A Clock Generator for High-Speed High-Resolution Pipelined A/D Converter Zhao Lei(赵磊) , Yang Yintang(杨银堂), Zhu Zhangming(朱樟明), Liu Lianxi(刘帘羲)

A clock generator circuit for a high-speed high-resolution pipelined A/D converter is presented.The circuit is realized by a delay locked loop(DLL),and a new differential structure is used to improve the precision of the charge pump.Meanwhile,a dynamic logic phase detector and a three transistor NAND logic circuit are proposed to reduce the output jitter by improving the steepness of the clock transition.The proposed circuit,designed by SM1C 0.18μm 3.3 V CMOS technology,is used as a clock generator for a 14 bit 100 MS/s pipelined ADC.The simulation results have shown that the duty cycle ranged from 10%to 90%and can be adjusted.The average duty cycle error is less than 1%.The lock-time is only 13 clock cycles.The active area is 0.05 mm2 and power consumption is less than 15 mW.     

CdS薄层对有机电致发光器件性能的影响

将光电材料硫化镉(CdS)薄层插入到结构为ITO/NPB/Rubrene/NPB/DPVBi/Alq3/LiF/Al的白光有机发光器件(OLED)的Alq3和LiF之间,研究了CdS对OLED性能的影响。结果表明,0.1nm厚的CdS插入Alq3和LiF之间的器件性能最好。器件电压从7 V变化到14 V时,色度均在白光的中心区域;当电压为7V时,器件的最大电流效率为9.09cd/A;当电压为14V时,器件的最大亮度为16 370cd/m2。不加CdS时,当电压为8V时,器件的最大效率为5.16cd/A;当电压为14V时,最大亮度为6 669cd/m2。加CdS的器件比不加CdS的器件最大效率提高了1.76倍,最大亮度提高了2.42倍。     

云计算安全可靠性探讨

根据云计算架构的典型层次,并结合3种云服务模式和云安全体系架构,分析了云计算中存在的安全风险,以及云计算中存在的数据安全、虚拟化安全及平台安全等主要的安全问题;同时详细地分析了云安全策略及关键技术。     

A Novel Lattice Reduction Precoding Method

In this work, a novel lattice reduction (LR) precoding method is proposed. The technique combines conventional LR precoding with a method of reducing the singular value coefficients of the LR-reduced basis matrix. The performance of the new technique was comparable to that of sphere encoding, while its complexity was lower than that of other sub-optimal methods.     

Queuing Scheme for Improved Downlink Throughput on WLANs

A transmission queuing scheme is described that increases downlink throughput on wireless local area networks (WLANs) while also increasing the total throughput. When the amount of uplink traffic increases on a WLAN, the carrier sense multiple access with collision avoidance (CSMA/CA) protocol, which is the prescribed scheme for IEEE 802.11 WLAN channel access, may substantially reduce the rate of downlink data frame transmission. This results in severe throughput degradation for mobile stations with downlink traffic. The proposed scheme comprises a transmission control function based on consecutive transmission, as described in the IEEE 802.11e standard, and a dynamic queue prioritization algorithm. Simulation results demonstrate that the proposed scheme increases the maximum total throughput for uplink and downlink traffic by 17% compared with the conventional distributed coordination function (DCF) scheme and that it reduces the difference between uplink and downlink throughput. In an environment where transmission errors occur, the difference in throughput is reduced by about 50% compared with the conventional schemes.     

Minimum-energy multicast in wireless ad hoc networks with adaptive antennas: MILP formulations and heuristic algorithms

In this paper, we consider wireless ad hoc networks that use adaptive antennas and have limited energy resources. To explore the advantages of power saving offered by the use of adaptive antennas, we consider the case of source initiated multicast traffic. We present a constraint formulation for the MEM (Minimum-Energy Multicast) problem in terms of MILP (Mixed Integer Linear Programming) for wireless ad hoc networks. An optimal solution to the MEM problem using our MILP model can always be obtained in a timely manner for moderately sized networks. In addition to the theoretical effort, we also present two polynomial-time heuristic algorithms called RB-MIDP and D-MIDP to handle larger networks for which the MILP model may not be computationally efficient. The experimental results show that our algorithms compare well with other proposals discussed in this paper.     

Si/SiGe resonant interband tunnel diode with f/sub r0/ 20.2 GHz and peak current density 218 kA/cm/sup 2/ for K-band mixed-signal applications

This letter presents the room-temperature high-frequency operation of Si/SiGe-based resonant interband tunnel diodes that were fabricated by low-temperature molecular beam epitaxy. The resulting devices show a resistive cutoff frequency f/sub r0/ of 20.2 GHz with a peak current density of 218 kA/cm/sup 2/, a speed index of 35.9 mV/ps, and a peak-to-valley current ratio of 1.47. A specific contact resistivity of 5.3/spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ extracted from RF measurements was achieved by Ni silicidation through a P /spl delta/-doped quantum well by rapid thermal sintering at 430/spl deg/C for 30 s. The resulting devices are very good candidates for RF high-power mixed-signal applications. The device structures presented here are compatible with a standard complementary metal-oxide-semiconductor or heterojunction bipolar transistor process.     

聚合物电致发光器件中用类金刚石碳膜增强电子注入

用正丁胺作碳源,采用射频辉光等离子系统制备类金刚石碳膜(DLC),沉积在聚合物发光器件中的发光层(MEH-PPV)和铝(Al)阴极间作电子注入层.制备了结构为ITO/MEH-PPV/DLC/Al的不同DLC厚度的器件,测量了器件的I-V特性、亮度及效率,研究了DLC层对器件电子注入性能影响的机制.结果表明:当DLC厚度小于1.0nm时,其器件有较ITO/MEH-PPV/Al高的启动电压和低的发光效率;当DLC厚度在1.0～5.0nm之间时,器件的性能随着DLC厚度增加而变好;当DLC厚度为5.0nm时,器件具有最低的启动电压与最高的发光效率;当DLC厚度继续增加时,器件的性能随着DLC厚度增加而变差.并对ITO/MEH-PPV/DLC/Al和ITO/MEH-PPV/LiF/Al的器件性能进行了比较研究.     

ZnO单晶薄膜光电响应特性

对采用MOCVD方法沉积的ZnO单晶薄膜的欧姆接触特性、光电特性进行了研究,并对比研究了射频溅射沉积SiO2抗反射膜对ZnO薄膜I-V、光电特性的影响.实验结果表明,非合金Al/ZnO金属体系与n型ZnO形成了良好的欧姆接触,溅射沉积SiO2在ZnO表面引入了载流子陷阱,影响I-V特性,延长了光响应下降时间.ZnO单晶薄膜光电导也具有时间退化现象.     

AlGaN/GaN HEMT二维静态模型与模拟

考虑AlGaN/GaN材料的自发、压电极化效应和量子效应,通过泊松方程、薛定谔方程和流体力学方程组的数值自洽求解方法,对AlGaN/GaN HEMT的二维静态模型与模拟问题进行了研究,得到了器件区域的导带图、二维电子气分布、电子温度特性、直流输出和转移特性,并对模拟结果进行了分析与讨论.