基于锁相环倍频的BLDCM速度控制系统设计

介绍一种基于锁相环六倍频速度采集的无刷直流电机(BLDCM)控制系统,以高性能处理器STM32为核心控制元件,采用锁相环倍频技术实现对电机转速的高精度控制.该系统包括处理器、驱动电路、逆变电路、倍频电路和电机,其中倍频电路对三路霍尔信号实现六倍频处理,输出作为系统的速度反馈.经仿真和实际测试,所设计的锁相环六倍频电路,...     

电荷泵锁相环电路建模与仿真

电荷泵锁相环是一种能够跟踪输入信号相位变化的闭环自动跟踪系统,此类电路具有负反馈闭环特点,系统状态多,工作特性复杂,其设计与仿真分析一直是电子设备时钟系统的难点问题。针对上述问题,研究了电荷泵锁相环电路的设计步骤与仿真分析方法。首先,推导电荷泵锁相环各模块的数学模型;其次,建立了各模块电路仿真模型,仿真分析了环路稳定性以及各模块对环路整体性能的影响。研究结果为电荷泵锁相环电路的设计与仿真提供了理论依据,对实际电路设计具有一定参考价值。     

高集成度超声相控发射电路的设计

以往超声相控发射电路采用分立元件,集成度低,由多块发射电路板组成,存在由于板间不同步造成的误差,影响发射精度.本文提出了一种高集成度高精度发射电路的设计.该设计利用FPGA内部锁相环的倍频和移相的技术取代了延时线,并采用多个4通道的高压脉冲产生芯片和8通道高压模拟开关芯片,集成于一块电路板上,大大提高了电路的集成度,避免了板间不同步的问题.同时对该电路实现电子扫查进行了相控分析,并通过仿真和实验,证明了电路的可行性.     

新型全数字锁相环在无功补偿系统中的应用

在无功补偿控制系统中,采用了新型全数字锁相环技术,其在传统全数字锁相环的基础上加入了自适应模值控制模块;该系统在采样中采用该新技术进行倍频锁相,对采样电压设计了同步6倍频,提供6相触发脉冲,同时设计了同步128倍频,以保证ad在每周期采样128点;给出了该装置的硬件实现方法,同时给出了软件设计的程序流程;仿真与试验结果表明新型全数字锁相环技术可以大大提高锁相速度和精度,进一步提高无功补偿系统的功率因数。     

一个改进型CMOS电荷泵锁相环的设计

本文针对传统电荷泵电路的非理想效应,对CMOS锁相环中的电荷泵电路进行了改进,设计了一种采用电流控制技术的新型pump-up电荷泵.采用标准chartered 0.35um/3.3V模型,通过Cadence Spectre仿真,仿真结果显示,该锁相环有效地抑制了电荷共享和电流失配非理想特性的影响,消除了锁相环输出抖动,可稳定输出13.56MHz时钟信号,稳定时间小于11.2us,功耗小于 18mW.     

一种实用的利用锁相环实现的倍频电路

叙述了锁相环的结构特点、工作原理及其应用，给出了一种利用锁相集成电路CD4046及计数/分频器CD4040实现的倍频电路。     

延迟锁相环的Verilog-A精确建模与仿真

分析了噪声以及器件失配对延迟锁相环的抖动影响,并对延迟锁相环的各模块进行了Verilog-A精确建模和性能仿真。仿真结果表明,器件失配对延迟链中间相输出的抖动影响最大,产生了约50ps的偏移;而噪声对延迟链最后一相输出的抖动影响最大,其peak-to-peak抖动值达到85ps。另外,与电路晶体管级仿真相比,通过Verilog-A建模节省了大量仿真时间,极大地提高了设计效率。     

一种用于高速PLL的CMOS电荷泵电路的设计

通过对电荷泵电路中存在的电荷注入、时钟馈通、电荷共享等现象的分析,设计了一个新型的高速电荷泵锁相环.电荷泵的设计是根据Mentor Graphics的eldo平台仿真CMOS0.35um技术.工艺,.仿真采用3.3V电源电压供电,功耗为0.47mW.仿真结果表明,该电荷泵电路可以很好地满足高速锁相环电路的要求.     

射频锁相环电路工作特性仿真与分析

射频锁相环是一种能够跟踪输入信号相位变化的闭环自动跟踪系统,此类电路具有负反馈闭环特点、系统状态多,工作特性复杂,其故障诊断和定位是无线电设备维修保障中的难点问题。针对上述问题,研究了射频锁相环电路的工作特性与故障定位方法。首先,针对典型射频锁相环电路,推导得到了其数学模型。然后,建立了其电路仿真的模型,仿真分析了环路四种主要工作状态和各模块对环路整体性能的影响。最后,采用开环故障隔离与关键节点信号比对法进行环路故障定位。研究结果为模拟锁相环电路故障诊断提供了理论依据,对实际电路故障诊断具有一定参考价值。     

基于FPGA的旋转编码器抗抖动四倍频电路设计

本文分析了旋转编码器工作原理,设计了一种高精度抗抖动四倍频电路。它主要由鉴相电路、脉冲加减计数电路、抗干扰电路、抗抖动电路和四倍频电路组成。电路采用Altera公司生产的FPGA,利用VHDL语言设计,具有计数频率高、可同时对多个编码器信号进行记数的优点。QuartusⅡ7.2的仿真结果表明,该电路准确可靠,定位精度明显提高,能有效地消除抖动的影响。     

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。     

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.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).