Digital subscriber lines (DSL) offer the possibility to deliver broadband services over the existing telephone network. Yet, before deploying DSL, the subscriber loops must be tested to see whether they can support high-speed data services, and at what rate. Single-ended automatic qualification is essential for achieving low-cost deployment of DSL, since it allows loops to be qualified in bulk without human intervention at the customer’s location. An even more ambitious challenge is to fully characterize the loop, i.e. to identify its loop topology (number of loop sections, length and cable type of each section). This paper discusses the feasibility and the problems of loop topology identification via single-ended measurements.

Wide band characterization of analog-digital converter integral nonlinearity (INL) based on parametric modeling and least-squares parameter fit is performed. In particular, the variations in the INL due to the frequency at the ADC stimuli are modeled. The INL is divided into two main entities describing the static and dynamic behavior of the ADC, respectively. The static component is modeled by a high code component (HCF) of piecewise linear segments centered around zero. A static low code (LCF) polynomial inherent to the INL data is added to the segments to describe the static part of the model. The INL dynamic part is modeled by an LCF polynomial. Method implementation is considered and is applied to 12-bit ADC data at 210 MSPS.

Analysis of circular scales accuracy calibration methods based on use of computer modelling and data processing including information entropy assessment here are presented. The computer simulation means for angular position measurement is presented using the circular scale simulation on the PC screen and giving a wide range of opportunities to change or select various scales’ parameters for further their analysis. Accuracy analysis of the circular scales is available applying the different methods of measurement and making experimental trials of newly developed methods. Different parameters of the scale can be simulated and an analysis of systematic and random errors can be performed as well. Methods of error correction of systematic errors can be applied and information entropy assessment can be made. The means and model of simulation give possibility to apply a wide range of parameters change with subsequent their analysis what is impossible and highly expensive in case of real experimental trials in-situ. The software developed permits to calculate accuracy parameters of thousands of angular values after simulation of measurement and using newly developed method of measurement of circular scales.

The paper aim inspects influence of the used RMS-value computing algorithm type and of window type and order on estimation of signal total harmonic distortion (THD). The THD relative bias is investigated by means of computer simulations in MATLAB. A test signal containing the fundamental and 12 higher-order harmonic components with magnitudes corresponding to an international compatibility levels standard and corresponding to the THD of approximately 11 % is used. Three algorithms of THD estimation are investigated, differing in total RMS value and the fundamental component’s RMS value estimation. The total RMS value is found either in time domain or in frequency domain, and the fundamental component RMS value is found either by processing signal components in the used window spectrum main lobe, or using DFT interpolated in frequency domain. Influence of energy leakage for non-quantized test signal and of the 1st order and the 3rd order cosine windows is investigated. The influence of signal quantization for the 12-bit and 16-bit ADC and the above-mentioned windows is also shown. Also the influence of phases of test signal harmonic components by THD estimation by non-coherent sampling using the three investigated algorithms and expression for THD uncertainty caused by quantization is presented.

A logarithmic current-to-voltage converter for measuring DC currents in a wide dynamic range (from 1 pA to 1 mA) is described here. The converter is based on an operational amplifier circuit with a standard commercially-available LED diode used as a nonlinear feedback. A temperature compensation method requiring only one reference amplifier was used. This significantly reduces the complexity and the resulting cost of the converter. The static transfer characteristics of the converter were measured and compared with the uncompensated case.