基于幅-频曲线的系统时域响应特性评价方法

在电磁兼容测量中,通常采用频率响应来描述一个系统的特性。而系统的频响特性一般仅提供了响应幅度的频域分布,很少给出相位信息。在连续波测量时这种幅－频信息是足够的,但在利用频域测量结果评价一个系统的脉冲响应特性时,还必须知道系统的相位信息。本文假设系统为最小相位系统,采用Ｈｉｌｂｅｒｔ变换根据系统响应的频谱幅度估计相位信息,进而将系统的频域信息转换到时域,用于评价系统的时域响应特性。根据一组磁场探头的     

具有任意频响的二维FIR数字滤波器设计的闭式最小二乘解

本文研究具有任意频响特性的二维ＦＩＲ数字滤波器的最小二乘设计问题。     

高速倾斜镜建模与传递函数辨识

为了在光束稳定控制系统中更好地对高速倾斜镜（FSM）实现稳定、精确地控制,对于由超磁致伸缩材料（GMM）作为位移产生元件的高速倾斜镜,根据GMM 材料的特性和倾斜镜的运动机理,经推导建立了倾斜镜的传递函数模型,并结合实测的倾斜镜幅频和相频响应特性,在Matlab 软件中利用Levy 法对倾斜镜的传递函数进行了辨识,得到了精确的倾斜镜传递函数。与实测结果相比,在中低频段,幅度辨识误差在0.3 dB 以内,相位辨识误差在5以内,结果表明:通过理论推导建立的倾斜镜模型是合理有效的,对于改善该倾斜镜在应用系统中的稳定性和精度提供了依据。     

有源微分电路设计

用理想运放模型设计的有源微分电路的不足表现为，幅频特性有远离微分规律的尖峰，符合微分规律的频带不宽。为此提出在有源微分电路的传递函数中计及实际运放幅频特性，增加与输入电容串联的电阻，可使有源微分电路的幅频特性没有不符合微分规律的尖峰，符合微分规律的频带达到最宽。     

Small signal modelling of Smart power IC

A method of small signal modelling for the smart power IC is presented. The method is based on the IC's typical operational characteristics and small signal frequency response data. Using the least square identification, the IC's dynamic model, which was expressed as the transfer function, was synthesised from the gain and phase data from the experiment were obtained. The effectiveness and practicality of the method were verified through experiments.     

Influence of core diameter on the 3-dB bandwidth of graded-indexoptical fibers

The frequency response and bandwidth of multimode silica glass fibers are investigated in this paper. The theoretical model incorporates both wavelength and modal effects including power coupling from random microbends. The 3-dB bandwidth is examined through the study of the fiber transfer function which introduces the wavelength and modal effects as two separate filter functions. The formal derivation of the chromatic transfer function is analytical. On the other hand, the modal bandwidth is obtained by numerically solving the power flow equation in the frequency domain using the Crank-Nicholson method. As an application, the transfer function is illustrated and subsequently discussed with special focus spent on analyzing the influence of the fiber size in combination with the launching conditions. We show in particular that the larger the core, the greater the bandwidth potential of the fiber when operated under selective mode excitation. Some measurements are also carried out and excellent agreement between this model and data is achieved     

宽带MIMO-OFDM系统信道估计算法研究

本文提出了MIMO-OFDM系统中基于LS准则的参数化信道估计方法(LSPCE),推导出其MSE性能的下界并给出一种最优导频序列.为了降低复杂度,本文还提出了一种迭代的算法,它利用有限冲击响应信道的抽头之间的相关性从噪声中提取出信道信息并同时估计出多径时延.仿真和分析表明,相比传统的LS信道估计算法,这种基于参数化的信道估计算法可以大大提高信道估计的精度,接收端的检测性能接近理想信道估计的性能.     

基于网络参量的频率响应研究

针对传递函数描述的模拟滤波器频率响应具有上凸尖峰的问题,引入微波网络理论,考察插入衰减这一工作特性参量,分析各自的物理意义,比较了传递函数与插入衰减的异同点,并推导了两者的转换关系式。计算和仿真首先由插入衰减得到了标准的滤波器频率响应,利用转换关系式可以从插入衰减得出传递函数的频率响应。结果分析表明,对于模拟滤波器,插入衰减描述其频率响应更准确;而对于数字滤波器,插入衰减和传递函数的概念是一致的,都可以得到标准的频率响应。     

基于探地雷达的有耗介质脱空薄层厚度估计方法

探地雷达在机场道面脱空检测中可以取得较好效果,但还不能准确估计有耗介质中的脱空厚度。针对此问题,本文通过分析脱空薄层复合反射回波的振幅响应和有耗介质中的电磁波传播模型,将常规薄层调谐厚度方法推广到有耗介质,提出了一种新的薄层厚度估计方法。首先推导有耗介质中脱空薄层反射回波的主频振幅随厚度变化的振幅响应,然后基于最小二乘曲线拟合方法修正主频振幅响应,减小接收信号未建模误差和参数估计误差对脱空厚度估计精度的影响。仿真结果表明,基于本文方法所取得的估计精度明显高于基于未修正的主频振幅响应方法。      

