基于AD7008的数字DDS信号发生器的实现

介绍DDS的基本原理和结构,DDS芯片AD7008的功能,16位单片机MSP430F435的基本使用,以及由该单片机和AD7008芯片组成的数字信号发生器的原理和结构.利用全数字频率合成技术,制作高质量低成本的信号发生器,使用单片机通过数字调节控制AD7008芯片,对信号进行放大滤波处理,提供稳定度高和失真度小,频率、相位、幅度可调的正弦波或余弦波信号.系统频率输出稳定度高、精度高,提供高质量的信号源,为高精度的计量和测试提供方便,易于控制,在实际应用中取得了明显的应用成效.     

具有50MHz时钟率的AD7008单片CMOS DDS调制器

AD7008是美国最新推出的单片CMOS DDS调制器,它把32 bit相位累加器、SIN/COS查找表、10 bit D/A变换器以及调制和控制电路集成到一起,集相位调制、频率调制、幅度调制及I/O正交调制等多种功能于一身,具有很高的性能价格比.AD7008的时钟速率可达50MHz,输出信号频率可达 20MHz,频率分辨率可达 0.02Hz.本文简要介绍了AD7008的原理、结构及使用方法.     

基于ISP技术的数字频率扫描信号发生系统

本文介绍了利用Isp芯片Lattice公司的ispLSI1032E以及DDS频率合成器AD7008构成的数字频率扫描信号发生系统，本系统可以任意设置信号的起始频率、终止频率、信号幅值以及信号在每个频率保持的时间，系统自动以一定的频率步进量完成频率扫描，频率改变不会影响波形的连续性，也不会造成的相位的突变，真正实现频率的线性连续变化。     

用DDS芯片AD9852实现MSK调制

文章介绍了最小移频键控(MSK)调制以及直接数字频率合成(DDS)的组成及工作原理,研制了基于AT89C51以及DDS芯片AD9852的MSK调制器.系统调试灵活方便,结果表明用DDS方法实现对相位要求较高的数字调制是完全可行的.     

基于AD9959的多通道信号源设计

给出了一种基于多通道DDS芯片AD9959的信号发生装置的软硬件设计,与传统信号发生装置相比,该系统结构简单,性能可靠,其输出信号易于调制,分辨率较高.     

应用DDS芯片AD9835开发的一种高精度频率信号发生器

介绍了一种DDS专用芯片AD9835,并利用该芯片设计了一种高精度频率信号发生器,讨论了DDS芯片的基本原理、应用及其与计算机、单片机的接口。并对实际结果进行了分析。     

基于DDS的线性调频信号源设计

研究并设计了一种线性调频信号源,采用直接数字频率合成(DDS)技术产生输出信号.介绍了DDS的基本结构和原理,然后对基于DDS的AD9910芯片做了简单的介绍,并在此基础上设计了一个线性调频信号源,并给出了仿真结果.     

基于DSP和DDS技术的EAS扫频信号源设计

介绍了一种基于DSP和DDS的高精度扫频信号源的软硬件实现方案.利用DSP芯片TMS320F2812控制DDS芯片AD9834,可以产生EAS系统需要的7.7～8.7MHz频率范围内周期变化的高分辨率、转换速度快、输出频谱纯的扫频信号.文中主要介绍了TMS320F2812最小系统、AD9834与DSP的硬件接口设计、整个系统的软件编程.     

基于DDS技术线性调频正弦信号发生器的设计

直接数字频率合成技术(DDS)具有频率转换速度快、分辨率高等优点,已经成为当今合成波形的主流方法.介绍了DDS芯片AD9850的基本工作原理,设计了一种线性调频正弦信号发生器,并利用单片机控制芯片AD9850使其产生的正弦信号频率连续可调,讨论了AD950与单片机的接口,并给出了按步进1HZ或1KHZ进行线性调频的具体...     

基于LPC2148的激光酒精检测系统的信号发生电路设计

本文主要完成了基于LPC2148的激光酒精检测系统的信号发生电路设计.在设计中使用LPC2148主控芯片对的AD9854 DDS（direct digital frequency synthesis,直接数字频率合成）芯片进行控制,以产生所需要的正弦信号.先进的DDS技术的应用使得AD9854芯片可以产生高度稳定的频率、振幅可编程的正弦和余弦输出.采用93C56B存储芯片使用户可以对设定的参数进行便捷地存储和读取.同时使用3.2英寸的触摸屏作为人机交互界面,为参数设定、存取以及正弦信号的使能与禁止提供友好的操控界面,提高了系统的易用性.本文主要介绍了相关硬件及软件系统的设计,实际电路测试表明该系统稳定可靠,使用简便可以很好地满足酒精检测系统对于信号发生电路的需求.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

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。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

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.