Mixed-mode sampling and error estimation in digital wattmeters

The problem of estimating the error due to the discrete-time approximation in sampling digital wattmeters is dealt with. The complementary characteristics of two different sampling strategies, based on equally spaced or randomly generated sampling instants, are discussed. A mixed-mode sampling strategy, which can also provide an estimate of the error, is proposed.     

Effects of sampling and quantization on single-tone frequencyestimation

The effects of sampling and quantization on frequency estimation for a single sinusoid are investigated. The Cramer-Rao bound for 1-bit quantization is derived and compared with the limit of infinite quantization. It is found that 1-bit quantization gives a slightly worse performance, however, with a dramatic increase of variance at certain frequencies. This can be avoided by using four times oversampling. The effect of sampling when using nonideal antialiasing lowpass filters is therefore investigated through derivation of the Cramer-Rao lower bounds. Finally, fast estimators for 1-bit quantization, in particular, correlation-based estimators, are derived, and their performance is investigated. The paper is concluded with simulation results for four times oversampled 1-bit quantization     

Information rates in sampling and quantization

A computer-aided analysis of a digital communications system has been conducted. Salient results compare the performance of approximately optimum PCM systems with the rate-distortion function, under the assumptions of Gaussian inputs and mean-square-error distortion measure. The calculated distortion is greater than the theoretical minimum by two or three decibels in most cases. The results presented also illuminate the tradeoff between sampling rate and number of quantization levels in a channel of fixed capacity. The presampling and reconstruction filters are represented in the computer by their impulse responses; that is, filtering of signals is accomplished by evaluating the convolution integrals numerically. Impulse responses with durations of20sample times or fewer are long enough to model most known results in optimum filtering of sampled stationary random functions. Procedures are described for computing the autocorrelation function of the quantizer output, and the cross correlation between the quantizer output and a signal correlated with the input. The procedure adopted is the naive one of integrating numerically the appropriate bivariate normal distribution.     

Scatter-glare estimation for digital radiographic systems: comparison of digital filtration and sampling techniques

The scatter and veiling glare distribution in images acquired with a digital subtraction angiography imaging system was estimated using a digital filtration and a beam-stop technique. The digital filtration technique utilizes exposure parameters and image gray levels to estimate scatter-glare intensity based on previous phantom measurements. The beam-stop technique uses an array of lead discs in order to sample scatter-glare intensity for each patient. To test the ability of digital filtration and beam-stop techniques to estimate the scatter-glare intensity, they were applied to images of postmortem swine animal models at different projections and beam energies. The systematic and root-mean-square (rms) percentage errors of these estimates were obtained by comparison to directly measured scatter-glare images using a scanning lead strip technique. The average rms percentage error for the digital filtration and beam-stop techniques were 8.07% and 6.67%, respectively. The changes in scatter-glare intensity due to contrast injection during coronary arteriography and ventriculography were also measured using the beam-stop technique. The maximum changes in scatter-glare intensities during coronary arteriography and ventriculography were 19 and 88%, respectively. The results indicate that the digital filtration technique is more suited for applications such as coronary arteriography and ventriculography where the iodinated contrast material significantly changes the scatter-glare intensity.     

Least-square estimation of average power in digital CMOS circuits

The estimation of average-power dissipation of a circuit through exhaustive simulation is impractical due to the large number of primary inputs and their combinations. In this work, two algorithms based on least square estimation are proposed for determining the average power dissipation in complementary metal-oxide-semiconductor (CMOS) circuits. Least square estimation converges faster by attempting to minimize the mean square error value during each iteration. Two statistical approaches namely, the sequential least square (SLS) estimation and the recursive least square estimation are investigated. The proposed methods are distribution independent in terms of the input samples, unbiased and point estimation based. Experimental results presented for the MCNC'91 and the ISCAS'89 benchmark circuits show that the least square estimation algorithms converge faster than other statistical techniques such as the Monte Carlo method and the DIPE     

Effects of parameter quantization on the poles of a digital filter

A configuration is proposed which leads to a digital filter that is less sensitive to parameter quantization than are the standard configurations. A few examples illustrate the differences between the various realizations.     