Statistics of deformations in histology and application to improved alignment with MRI

An exact registration of magnetic resonance images (MRI) with histological sections is impeded by local deformations resulting from histological preparation procedures. Therefore, it is desirable to know the probability density function of spatial deformations in order to estimate optimal global least-square transformation parameters from suitable landmarks. For this reason, the statistics of deformations is investigated. It is shown analytically that the frequency of occurrence of the absolute geometrical differences (deformations) are Rayleigh-Bessel distributed for anisotropic histological preparation procedures and Rayleigh distributed in the case of isotropic procedures. The probabilistic analysis is given in conjunction with an iterative optimization technique in order to ensure that the probability density function is within a threshold required for the application to experimental data. The application of the analytical model is investigated with real data. It is shown with this data that the extent of deformations varies with the size of the histological section. An individual threshold can be selected on the basis of a Rayleigh-function restricting local corrections to small parts of the image. Thus, global misalignment in each section can be avoided, resulting in an improved 3-D reconstruction of the volume, i.e., the transitions from one section to the next are more continuous.     

Influence of fiber nonlinearity on the fiber transfer function:theoretical and experimental analysis

The influence of fiber nonlinearity on the fiber transfer function is investigated theoretically and experimentally. A rigorous expression for the fiber transfer function using a directly modulated semiconductor laser as an optical transmitter is presented. Very good agreement of fiber transfer function between experimental data and theoretical predictions is achieved. Furthermore, the fiber parameter values extracted from fitting are the same as those obtained from relative intensity noise measurements, and the fiber nonlinearity coefficient value is compared with other published results. A thorough physical explanation for the effect of fiber nonlinearity on the fiber transfer function at low-medium frequencies is provided. Results reveal that in the anomalous dispersion regime the fiber nonlinearity enhances the high-pass behavior typical of the fiber transfer function using a directly modulated laser operating at high bias current, shifts the transfer function dips toward higher frequency, and consequently leads to a larger bandwidth. Furthermore, it is shown that the fiber nonlinearity can provide partial or total compensation of the nonuniform frequency response at low-medium frequencies resulting from a directly modulated laser operated at low bias current     

Evaluation of the pole expressions of nano-scale multistage amplifiers based on equivalent output impedance

Several frequency compensation schemes have been proposed to stabilize multistage amplifiers with negative feedback. The performance of these amplifiers can be analyzed by inspecting their input-output transfer function as representation of their frequency response. With many circuit elements affecting the output response, it is relatively difficult to obtain the real transfer function of multistage amplifiers based on only the original small-signal expressions. Instead, certain techniques such as Miller’s theorem are used to approximate important parameters such as DC gain and dominant pole. These methods are not generally helpful for approximating the nondominant poles which have a critical role on the loop stability of nano-scale amplifiers. With this issue in mind, this work proposes a systematic methodology to achieve the pole expressions of multistage amplifiers with frequency compensation. The key in the proposed technique is to model the equivalent impedance of the compensation loop at the output. The effectiveness of the proposed approach has been verified through comparison between the transfer functions obtained from theory and those transfer functions found in the literature.     

A physically based small-signal circuit model for heterostructureacoustic charge transport devices

A physically based small-signal circuit model for GaAs-AlGaAs Schottky gate heterostructure acoustic charge transport (HACT) devices is presented. Analytical expressions for the instantaneous and average channel current as a function of gate voltage are obtained from physical device parameters. The charge injection model is based on subthreshold current models for GaAs MESFETs. It is shown that the shape of the sampling aperture of the charge injection operation is approximately Gaussian. Good agreement is obtained between the measured DC channel current versus gate voltage and that predicted by the model. Equivalent circuits for the transfer and output sensing operations and expressions for noise sources due to the physical processes that occur within the device are developed. Thermal, shot, and transfer noise are treated. The form of the analytic expressions for frequency response and noise figure allows easy implementation on commercially available CAE software. Simulations of both gain and noise figure performed on Libra show good agreement with measured data     

Determination of a transfer function from phase response data

This letter discusses the use of an iterative least squares procedure for rational function curve fitting to determine a transfer function from phase frequency response data.     

Accurate Time-Domain Simulation of Continuous-Time Sigma–Delta Modulators

In this paper, we present a methodology for the simulation of continuous-time (CT) sigma-delta converters. This method, based on a fixed-step algorithm, permits not only a time-domain simulation of the modulator output but also the simulation of intermediary signals. The method is based on the discretization of the CT models and the use of a discrete simulator such as Simulink, which is more efficient than an analog simulator. By using filters with a sampling frequency that is higher than the modulator output frequency, the model can simulate input signals with a bandwidth that is higher than half the modulator sampling frequency. The transformation is exact in terms of noise transfer function and asymptotically exact in terms of signal transfer function (the transfer function from the modulator input to each stage filter output rapidly tends to the CT-model transfer function when the number of steps increases).     

