Nonrandom quantization errors in timebases

Timebase distortion causes nonlinear distortion of waveforms measured by sampling instruments. When such instruments are used to measure the RMS amplitude of the sampled waveforms, such distortions result in errors in the measured RMS values. This paper looks at the nature of the errors that result from nonrandom quantization errors in an instrument timebase circuit. Simulations and measurements on a sampling voltmeter show that the errors in measured RMS amplitude have a nonnormal probability distribution, such that the probability of large errors is much greater than would be expected from the usual quantization noise model. A novel timebase compensation method is proposed which makes the measured RMS errors normally distributed and reduces their standard deviation by a factor of 25. This compensation method was applied to a sampling voltmeter and the improved accuracy was realized     

Noncoherent spectral analysis of ADC using filter Bank

The aim of this paper is to propose a new spectral analysis method for an on-chip analog-to-digital converter (ADC) dynamic test. ADC characterization by spectral analysis has traditionally been done with discrete Fourier transform. This method imposes restrictions to optimize results; one of these is coherent sampling. Recently, some filter structures have been used for spectral analysis of a sinusoidal signal corrupted by harmonics and noise. In this paper, we present a new filter bank structure used for decomposing a signal into its main spectral components. The main application examined is ADC spectral parameter estimation, like signal-to-noise and distortion ratio, signal to noise ratio, total harmonic distortion, and so on, in noncoherent sampling. Computer simulations are used to demonstrate the performance of the proposed filter bank scheme. This structure is a promising built-in self-test (BIST) approach for ADC ICs.     

Testing an ADC linearized with pseudorandom dither

When a pure sinewave is digitized by an analog-to-digital converter (ADC), the errors are determined by the input voltage and, hence, the phase of the sinewave. The errors generate signal harmonics coherently. One technique used to reduce the harmonic distortion is dithering by combining a pseudorandom wide bandwidth dither signal with the input signal. When pseudorandom dither is added to a sinusoidal signal, it randomizes the ADC errors with respect to the sinewave so that the errors cannot add coherently. The dominant effect of the dither component is to reduce large spurious harmonic distortion components by spreading them into many smaller ones. This paper presents a test method for testing an ADC linearized with pseudorandom dither. We present results of testing a 12-bit, 5 MHz converter and a state-of-the-art, 14-15-bit, 10 MHz converter     

Uncertainty of oscilloscope timebase distortion estimate

We study several problems related to the characterization of the timebase in high-speed sampling oscilloscopes. First, we examine the bias of using the method of the first-order approximation to estimate the additive and time jitter noises, and present a procedure to adjust for the bias in the estimates. We then study the bias and variance of a least-squares timebase distortion estimate that uses multiple sets of waveforms. Based on simulations, a method for calculating the uncertainty of the timebase distortion estimate is proposed. We also study the effects of amplitude and phase drifts, as well as jitter error on the estimation of timebase distortion. Results are shown using simulations with parameters that are closely related to those we observe in our laboratory     

Estimation of signal parameters in the frequency domain in the presence of harmonic interference: a comparative analysis

In this paper, a novel method for the estimation of the parameters of the spectral components of a signal, also in the case of harmonic interference, is characterized and compared to other methods proposed in literature. The comparison criteria include the evaluation of residual errors and uncertainties on estimated parameters for different multicomponent signals.     

An induction motor speed measurement method based on current harmonic analysis with the chirp-Z transform

This paper presents a new method to measure motor speed by means of frequency estimation of rotor slot spectral components in the supply current of squirrel single-cage induction motors. The novelty of the method consists in the harmonic analysis of the supply current by means of the chirp-Z transform (CZT). The advantages are improved accuracy due to better spectral resolution and resolvability. Moreover, a shorter observation window is required, thus reducing errors related to nonstationary current signals. The experimental results are presented to validate the proposed method and to make a comparison with a similar method based on the fast Fourier transform (FFT).     

听觉掩蔽效应语音增强的改进算法

含噪信号利用掩蔽效应去噪后,噪声估计的误差导致语音失真。在利用听觉阈值计算谱减系数时提出了一种改进的计算方法,通过增加修改参数来抑制语音的过分衰减,减少了语音失真,然后基于MMSE准则对增强的语音谱再进行平滑处理,进一步抑制音乐噪声。实验表明该算法在不影响语音失真的基础上,提高了信噪比,消除了音-／乐噪声,主观测听的语音音质明显提高。     

A fast-pulse oscilloscope calibration system

A system is described for calibrating high-bandwidth oscilloscopes using pulse signals. The fast-pulse oscilloscope calibration system (FPOCS) is to be used to determine the step response parameters for digitizing oscilloscopes having bandwidths of ~20 GHz. The system can provide measurement traceability to standards maintained at the U.S. National Institute of Standards and Technology (NIST). It comprises fast electrical step generation hardware, a personal computer (PC) and software, and a reference waveform, i.e., a data file containing an estimate of the step generator output signal. The reference waveform is produced by prior measurement by NIST of the step generator output signal (calibration step signal). When the FPOCS is in use, the calibration step signal is applied to the device under test, which is an oscilloscope sampling channel. The measured step waveform is corrected for timebase errors, then the reference waveform is deconvolved from it. The results are impulse, step, and frequency response estimates, and their associated parameters (e.g., transition duration, transition amplitude, -3 dB bandwidth) and uncertainties. The system and its components are described, and preliminary test results are presented     

