Evaluation of the pole expressions of nano-scale multistage amplifiers based on equivalent output impedance

Several frequency compensation schemes have been proposed to stabilize multistage amplifiers with negative feedback. The performance of these amplifiers can be analyzed by inspecting their input-output transfer function as representation of their frequency response. With many circuit elements affecting the output response, it is relatively difficult to obtain the real transfer function of multistage amplifiers based on only the original small-signal expressions. Instead, certain techniques such as Miller’s theorem are used to approximate important parameters such as DC gain and dominant pole. These methods are not generally helpful for approximating the nondominant poles which have a critical role on the loop stability of nano-scale amplifiers. With this issue in mind, this work proposes a systematic methodology to achieve the pole expressions of multistage amplifiers with frequency compensation. The key in the proposed technique is to model the equivalent impedance of the compensation loop at the output. The effectiveness of the proposed approach has been verified through comparison between the transfer functions obtained from theory and those transfer functions found in the literature.     

电场力显微镜不同探针对表面电荷注入的影响

在电场力显微镜(EFM)下利用不同金属镀层微探针,在微纳米尺度下对聚酰亚胺薄膜的表面电荷生成特性进行研究。采用电场力显微镜导电探针在聚酰亚胺薄膜表面注入电荷,并对微纳米区域产生的电荷进行表征,结果表明不同金属镀层的微探针对聚酰亚胺薄膜上电荷注入效果不同。铂铱合金镀层具有比钴铬合金镀层更高的功函数fm,因此前者在金属-电介质接触中产生更大肖特基势垒,进而降低了电荷的注入程度。该研究为微纳米尺度下探索聚合物绝缘材料表面电荷生成、发展机理提供了一个新的研究方法和途径。     

基于大系统方法的上行CDMA蜂窝系统性能分析

结合大尺度和小尺度衰落,采用大系统分析方法对CDMA蜂窝系统上行链路的性能进行分析。首先分析了小区内多址干扰和小区间干扰的情况;其次推导出了通过匹配滤波器后的信干噪比值,该值只与小区负载、用户功率、信道增益有关;最后分析了系统的误码率、吞吐量和频谱效率,并通过仿真验证了分析的准确性。仿真结果发现,随着小区负载的增大,系统的误码率增大,吞吐量下降,但频谱效率有所提高。     

基于效用函数的通信对抗作战能力评估

通信对抗作战能力评估是解决装备实力比较和兵力规划等问题的前提和基础,如何有效描述通信对抗作战能力,是评估问题的关键所在。根据通信对抗作战能力指标不可公度性的特点,利用效用函数对指标进行描述;并通过对聚合模型的讨论,建立评估模型;最后通过实例验证了利用效用函数法进行通信对抗作战能力评估的可行性和合理性。     

基于特征描述子的匹配方法

利用一种效率和匹配率均较高且存储空间小的基于特征描述子的指纹识别算法,实现了指纹匹配且可应用到嵌入式系统。由于自动指纹识别系统一般在嵌入式系统上实现,对算法的复杂度、运算速度、存储空间需要等均有较高要求,因此选用普遍使用的基于细节特征的匹配算法。该算法运算速度快,一幅300×300像素的指纹图像,仅需几十个特征向量。实验证明,算法克服了点匹配计算量大、速度慢和参考点确定难等缺点,且对图像的旋转和平移具有较好的鲁棒性。可以使基于特征描述子的随机局部区域描述子特征的匹配性能进一步提高。     

碳纳米管随机网络场效应晶体管电学性能分析

利用电子束蒸发技术在Si衬底形成Au电极作为底栅电极,在底栅电极上生长SiO₂薄膜。超声分散CVD法合成的商用单壁碳纳米管(SWCNTs),使用匀胶机将单壁碳纳米管悬浮液均匀旋涂于SiO₂薄膜上。再利用荫罩式电子束蒸发技术,在单壁碳纳米管随机网络薄膜表面制备漏源电极。该工艺过程避免了碳纳米管过多的化学接触,有效地保护了碳纳米管的性状。在室温条件下对器件电学性能进行测试和分析。使用该方法制备的单壁碳纳米管随机网络薄膜场效应晶体管,具有器件性能稳定、重复性和一致性较好等优点,并可用于构建碳纳米管逻辑电路。该方法对于研究基于碳纳米管的大规模、低成本的集成电路,具有较高的借鉴价值。     

写光波长对光折变空间光调制器分辨率的影响

结合光学实验及数值模拟,对写光波长的变化对基于Bi12SiO20(BSO)光折变晶体的光寻址空间光调制器(SLM)的调制传递函数(MTF)空间频率响应的影响进行了分析.光学实验分析结果和数值模拟分析相吻合,写光波长以及电荷位置对SLM的MTF空间频率响应的影响在本质上得到了统一.根据分析及讨论,较短波长的写光有利于获得较好的MTF空间频率响应.     

