DBS成像技术在毫米波雷达导引头中的应用

本文介绍了DBS技术的基本概念及工作原理,并且结合毫米波雷达回波信号的特点,研究适合快速实时成像、且具有实际工程意义的DBS成像算法——SPECAN算法及其实现流程。在理论分析的基础上,给出了系统仿真的结果和性能参数,证明了理论的可行性,为实际工程上的应用打下了基础。     

System Throughput Analysis of Rate Adaptive TDMA System Supporting Two Class Services

In this paper, an adaptive transmission scheme is proposed to improve the spectral efficiency of TDMA systems. Services accommodated in such systems are classified as QoS services and BE services. Unlike conventional adaptive TDMA systems where the time slot duration is fixed for each user, our proposed system employs transmission slots with adaptive duration. For QoS services, rate adaptive modulation is adopted to make use of the instantaneous channel conditions of individual user. For BE services, a media access control strategy (MAC) that takes the instantaneous transmission conditions of all physical links of all BE services into consideration is employed. A framework to study the proposed system in terms of the average packet loss and the average system throughput is presented. The maximum number of QoS services that can be supported in the system while a predefined requirement on the average packet loss is still satisfied is investigated. A comparison study shows that our proposed scheme has higher system throughput over both conventional fixed and adaptive TDMA systems. Ronghong Mo received her B.Sc. and M. Sc. Degree from Zhongshan University, Guangzhou, China, both in Physics. From July 1999 to July 2003, she was a research scholar in the department of Electrical and Computer Engineering in National University of Singapore (NUS), toward her PhD degree. She is currently working as a research engineer in NUS. Her research interests include adaptive modulation, synchronization and channel estimation in wireless communications. Yong Huat Chew received the B.Eng, M.Eng and Ph.D. degrees in Electrical Engineering from National University of Singapore, Singapore. Since 1996, he has been with the Institute for Infocomm Research (formerly also known as Center for Wireless Communications and Institute for Communications Research), an institute under Agency for Science, Technology and Research, where he is presently a lead Scientist. His research interests are in wireless communications, transmission over HFC, DSL and all-optical networks.     

一种带新型直流失调补偿电路的模拟数字控制可配置的自动增益控制器

本文提出一种可用于零中频接收机的模拟/数字控制可配置的自动增益控制环路的设计,应用一种新型的直流失调消除电路。这种自动增益控制环路可配置于模拟或者数字控制,以便与不同的基带芯片兼容。本文更进一步提出了一种新型的直流失调消除电路,这种直流失调消除电路实现了低于10KHz的下限截止频率（HPCF,high pass cutoff frequency）。自动增益控制环路电路采用0.18um CMOS工艺。当配置于模拟控制模式下,这种自动增益控制环路的增益动态范围为70dB,3dB带宽大于60M。当配置于数字控制模式下,通过5比特的数字控制码控制,这种自动增益控制环路的增益动态范围为64dB,步进精度2dB,步进误差小于0.3dB。当输入引入40mV直流失调,电路输出直流失调电压小于1.5mV。电路整体功耗小于3.5mA,面积800um*300um。     

Effect of Contact Mode on the Electrical Transport and Field‐Emission Performance of Individual Boron Nanowires

Vapor–liquid–solid processing of boron nanowires (BNWs) can be carried out either using a bottom‐up or top‐down growth mode, which results in different contact modes between the nanowire and the substrate. The contact mode may strongly affect the electrical transport and field‐emission performance of the individual boron nanowires grown on a Si substrate. The electrical transport and field‐emission characteristics of individual boron nanowires of different contact modes are investigated in situ using a scanning electron microscope. The contact barriers are very distinct for the different contact modes. Moreover, the transition from a “contact‐limited” to a “bulk‐limited” field‐emission (FE) process is demonstrated in nanoemitters for the first time, and the proposed improved metal–insulator–vacuum (MIV) model may better illustrate the nonlinear behavior of the Fowler‐Nordheim (FN) plots in these nanoscale systems. Individual BNWs with different contact modes have a discrepancy in their emission stability and vacuum breakdown characteristics though they have similar aspect ratios, which suggests that their electrical transport and field‐emission performance are closely related to their contact mode. Boron nanowires grown in the base‐up mode have better field‐emission performances and are more beneficial than those grown in the top‐down mode for various device applications.     