Uncertainty of signal reconstruction in the case of jittery andnoisy measurements

Time domain measurements are distorted by the measurement system if the bandwidth of the system is not sufficiently high compared to that of the signal to be measured. If the distortion is known the measured signal can be compensated for it (inverse filtering or deconvolution). Since the measurement is always corrupted by noise, the reconstruction is an estimation task, i.e., the reconstructed signal may vary depending on the actual noise record. Our aim is to investigate the errors related to the signal reconstruction, and to provide an error bound around the reconstructed time domain waveform. Based on their nature we can distinguish between systematic and stochastic errors. In this paper, we investigate the stochastic type of errors and suggest a method to calculate the uncertainty (variance) of the reconstruction. We developed a method for the calibration of high-speed sampling systems. Both stationary and jitter noises will be investigated     

The modulo time plot-a useful data aquisition diagnostic tool

This paper illustrates the use of the Modulo Time Plot to facilitate diagnosis of data acquisition systems and components. While conventional techniques, involving spectral analysis and histograms, provide certain useful and necessary measures of performance, the use of reordered sample sets has gained considerable popularity in recent work aimed at characterizing analog-to-digital converter error mechanisms. Examples show that the Modulo Time Plot is useful for quick visual inspection of system performance including dynamic range, distortion and error plots, the detection of random bit errors, and timing errors between the test signal and the sample clock     

基于空间平滑处理的稳健宽带高分辨方位估计算法

实际系统中阵列误差导致的模型失配问题一直是高分辨方位估计技术走向实用化的一个瓶颈。相对于窄带信号,宽带信号阵列模型误差更加复杂和多样,通过建立宽带阵列信号误差模型,得出了基于空间平滑的稳健的宽带高分辨算法是一种抑制阵列误差的有效方法的结论,这种基于空间平滑的宽带高分辨算法,通过空间平滑后对各频率处不同子阵的互谱密度矩阵求和,一定程度上减弱了阵列误差的影响,具有较高的稳健性。本文结合消声水池试验,分析并验证了其效果。     

A New Spectral Average-Based Bearing Fault Diagnostic Approach

The diagnosis of bearing health through the quantification of accelerometer data has been an area of interest for many years and has resulted in numerous signal processing methods and algorithms. This paper proposes a new diagnostic approach that combines envelope analysis, time synchronous resampling, and spectral averaging of vibration signals to extract condition indicators (CIs) used for rolling-element bearing fault diagnosis. First, the accelerometer signal is digitized simultaneously with tachometer signal acquisition. Then, the digitized vibration signal is band pass filtered to retain the information associated with the bearing defects. Finally, the tachometer signal is used to time synchronously resample the vibration data which allows the computation of a spectral average and the extraction of the CIs used for bearing fault diagnosis. The proposed technique is validated using the vibration output of seeded fault steel bearings on a bearing test rig. The result is an effective approach validated to diagnose all four bearing fault types: inner race, outer race, ball, and cage.     

Finite-Sample Bias Propagation in Autoregressive Estimation With the Yule–Walker Method

The Yule-Walker (YW) method for autoregressive (AR) estimation uses lagged-product (LP) autocorrelation estimates to compute an AR parametric spectral model. The LP estimates only have a small triangular bias in the estimated autocorrelation function and are asymptotically unbiased. However, using them in finite samples with the YW method for AR estimation can give a strong distortion in the weak parts of the power spectral density. The distortion is shown to be influential in an example without strong spectral peaks. The true biased AR model, which is computed by applying the triangular bias to the true autocorrelation function, has an infinite order. A new objective measure is introduced to determine the smallest sample size for which the unbiased asymptotic theory can be considered as a fair approximation.     

Phase-plane-derived distortion modeling of a fast and accurate digitizing sampler

Continued efforts to model the distortion behavior of custom-designed digitizing samplers for accurate measurement of dynamic signals are reported. This work is part of ongoing efforts at the National Institute of Standards and Technology (NIST) to advance the state of the art in waveform sampling metrology. In this paper, an analytic error model for a sampler having a -3-dB 6-GHz bandwidth is described. The model is derived from examination of the sampler's error behavior in the phase plane. The model takes as inputs the per-sample estimates of signal amplitude, first derivative, and second derivative, where the derivatives are with respect to time. The model's analytic form consists of polynomials in these terms, which are chosen from consideration of the voltage dependence of the digitizer input capacitance and the previously studied error behavior in a predecessor digitizer. At 1 GHz, an improvement in total harmonic distortion from -32 to -46 dB is obtained when model-generated sample corrections are applied to the waveform. The effect of timebase distortion in the sampling system is also accounted for and corrected. The inclusion of second-derivative dependence in the model is shown to improve the model's fit to the measured data by providing fine temporal adjustment of the fitted waveform.     

