Raychem快速动作表面贴装保险丝

泰科电子Raychem电路保护部日前推出面向笔记本电脑、多媒体设备、移动电话和其它便携式电子设备的电子片式保险丝全新系列产品。这款快速动作型保险丝能够为采用高达125伏交流电的直流电源系统提供过流保护。     

HVArc Guard MLCC：表面贴装多层陶瓷电容器

随着Vishay在高压多层陶瓷电容器（MLCC）技术上的一系列突破,Vishsy制造出了一种新的表面贴装MLCC,比以往任何类型的电容器都更适合镇流器应用。这些新的HVArc Guard电容器采用NP0和X7R电介质,电压等级从直流250V到直流1000V。     

表面贴装元器件的热设计

对于电子产品的设计来说,尺寸越小越好。从最新的移动电话到个人数字助理(PDA),消费类电子产品市场关注于在愈来愈小的空间内塞入更加强大的功能。在推动外形尺寸小形化的同时,人们要求产品具有更强的功能和更好的质量。 但是组装密度的不断提高,形成了局部的高热密度。由于高温会对电子元器件的性能产生非常有害的影响,例如高温会危及到半导体的结点、损伤电路的连接界面,增加导体的阻值和形成机械应力的损伤,因此确保发热电子元器件所产生的热量能够及时排出,是系统组装设计的一个重要方面。电子设备的可靠性及其性能,在很大程度上取决于设备是否具有良好的热设计考虑,以及所采取的散热措施是否有效。     

高压表面贴装MLCC的新进展

高压表面贴装MLCC（多层陶瓷电容器）的额定值通常设定在500VDC或更高。这些MLCC广泛应用在电源当中,用来隔离和滤波DC和AC电压。它们在减少纹波噪声和消除开关稳压器所引起的潜在的不安全瞬变方面作用尤为重要。其他值得注意的应用是在灯镇流器中作为缓冲电容器;最近MLCC也已经集成在可植入医疗器械当中,以保护低电压电路免受外部去心脏纤颤引起的瞬变的影响。不过,当电压升高至750VDC以上时,在接线端之间以及安装在电路板上的其他器件之间就会出现比较严重的表面弧问题。     

基于表面贴装工艺技术的印制板焊盘设计

伴随表面贴装技术的广泛运用,印刷电路板设计工艺变得越来越重要,焊盘设计要求也变得越来越高。本文针对焊盘设计存在的缺陷加以归纳并给出了较详细的改进措施。     

表面贴装PCB的可制造性设计

可制造性设计是一种新颖的设计方法,它是生产工艺质量的保证,并有助于提高生产效率。就表面贴装PCB设计时需考虑的一些制造工艺性问题进行阐述,给设计人员提供一个参考。     

多层陶瓷外壳设计与使用中的几个问题

本文叙述了多层陶瓷外壳的基本工艺和设计,主要原材料的选用以及在科研和生产过程中的一些问题。     

新0．5W表面贴装LED产品

ASMT-QxBB高亮度大功率LED产品在设计上可以更有效散热,新推出的0．5W输出ASMT-QWBB冷白光和ASMT—QYBB暖白光系列表面贴装LED可以应用在仪表板背光、车室灯以及地图灯、脚踏板灯、倒车指示灯以及牌照灯等汽车照明应用。ASMT—QxBB系列还可以作为装饰照明、电子标志和信号灯应用中的通道标示,以及工业设备、办公室自动化和家用电器应用的操作面板和显示背光,另外,Avago0．5W大功率LED系列所具备的单颗LED高亮度输出,以及仅3．2mm长x2．8mm宽×1．9mm高的小型化封装尺寸,更可以为照明设计工程师带来照明设备尺寸、外型和外观设计上的更高灵活度。     

基于金属陶瓷贴片封装的数控衰减器设计

衰减器作为幅度调制器件被广泛用于电子战、雷达、测试设备、通信等各种微波领域。随着信息革命的深入发展,通信、雷达、测试设备等各种微波领域的电子设备趋向于小型化、低成本,对元器件的体积、功耗、可靠性、使用方便性的要求越来越高。文章介绍了一款采用GaAsPHEMT工艺和金属陶瓷贴片封装制作的L波段高精度单片六位数控衰减器的设计方法和研制结果。测试结果表明在频率为DC～2GHz内,衰减步进0.5dB,衰减范围0～31.5dB,插入损耗IL<2.5dB,输入输出驻波比VSWR<1.4,衰减精度|△A_i|<(0.2+3%A_i)dB。附加相移|△φ|<3°,控制方式为TTL电平。     

Surface-mount dual-loop antenna for 2.4/5 GHz WLAN operation

A surface-mount dual-loop antenna suitable for dual-frequency WLAN operation is presented. For achieving dual-frequency operation with a compact size, the antenna comprises two loop strips of different sizes printed on a flexible printed circuit board, which is then bent and attached onto a foam base of compact size. The antenna shows an attractive feature of high antenna gain, about 4 and 5 dBi for frequencies across the 2.4 and 5 GHz WLAN bands, respectively.     