Si(111)衬底高温AlN缓冲层厚度及其结构特性

通过高分辨X射线衍射、光致发光、二次离子质谱（SIMS) 、原子力显微镜和同步辐射X射线衍射分析了AlN缓冲层的厚度对GaN外延层的影响. 实验表明，在缓冲层厚度为13～20nm之间时，GaN外延层的张应力最小，同时晶体质量和光学质量达到最优值. 此外，SIMS分析表明，当AlN缓冲层位于13～20nm之间时，可有效抑制Si的扩散.     

Improvement of Linear Model of Plasma Filled Dielectric Cerenkov Maser

The plasma filled dielectric Cerenkov maser considering the effect of the plasma grating has been studied. The plasma grating is formed by the modulation of the strong fields. According to the plasma-grating model, An equivalent model is constructed. The modified dispersion relation has been derived .The numerical results show that when the modulation over the background plasma increases, the operation frequency also increases, however, the growth rate varies slightly. Compared with the calculation results obtained by treating the plasma as uniform fluids, the calculation results with the equivalent model describe the bounded bandwidth of the dielectric oscillator more precisely.     

增益提高型套筒式全差分跨导放大器的设计与分析

提出了一种应用于流水线型模数转换器(ADC)的增益提高型套筒式全差分跨导放大器(OTA)的设计与分析方法.通过ADC的性能要求推导出OTA的设计指标.该设计中OTA的架构由主运放、增益辅助运放及共模反馈电路3部分子电路组成.设计采用SMIC CMOS 0.18mm工艺平台.该设计方法的实验结果表明:1pF负载下,跨导放大器.的直流增益达到145dB,单位增益带宽超过750MHz,相位裕度达到58°.闭环增益为4时,放大器在20ns内稳定到0.05%的精度.     

