高频数字抽取滤波器的设计

设计了采样频率为640 MHz、过采样率为64的高频数字抽取滤波器。该数字抽取滤波器由CIC(Cascaded Integrator Comb)滤波器(降16倍)、CIC补偿滤波器(降2倍)和半带滤波器(降2倍)组成。为了实现高频工作,CIC滤波器采用两级结构,第一级采用多相分解技术,使大部分结构工作在较低时钟频率下,极大地降低了CIC的功耗,第二级采用传统结构。CIC补偿滤波器使信号通带平坦,半带滤波器满足了阻带的衰减要求。为了验证数字滤波器的性能,搭建了四阶前馈—反馈结构ΣΔ调制器,作为数字抽取滤波器的输入,最终在输入信号频率为0.5 MHz时,数字抽取滤波器输出的信噪比为97.40 dB。     

时钟芯片的低功耗设计

在时钟芯片设计的各个层次上深入探讨了影响时钟芯片功耗的主要因素,确定了电路功耗主要来源与振荡电路和分频电路。在电路实现过程中,通过采用不同工作电压和对主要功耗电路的结构和参数进行优化设计等多种手段来控制功耗。通过1.2滋m工艺流片验证,在工作电压为5V时,芯片工作电流为0.17mA,实现了低功耗时钟芯片的设计。     

基于多相分解和曲线拟合的改进CIC抽取器

传统的CIC（Cascaded integrator comb）抽取器设计往往不能同时满足改善频响特性、降低采样率和降低功耗的要求,需采取折中的办法。本文提出了一种改进的CIC抽取器结构,用多项分解的方法降低了抽取滤波器工作的采样率,同时降低了功耗;再用曲线拟合技术改进频响特性,这种抽取器在降低采样率、减少硬件资源和改善频响特性3个方面同时得到满足,数值仿真验证了这一结论。     

应用于∑-△A/D转换器的数字抽取滤波器的设计

设计了一种应用于∑-AA/D转换器的滤波器结构,采用梳状滤波器和半带滤波器级联的多级形式实现.梳状滤波器采用开关降频和流水线级联形式,降低了功耗和复杂度;半带滤波器采用多相结构,数据量减少了近50%.该抽取滤波器信噪比达到98dB,可以满足高精度A/D转换器的设计要求.     

改进的抽取滤波器设计

在Sigma-Delta ADC芯片中,数字抽取滤波器电路占据了大部分面积。所设计的改进型Hogenauer CIC滤波器,将梳状部分进行优化,采用控制单元、加法器和寄存器代替传统Hogenauer CIC滤波器中的差分器,从而减小数字电路的面积。一个采用这种结构的4阶32倍降采样数字滤波器在Stratix Ⅱ系列2S30 FPGA芯片中实现。经过测试,耗费的硬件资源比传统Hogenauer结构滤波器减少11%。     

一种新型的抽取滤波器设计

文章基于面积和功耗方面考虑提出了一种低功耗多相变级数非递归梳状滤波器结构,这种滤波器适合高阶过采样sigmadeltaA/D转换器。抽取滤波器采用Top-down方法设计,用0.6-μmCMOS标准单元实现,相比同样速度下的标准的非递归结构抽取滤波器节省了约1/3面积和功耗。     

分数抽样率变换中线性相位FIR滤波器多相分解的对称性研究

为提高分数抽样率变换系统的计算效率, 在讨论其滤波器多相分解结构的基础上, 利用线性相位FIR滤波器的系数对称性, 构造多相分解系数的中心对称矩阵, 推导出适用于任意分数抽样率和任意滤波器阶数的高效实现方法, 并给出所需乘法与加法运算量的计算公式. 测试结果表明, 与直接计算相比, 采用本文方法可减少50%乘法运算和30%加法运算, 计算效率显著提高.     

低轨卫星系统数字上变频器的多级内插设计

在研究了低轨卫星DS-CDMA系统数字上变频器的内插技术之后,提出了以成型滤波器、半带滤波器和CIC滤波器等多级内插级联的结构来实现抽样率的变换。在具体实现上采用了基于多相结构实现的成型滤波器、高效的半带滤波器和改进的多级CIC滤波器,节省了系统的硬件资源,提高了系统的性能。     

改进的时钟偏斜误差校正方法的FPGA实现

利用改进的完美重构方法对多A/D采样系统的时钟偏斜误差校正方法进行了FPGA实现。采用自顶向下和模块化的设计方法,实现了多路采样数据的相位同步模块、数据位置映射模块、并行多相滤波器组模块以及多路数据合成模块。对完美重构方法中的滤波器组运用多相分解技术将其化为并行结构滤波器组,对输出数据采用流水线结构加法器组进行处理,降低了系统运算延迟,提高了系统的实时性。在MATLAB和Model Sim中进行仿真,结果表明了该实现的正确性和有效性。     

一种半带滤波器的低功耗实现方法

半带滤波器常被用于实现数字变频中数字信号的2倍抽取过程。对于抽取半带滤波器的无乘法器实现结构,常使用移位相加代替乘法操作减少硬件资源的使用,利用多相分解技术降低整体滤波的运算量,降低硬件实现总体功耗。在此基础上进一步提出了一种低功耗的实现方法。通过Modelsim软件仿真验证功能正确后,最后由Design Complier软件的综合结果表明,与传统一般移位相加实现结构相比,所提出的结构有效地降低了半带滤波器的面积及功耗。     

Commercial digital image libraries,digital images and digital discontent

Publications such as consumer magazines rely heavily on image libraries as sources for the images they use in their issues. Traditionally, magazine editorial staff have discussed their image requirements over the telephone with library staff and the library has conducted the search. Many libraries have now developed Web sites and their customers search them for images themselves. A minority have e-commerce capabilities, and enable customers to purchase and download digital images from their sites. This survey found that magazine staff do not often choose to search digital libraries, preferring instead to continue to contact the library by telephone. Most also choose not to buy the use of digital images, but prefer to continue to work with conventional transparencies and slides. The reasons for these preferences, and the reasons they are unlikely to change in the short term, are explored.     

