全差分放大器(二)

5 应用电路 研究典型应用时,假设放大器的工作频率满足a(f)＞＞1,并且假设采用对称反馈,即β1=β2=Rg/Rg Rf. 5.1 输入电源端接 双端接通常用于高速系统,以降低输电线路反射并改进信号的完整性.双端接情况下,源端输出阻抗和终端端接与传输线阻抗匹配.源端输出阻抗值一般为50 Ω、75 Ω、100 Ω和600 Ω.采用差分输入源时,端接置于线路两端.采用单端输入源时,端接置于传输线和地之间.     

高速电路设计中信号完整性的反射分析

针对高速电路设计中信号完整性的问题,文中通过对高速电路中传输线等效电路的分析,从理论及计算角度给出了信号反射现象的形成原因。介绍了两类常用的抑制反射的端接方案, 阐述了6种阻抗端接匹配方法消除反射的原理。通过Cadence公司的SpecctraQuest仿真工具对点对点信号传输网络进行了反射仿真,给出了在不同阻抗匹配方式下的仿真测试结果。结果表明,适当的阻抗匹配方式可以改善信号传输的反射现象。     

VGA分配器中的阻抗匹配研究

通过对高速信号布线中经常出现的阻抗匹配问题的研究,结合一个VGA(视频图形阵列)分配器的设计实例,分析了阻抗匹配问题出现的原因和两种常用解决方案的端接方法,然后通过分析VGA分配器的电路特点,采用源端串联匹配的端接方式,利用传输阻抗计算软件SI6000计算传输线的特性阻抗,从而选择相应的阻值与其进行匹配,最后使用Hyperlynx仿真软件进行BOARDSIM仿真,仿真结果显示此种方案可以很好地改善视频信号传输过程中的阻抗匹配问题。     

长线传输的阻抗匹配设计

通过计算长线传输中的阻抗匹配和设计隔离电路,达到了减少高频信号反射,提升能源效益的目的.根据多种设计原则,提出了一种行之有效的匹配方法.采用该匹配方法可减小雷达信号的传输误差,并为测试系统技术在阻抗匹配研究中的应用,以及分析控制特征阻抗带来一定的参考价值.     

乘性噪声干扰下的通信信号偏差控制器设计与研究

乘性噪声干扰相对于加性噪声干扰具有更强的时变特性和抗滤波性,传统方法难以实现有效的滤波控制,乘性噪声在远程无线通信中会导致信道偏差,为解决这一问题提出了一种基于窄带阻抗匹配的乘性噪声干扰下的通信信号偏差控制方法,并进行控制器的硬件系统设计。设计了基于窄带阻抗匹配远程通信信号的乘性噪声干扰滤波算法,以此为基础进行通信信号偏差控制器系统硬件电路设计。在EPM7128AETI100上连入各芯片的读/写程序,得到3种通信信号偏差复位方式,采用MAX7000AE系列器件实现硬件接口设计,采用分段拟合的方式补偿非线性失真,实现乘性噪声干扰滤波器设计和信号偏差控制器设计。实验结果表明,采用该设计系统能有效滤除了通信信号中的乘性噪声污染,接收信号及其频谱的畸变得到有效补偿,改善了通信质量,提高了远程无线通信的稳定性和可靠性。     

高速数字PCB板设计中的信号完整性分析

当今飞速发展的电子设计领域,信号频率的不断提高,印制电路板变小,布线密度加大都使得信号完整性问题越来越成为一个值得关注的问题.尤其是串扰和反射,常造成数字电路的误动作,从信号完整性的定义出发,介绍了信号完整性的主要问题,提出了解决串扰和反射的方法,并在Altium Designer环境下对一种端接技术进行了验证,结果表明:合理的端接可以改善信号完整性中的反射现象.     

