三芯片集成高显色指数白光LED的研究

运用基于蒙特卡罗的光线追迹方法,对采用"光转换"兼"多色混合"技术的白光LED的显色指数、相关色温、光通量、光辐射功率、荧光粉颗粒密度和色坐标进行了仿真计算和优化选择。通过改变红、绿、蓝三种LED芯片的组合方式和红、绿、黄三种荧光粉的混合方式及各色荧光粉的密度,在保证有合理的光通量输出的条件下,得到了不同色温区的高显色指数白光LED。从显色指数角度看,冷白、正白和暖白光应分别选择BBB芯片+绿、红色荧光粉、BBB芯片+黄、红色荧光粉和RBB芯片+黄色荧光粉组合。实验上测试了采用这几种组合方式的白光LED光谱、显色指数、色温、光通量和色坐标,实验数据与仿真结果基本吻合。     

可调色温的高显色指数LED白光光源的实验研究

采用暖白、绿、蓝LED混光和PWM调光技术,研究了光源的光谱、色温可调和显色指数特性。实验通过控制驱动电流的占空比,调节暖白、绿、蓝LED之间的光通量配比,实现了在3 000~6 500K范围内色温可调、Ra为85~95的高显色指数LED白光。混合光源的实验参数与理论计算值相一致。     

双通道PWM的冷暖白光LED混色模型研究

LED光色度的动态调节是实现智能照明的基础, 采用冷暖白光LED和双通道脉冲宽度调制(PWM)法,基于1931CIE标准建立混合光源模型,推导出混合光源色坐标、相关色温 、最大亮度、显色指数与双通道调制脉冲 占空比比值的关系式。采用暖白光(色温3282 K)和冷白光(色温12930K)两种白光LED进行 混色实验, 通过微控制器输出PWM信号控制LED驱动电源,改变冷色光和暖色光的比重,得到的混合 光源色坐 标、最大亮度、相关色温及显色指数值与理论计算值吻合很好,证明了理论模型的正确性。 理论和实验结 果还表明,混合光源在双通道调制脉冲占空比比值为1的附近可得到低色温、高显色性和大 光通量的混合白光。     

两基色白光LED的配色研究

从色度学原理出发,简述了两基色白光LED的配色原理,确定了可合成白光的两基色的选取范围和两基色的配比范围,计算分析了两基色白光LED的光视效能和一般显色指数。两基色白光LED具有较高的光视效能,但其显色性却较差,主波长为450 nm左右的蓝光LED与主波长572 nm左右的黄绿光混合得到的白光的光视效能值最大,约为400 lm/w,已接近等能纯白点的理论极值,但一般显色指数只有—0.5。主波长为480 nm左右的LED与主波长为580 nm左右的LED混合得到的白光的一般显色指数值最大,仅为16.2。     

四芯片色温可调白光LED的研究

为了实现高光效、高显色性且色温可调的白光LED,对四种单基色蓝、绿、黄、红光LED的混光进行了研究.基于Yoshi-单色光模型和光的叠加原理,通过改变四种LED芯片的组合方式(峰值波长、相对光功率配比),对不同色温区的混合白光的显色指数(Ra)、色品质数(Qa)和光视效能(K)进行了仿真计算和光谱优化选择.结果表明:在2 700～6 500 K色温范围内,峰值波长为445 nm,500 nm,560 nm,620 nm的组合可以得到高Ra值和高Qa值;峰值波长为445 nm,535nm,590 nm,615 nm的组合可以得到较高K值.此外还分析了组合白光LED光谱参数对Ra、Qa、K及相关色温的影响.     

有机材料MEH-PPV对白光LED光谱特性的影响

分别将质量分数为5、10、15和20%的有机材料MEH-PPV混合加入YAG荧光粉中,观察发光二极管(LED)显色指数的变化。实验结果表明,MEH-PPV在450～550nm区域吸光度逐渐增强,可吸收黄绿光,在615nm附近辐射出较强红光,补充了传统蓝光LED芯片激发YAG荧光粉中缺失的红光成分,使发射带延伸至700nm;当MEH-PPV混合质量分数为15%时,制备的白光LED的显色指数最高,可达到92。随着质量分数从15%持续增加到20%,器件的显色指数开始降低,这是因为LED芯片发出的能量能够激发有机材料MEH-PPV的同时,使MEH-PPV对荧光粉发出的绿光区域有较强吸收,因此存在一个最佳色比使器件的性能达到最佳。     