A new approach to power estimation and reduction in CMOS digital circuits

Modelling and optimization of dynamic capacitive power consumption in digital static CMOS circuits, taking into consideration a reason of a gate switching—gate control mode, is discussed in the present paper. The term ‘gate control mode’ means that a number and type of signals applied to input terminals of the gate have an influence on total amount of energy dissipated during a single switching cycle. Moreover, changes of input signals, which keep the gate output in a steady state, can also cause power consumption. Based on this observation, complex reasons of power losses have been considered. In consequence, the authors propose a new model of dynamic power consumption in static CMOS gates. Appropriate parameters’ calculation method for the new model was developed. The gate power model has been extended to logic networks, and consequently a new measure of the circuit activity was proposed. Switching activity, which is commonly used as a traditional measure, characterizes only the number of signal changes at the circuit node, and it is not sufficient for the proposed model. As the power consumption parameters of CMOS are dependent on their control mode, the authors used probability of the node control mode as a new measure of the circuit activity. Based on the proposed model, a procedure of combinational circuit optimization for power dissipation reduction has been developed. The procedure can be included in a design flow, after technology mapping. Results of the power estimation received for some benchmark circuits are much closer to SPICE simulations than values obtained for other methods. So the model proposed in this study improves the estimation accuracy. Additionally, we can save several percent of the consumed energy.     

A brief summary of a generalized framework for power spectral estimation

This correspondence presents a brief summary of a generalized framework for power spectral estimation and shows how three previous estimation methods fit into this framework as special cases. Further, this correspondence clarifies some recent comments made on spectral estimation; in particular specific references are given that strongly support the use of overlapped weighted segment averaging for spectral estimation.     

Two's complement quantization in periodic digital filters

The stability of periodically shift variant (PSV) filters are studied when implemented with two's complement truncation (TCT) quantization. Block form and standard (nonblock) form implementations are considered, and two sufficient conditions are established for stability. As a special case, second-order coupled-form PSV filters are then investigated under TCT quantization. Stability regions are established within the parameter space for block implementations. Examples are given to illustrate the results     

Determination of quantization error in two-dimensional digital filters

The evaluation of the quantization error in two-dimensional (2-D) digital filters involves the following computation J = Σm=0^∞Σn=0^∞y²(m, n). In this paper general method for the evaluation of J based on Laurent expansion of the integrand is presented. Illustrative example for such a computation is given. Notations: We denote with V^-2= {(z1, z2): |z1| ≤ 1, |z2| ≤ 1} the closed unit bidisc, with V²= {(z1, z2): |z1| < 1, |z2| < 1} the open unit bidisc, and with T2= {(z1, z2): |z1| = 1, |z2| = 1} the distinguished boundary of the unit bidisc.     

Dynamic finite-state vector quantization of digital images

A vector quantization (VQ) scheme with finite memory called dynamic finite-state vector quantization (DFSVQ) is presented. The encoder consists of a large codebook, so called super-codebook, where for each input vector a fixed number of its codevectors are chosen to generate a much smaller codebook (sub-codebook). This sub-codebook represents the best matching codevectors that could be found in the super-codebook for encoding the current input vector. The choice for the codevectors in the sub-codebook is based on the information obtained from the previously encoded blocks where directional conditional block probability (histogram) matrices are used in the selection of the codevectors. The index of the best matching codevector in the sub-codebook is transmitted to the receiver. An adaptive DFSVQ scheme is also proposed in which, when encoding an input vector, first the sub-codebook is searched for a matching codevector to satisfy a pre-specified waveform distortion. If such a codevector is not found in tile current sub-codebook then the whole super-codebook is checked for a better match. If a better match is found then a signaling flag along with the corresponding index of the codevector is transmitted to the receiver. Both the DFSVQ encoder and its adaptive version are implemented. Experimental results for several monochrome images with a super-codebook size of 256 or 512 and different sub-codebook sizes are presented     

Two's complement quantization in orthogonal biquad digital filters

A special class of complex biquad digital filters called orthogonal filters are investigated for stability under two's complement quantization. A sufficient condition is derived for the asymptotic stability of the nonlinear filter. Bounds on the possible limit cycles are also obtained. Using these bounds, any given filter can be tested for stability. The stability triangle is then scanned using a dense grid, and each point on the grid is tested for stability/limit cycles. By this method, the stability region given by the sufficient condition is extended. Regions within the linear stability triangle where various types of limit cycles are possible are also identified.     