差分测量的重要性

许多实际应用都要求放大强噪声环境中的微弱信号。通常,信号传感器离放大器有一定的距离,所以经常引入大量的噪声和杂音。有效的信号恢复常常依赖于为具体的应用精心地选择最佳的放大器。有三种常见的应用系统类型:单端输入和单端输出(基于运算放大器)系统;差分输入和单端输出(     

传输线的反射干扰

在数字信号处理系统中,时钟信号和数字信号传输因传输始端和终端阻抗不匹配而引起反射干扰,使传输信号的波形出现上冲、下降和振荡。为了抑制这种因阻抗不匹配引起的反射,本文首先从产生这种反射的原因和造成的重大危害分析,提出了反射干扰这一亟待解决的问题;接着从传输线的阻抗特性以及阻抗匹配原理出发,提出了始端和终端阻抗匹配原则,最后给出了几种减小和抑制反射干扰的方法,实践证明使用阻抗匹配这一方法在减小反射干扰是十分有效的。     

差分测量的重要性

许多实际应用都要求放大强噪声环境中的徵弱信号。通常，信号传感器离放大器有一定的距离，所以经常引入大量的噪声和杂音。有效的信号恢复常常依赖于为具体的应用精心地选择最佳的放大器。有三种常见的应用系统类型：单端输入和单端输出(基于运算放大器)系统；差分输入和单端输出(基于仪表放大器)系统；以及差分输入和差分辅出(基于差分放大器)系统。有些设计工程师可能要使用单端输人、屏蔽电缆系统，类似图A所示。这里，首先在屏蔽电缆和公共端(或者“地”)之间施加输入信号，然后它通过电缆传送到运算放大器。像这样的单端系统很容易引…     

封装设计中传输线损耗的理论计算

针对高速信号设计中反射引起的信号完整性问题,推导了单一网络中散射参数关于阻抗分布的数学表达式,明确了传输结构中阻抗失配程度与分布长度对回波损耗的影响。基于该表达式,进一步阐述了时域、频域中反射计算的差异性。结合常见的频域现象和仿真预测,解释了回波损耗高频恶化、回波损耗不对称的原因,提出了适用于特定频率范围的反常规阻抗匹配设计思路,为初涉信号完整性设计领域的人员深入浅出地理解阻抗匹配提供了参考。     

A Method for Measuring the Characteristics of an EMI Suppression Ferrite Core

Almost all digital equipment has electromagnetic interference (EMI) suppression ferrite cores to encircle cables, such as mains and peripheral cables. However, their EMI suppression capability is hardly evaluated from the impedance characteristics provided by the manufacturers. Hence, this paper proposes to characterize the ferrite cores in terms of the insertion loss and the reflection coefficient. Theoretical and experimental investigations are carried out to develop a measurement jig for these parameters in the frequency range from 30 to 1000 MHz. It consists of a cylindrical metal rod placed above a metal ground plane, yielding a characteristic impedance of 270 Omega. In addition, a simple method is proposed for measuring the insertion loss and the reflection coefficient of a ferrite core under test. It is found that the proposed method can provide insertion loss data with an error of less than plusmn1.2 dB by using commercially available matching networks (baluns). The reflection coefficient of a ferrite core can be measured with an error less than plusmn1.0 dB. The matching characteristics of the adapters are critical factors that deteriorate measurement accuracy     

A Power Reflection Technique for Characterization of High Quality Varactor Diodes

High quality varactor diodes are currently characterized by either a "relative impedance" or a "transmission" technique. In view of the present limitations of these methods, a third method, a "reflection" technique, has been proposed. This method requires measuring the power reflected from a diode near its series resonant frequency. The diode is located as the termination of a low impedance coaxial line.The primary virtue of the power reflection technique is the possibility of accurate determination of the diode series resistance. Both the reflection method and the transmission method offer the advantage of microwave characterization near the diode series resonant frequency. The power reflection technique is presently limited to diodes that series resonante below 24 GHz. The accuracy of the technique is limited by possible impedance transformations due to the diode mount and diode package.     

