电路系统中的噪声问题研究

本文从电原理图设计和PCB板设计两方面阐述了电磁兼容的重要性,并对电路系统中的噪声问题进行了深入的研究和分析,给出了相应的解决措施,为电子应用工程师在实际工作中处理噪声问题提供了很好的参考。     

改进的图像重建迭代算法

针对不完全数据图像重建问题,该文从积分方程角度提出一种改进的图像重建迭代算法(Im-proved Iterative Reprojection Reconstruction,IIRR),并证明其在范数下收敛。该算法的图像重建收敛速度和重建图像误差依赖于引入的参数因子、已知的投影数据与图像的先验信息。重建图像可以表示为由已知投影数据所构成图像的级数形式。数值模拟结果表明,IIRR算法在不完全数据的情况下具有较好的图像重建能力。     

双能谱CT的迭代重建模型及重建方法

双能谱CT能够重建被测物体的等效原子序数和电子密度或是基材料的密度图像.与传统的单能谱CT相比,有更好的物质区分能力,有着广泛的应用前景.但是双能谱CT重建问题的非线性性给重建带来了困难.针对该问题,本文提出一种适于双能谱CT的Newton型迭代重建方法.该方法首先将双能谱CT对应的非线性问题线性化得到一个线性方程组,然后利用SART方法对该线性方程组进行求解,最后利用求得的方程组的解对图像进行更新.该方法的主要优点是其灵活性.它能够适用于常用的各种扫描模式,对于几何一致和不一致投影均有效.同时容易将该方法推广到多能谱CT和慢电压切换的CT系统.数值实验表明,该方法能够正确重建出基材料的密度图像.另外该方法能有效去除重建图像中的硬化伪影.     

Iterative Phase Noise Suppression for Full-Duplex Communication Systems

Oscillator phase noise is one of the bottlenecks that limits the self-interference(SI) cancellation capability of full-duplex systems. In this paper,we propose a method for the suppression of common phase error(CPE) and intercarrier interference(ICI)induced by the phase noise in full-duplex orthogonal frequency division multiplexing(OFDM) systems.First, we regard the effect of CPE as a portion of the SI channel and perform estimation, reconstruction and elimination in the time domain. Then, the ...     

A Statistical Analysis of Pupil Noise

The random fluctuations of human pupillary area provide an interesting example of a stochastic process in a biological system. Statistical theory and system analysis have guided the authors in performing experiments which reveal important properties involved in the random process.     

Noise Modeling in Lateral Nonuniform MOSFET

In this paper, we present an analytical noise modeling methodology for lateral nonuniform MOSFET. We demonstrate that the noise properties of lateral nonuniform MOSFETs are considerably different from the prediction obtained with the conventional Klaassen-Prins (KP)-based methods which, at low gate voltages, depending on the doping profile can overestimate the thermal noise by 2-3 orders of magnitude. We show that the presence of lateral nonuniformity makes the vector impedance field (the quantity responsible for noise propagation) position and bias dependent. This insight clearly explains the observed discrepancy and shows that the bias dependence of the important noise parameters cannot be predicted by conventional KP-based methods.     

电子电路中谐波噪声的抑制措施

为了揭示谐波噪声的根源,对传输信号的谐波电流进行比较实验。采用两种主要方法消灭谐波噪声:(1)被动降噪法,即采用旁路、屏蔽、接地、无源或有源滤波方法来限制谐波噪声;(2)主动降噪法,即设计乘法器方式整流电路来改善电子产品开关电源的电压与电流的相位,完成两者同相,减少电源中谐波含量。实践中,使用这些措施去抑制电子产品的谐波噪声,都达到了事半功倍的效果。     

Statistical Based Impulsive Noise Removal in Digital Radiography

A new filter to restore radiographic images corrupted by impulsive noise is proposed. It is based on a switching scheme where all the pulses are first detected and then corrected through a median filter. The pulse detector is based on the hypothesis that the major contribution to image noise is given by the photon counting process, with some pixels corrupted by impulsive noise. Such statistics is described by an adequate mixture model. The filter is also able to reliably estimate the sensor gain. Its operation has been verified on both synthetic and real images; the experimental results demonstrate the superiority of the proposed approach in comparison with more traditional methods.      

最大熵重建的迭代凸I投影算法

本文探讨了用迭代凸Ｉ投影（ＩｔｅｒａｔｉｖｅＣｏｎｖｅｘＩ－Ｐｒｏｊｅｃｔｉｏｎ，ＩＣＩＰ）算法求解最大熵Ｘ－ＣＴ重建问题．其思路是将这个复杂问题转化为多个简单子问题，然后迭代地求解这种单约束子问题．理论证明，这种算法收敛并能收敛到问题的最大熵解．这种算法形式优美，仿真结果表明算法同时也是有效的．     

Model-Based Iterative Reconstruction for Radial Fast Spin-Echo MRI

In radial fast spin-echo magnetic resonance imaging (MRI), a set of overlapping spokes with an inconsistent T2 weighting is acquired, which results in an averaged image contrast when employing conventional image reconstruction techniques. This work demonstrates that the problem may be overcome with the use of a dedicated reconstruction method that further allows for T2 quantification by extracting the embedded relaxation information. Thus, the proposed reconstruction method directly yields a spin-density and relaxivity map from only a single radial data set. The method is based on an inverse formulation of the problem and involves a modeling of the received MRI signal. Because the solution is found by numerical optimization, the approach exploits all data acquired. Further, it handles multicoil data and optionally allows for the incorporation of additional prior knowledge. Simulations and experimental results for a phantom and human brain in vivo demonstrate that the method yields spin-density and relaxivity maps that are neither affected by the typical artifacts from TE mixing, nor by streaking artifacts from the incomplete k-space coverage at individual echo times.      