Teaching digital library concepts using digital library applications

Many digital library topics may be taught using digital library applications, in the context of project-based digital library courses. Several digital library applications exist, and these applications are used as teaching tools to illustrate the functionality of digital libraries as well as the design decisions that go into them. Using digital library applications as teaching tools provides a valuable learning experience for students, and may provide useful feedback to the developers of DL applications. This paper identifies and explores DL topics that may most effectively be taught using DL applications, in the context of project-based DL courses.     

Bionic digital brain realizing the digital twin-cutting process

A digital twin (DT) is an effective means of achieving physical and information fusion and has great potential for achieving a new paradigm of cutting process (CP) intelligence. This paper traces the relevant studies of digital technology in manufacturing and proposes a bionic digital brain (BDB) as the intelligent core of a digital twin-cutting process (DTCP) framework. The BDB was built with digital neurons (DN) as the basic functional unit, and the reaction mechanism between the DN stimulated the BDB to compute intelligently in real time (RT). The left brain obtains the prophetic theoretical processing information through the DN. The right brain receives actual perceptive processing information through the DN. After the corpus callosum fuses the left and right brain information, the DN outputs the optimal control solutions in RT to ensure demand. The details of monitoring, predicting, optimizing, and controlling the CP based on this framework are described in detail through a case study, demonstrating the powerful information processing capability of the BDB and the RT precision intelligent machining effects. The developed DTCP system confirmed the feasibility and effectiveness of the proposed framework. It provided a theoretical and technical reference for applying and promoting DT technology in the CP.     

多通道雷达数字接收机数字下变频设计

提出一种基于时分复用原理的双频段多通道数字接收机DDC模块的设计方法,并利用FPGA的数控振荡器和FIR滤波器的IP核完成了DDC模块的设计与实现。仿真结果表明,该设计实现了数字混频、抽取和滤波的功能,与其他设计方案对比表明,本方案有效地减少了FPGA资源的使用量,降低了硬件设计的复杂度,节约了硬件成本。     

手机及小型手持数字设备数字取证研究综述

现代社会以手机和个人数字助理为代表的小型手持电子设备已经成为人们不可或缺的日常工具。随着信息和通信技术的发展,这些手持设备功能越来越增强,普及度越来越高,在各类案件中都可以见到这类数字手持设备的身影。因而对于这一类小型数字电子设备取证成为紧迫性的新研究领域。对这一类数字取证现状和相应工具作一综述。     

A novel digital information service for federating distributed digital entities

We investigate the performance and the scalability metrics of a Digital Information Service framework that is used for unifying and federating online digital entities by retrieving and managing information located on the web. The Digital Information Service consists of tools and web services for supporting Cyberinfrastructure based scientific research. This system supports a number of existing online Web 2.0 research tools (social bookmarking, academic search, scientific databases, journal and conference content management systems) and aims to develop added-value community building tools that leverage the management and federation of digital entities and their metadata obtained from multiple services. We introduce a prototype implementation and present its evaluation. As the results indicate, the proposed system achieves federation and unification of digital entities coming from different sources with negligible processing overheads.     

Debunking the ‘digital native’: beyond digital apartheid,towards digital democracy

This paper interrogates the currently pervasive discourse of the ‘net generation’ finding the concept of the ‘digital native’ especially problematic, both empirically and conceptually. We draw on a research project of South African higher education students' access to and use of Information and Communication Technologies (ICTs) to show that age is not a determining factor in students' digital lives; rather, their familiarity and experience using ICTs is more relevant. We also demonstrate that the notion of a generation of ‘digital natives’ is inaccurate: those with such attributes are effectively a digital elite. Instead of a new net generation growing up to replace an older analogue generation, there is a deepening digital divide in South Africa characterized not by age but by access and opportunity; indeed, digital apartheid is alive and well. We suggest that the possibility for digital democracy does exist in the form of a mobile society which is not age specific, and which is ubiquitous. Finally, we propose redefining the concepts ‘digital’, ‘net’, ‘native’, and ‘generation’ in favour of reclaiming the term ‘digitizen’.     

Three-dimensional digital planes

Definitions of 3-D digital surface and plane are introduced. Many geometric properties of these objects are examined. In particular, it is shown that digital convexity is neither a necessary nor a sufficient condition for a digital surface element to be a convex digital plane element, but it is both necessary and sufficient for a digital surface to be a digital plane. Also algorithms are presented to determine whether or not a finite set of digital points is a (convex) digital plane element.     

Paper-based digital microfluidics

In this paper, a new fabrication method for digital microfluidics is proposed. In which, paper, graphite, and adhesive tape are used as substrate, electrodes, and dielectric layer, respectively. The graphite is sprayed over a template on the paper substrate. Two different water repellants are used as the hydrophobic layer, which replace with expensive materials such as Teflon-AF^®. The paper substrate is low cost, available, and flexible. The proposed device is disposable, and its fabrication procedure is simple, fast, and low cost which allows creation of a new device for each individual experiment. Therefore, problems such as adsorption and dielectric breakdown will not occur in this type of digital microfluidics. This device can perform two types of droplet operations, merging and moving on droplets in volumes of 15–50 μL.     

Multirate digital filters

This paper provides a review of recent developments in multirate digital filters and attempts to fill a long existing gap between multirate digital filters and multirate sampled-data feedback control systems.