Fault Diagnosis of Linear Analog Electronic Circuit Based on Natural Response Specification using K-NN Algorithm

This paper reports a novel method for parametric fault diagnosis in linear analog electronic circuits using distance weighted cosine K-Nearest Neighbours (K-NN) algorithm that performs data classification on the basis of cosine similarity between data features or attributes. In this approach the analog electronic Circuit Under Test (CUT) is represented in the form of a transfer function model and natural response specifications of the system such as damping ratio, natural frequency and static gain of the system are extracted as features from this model. For experimentation purpose a second order Sallen-Key band pass filter and a fourth order Chebychev Type 1 low pass filter is considered, the corresponding fault classes are created for each of the circuit. The parameter values of the passive components in the system have been varied to derive the features, and each component whose tolerance varied is labelled with a corresponding fault class. The proposed methodology classifies faulty classes with accuracy greater than 95%.

     

On Analog Networks and Mixed-Domain Spatio-Temporal Frequency Response

In this paper, we extend the linear cellular neural network (CNN) paradigm by introducing temporal derivative diffusion connections between neighboring cells. Our proposal results in an analog network topology for implementing general continuous-time discrete-space mixed-domain 3-D rational transfer functions for linear filtering. The network connections correspond one-to-one to the transfer function coefficients. The mixed-domain frequency response is treated as a temporal frequency-dependent spatial function and we show how nonseparable properties of the spatio-temporal magnitude response can be derived from the combination of: 1) sinusoidal functions of spatial frequencies and 2) polynomials of the continuous-time frequency in the 3-D frequency response expression. A generic VLSI-compatible implementation of the network based on continuous-time integrators is also proposed. Based on our proposed CNN extension, the analysis of a spatio-temporal filtering example originated from analytical modeling of receptive fields of the visual cortex is presented and a spatio-temporal cone filter is designed and presented with numerical simulation results.      

Monitoring of polyethylene wear in nonmetal-backed acetubular cups by digitized anteroposterior pelvic radiography

The aim of this study was to assess polyethylene wear in a total hip prosthesis by digitized radiography of the whole pelvis in the anteroposterior (AP) plane. The three-dimensional (3-D) pose of the nonmetal-backed acetubular cup, materialized by its metal ring and the femoral head made of metal or ceramic, was estimated using iterative algebraic algorithms with inner bias correction and bootstrapping for variance reduction. Points of interest were obtained by maximizing the correlation between sampled density profiles and 3-D geometric models degraded by the modulation transfer function (MTF) of the radiographic system and the film scanner. The error in the maximal correlation estimate were inferred from noise power spectra (NPS) and allowed the calculation of the point covariance matrix. Both NPS and MTF were modeled for each stage and estimated using least-square fitting of the overall NPS model to the autospectral density function calculated in stationary regions. Comparison of the radiographic time series was made possible by the high accuracy level and 3-D matching from the cup orientation. The feasibility of the full 3-D measurement, the assumption of negligible lateral wear and its influence on AP wear are discussed on simulated and real radiographic data.     

Seismic wavelet estimation: a frequency domain solution to ageophysical noisy input-output problem

In seismic reflection prospecting for oil and gas a key step is the ability to estimate the seismic wavelet (impulse response) traveling through the Earth. Such estimation enables filters to be designed to deblur the recorded seismic time series and allows the integration of “downhole” and surface seismic data for seismic interpretation purposes. An appropriate model for the seismic time series is a noisy-input/noisy-output linear model. The authors tackle the estimation of the impulse response in the frequency domain by estimating its frequency response function. They use a novel approach where multiple coherence analysis is applied to the replicated observed output series to estimate the output signal-to-noise ratio (SNR) at each frequency. This, combined with an estimate of the ordinary coherence between observed input and observed output, and with the spectrum of the observed input and cross-spectrum of the observed input and output, enables estimation of the frequency response function. The methodology is seen to work well on real and synthetic data     

PLL频率合成器中有源环路滤波器的设计与仿真

为提高PLL频率合成器的性能,简化环路滤波器的设计过程,提出了PLL频率合成器中有源环路滤波器的一种设计方法。首先给出一种实用的三次特性的有源环路滤波器结构,根据电路结构求出其频率特性,结合PLL频率合成器中鉴相器-VCO-分频器的相位传递函数,确定使系统稳定的相位最大返回处频率,合理分配滤波器的零、极点,进而综合出环路滤波器的设计方法,以及电路中各元件的计算公式。文中给出了设计实例并进行了PSPICE仿真,结果表明其性能完全能达到设计要求。