Vladimir Haasz

ADC nonlinearity correction based on INL(n) approximations

One of the most important parameter of ADC which negatively influence its quality is its nonlinearity. The correction of this imperfection can be accomplished in the output data but only if the nonlinearity is well characterized. Two methods — application of look-up table or an analytical inverse function of INL(n) curve — from other possibilities can be used for the ADC nonlinearity correction. The first results of correction using look-up table were published in [5]. The application of inverse function, which is dependent on the possibility to derive the inverse function to the function approximating the INL(n) curve, is published in the paper.

Performance of data acquisition systems from the user's point of view

In this paper the authors comment on a set of problems related to data acquisition system specification from users point of view and present examples that justify their concerns with the past lack of standardization in this domain. References to the new project of standard 85/227/NP are made and reveal that authors expect it to be a positive contribution to overcome users problems when designing systems requiring data acquisition capabilities.

The error analysis of digital measurements of electrical power

Abstract Digital methods of electrical power measurements with non-sinusoidal current have become more important owing to the growing application of thyristor control. The estimation of errors by the sampling methods of measurement is complicated on account of the wide and often difficult to define frequency voltage and current spectrum. Two possible methods of error estimation are described in this paper; partly for measurement in an AC circuit with thyristor control, partly for measurement on pulse-controlled induction motors.

Evaluation of ADC testing systems using ADC transfer standard

A transportable high stable reference AD device was designed and built for a comparison of systems for testing of the dynamic quality of ADCs or modules. Three different input modules enable its use in the frequency range up to 5 MHz. First, this paper refers to the results of the AD device application in the frequency range of the testing signal up to 100 kHz (comparison of four ADC testing systems in different laboratories, evaluation of a short time amplitude and/or frequency instability of testing signal generators). Second, it describes the first experience of its application in the frequency range from 100 kHz to 5 MHz.

Models of the ADC transfer function - sensitivity to noise

This paper describes several approaches of modeling nonlinearities of analog to digital converters (ADC). First results of three approximations are introduced and compared - the common polynomials, Chebyshev polynomials Fourier series.

System for Testing Middle-Resolution Digitizers using Test Signal up to 20 MHz

A system for the testing of ADCs at the frequency range of 1 MHz, which was designed and prototyped at the Dept. of Measurement, CTU FEE last year, was extended up to 20 MHz. Low-cost as well as high-quality filters for frequencies about 4.4, 9.5 and 19.5 MHz were manufactured. Experimental results showed that the system is directly applicable for the testing of ADCs with the ENOB up to 11-13 in case of low-cost filters and up to 20 in case of high-quality filters

Frequency spectrum correction method for the ADC testing

The main issue of high resolution ADC testing in the frequency range from hundreds of KHz to several MHz is the spectral purity of a testing signal. Commercial low distortion generators can operate only up to the frequency of one or two hundreds of KHz; generators operating in higher frequency range have generally the spectral purity worse than the one corresponding to the ADC resolution. Some improvements can be brought by filtering of the testing signal. Most of the LC filters for the frequency range up to several MHz contain coils with ferromagnetic cores. This causes the rise of higher harmonic components. If those components are known or determined by measurement, they can be subtracted from the frequency spectrum measured by the tested ADC. In the ideal case, only a frequency spectrum corresponding to the ADC non-linearity remains. The measurement system designed for frequency spectrum correction and the first results achieved by applying this method are introduced in the paper.

New trends in ADC testing and modelling

This Special Issue is devoted to selected problems invited plenary lecture of the conference. New state of of A/D conversion. It contains six selected papers form two prestige events dealing with A/D and D/A conversion techniques — the 4th International Conference on Advanced A/D and D/A Conversion Techniques and their Applications and the 7th European Workshop on ADC Modelling and Testing, which both jointly took place in June 2002 in Prague (ADDA & EWADC 2002). The primary objective of ADDA conferences and the European workshops EWADC is to promote the international exchange of scientific and technical information in the field of analogue-to-digital and digital-toanalogue conversion. This was the first time that the two main conferences ADDA and EWADC were commonly organised. IEE, IEEE, IMEKO, and relevant academic and industrial organisations supported the event. It was an excellent opportunity to exchange ideas and information about their research findings and to refresh personal contacts and established new ones. Regarding the fact that stand-alone A/D converters and A/D modules of various implementations form integral parts of the majority of measurement instruments and systems, new smart versions of ADCs with excellent parameters are designed. It is true for example for fast or narrow-band ADCs for VHF applications or new directions in A–D conversion for general use (e.g. audio applications). For that reason also, new methods for their testing have to be developed and implemented to be possible to determine their real parameters. The culmination of these activities should be the standards covering the applications of A/D converters and A/D modules. Six selected papers covering some of the topics mentioned above are presented in this Special Issue. The issue is introduced by a paper from A.C. Serra: New trends in ADC testing, which was presented as the

Some aspects of standardising performance characteristics for modular data acquisition systems

To estimate the measurement uncertainty using a modular DAQ system, factors influencing the quality of A/D modules have to be determined. While integral and differential non-linearities describe the static quality of an ADC, the effective number of bits or SINAD are typical integral parameters characterising the dynamic quality of an A/D module. The paper analyses how individual disturbing factors and imperfections of the A/D module influence the quality of digitalisation, and how they could be specified for a future standardisation. It is shown that (in the case of a time-variable input signal) the factors mentioned above induce disturbing undesirable components in the digital output and so they influence the value of SINAD of the investigated A/D module.

Influence of test signal phase noise on high-resolution ADC testing

The testing of high-resolution ADCs based on the majority of standardized methods requires pure sine-wave test signal. The reason of the requirement for signals purity is that measured ADC parameters are potentially influenced by test signal imperfections such as distortion and wideband noise but also its short term frequency changes (phase noise). The influence of signal distortion and noise has already been the subject of many contributions; an analysis of phase noise, its effect on test results and possibilities of its suppression or correction are the subject of this paper. The validity of phase noise analysis and of proposed methods is also demonstrated on experimental measurements.