离散傅里叶变换的算术傅里叶变换算法

离散傅里叶变换(DFT)在数字信号处理等许多领域中起着重要作用.本文采用一种新的傅里叶分析技术—算术傅里叶变换(AFT)来计算DFT.这种算法的乘法计算量仅为O(N);算法的计算过程简单,公式一致,克服了任意长度DFT传统快速算法(FFT)程序复杂、子进程多等缺点;算法易于并行,尤其适合VLSI设计;对于含较大素因子,特别是素数长度的DFT,其速度比传统的FFT方法快;算法为任意长度DFT的快速计算开辟了新的思路和途径.     

用FPGA实现FFT算法

引言 DFT（Discrete Fourier Transformation）是数字信号分析与处理如图形、语音及图像等领域的重要变换工具,直接计算DFT的计算量与变换区间长度N的平方成正比。当N较大时,因计算量太大,直接用DFT算法进行谱分析和信号的实时处理是不切实际的。快速傅立叶变换（Fast FourierTransformation,简称FFT）使DFT运算效率提高1～2个数量级。其原因是当N较大时,对DFT进行了基4和基2分解运算。FFT算法除了必需的数据存储器ram和旋转因子rom外,仍需较复杂的运算和控制电路单元,即使现在,实现长点数的FFT仍然是很困难。本文提出的FFT实现算法是基于FPGA之上的,算法完成对一个序列的FFT计算,完全由脉冲解发,外部只输入一脉冲头和输入数据,便可以得到该脉冲头作为起始标志的N点FFT输出结果。由于使用了双     

基于DSP的电力谐波装置研究

DFT/FFT是进行谐波检测的有效方法,其算法简单,易于实现。在改进DFT算法的基础上,利用CCS仿真与硬件DSP相结合的方式验证算法,通过将加窗插值FFT算法与改进DFT算法进行对比对数据进行分析,比较各次谐波幅值、相位以及频率的误差。利用信号发生器产生三角波进行DSP硬件测试,分析两种算法在通过数据采集、A/D转换后受到的精度影响,验证算法的实时性、准确性和稳定性。最终分析出在非同步采样时,改进DFT算法具有较高的检测精度,而加窗插值FFT算法实时性比较好。     

LTE系统中混合基FFT算法分析与硬件实现

在LTE系统设计过程中,上行链路采用单载波频分多址技术(SC-FDMA),下行链路采用正交频分多址技术(OFDMA)。在用这两种技术实现LTE的过程中,都采用了DFT或FFT的处理方法,而直接计算DFT的计算量太大。因此本文通过对LTE系统中各种FFT算法进行了分析,重点对Cooley-Tukey FFT算法进行了研究,同时以变换区间N=12和N=15为例,通过电路复用的方式进行了FPGA实现与验证。     

基于Matlab的DFT及FFT频谱分析

DFT及FFT是数字信号处理的重要内容。DFT是FFT的基础,FFT是DFT的快速算法,在MATLAB中可以利用函数FFT来计算序列的离散傅里叶变换DFT。基于此首先介绍了Matlab软件;其次给出了基于Matlab软件的DFT和FFT频谱分析的方法,利用Matlab软件方法,使得设计方便、快捷,大大减轻了工作量;最后结合实例给出了仿真结果。     

Cooley-TukeyFFT算法在LTE系统中的研究与应用

快速傅里叶变换（FFT）作为数字信号处理的核心技术,使离散傅里叶变换（DFT）的运算时间缩短了几个数量级,并在LTE系统中有着重要的应用。在LTE系统中,上行链路采用单载波频分多址技术（SC-FDMA）,下行链路采用正交频分多址技术（OFDMA）。在这两种技术实现的过程中,都采用了离散傅里叶变换进行处理,而直接计算DFT的计算量太大。通过对LTE系统中Cooley-Tukey FFT算法进行了研究,同时利用Verilog HDL描述的方式实现了不定点FFT系统设计,并以FPGA芯片virtex5为硬件平台,进行了仿真、综合等工作,仿真结果表明其计算结果达到了一定的精度。     

一种频率无关的正弦信号相量计算方法

为寻求一种频率无关的实时相量计算方法,通过分析传统算法,提出一种可变数据窗正弦相量插值计算方法。该算法通过等间隔采样获得信号一个周期左右的样本数据,采样数据计算出信号的基波频率并确定信号的一个基频周期所需的最大采样点数N,计算信号N点DFT和N+1点DFT,再利用两次DFT计算结果进行线性插值得到信号真实频点上各次谐波的实部和虚部,计算出信号各次谐波的幅值和瞬时相位。仿真分析和实际测量表明,该算法的计算精度和实时性较高,能够满足频率随机变化的应用要求。     

FIR数字滤波器的一种快速算法

FIR数字滤波器本质上是一种线性卷积的运算,当数字滤波器的阶次N很大时,计算量很大,计算速度很慢,达不到系统对实时性的要求。文章介绍了一种数字信号处理算法,该算法将线性卷积运算转换成加法运算,利用加法运算进行求解,避免了数据堆积,加快了运算速度,从而使数字滤波器处理过程实时、快速。     

一种改进的滑动窗FFT递推算法

在信号谱线分析中,经常用到滑动窗的FFT计算,由于传统的FFT在N值较大和滑动步进较小时,计算量较大,在实时通信系统中难以实现,本文提出一种连续滑动窗的递推FFT算法,该算法充分利用了前窗的计算结果并将输入序列转换为一个输入端仅有少数非零点的特殊序列,不仅降低了计算量,而且提高了使用的灵活性和实时性。     

基于ADuC841单片机和FFT的市电谐波测量的实现

为了提高市电谐波检测的速度,在传统DFT算法的基础上,利用DFT的周期性和对称性,对其实现方法进行了改进。运用基8FFT算法,简化了运算,提高了运算的实时性。结合ADI公司的ADuC841微控制器芯片的特性,提出了一种快速完成市电电网中谐波成分测量的方法。测试数据显示所提出的方法,具有足够的测量精度以及测量速度,并且所设计的系统具有使用方便、成本低等优点。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.