Reducing Encoder Bit-Rate Variation in MPEG Video

A shortcoming of current video transmission using the MPEG standard is that its encoder produces a variable bit rate (VBR). Due to this, the encoder output has to be buffered and released over the network at a constant rate. This buffering of the encoder output introduces an additional delay between the encoding and decoding phases of the video transmission. To remedy this problem, we present a strategy to distribute the load produced by the encoder as evenly as possible, i.e., try to have a constant bit rate (CBR). This is done by treating the slices in each frame separately while compressing them and then mixing the different kinds of slices that are sent over the network. The resulting load variation is much more uniform, reducing the buffering delay and making future bandwidth requirement estimates more accurate.This material is based upon work supported in part by the National Science Foundation under Award No. IRI-9526004, by the Texas Advanced Research Program under Grant No. 3652270, and by a grant from the University of Houston Institute of Space Systems Operations. Rajat Agarwal is now with Lucent Technologies. This paper is an extended version of a shorter paper presented at IEEE ICMCS 1999.Albert Mo Kim Cheng received the B.A. with Highest Honors in Computer Science at age 19, graduating Phi Beta Kappa, the M.S. in Computer Science with a minor in Electrical Engineering at age 21, and the Ph.D. in Computer Science at age 25, all from The University of Texas at Austin, where he held a GTE Foundation Doctoral Fellowship. Dr. Cheng is currently a tenured Associate Professor in the Department of Computer Science at the University of Houston, where he is the founding Director of the Real-Time Systems Laboratory. He has served as a technical consultant for several organizations, including IBM, and was also a visiting faculty in the Departments of Computer Science at Rice University (2000) and at the City University of Hong Kong (1995).He is the author/co-author of over seventy refereed publications in IEEE Transactions on Software Engineering, IEEE Transactions on Knowledge and Data Engineering, Real-Time Systems Symposium, Real-Time and Embedded Technology and Applications Symposium, and other leading conferences. One of his recent work presents a timing analysis of the NASA X-38 Space Station Crew Return Vehicle Avionics, which contains a fault-tolerant distributed system.Dr. Cheng has received numerous awards, including the National Science Foundation Research Initiation Award (now known as the NSF CAREER award). He has been invited to present seminars and tutorials at over 30 conferences, and has given invited seminars/keynotes at over 20 universities and organizations, most recently at ICEIS, Ecole Superieure de l Ouest (ESEO), Angers, France, April 2003. His next invited keynote speech will be at the 1st Intl. Conf. on Informatics in Control, Automation and Robotics (ICINCO), Setubal, Portugal, August 2004.He is an Associate Editor of the IEEE Transactions on Software Engineering (1998-2003), a Guest Co-Editor of two IEEE TSE Special Issues on Software and Performance (Nov. and Dec. 2000), an Associate Editor of the International Journal of Computer and Information Science, the work-in-progress program chair of the 2001 IEEE-CS Real-Time Technology and Applications Symposium, the work-in-progress session chair of the 2003 IEEE-CS Real-Time Systems Symposium, and the invited special panel chair for the software engineering for multimedia session at the 1999 IEEE-CS International Conference on Multimedia Computing Systems (ICMCS). Currently, he is a member of the program committees of RTSS, RTAS, ICEIS, ICECCS, RTAS, LCN, COMPSAC, ICCCN, AIA, DBA, PDCN, SE, and ICINCO. Dr. Cheng is an Honorary Member of the Institute for Systems and Technologies of Information, Control and Communication (INSTICC). He is a Senior Member of the IEEE.Dr. Cheng is the author of several book chapters on E-commerce/Enterprise Information Systems, and an article entitled Embedded OS, in the upcoming Encyclopedia of Computer Science and Engineering (John Wiley & Sons). He is the author of the new senior/graduate-level textbook entitled Real-Time Systems: Scheduling, Analysis, and Verification (John Wiley & Sons). cheng@cs.uh.eduRajat Agarwal received the M.S. in Computer Science from the University of Houston. He is currently a Member of the Technical Staff at Lucent Technologies. His research interest is in real-time multimedia systems.     

Si衬底MOCVD生长GaN/InGaN多量子阱缺陷TEM研究

用透射电子显微镜对Si衬底生长GaN/InGaN多量子阱材料进行横断面测试,在衬底和缓冲层区域进行高分辨电子显微成像(HRTEM)、电子衍射衬度成像、选区电子衍射成像,在量子阱附近区域进行了双束近似电子衍衬像对其位错特性进行研究;用场发射扫描电子显微镜对饱和KoH溶液腐蚀前后材料成像.结果发现,AIN缓冲层具有多孔结构,高温GaN层位错平均密度达108cm-2,同扫描电子显微镜得到的六角腐蚀坑密度一致,量子阱以下发现大量位错发生90°弯曲,而使穿过量子阱位错密度大大降低.在线位错中,以刃位错居多,其次是混合位错,所观察区域几乎未见螺位错.     

Instruction-Vulnerability-Factor-Based Reliability Analysis Model for Program Memory

Bit faults induced by single-event upsets in instruction may not cause a system to experience an error. The instruction vulnerability factor (IVF) is first defined to quantify the effect of non-effective upsets on program reliability in this paper; and the mean time to failure (MTTF) model of program memory is then derived based on IVF. Further analysis of MTTF model concludes that the MTTF of program memory using error correcting code (ECC) and scrubbing is not always better than unhardened program memory. The constraints that should be met upon utilizing ECC and scrubbing in program memory are presented for the first time, to the best of authors’ knowledge. Additionally, the proposed models and conclusions are validated by Monte Carlo simulations in MATLAB. These results show that the proposed models have a good accuracy and their margin of error is less than 3 % compared with MATLAB simulation results. It should be highlighted that our conclusions may be used to contribute to selecting the optimal fault-tolerant technique to harden the program memory.