低采样率高分辨率压缩功率谱估计方法的仿真研究

低采样率的宽带功率谱估计在很多领域具有应用价值.采用压缩多核采样结构得到信号的压缩测量值, 然后建立测量值相关函数与信号相关函数之间的关系, 用最小二乘法实现相关函数估计, 最后实现功率谱的估计.该压缩采样方法的等效采样率为M/N·f_s, 可在没有任何对时域或频域稀疏性的假设条件下降低采样率.仿真分析表明, 该方法的系统噪声与加性噪声性能比周期图法略有降低, 但只要系统设计合理, 对于一定信噪比的信号, 系统噪声与加性噪声基本可以忽略, 并给出了对应的理论分析.估计分辨率与周期图法相比, 等效长度相同时略有提高; 由于本文方法降低了测量值的数目, 对于一定长度的数据来说, 估计分辨率得到了极大的提高.本文方法适用于低信噪比信号的低采样率高分辨率功率谱估计.     

Variance estimation and adaptive quantization (Corresp.)

The relationship between variance estimation and adaptive quantization is investigated for memoryless Laplacian and Gaussian sources. Comparison of block average, exponential average, and maximum likelihood estimators in an adaptive quantization scheme indicates that estimator precision (variance) is more important than accuracy (bias) in minimizing distortion. Further, the block average and exponential average estimators are inconsistent when used in backward adaptive quantization.     

A digital power spectrum estimation method for the adaptation of high-speed equalizers

This work presents a method to estimate the power spectrum of digital signals, which is then used to generate an error signal to tune Gbps data rate equalizers for digital communications. The proposed power spectrum estimation method can be realized with standard digital circuits and has been fabricated and tested in 0.35-/spl mu/m CMOS technology for 1-Gbps data rate. Compared with the traditional bandpass filter followed by a rectifier implementation, this method has wider input signal range and is scalable to higher speed technologies beyond the gigahertz range, in addition to largely reduced power dissipation and die area. Also presented are system simulations on the bit-error rate performance and the error space analysis of the proposed method in comparison with the method of using a bandpass filter followed by a rectifier.     

Low-complexity predictive trellis-coded quantization of speech line spectral frequencies

Low-complexity block-constrained trellis coded quantization (BC-TCQ) structures are studied, and a predictive BC-TCQ encoding method is developed for quantization of line spectrum frequency (LSF) parameters for speech coding applications. The performance is compared with the linear predictive coding (LPC) vector quantizers used in the AMR-WB (ITU-G.722.2) and IS-641 speech coding standards, demonstrating reduction in spectral distortion (SD) and significant reduction in encoding complexity.     

基于等效和实时采样的数字示波器设计

基于数字示波器的基本原理,以单片机和FPGA组成的最小系统为控制核心,实现了普通示波器对被测信号的采样、存储与回放,并且增加了等效采样和采样保持功能,极大地提高了系统的测量范围。该系统具有实时采样和等效采样两种方式,以不大于1Ms／s的A／D转换实现200MS／s的等效采样率对输入1Hz-10MHz,yp-p为2mV-8V的信号进行采样处理,并能进行单次触发,自动和存储／输出波形。     

基于等效和实时采样的数字示波器设计

基于数字示波器的基本原理,以单片机和FPGA组成的最小系统为控制核心,实现了普通示波器对被测信号的采样、存储与回放,并且增加了等效采样和采样保持功能,极大地提高了系统的测量范围.该系统具有实时采样和等效采样两种方式,以不大于1 Ms/s的A/D转换实现200 MS/s的等效采样率对输入1 Hz～10 MHz,Vp-P为2 mV～8 V的信号进行采样处理,并能进行单次触发,自动和存储,榆出波形.     

基于坐标变换的射频功放预失真参数估计方法

在低中频预失真器构架的基础上,提出了一种基于坐标变换的预失真参数估计方法,从而降低了传统数字基带预失真系统的硬件成本和数值计算量。算法将传统算法中的复数乘法转换为极坐标中的幅度乘法和相位加法,使同样的计算步骤所消耗的乘法和加法次数分别降低了75%和50%。算法由通用的通带Volterra非线性模型进行推导得出,适用于当前的任意系统模型。对实际射频功放的测试实验结果验证了其有效性。     

Standby power consumption estimation by interacting leakage current mechanisms in nanoscaled CMOS digital circuits

Leakage currents are gaining importance as design parameters in nanometer CMOS technologies. A novel leakage current estimation method, which takes into account the dependency of leakage mechanisms, is proposed for general CMOS complex gates, including non-series-parallel transistor arrangements, not covered by existing approaches. The main contribution of this work is a fast, accurate, and systematic procedure to determine the potentials at transistor network nodes for calculating standby static currents. The proposed method has been validated through electrical simulations, showing an error smaller than 7% and an 80× speed-up when comparing to electrical simulation.