了恢复时间对PFD电路最大工作频率的影响以及降低PFD恢复时间的设计方法，仿真结果同理论极为相符。     

一种用于高速锁相环的零死区鉴频鉴相器

本文探讨鉴频鉴相器(PFD)设计中死区的产生原因和消除方法。设计了一种用于高速锁相环的零死区PFD。这种PFD采用无反馈回路结构,在保证死区为零的前提下,兼顾功耗和速度性能。尤其适用于基于锁相环的高速时钟和数据恢复电路(CDR)、高速频率合成器等对速度和抖动性能有很高要求的电路。     

一种具有新型延时单元的鉴频鉴相器设计

鉴频鉴相器是电荷泵锁相环的关键模块。死区表征鉴频鉴相器对两个输入信号最小相位差的鉴别能力,会使锁相环的杂散特性恶化,是鉴频鉴相器主要的设计考虑之一。基于TSMC 0.18μm RF CMOS工艺,设计了一款具有新型延时单元的无死区鉴频鉴相器。该延时单元基于传输门及反相器设计,利用3位数字控制,实现8种不同的复位延时,可灵活配置,有效消除死区。其具备占用面积小、结构简单、易扩展和易移植等特点。仿真结果表明,设计的鉴频鉴相器具备消除死区的能力,能够应用于锁相环电路。     

一种应用于电荷泵锁相环的高性能鉴频鉴相器

鉴频鉴相器是电荷泵锁相环中的一个重要模块,它的死区、速度、鉴相范围、鉴相灵敏度等因素影响整个锁相环的性能,其中死区和速度是两个非常重要但相互矛盾的技术指标。本设计为一种预充电型鉴频鉴相器,采用了TSMC 0.18μm RF CMOS工艺,利用Agilent公司推出的系统分析软件ADS(Advanced Design System)完成对电路的仿真。仿真结果表明鉴频鉴相器鉴相灵敏度好,速度快,鉴相死区仅为5ps,很好地解决了速度与死区之间的矛盾。     

一种实现快速锁定的锁相环的研究

本文对电荷泵型锁相环（CPPLL）结构里传统的固定电荷泵电流模式进行了改进，有效减少了锁相环系统的锁定时间。本文提出的PLL设计．在0．6μm标准CMOS工艺、3．3V工作电压下，使用应用广泛的高速鉴频鉴相器（r11SPC）结构、差分电荷泵电路实现。经过Spectre仿真，改进后的锁相环锁定时间减少为改进前时的112。     

一种用于高速锁相环的双斜鉴频鉴相器设计

文中提出了一种用于高速锁相环的双斜鉴频鉴相器的结构设计。这种结构是基于两个调谐电路：细调电路和粗调电路。细调电路用来完成精确调制，粗调电路用来加快锁定速度。用MENTOR GRAPHICS-ADMS对电路进行仿真。结果表明所提出的结构比普通型锁相环的锁定时间减少了50％以上。     

基于时钟恢复系统中的锁相环电路的设计

本文主要设计了基于相位控制技术的时钟恢复系统的PLL锁相环路.分别对各单元电路结构棗鉴频鉴相器、电荷泵、环路滤波器、压控振荡器、分频器进行设计.采用2.5V,0.25μm First Sillcon CMOS工艺来实现,并在SPICE平台下进行仿真.仿真结果表明,该PLL环路的锁定时间仅为2.4us,并且输出的频谱呈现出较高的纯度,具有高速、低噪声的特点.     

应用于USB全速设备中的锁相环设计

针对USB全速设备中通常需要外接晶振来为芯片提供时钟这一问题,提出了一种适用于USB全速设备的低功耗锁相环的实现方法.根据USB全速设备中的数据传输速率,该锁相环设计在标准电荷泵锁相环的结构上增加了时钟信息提取单元和低功耗控制模块,采用了改进的鉴频鉴相器和和差分型压控振荡器实现,并在0.35μm标准工艺下完成了锁相环版图.实验结果验证了该锁相环电路性能,结果满足USB协议要求.     

新型锁相频率合成器的设计

文中提出了一种新型锁相频率合成器的设计实现方法.这种锁相频率合成器的各个部件都进行了优化设计,其中鉴相器采用了加入反相器链取出输入信号边沿的结构很好的消除了鉴相死区;电荷泵采用了差分电路结构消除了跳跃现象;压控振荡器采用了电流模驱动延迟环结构得到了优良的性能;尤其是分频器的设计采用了内、外两分频器的结构,通过改变两个分频器的倍频数N和M的值,可以合成多种时钟频率.     

全数字低频锁相环的研究与应用

采用嵌入式微机检测与控制技术开发了一种新型的低频锁相环控制系统;鉴相器采用时间数字转换器设计,克服了传统鉴相器存在鉴相死区的缺点;由于采用阻容式低频信号滤波器设计难度较大,采用计算机软件算术平均和滑动平均值滤波方案,解决了低频鉴相环路滤波器设计难题;该锁相环在GPS驯服晶振课题中应用,有效克服了GPS秒脉冲抖动噪声,结果表明,该锁相环结构简洁,控制参数调节方便,锁定后晶振频率准确度优于5E-11.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.