射频MOSFET噪声模型研究

对0.13μm MOSFET噪声建模和参数提取技术进行了研究,在精确地提取了小信号模型参数之后,利用噪声相关矩阵技术从测量的散射参数和射频噪声参数直接提取了栅极感应噪声电流■、沟道噪声电流■和它们的相关系数,并用PRC模型中的参数来表示。将参数提取结果带入ADS中进行仿真,在2～8GHz频段上仿真结果与测量数据吻合良好。     

低噪声UHF电子调谐器

本文叙述采用双栅砷化镓场效应晶体管和高优值硅外延变容二极管实现UHF电子调谐器低噪声化的有关设计和实验结果.制作的UHF电子调谐器噪声系数为5.3分贝,自动增益控制能力达50分贝以上.     

1/f噪声的统计动力学分析

从理论分析的角度,得出结论:1/f噪声拥有一定的能谱.得到了一个普适的公式,扩展了1/f噪声理论的应用范围.     

一种深亚微米MOSFET高频噪声模型

基于深亚微米MOSFET的短沟道效应(迁移率退化、热载流子效应、体电荷效应、沟道长度调制效应等),提出了一种高频沟道噪声分析模型.该分析模型不仅具有较高的精确性,而且只包括MOSFET的工艺参数和电学参数,不含有微积分和拟合参数,较大地提高了MOSFET高频噪声模型的易用性.根据MOSFET的高频等效电路,得出了MOSFET的噪声系数模型.实验结果证明,提出的深亚微米MOSFET高频噪声模型的仿真结果与测试结果的平均误差不到0.4 dB,并与其他高频沟道噪声分析模型进行了比较.     

电子对抗中噪声干扰效果评估

阐述了干扰效果评估的有关概念,分析了各种干扰效果评估准则的特点及使用,找出了特定电子干扰效果评估的最佳使用准则及方法,给出了用功率准则来评估噪声压制干扰效果的几种方法,提出了对电子对抗作战效能的评估由定性分析到定量分析转变的思想。     

电子线路的噪声抑制技术

由各种电子线路组成的智能仪表和自动化控制系统设备地实际应用中，会受到来自各种各样噪声源的干扰，致使仪表和设备（特别是数字仪表）不能正常运转，严重影响自动化控制系统精度和产品质量，本文结合生产工作实际，综合分析电子线路的种噪声干扰源，论述了抑制噪声干扰的各种措施，为设计制造仪器仪表、控制设备和电子线路安装调试者提供抑制噪声的参考方法，确保设备控制精度和产品质量。     

On the Iterative Image Space Reconstruction Algorthm for ECT

The ISRA of [1] is shown to be an iterative algorithm that aims to converge to the least-squares estimates of emission densities. Convergence is established in the case where a unique least-squares estimate exists that is, elementwise, strictly positive. It is pointed out that, in terms of asymptotic theory, the resulting estimators are inferior to the maximum likelihood estimators, for which the EM algorithm is a computational procedure. Potential difficulties with the behavior of the ISRA are illustrated using very simple examples.     

线性迭代子空间射影重建法

该文提出了一种基于子空间线性迭代的射影重建方法,该方法利用所有的图像序列构成的行向量生成的线性子空间之和与射影重建结构点构成的行向量生成的子空间是同一线性子空间及在该子空间中任何一个基底都可以作为射影重建的特性,线性迭代地求取射影重建及图像深度因子。模拟实验和真实实验表明,该射影重建方法具有鲁棒性好、收敛性好及重投影误差小等优点。     

基于迭代交替优化的图像盲超分辨率重建

基于深度卷积神经网络的图像超分辨率重建算法通常假设低分辨率图像的降质是固定且已知的,如双3次下采样等,因此难以处理降质(如模糊核及噪声水平)未知的图像。针对此问题,该文提出联合估计模糊核、噪声水平和高分辨率图像,设计了一种基于迭代交替优化的图像盲超分辨率重建网络。在所提网络中,图像重建器以估计的模糊核和噪声水平作为先验信息,由低分辨率图像重建出高分辨率图像;同时,综合低分辨率图像和估计的高分辨率图像,模糊核及噪声水平估计器分别实现模糊核和噪声水平的估计。进一步地,该文提出对模糊核/噪声水平估计器及图像重建器进行迭代交替的端对端优化,以提高它们的兼容性并使其相互促进。实验结果表明,与IKC, DASR, MANet, DAN等现有算法相比,提出方法在常用公开测试集(Set5, Set14, B100, Urban100)及真实场景图像上都取得了更优的性能,能够更好地对降质未知的图像进行重建;同时,提出方法在参数量或处理效率上也有一定的优势。     

Iterative Ray Tracing between Boreholes for Underground Image Reconstruction

A computerized method is described for calculating an image of the refractive index distribution in a plane bounded by two underground boreholes. The scanning geometry is assumed to be limited to probing from borehole to borehole, with rays at numerous depths and angles to effectively cover the cross section between holes. A geometrical optics model is assumed for the transmission data. We stress situations where significant bending of electromagnetic or seismic rays occurs. Image reconstruction involves an iterated sequence of numerical ray tracing and linear system inversion. A similar approach, discussed in the literature, sometimes fails to converge. We report here our refinements of this method, including use of a smoothness constraint.