反射面相控馈源阵的动态阻抗匹配

对于相控阵馈源,其前端低噪放的噪声系数直接影响系统整体性能,在技术途径上,减小系统前端噪声系数的关键之一就是改善阵元与有源前端的匹配,即阻抗匹配。对于单个天线,阻抗匹配就是使得天线的输入阻抗等于低噪放的最佳源阻抗。但是对于相控阵,阵列的动态阻抗依赖于波束形成系数并且随着波束指向的变化而变化,阻抗匹配是比较复杂的。针对反射面相控馈源阵系统,采用HFSS鄄MATLAB 联合仿真的方法,设计了馈源天线和低噪放,自动完成天线参数和低噪放最佳源阻抗的优化实现动态阻抗匹配和多波束平均最优阻抗匹配,最后系统仿真进行了验证。     

G.fast数字用户线路阻抗不匹配信道模型研究

基于数字信号传播理论中的反射原理,采用反射系数刻画线路阻抗不匹配程度,利用线路阻抗匹配时测量得到的信道数据（直接信道、远端串扰信道和近端串扰信道）,建立了一个G.fast数字用户线路阻抗不匹配时信道数学模型.当线路终端处于断开时,利用该模型生成的信道数据与实际测量的信道数据基本吻合,证明了该模型的正确性.由于采用反射系数刻画线路阻抗不匹配程度,该信道模型可仿真终端设备在不同阻抗值的情况下对通信系统信噪比的影响,从而提出线路终端设备阻抗最大允许的变化范围,为终端设备制造商在阻抗设计时提供一定的理论指导.     

声表面波器件输入及输出负载阻抗匹配研究

针对声表面波器件测量中网络分析仪的负载阻抗与射频传输线特性阻抗不匹配,导致传输线上反射波幅值较大的问题,提出一种减少传输线上反射波的负载阻抗匹配系统与方案。负载阻抗匹配方案针对声表面波器件测量中输入与输出端分别设计不同的无源负载阻抗匹配网络,使输入输出端同时达到匹配状态。负载阻抗匹配系统集成了未匹配通道与匹配通道,根据负载阻抗不同调整匹配参数。对一个中心频率为101.764MHz,带宽为30MHz的声表面波器件使用该匹配方案前后中心频率处的衰减进行测量对比,实验结果表明采用该匹配方案后在中心频率点处输入及输出反射损耗分别为-49.36dB和-38.13dB,比未采用匹配方案时分别减少了44.99dB和29.44dB。     

Improving the Accuracy and Reliability of Remote System-Calibration-Free Eye-Gaze Tracking

Remote eye-gaze tracking provides a means for nonintrusive tracking of the point-of-gaze (POG) of a user. For application as a user interface for the disabled, a remote system that is noncontact, reliable, and permits head motion is very desirable. The system-calibration-free pupil-corneal reflection (P-CR) vector technique for POG estimation is a popular method due to its simplicity, however, accuracy has been shown to be degraded with head displacement. Model-based POG-estimation methods were developed, which improve system accuracy during head displacement, however, these methods require complex system calibration in addition to user calibration. In this paper, the use of multiple corneal reflections and point-pattern matching allows for a scaling correction of the P-CR vector for head displacements as well as an improvement in system robustness to corneal reflection distortion, leading to improved POG-estimation accuracy. To demonstrate the improvement in performance, the enhanced multiple corneal reflection P-CR method is compared to the monocular and binocular accuracy of the traditional single corneal reflection P-CR method, and a model-based method of POG estimation for various head displacements.     

Exponentially tapered transmission line model of the arterialsystem

The arterial systemic tree is intricate and complex due to its numerous branches, nonuniform cross section and elasticity, and the rich harmonic composition of its pressure- and flow-pulses. To deal with this complexity, the modeling of the arterial system based on the technique of nonuniform transmission lines was undertaken. The main advantages of the technique are that it maintains a satisfactory response over a wide range of frequencies and that it analyzes the impedance and local reflection factor of various segments. The model, which utilizes far fewer parameters than previous models, supplies important information about reflections at bifurcations and impedance matching at the termination line     

T／R组件中滤波低噪声放大器一体化设计

常规低噪声放大器的设计中,输入输出匹配网络一般不考虑带外抑制的要求,主要考虑的是实现最佳噪声和输出功率匹配,因而带外抑制性能较差。本文研制了一种相控阵雷达T/R组件用滤波低噪声放大器,该放大器通过改进输入输出匹配电路的设计,实现了滤波器和低噪声放大器的一体化,在低噪声放大的同时具有较好的带外抑制作用。采用这种设计将会多个方面改善T/R组件的性能。