基于红白蓝模式色温可调的LED照明系统

根据混色原理,证明了利用红光、正白光和蓝光三种颜色的LED混合实现色温调节的可行性。把色温可调白光LED照明系统分为五个模块,对五个模块进行设计和优化,实现了显色指数高、色温动态可调、光谱覆盖范围广、能适应不同时间、场所对色温可变要求的LED照明系统。     

近紫外芯片激发三基色荧光粉制作的白光LED

使用发射波长为395～400 nm的近紫外LED芯片来激发发射峰值波长分别在615,505和445 nm的红绿蓝三基色荧光粉,建立三基色荧光粉混光理论模型,制作不同色温下高显色指数白光发光二极管,研究其光电特性。实验结果表明,采用近紫外激发的三基色白光器件色温为3 000～9 000 K范围内,其显色指数均能保持在80～90之间;当色温大于5 000 K时,显色指数可以达到85;测试结果与理论计算吻合良好。最后,实验证明加入TiO2粉末可消除白光LED中残余近紫外线,三基色荧光粉白光LED色度参数受工作电流变化的影响较小。     

Bookham公司为LED投影系统推出复用模块

Bookham公司宣布推出ZoroLight LED多路复用模块。该模块为LED多工技术解决方案产品，支持下一代使用LED照明取代传统UHP（Ultra High Performance）灯泡的背投电视和袖珍投影仪。模块中光学薄膜滤波技术的使用使其结构更加紧凑并更高效。ZoroLight具备红、蓝、绿三色LED信号，支持数字光处理器（DLP）投影设备，并且在光机装配中仅需最基础的对准。     

一种基于混合量子点的橙光量子点LED制备

为研究混合量子点(QD)发光二极管(QLED)的性能, 利用红、绿量子点混合作为发光层,制备了结构为 ITO/PEDOT:PSS/poly-TPD/QDs(红、绿1∶1混合)/ZnO/Al的橙光QLED,并与 结构为 ITO/PEDOT:PSS/poly-TPD/QDs(红光)/ZnO/Al的红光QLED进行了对比。实验结果表明, 基于红、绿QD混合的橙光QLED的制备方法是有效的,制备的橙光QLED 电流密度和亮度均小 于红光QLED, 但电流效率远大于红光QLED。研究发现,器件性能与各功能层能级以及厚度密切相关,应通 过选取适当能 级的发光层材料,将注入的空穴以及电子同时限制在发光层内从而提高器件的电流效率,并 调节各功能层 厚度使得载流子注入平衡从而提高器件性能。     

聚对苯撑苯并双(口恶)唑发光及其器件制备

采用光谱技术,研究了聚对苯撑苯并双(口恶)唑(PBO)溶液的光敏发光特性,并用相对法估算出溶液发光效率在50%范围.结合光谱技术、半导体电学和电化学等研究手段,具体研究了以PBO为发光层的单层电致发光器件,研究结果显示,电致发光与薄膜的光致发光有具有相同的发光中心,峰值位于510 nm左右.同时发现,由于存制备过程中不同处理条件使得不同厚度薄膜残留的掺杂物质浓度不同,从而引起薄膜的导电性的不同.使得器件的阈值场强随PBO厚度的减小而逐渐增加.     

系统级封装新型埋入式电源滤波结构的研究

在高密度小尺寸的系统级封装(SiP)中,对供电系统的完整性要求越来越高,多芯片共用一个电源网路所产生的电压抖动除了会影响到芯片的正常工作,还会通过供电网路干扰到临近电路和其他敏感电路,导致芯片误动作,以及信号完整性和其他电磁干扰问题.这种电压抖动所占频带相当宽,几百MHz到几个GHz的中频电源噪声普通方法很难去除.结合埋入式电容和电源分割方法的特点,提出一种新型高性能埋入式电源低通滤波结构直接替代电源/地平面.研究表明,在0.65～4GHz的频带内隔离深度可达-40～75 dB,电源阻抗均在0.25ohm以下,实现了宽频高隔离度的高性能滤波作用.分别用电磁场和广义传输线两种仿真器模拟,高频等效电路模型分析这种低通滤波器的工作原理以及结构对隔离性能的影响,并进行了实验验证.     

Emerging interconnects: a state-of-the-art review and emerging solutions

Aluminium was a primary material for interconnection in integrated circuits (ICs) since their inception. Later, copper was introduced as interconnect material which has better metallic conductivity and resistance to electromigration. As the aggressive technology scaling continues, the copper resistivity increased because of size effects, which causes increase in delay, power dissipation and electromigration. The need to reduce the resistor-capacitor??????? delay, dynamic power utilisation and the crosstalk commotion is as of now the fundamental main impetus behind the presentation of new materials. The purpose of this paper is to do a survey of interconnect material used in IC from introduction of ICs to till date. This paper studies and reviews new materials available for interconnect application which are optical interconnects, carbon nanotube (CNT), graphene nanoribbons (GNRs) and silicon nanowires which are alternatives to copper. While doing a survey of interconnect material, it is found that multiwalled CNTs, multilayer GNR and mixed CNT bundles are promising candidates and are ultimate choice that can strongly address the problems faced by copper but on integration basis copper would last for coming years.     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.     