非ARMA随机信号谱估计的数字滤波算法及性能分析

为克服传统的周期图谱估计方法存在的分辨率低及非一致估计等缺点而迅速发展的各种近代谱估计法只能适用于ＡＲＭＡ（Ａｕｔｏｒｅｇｒｅｓｓｉｖｅ－ｍｏｖｉｎｇａｖｅｒａｇｅ）信号的谱估计。为解决存在于各种物理过程中的非ＡＲＭＡ随机过程（包括１／ｆ过程）的谱估计，本文提出了一种对非ＡＲＭＡ随机信号的非递归数字滤波算法，重点研究了算法主要参数（滤波器长度、数据长度）的选择原则及对谱估计准确度和精度的影响。理论分析及实际测量证明，此方法具有分辨率高、谱估计精确较好及一致估计等优点，特别适用于对非ＡＲＭＡ信号的某些特征频率点的谱估计。     

Quasi-synchronous sampling algorithm and its applications

Synchronous sampling is a commonly used method with good performance. However, when perfect synchronization is impossible, or when the signal contains interharmonics, undesirable asynchronous deviations between the sampling and some components of the signal may exist. Consequently, possibly large leakage or truncation errors may occur. Consisting of a quasi-synchronous window to reduce the long-range leakage, and a compensation algorithm to reduce the short-range leakage after normal FFT, the method described in this paper will give much more accurate measurement of many electrical quantities, e.g., spectral content of signal and phase difference between two periodic signals in power networks, than the traditional one     

"Real time" noise measurements with sensitivity exceeding the standard thermal noise limit

A possibility of "real-time" noise measurements with spectral resolution better than a standard thermal noise limit has been experimentally demonstrated at microwave frequencies. The enhancement in the sensitivity of spectral measurements was achieved due to more efficient use of the signal power via the power recycling technique. By utilizing such a technique, the noise floor of a 9 GHz "real time" measurement system was reduced by 3 dB below the standard thermal noise limit. This makes possible the characterization of intrinsic fluctuations in individual low-noise microwave components, such as ferrite circulators, without the need for cascading them or using the cross-correlation signal processing.     

Effects of chromatic dispersion on microwave and millimetre wave carrier transmission in optical fibres

Abstract

A new formalism for the analysis of optical (phase) noise in fibre-optic communication links is presented. The formalism is applied to an amplitude modulated millimetre-wave (or microwave) link with chromatic dispersion. A realistic link model is described and rigorously solved. In general, the power spectrum of the output signal consists of a ‘comb’ of spectral components with centre separation equal to the modulation frequency. Each spectral component contains a smooth ‘noise’ curve and a narrow spike which represents a modulated field component (carrier). With the new method it is possible to compute each spectral component and, consequently, the full power spectrum. From the power spectrum one can compute quantities relevant to the link design, in particular the carrier-to-noise ratio. Several graphs are presented, showing the power spectrum and the carrier-to-noise ratio for different values of the modulation frequency, link dispersion and modulation index. Several conclusions regarding the millimetre-wave fibre-optic link are dis-cussed.     

AR模型在爆破震动信号频谱分析中的应用

爆破震动信号的频谱分析以傅氏变换为基础的经典谱估计方法为主,该方法存在方差性能差、易产生虚假峰值、谱曲线起伏大等缺点。AR模型谱估计方法计算精确度高、且简单,并能弥补经典谱估计在信号分析中的不足。采用经典、AR模型谱估计方法对不同类型的工程实测爆破震动信号进行频谱分析,其中以AR模型谱估计方法得到爆破震动信号的频谱曲线平滑、方差小、主频明确,且主频附近无虚假峰值,表明AR模型现代谱估计比经典谱估计在爆破震动信号的频谱分析中更具优越性。     

局部置信度增强的单矢量水听器互谱方位直方图

单矢量水听器互谱方位直方图具有一定的多目标分辨能力,但其性能受到目标信号分离正交性(Window Disjoint Orthogonality, WDO)的制约。WDO特性越强,表示主导目标的能量占比越大,互谱方位估计的结果越接近主导目标的真实方位。文章提出利用局部置信度增强互谱方位直方图的多目标分辨性能。局部置信度表示样本中主成分与其他成分之间的比值关系,因此可以作为信号WDO特性强弱的估计。在统计互谱方位直方图时,利用局部置信度对时频点的方位估计结果进行加权,增加WDO特性强的时频点的方位估计结果在方位直方图中的贡献,提高目标真实方位处的谱峰,从而增强方位直方图多目标分辨的效果。湖试数据的分析表明了利用局部置信度加权能够有效提高多目标分辨的效果。