All-Digital PLL With Ultra Fast Settling

A fully digital frequency synthesizer for RF wireless applications has recently been proposed. At its foundation lies a digitally controlled oscillator with sufficiently fine frequency resolution to avoid analog tuning. The conventional phase/frequency detector, charge pump and RC loop filter are replaced by a time-to-digital converter and a simple digital loop filter. When implemented in highly scaled digital CMOS processes, the proposed architecture is more advantageous over conventional charge-pump-based phase-locked loops (PLLs) since it exploits signal processing capabilities of digital circuits and avoids relying on the fine voltage resolution of analog circuits. In this brief, we present novel techniques used in the all-digital PLL to achieve an ultra-fast frequency acquisition of <50 mus while maintaining excellent phase noise and spurious performance during transmission and reception. This approach has been validated and incorporated in commercial single-chip Bluetooth and Global System for Mobile Communications radios realized in deep-submicrometer CMOS     

Fast Configurable-Cache Tuning With a Unified Second-Level Cache

Tuning a configurable cache subsystem to an application can greatly reduce memory hierarchy energy consumption. Previous tuning methods use a level one configurable cache only, or a second level with separate instruction and data configurable caches. We instead use a commercially-common unified second level cache, a seemingly minor difference that actually expands the configuration space from 500 to about 20$thinspace$000. We develop additive way tuning for tuning a cache subsystem with this large space, yielding 61% energy savings and 9% performance improvements over a nonconfigurable cache, greatly outperforming an extension of a previous method.      

SAR Image Regularization With Fast Approximate Discrete Minimization

Synthetic aperture radar (SAR) images, like other coherent imaging modalities, suffer from speckle noise. The presence of this noise makes the automatic interpretation of images a challenging task and noise reduction is often a prerequisite for successful use of classical image processing algorithms. Numerous approaches have been proposed to filter speckle noise. Markov random field (MRF) modelization provides a convenient way to express both data fidelity constraints and desirable properties of the filtered image. In this context, total variation minimization has been extensively used to constrain the oscillations in the regularized image while preserving its edges. Speckle noise follows heavy-tailed distributions, and the MRF formulation leads to a minimization problem involving nonconvex log-likelihood terms. Such a minimization can be performed efficiently by computing minimum cuts on weighted graphs. Due to memory constraints, exact minimization, although theoretically possible, is not achievable on large images required by remote sensing applications. The computational burden of the state-of-the-art algorithm for approximate minimization (namely the alpha -expansion) is too heavy specially when considering joint regularization of several images. We show that a satisfying solution can be reached, in few iterations, by performing a graph-cut-based combinatorial exploration of large trial moves. This algorithm is applied to joint regularization of the amplitude and interferometric phase in urban area SAR images.     

金属陶瓷贴片封装的S波段六位数控移相器

介绍了一款自主设计采用0.25μm GaAs PHMET开关工艺制作的的S波段六位数控移相器芯片和金属陶瓷表贴管壳内的设计方法和研制结果.该移相器在工作频带2.8～3.6 GHz内64个移相态的移相精度RMS＜1.0°、插入损耗IL＜5 dB、输入输出驻波比VSWR＜1.5、幅度均衡△IL＜0.3 dB、1分贝压缩输入...     

多层网络中的生存性

未来传输网络中,不同的网络技术(如IP、SDH和WDM技术)的融合需要不同网络层次之间进行有效地配合,特别是网络生存性领域更是如此。首先对多层网络生存性机制的框架以及在多层网络环境下实现网络生存性的技术进行了概述,同时以IP over WDM为例,说明了这些方法的应用方式。     

LTCC带通滤波器的实现

为解决移动通信中滤波器小型化问题,提出了一种基于LTCC(Lowtemperatureco-firedceramic)技术的带通滤波器实现的有效方法。在设计中应用宽边耦合加长电长度,以不足λ/8的微带线达到所需的滤波特性。根据理论计算的结果,在Ansoft-HFSS中建立模型进行仿真,最终加工生产了适用于蓝牙频段的样品,并与仿真性能进行了比较,取得了很好的一致性。     

Fast Analysis of Photonic Crystal Structures With Mixed-Order Prism Macroelements

In this paper, a new concept of a mixed-order prism macroelement is introduced for the analysis of photonic crystal slabs and waveguiding structures. The mixed-order concept used here implies arbitrary orders of variation towards different directions and it differs essentially from the well-known mixed-order approximation that is an integral part of every Whitney element. The reduction of degrees of freedom, achieved by the employment of such elements, facilitates the solution of the resulting eigenvalue equation. Thus, an efficient 3-D finite-element analysis tool is developed to calculate the band structure of both symmetric and asymmetric photonic crystal slabs. Dispersion relation results for two different types of photonic crystal waveguides are also presented, to further verify the method.      

Negative Index Materials With Gain Media for Fast Optical Modulation

We discuss the origin of negative index behavior that is observed in certain artificial structures known as metamaterials that are periodic structures supporting backward optical waves with generally antiparallel phase and group velocities. Slab-like metamaterials, metal-dielectric, and purely dielectric ones support surface-plasmon polaritons that may be coupled into by an incident field. When this is the case, these surface waves can be pumped by the source, lead to pumping of the evanescent waves, and, as a result, enable subwavelength resolution. The main limiting factors for subwavelength resolution are losses and surface imperfections. Metal-dielectric metamaterials and systems are of special interest to nanophotonics, the focus of this paper, since they obviously provide high dielectric contrast, much larger than all-dielectric/semiconductor systems. This makes them promising for applications in dense integrated optical systems, since the mode volume is small. We consider various ways of combining metallic materials for negative dielectric constant and a gain medium to compensate for optical losses. Ultimately, one would like to make Si-compatible subwavelength optical components using metamaterials.