Mario Savino

Windows and interpolation algorithms to improve electrical measurement accuracy

An FFT-based measurement technique, which can be easily used to determine accurately the frequency, amplitude, and phase of all the harmonic and interharmonic components of a distorted signal, is examined. Suitable windows and interpolation algorithms are examined in order to reduce undesirable effects due to spectral leakage caused by a sampling process that is not synchronized. Several results concerning the application of different windows on a set of simulated signals are compared to verify the capability of the proposed procedure. The influence of the noise is examined to study the filtering properties of the weighting functions. >

FFT test of A/D converters to determine the integral nonlinearity

In this paper, the use of the fast Fourier transform (FFT) test to measure the integral nonlinearity (INL) of analog-to-digital (A/D) converters is examined. The derived INL is a linear combination of Chebyshev polynomials, where the coefficients are the spurious harmonics of the output spectrum. The accuracy of the test is examined theoretically, in simulations and in practical devices, particularly for the critical (and typical) case when sudden jumps are present in the actual INL. The examined methodology appears to be very convenient when the device under test has high resolution (16-20 bits) and a smoothed approximation of the INL is sufficient, as the FFT test is in this case thousands of times faster than the customary histogram test and static nonlinearity test.

Uncertainty Analysis in Photovoltaic Cell Parameter Estimation

This paper describes a theoretical approach to evaluate the uncertainty on the series and shunt resistances estimated by the seven-parameter (double diode) model of a photovoltaic (PV) cell using data commonly provided by panel manufacturers, measured environmental parameters, and semiempirical equations. After a brief survey on the state of the art and the treatment of the double-diode model, the procedure proposed by the authors, to estimate the unknown parameters, is illustrated. The theoretical expression of the uncertainty, which affects the estimation of the series and shunt resistances (namely, and ) of a PV cell, is then derived. A statistical analysis performed by means of a Monte Carlo simulation is in agreement with the theoretical expression of the uncertainty.

Application of Wigner-Ville distribution to measurements on transient signals

The authors deal with an application of the Wigner-Ville distribution (WWD) and with usual digital-processing techniques, such as the short-time Fourier transform (STFT), used in dedicated instrumentation for measuring non-stationary signals. A WWD- and STFT-based virtual instrument (VI) to measure instantaneous frequency and amplitude of the fundamental component of transient signals is presented. The applied algorithms include original interpolation techniques for accurately determining the actual instantaneous frequency, and a suitable flat-top window function for measuring the fundamental amplitude without further amplitude interpolation algorithms. The digital system, uses the Lab View software for easily processing the data sequences, simulated or acquired by a suitable board. Many simulations have confirmed that using the proposed low-cost VI gives measurements of good accuracy, also in the presence of noise.<<ETX>>

An acoustic method for soil moisture measurement

The paper deals with the problem of measuring the soil moisture by an accurate, in-situ, real-time method. Like this a mathematical model which describes a functional relationship between water content of agricultural soil and velocity of propagation of sound waves is analyzed in systematic way. After studying the conditions that guarantee the applicability of proposed model, the velocity curves relevant to different kinds of soils are determined. This model seems to be promising for moisture soil measurements in greenhouse where the soil characteristics are well known but further investigation are necessary.

A Suitable Threshold for Speckle Reduction in Ultrasound Images

This paper presents a novel parametric thresholding procedure to reduce the effect of speckle noise in ultrasound (US) medical images. The method comprises the use of an adaptive data-driven exponential operator that operates on wavelet coefficients of the US image to suppress undesired effects of disturbances, preserving signal details. The obtained results demonstrate that the proposed denoising method increases the medical image quality and, therefore, it can be a useful tool in medical diagnosis.

FFT-based algorithms oriented to measurements on multifrequency signals

Abstract This paper reports original windows to be used in spectral analyses which require high levels of accuracy in harmonic amplitude estimation of multiple-tone signals. The proposed technique allows the user to avoid time-consuming interpolation algorithms after computing the tapered DFT of an observed stretch of time-series. This aim is pursued by using specialized cosine flat-top data windows, which perform tapering with a very low amplitude degradation (less than 0.01 dB) owing to their main-lobe flatness across a frequency range equal to the DFT bin width. The selection of this kind of data windows requires the preventive estimation of the noise floor as the wider bandwidths do not allow their use at low SNRs ( dB ). The global accuracy attained at higher SNRs is far better than with non-interpolated DFT, tapered by classical cosine windows, as bias due to leakage, which is negligible after flat-top windowing, contributes to r.m.s. error more than variance with increasing of SNRs. This may compensate for their reduced selectivity performance and makes them more suitable for calibration purposes.

Testing and optimizing ADC performance: a probabilistic approach

A novel approach to the topic of analog-to-digital converter (ADC) characterization is proposed. The key idea is to describe the behaviour of the device via a suitable conditional probability function, estimated through a modified version of the popular histogram test. Any traditional figure of merit for ADCs can be accurately evaluated from the proposed probabilistic characterization. Besides, this allows one to optimize the ADC overall performance, determining the best allocation of the output reconstruction levels. The parameters of the modified histogram test are determined as a function of the desired accuracy. Finally, computer simulations illustrate the performance of the method.

Interpolated smoothed pseudo Wigner-Ville distribution for accurate spectrum analysis

This paper deals with a new application of the time-domain windowed (smoothed version) of the pseudo Wigner-Ville distribution (PWD), that can be easily implemented in a dedicate digital instrument to be used as a spectral analyzer for time-frequency analysis of nonstationary signals. New computational algorithms are studied and developed to attain high time-frequency resolution, accuracy, flexibility and computational efficiency. Particularly, to reduce the negative effects due to leakage during frequency changes, a new interpolation formula is derived by using the windowing theory. The suggested technique allows the users to perform optimal evaluations of the instantaneous amplitudes and frequencies of analyzed signals.

Improved Static Testing of A/D Converters for DC Measurements

A new method is presented for the calibration and the linearity testing of analog-to-digital converters (ADCs) and dc digital instruments, such as digital voltmeters (DVMs). The test is truly static, because it uses only dc voltages with a small superimposed noise (dithering). It is much faster than that described in the IEEE Standard 1057/94 since it uses a minimal number of test signals and acquired samples in a theoretically nearly optimal manner, i.e., maximum-likelihood estimation. In addition, contrary to the test described in the IEEE Standard 1241/00, it allows offline measurements and testing of stand-alone instruments, such as DVMs. Another advantage of the proposed method is that the resolution requirements for the source of test signals are relaxed. After a review of the state of the art, this paper provides the mathematical derivation of the employed estimator. Simulations, theoretical analyses, and experimental results are also provided to illustrate the performances of the proposed test method.