光子晶体微腔发光二极管

光子晶体微腔因其具有增强自发辐射、定向输出和单模工作的能力而受到广泛关注。介绍了光子晶体微腔发光二极管的基本原理、设计、特性、制作及其典型器件。     

Comparative study of maximum power point tracking techniques for hybrid renewable energy system

The power generation demand is increasing day-by-day throughout the world, therefore, the use of hybrid systems becomes a significant solution. The hybrid renewable energy system (HRES) is used for delivering power in various regions in order to overcome intermittence of wind and solar resources. Because of increasing environmental problems, for example, greenhouse gas emission and energy cost have interested novel research into substitute methods in favour of electrical power generation. Maximum Power Point Tracking (MPPT) control method is a vast deal of novel research used for enhancing the efficiency of HRES. The authors have revealed that the hybrid techniques i.e. Global MPPT, fuzzy-neuro systems, Adaptive Neuro-Fuzzy Inference System (ANFIS), Perturbed and Observe (P&O) + Adaptive Neural Network (ANN) etc. can provide best results as compared to other MPPT control methods. This paper offering a state of art review of MPPT control techniques for HRES.     

用于单光子TOF测量的时间-幅度变换器

基于新型共源共栅电流源的积分方法,设计了一种用于单光子飞行时间(TOF)测量的时间-幅度变换器(TAC)。该方法有效简化了TAC电路结构,减小了TAC占用面积,显著提高了TOF的满量程范围(FSR)。采用0.18 μm标准CMOS工艺设计。集成TAC的单光子探测器像素单元的填充因子可达到26.8%。后仿真结果表明,该TAC在120 ns的FSR内具有230 ps的定时分辨率,微分非线性(DNL)低于0.05 LSB,积分非线性(INL)低于1.1 LSB。蒙特卡洛仿真表明,512个TAC像素间的不均匀性低于0.5 %。该TAC非常适用于高密度时间相关的单光子计数(TCSPC)探测器阵列。     

Joint estimation of TOA and DOA in IR-UWB system using a successive propagator method

Impulse radio ultra-wideband (IR-UWB) ranging and positioning require accurate estimation of time-of-arrival (TOA) and direction-of-arrival (DOA). With receiver of two antennas, both of the TOA and DOA parameters can be estimated via two-dimensional (2D) propagator method (PM), in which the 2D spectral peak searching, however, renders much higher computational complexity. This paper proposes a successive PM algorithm for joint TOA and DOA estimation in IR-UWB system to avoid 2D spectral peak searching. The proposed algorithm firstly gets the initial TOA estimates in the two antennas from the propagation matrix, then utilises successively one-dimensional (1D) local searches to achieve the estimation of TOAs in the two antennas, and finally obtains the DOA estimates via the difference in the TOAs between the two antennas. The proposed algorithm, which only requires 1D local searches, can avoid the high computational cost in 2D-PM algorithm. Furthermore, the proposed algorithm can obtain automatically paired parameters and has better joint TOA and DOA estimation performance than conventional PM algorithm, estimation of signal parameters via rotational invariance techniques algorithm and matrix pencil algorithm. Meanwhile, it has very close parameter estimation to that of 2D-PM algorithm. We have also derived the mean square error of TOA and DOA estimation of the proposed algorithm and the Cramer-Rao bound of TOA and DOA estimation in this paper. The simulation results verify the usefulness of the proposed algorithm.     

多孔硅发光机制的分析

从量子力学的基本理论出发讨论了量子限制效应，推导出多孔硅有效禁带宽度增量并用量子限制效应和表面态及其物质在发光中作用的理论解释了ＰＳ光致发光的实验现象。     

一种基于分段CRC的LDPC译码的改进算法

级联多个循环冗余校验(CRC)的LDPC译码算法有效地改善了译码的收敛特性。然而在其译码算法中,当CRC检测的整体漏检概率不够低时,出现误码平台。因此,该文提出了改进算法,通过减少在译码算法中CRC检测的次数,降低整体漏检概率,提高了误码性能。仿真表明改进的算法提高了误码性能,译码复杂度也增加不大。