S类功放的频率可调带通ΔΣ调制器研究与实现

S类射频功率放大器同时具有高效率和高线性特性,适合在全数字发信机中应用。但需要将任意输入的射频信号转换为两电平脉冲调制信号,带通增量求和(ΔΣ)调制才可以很好地实现上述功能。为实现S类功放的宽频带工作,带通ΔΣ调制器的中心频率必须实现与输入信号频率的实时跟随。通过对ΔΣ调制算法的研究,提出了一种频率可调带通ΔΣ调制器的设计方法,并利用Matlab软件和FPGA对设计的调制器分别进行了仿真和实验验证。验证结果证明了该设计方法的可行性和有效性。     

基于STM32微控制器的高频脉宽调制器的设计

高频脉冲电源对提高微细电解加工的工艺性有着重要的作用,而脉宽调制器经驱动电路生成IGBT控制信号决定着高频高压脉冲电源的输出频率及占空比;针对电解加工工艺的特殊性,创新性地提出基于32位微型控制器芯片STM32F103RCT6为核心的调频调占空比的方案;根据脉冲频率、占空比可调的要求,完成了脉宽调制器的软硬件设计,通过编译运行程序代码进行一系列的调频、调占空比实验并利用示波器采集两路输出的PWM波形;实验表明,自行研制的脉宽调制器能稳定地调节两路PWM控制信号的频率及占空比,验证了装置及设计的合理性。     

创新的自适应脉宽调制器为固定通/断时间可控的稳压器提供恒定开关频率

本文介绍一种创新的自适应稳压器(AC/DC或DC/DC)脉宽调制器(PWM) ,基于"固定关断时间(FOT)"或"恒定导通时间(COT)"控制方法,可以在全工况下(例如满负载CCM或中低负载DCM模式,宽输入输出电压) 以恒定开关频率工作,无转换器的寄生参数(例如功率开关和滤波电感器的电阻)的负面影响.此外,本文提出的调制器电路与转换器拓扑无关(升压、降压、反激式等),只与功率开关管栅极驱动逻辑信号(GD)有关,可以节省芯片引脚数量,且/或降低设计复杂程度.     

全数字QAM调制射频输出的FPGA实现

一种采用AD9739与FPGA相结合、在FPGA上实现全数字QAM射频调制的方法。阐述了柰奎斯特滤波器、插值滤波器、多相滤波器、多相数字频率合成器的实现方法,并采用多相滤波技术和OSERDES技术解决了射频信号高采样率问题。介绍了AD9739的接口设计,并给出调制器的射频输出信号的实测结果,性能指标符合国家制定的DVB_C标准。     

彩色电视PFM-IM制式光纤传输系统中PFM调制器的工程设计

<正> 宽范围、高线性的脉冲频率调制器是PFM-IM制式彩色电视光纤传输系统的核心。用PFM-IM方式进行彩色电视信号的光纤传输,失真小,传输信噪比高,传输距离远,系统造价适中,所以受到国内外重视。其中的脉冲频率调制器对系统的指标起着重要作用。本文先简述其工作原理,进而讨论设计原则,最后导出工程设计方法,并给出设计实例。一、PFM调制器的工作原理 PFM-IM彩色电视光纤传输系统中的脉冲频率调制器实际上是一个高工作频率、高线性度,宽频率复盖范围的压控振荡器,控制电压就是所要传输的彩色电视信号(需要时还可混入伴音调频信号和数字调制信号,共同组成基带信号)。定量充放电型压控振荡器可以很好地满足各项要求。它的调制特性如图1所示,工作原理可由图2说明。图2中is为电容C的充电恒流源,它随控制电压     

QPSK高性能数字调制器的FPGA实现

本文提出了一种QPSK高性能数字调制器的FPGA实现方案,由Altera的IP核NCO2.3.0提供QPSK高稳定度的数字正弦信号,给出了QPSK的实验仿真结果。结果表明,基于NCO的QPSK数字调制器极大地改善了无杂散动态范围及信噪比,有效地降低了FPGA的硬件开销,QPSK调制器工作稳定、可靠,达到设计要求。     

一种用于压电式喷墨打印头的梯形波脉冲信号源设计

压电式喷墨打印技术是当今印刷行业的重要技术,压电式喷墨打印喷头需要一个精确、稳定的脉冲信号作为驱动电源.介绍了基于FPGA的DDS原理的梯形波脉冲信号源的原理、结构以及各模块的设计方法和实现方案.采用基于FPGA的DDS原理产生的梯形波脉冲信号源,波形参数比较精确、输出信号比较稳定且输出频率范围较大.该设计可实现电压幅值为0～2.5 V、梯形波脉宽10～25μs和输出信号频率0～30 kHz的梯形波脉冲信号输出,可较好地匹配压电式喷墨打印喷头.仿真结果表明,该设计合理正确,实现了输出的梯形波脉冲信号的幅值、脉宽以及输出频率可调,并且可过滤大部分高频杂散和干扰,输出信号基本不出现失真.     

电耦合型人体通信收发器的设计与实现

针对电流耦合型人体通信的特点,以FPGA为平台,分别设计出基于DDS的2CPFSK调制器、全数字锁相环位同步电路和信号解调器.此外,外围电路实现了发送端低通滤波、信号保持和接收端前处理等功能.最后对电流耦合型人体通信收发器的进行人体实验.实验结果表明收发器满足设计要求,可以实现数字基带信号在人体内的传榆.     

一种用于无人机测控系统的DS-BPSK调制的实现

阐述了直扩BPSK调制原理,给出了调制模型,论述了基于FPGA和直接数字频率合成技术的DS-BPSK调制器的设计与电路实现;根据伪码的产生原理,给出了在FPGA中实现平衡Gold码的方法及时序仿真;针对调制器的测试结果,提出了提高频谱纯度的高斯滤波器的优化设计方法,实现了对上行信号的DS-BPSK调制;通过无人机测控系统的搭载实验与应用证明:该调制器不仅实现了遥控数据的扩频功能,而且解决了无人机数据链中上行数据加密和抗干扰问题,扩大了无人机无线电的控制距离。     

基于FPGA的数字频率计的设计与实现

介绍了一种运用FPGA开发软件QuartusⅡ设计的数字频率计。该数字频率计的1Hz～1MHz输入被测脉冲信号具有频率测量、周期测量、脉宽测量和占空比测量等多种用途，其测试结果由3只七段数码管稳定显示，测试量程可自动切换，测量误差小于等于0．1％。     

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).