Throughput Scalability of Wireless Hybrid Networks over a Random Geometric Graph

In this paper, we consider the transport capacity of ad hoc networks with a random flat topology under the present support of an infinite capacity infrastructure network. Such a network architecture allows ad hoc nodes to communicate with each other by purely using the remaining ad hoc nodes as their relays. In addition, ad hoc nodes can also utilize the existing infrastructure fully or partially by reaching any access point (or gateway) of the infrastructure network in a single or multi-hop fashion. Using the same tools as in [9], we show that the per source node capacity of Θ(W/log(N)) can be achieved in a random network scenario with the following assumptions: (i) The number of ad hoc nodes per access point is bounded above, (ii) each wireless node, including the access points, is able to transmit at W bits/sec using a fixed transmission range, and (iii) N ad hoc nodes, excluding the access points, constitute a connected topology graph. This is a significant improvement over the capacity of random ad hoc networks with no infrastructure support which is found as in [9]. We also show that even when less stringent requirements are imposed on topology connectivity, a per source node capacity figure that is arbitrarily close to Θ(1) cannot be obtained. Nevertheless, under these weak conditions, we can further improve per node throughput significantly. We also provide a limited extension on our results when the number of ad hoc nodes per access point is not bounded.Ulaş C. Kozat was born in 1975, in Adana, Turkey. He received his B.Sc. degree in Electrical and Electronics Engineering from Bilkent University, Ankara, Turkey and his M.Sc. in Electrical Engineering from The George Washington University, Washington D.C. in 1997 and 1999 respectively. He has received his Ph.D. degree in May 2004 from the Department of Electrical and Computer Engineering at University of Maryland, College Park. He has conducted research under the Institute for Systems Research (ISR) and Center for Hybrid and Satellite Networks (CSHCN) at the same university. He worked at HRL Laboratories and Telcordia Technologies Applied Research as a research intern. His current research interests primarily focus on wireless and hybrid networks that span multiple communication layers and networking technologies. Mathematical modelling, resource discovery and allocation, vertical integration of wireless systems and communication layers, performance analysis, architecture and protocol development are the main emphasis of his work. E-mail: kozat@isr.umd.eduLeandros Tassiulas (S′89, M′91) was born in 1965, in Katerini, Greece. He obtained the Diploma in Electrical Engineering from the Aristotelian University of Thessaloniki, Thessaloniki, Greece in 1987, and the M.S. and Ph.D. degrees in Electrical Engineering from the University of Maryland, College Park in 1989 and 1991 respectively.He is Professor in the Dept. of Computer and Telecommunications Engineering, University of Thessaly, Greece and Research Professor in the Dept. of Electrical and Computer Eng and the Institute for Systems Research, University of Maryland College Park since 2001. He has held positions as Assistant Professor at Polytechnic University New York (1991–95), Assistant and Associate Professor University of Maryland College Park (1995–2001) and Professor University of Ioannina Greece (1999–2001).His research interests are in the field of computer and communication networks with emphasis on fundamental mathematical models, architectures and protocols of wireless systems, sensor networks, high-speed internet and satellite communications.Dr. Tassiulas received a National Science Foundation (NSF) Research Initiation Award in 1992, an NSF CAREER Award in 1995 an Office of Naval Research, Young Investigator Award in 1997 and a Bodosaki Foundation award in 1999 and the INFOCOM′94 best paper award. E-mail: leandros@isr.umd.edu     

Taylor 四相码信号及其模糊图的绘制

介绍了Taylor四相码信号的特点及其研究现状，运用模糊函数的卷积算法，通过MatIab语言计算并绘制出了其三维立体模糊图，制作了ξ切面图、τ切面图和模糊度图，并给出了绘制方法。     

采用线性正则域模糊函数的QFM信号参数估计算法输出信噪比分析

采用线性正则域模糊函数的二次调频 (quadratic frequency modulated,QFM) 信号参数估计算法简单易解,估计精度较高,误差传递小,在实际应用中有较好的前景。本文对该算法的输出信噪比进行了较为深入而详细的分析,推导了输出信噪比与输入信噪比及信号采样点数之间的关系表达式;通过仿真实验比较了在同等条件下本算法和积分广义模糊函数算法(integrated generalized ambiguity function, IGAF))以及多项式相位变换(polynomial-phase transform, PPT)算法的输出信噪比大小,以及达到相同大小输出信噪比所需采样点数。发现本算法的输出信噪比要大于IGAF算法和PPT算法,且达到相同大小的输出信噪比所需采样点数分别是IGAF算法和PPT算法的1/4和1/9,即得到相同大小的输出信噪比时本算法所需的采样点数更少.