Effect of organic/inorganic coating on moisture diffusion in a chip-on-board package with globtop

The moisture diffusion in globtop material for a chip-on-board (COB) package coated with SiN_x and silicone, respectively, or coated with SiN_x plus silicone were measured by embedding a humidity sensor in the globtop and recording the capacitive change in three different temperature/humidity environments. The experimental results were simulated by Fick’s diffusion law with finite-element method modeling. The moisture diffusion coefficients and activation energies were calculated to quantitatively compare the moisture-resistance effects of different coatings. For example, at 85°C/85% RH, the moisture diffusion coefficients for the uncoated reference, SiN_x-coated, silicone-coated, and silicone/SiN_x double-layered coated samples are 1E-5, 0.8E-5, 0.7E-5, and 0.2E-5 mm²/s, respectively. The experimental and simulation results show that double-layered coating with silicone/SiN_x has excellent moisture-resistance properties because it not only smoothes the steps on a printed circuit board (PCB) but also keeps the good moisture resistance of the inorganic films.     

Bayesian bounds for matched-field parameter estimation

Matched-field methods concern estimation of source locations and/or ocean environmental parameters by exploiting full wave modeling of acoustic waveguide propagation. Because of the nonlinear parameter-dependence of the signal field, the estimate is subject to ambiguities and the sidelobe contribution often dominates the estimation error below a threshold signal-to-noise ratio (SNR). To study the matched-field performance, three Bayesian lower bounds on mean-square error are developed: the Bayesian Crame/spl acute/r-Rao bound (BCRB), the Weiss-Weinstein bound (WWB), and the Ziv-Zakai bound (ZZB). Particularly, for a multiple-frequency, multiple-snapshot random signal model, a closed-form minimum probability of error associated with the likelihood ratio test is derived, which facilitates error analysis in a wide scope of applications. Analysis and example simulations demonstrate that 1) unlike the local CRB, the BCRB is not achieved by the maximum likelihood estimate (MLE) even at high SNR if the local performance is not uniform across the prior parameter space; 2) the ZZB gives the closest MLE performance prediction at most SNR levels of practical interest; 3) the ZZB can also be used to determine the necessary number of independent snapshots achieving the asymptotic performance of the MLE at a given SNR; 4) incoherent frequency averaging, which is a popular multitone processing approach, reduces the peak sidelobe error but may not improve the overall performance due to the increased ambiguity baseline; and finally, 5) effects of adding additional parameters (e.g., environmental uncertainty) can be well predicted from the parameter coupling.     

On the Feasibility of Growing Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystals

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg_1/3‐Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d₃₃, in the range of 1800–2200 pC N^–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states.     

ZCZ‐CDMA and OFDMA using M‐QAM for broadband wireless communications

This paper considers direct‐sequence code‐division multiple‐access with zero‐correlation zone sequences (ZCZ‐CDMA) and orthogonal frequency‐division multiple‐access (OFDMA) schemes using M‐ary QAM signaling for broadband wireless communications. Their system structures, complexities and performances in both AWGN and multipath frequency‐selective fading channels are evaluated and compared. For ZCZ‐CDMA, joint suppression of the multipath fading interference and multiple‐access interference can be achieved with a reduced family‐size of the spreading sequences. For OFDMA, analytical and simulation results indicate that it has the same performance as ZCZ‐CDMA in fast time‐varying multipath fading channels. In time‐invariant or slowly time‐varying channels, where the channel information can be made available to transmitters, OFDMA outperforms ZCZ‐CDMA, offers a higher capacity and is more flexible for system reconfiguration with a comparable computational complexity. Copyright © 2004 John Wiley & Sons, Ltd.     

部分并行的蒙哥马利模乘法器实现研究

通讯技术的高速发展需要更高性能的密码处理设备.本文系统的研究了利用部分并行的脉动阵列结构实现模乘法器的问题,在分析了各类结构的性能结果的基础上,找到性能最高的和性能-代价比最高的结构配置.结果表明,如果以关键路径延迟×单元面积作为时间-面积代价指标,那么每个运算单元处理一位数据的设计,在0.18 μ m工艺和0.25 μ m工艺条件下,具有最高的运算性能,同时也是性价比最高的设计之一.     

一种小波系数模型在图像噪声参数估计中的应用

在小波图像处理中,通常利用HH子带来估计高斯白噪声方差,目前流行的估计方法是由Donoho和Johnstone提出的(简称DJ法),但是该方法给出的估计值通常都偏大。针对这一点,该文将他们的方法结合双随机小波系数模型,提出了一种新的、递归的方差估计方法。在已由Donoho的方法获得噪声方差估计的粗略估计的情况下,新方法利用统计学理论将HH子带中的信号滤除从而得到更接近于纯噪声的HH子带,然后利用这一新的HH子带来估计噪声的方差。结合EM参数估计方法,该方法还可以实现非高斯噪声参数的估计,实验表明新方法同Donoho法相比有很大的改善。     

自动交换光网络中恢复路径提供机制的研究

为了获得高效的网络生存性能,基于自动交换光网络(ASON)的框架,该文提出了一种新型的可恢复路径选择算法-联合可变权重可恢复路径(JVWR)选择算法,并进行了数值仿真分析,仿真结果表明,此恢复路径选择算法具有明显的业务量均衡能力,并降低了动态连接请求的阻塞概率,同时具有良好的带宽利用率和恢复资源共享效率。该文还对mesh网络业务路径和恢复路径的建立机制进行了讨论,在ASON功能框架之内,基于通用多协议标记交换提出了并行mesh共享恢复路径建立机制,从而较系统地对分布式恢复路径动态建立机制进行了研究。     

矩形波导填充带有空气柱介质不连续性的边界元法分析

应用边界元法分析了矩形波导中填充带有空气柱介质不连续性的散射特性，编制了一个通用的计算机程序，对几个算例进行了计算。数值结果表明了该方法的有效性。     

渐近波形估计技术在涂敷导体柱宽角度RCS快速计算中的应用

采用渐近波形估计技术 (AWE)和矩量法相结合的方法 ,计算了TM波入射下表面涂敷有耗介质的导体柱的宽角度单站RCS ,本方法首先采用矩量法求解由电磁场等效原理得到的介质层表面等效电磁流耦合方程 ,得到柱体在某一给定方向入射波照射下的电流和磁流密度 ,然后采用渐近波形估计技术将任意角度入射波照射下的电流和磁流密度在给定的角度附近按Taylor级数展开 ,通过Pad埁逼近将Ｔａｙｌｏｒ级数转化为有理函数 ,由此可以得到涂敷导体柱在任意角度TM波入射下的电流和磁流密度 ,进而可以得到柱体的宽角度RCS。此方法得到的结果与由MOM计算的结果完全吻合 ,而AWE的计算效率却提高了一个数量级。     

基于CORDIC的一种高速实时定点FFT的FPGA实现

本文论述了一种利用CORDIC算法在FPGA上实现高速实时定点FFF的设计方案。利用CORDIC算法来实现复数乘法，与使用乘法器相比降低了系统的资源占用率，提高了系统速度[1]。设计基于基4时序抽取FFT算法，采用双端口内置RAM和流水线串行工作方式。本设计针对256点、24位长数据进行运算，在XilnxSpartan2E系列的xc2s300e器件下载验证通过，完成一次运算约为12μs，可运用于高速DSP、数字签名算法等对速度要求高的领域。