Zdenek Kolka

Statistical model of free-space optical data link

The paper deals with a statistical model of free-space optical (FSO) data link that takes into account the duration of individual fade events. It is well known that a general data transmission using the Internet protocol (IP) is almost insensitive to link interruptions for hundreds of milliseconds while real-time video services will be badly affected. The statistical model is based on the knowledge of the probability density function of random attenuations and the probability density function of durations of the fades. The paper shows the results from our test site obtained from 1999 to 2001.

SIMPLEST ODE EQUIVALENTS OF CHUA'S EQUATIONS

The so-called elementary canonical state models of the third-order piecewise-linear (PWL) dynamical systems, as the simplest ODE equivalents of Chuas equations, are presented. Their mutual relations using the linear topological conjugacy are demonstrated in order to show in detail that Chuas equations and their canonical ODE equivalents represent various forms of qualitatively equivalent models of third-order dynamical systems. New geometrical aspects of the corresponding transformations together with examples of typical chaotic attractors in the stereoscopic view, give the possibility of a deeper insight into the third-order system dynamics.

The Art of Finding Accurate Memristor Model Solutions

One of the main issues preventing a large-scale exploration of the full potential of memristors in electrical circuits lies in the convergence issues and numerical errors encountered in the computer-aided integration of the differential algebraic equation set governing the peculiar dynamical behavior of these nonlinear two-terminal electrical components. In most cases the complexity of this equation set prevents an analytical derivation of closed-form state solutions. Therefore the investigation of the nonlinear dynamics of memristors and circuits based upon them relies on software-based integration of the mathematical equations. In this paper, we highlight solution accuracy issues which may arise from an improper numerical integration of the equations, and then propose techniques addressing the problems properly. These guidelines represent a useful guide to engineers interested in the numerical analysis of memristor models.

Fully Balanced Voltage Differencing Buffered Amplifier and its applications

An active circuit element, namely Fully Balanced Voltage Differencing Buffered Amplifier (FB-VDBA), is introduced. Its input stage is composed of a fully-differential operational transconductance amplifier (OTA). Voltage buffer is connected to each OTA output. Several applications are proposed which demonstrate the elements versatility. The results of SPICE simulation and measurements on experimental specimen are included.

Mutators for transforming nonlinear resistor into memristor

A method of analogue emulation of the memristor with its prescribed charge (q<inf>M</inf>) - flux (ϕ<inf>M</inf>) constitutive relation is presented. The memristor is emulated via a resistor with nonlinear current (i<inf>R</inf>) - voltage (v<inf>R</inf>) relationship, and a mutator. The purpose of the mutator is to provide a similarity transformation of the current-voltage characteristic of the resistor into the constitutive relation of the memristor according to the equations q<inf>M</inf>=k<inf>y</inf>i<inf>R</inf>, ϕ<inf>M</inf> =k<inf>x</inf>v<inf>R</inf>, or ϕ<inf>M</inf>=k<inf>y</inf>i<inf>R</inf>, q<inf>M</inf>=k<inf>x</inf>v<inf>R</inf>, where k<inf>x</inf>, k<inf>y</inf> are real numbers fulfilling the condition k<inf>x</inf>k<inf>y</inf>>0. It is shown that there are eight versions of these mutators. One of them is selected for experimental verification.

Single-input multi-output resistorless current-mode biquad

A universal current-mode 2nd-order filter employing two ZC-CITA (Z-Copy Current Inverter Transconductance Amplifier) active elements and two grounded capacitors is proposed. The filter has one low-impedance current input and several high-impedance current outputs which are easy to combine to yield all basic types of transfer functions. The active element is implemented on the basis of commercial integrated circuits. The filter is manufactured and the results measured are compared with theoretical responses.

Measurements and evaluation of PLC modem with G3 and PRIME standards for Street Lighting Control

The paper surveys narrowband power line communications (PLCs) in the context of Smart Grid and remote Street Lighting Control. The specifications G3-PLC and PRIME are discussed. The field test results and data rate measurements are presented for different scenarios. They demonstrate the problems encountered when the PLC signal is necessary to be sent through the switchgear, complicated topology, noisy topology and topology similar to simple street-light topology.

Optical communication in free space

The success of free-space optical links operating indoors or in the atmosphere or deep space shows a good perspective of the technology. There is no doubt that free-space technology is ready for wide practical application. Optical links have several advantages in comparison with radio links, namely high transmission rates and high security. Advance in systems for the detection and tracking of moving objects allowed the development of mobile optical wireless links. This paper is focused on satellite and mobile optical links. Included are basic characteristics of such links and current results of international research projects.

Parametric reduction of Jacobian matrix for fault analysis

The paper deals with a fast numerical method for generating the Jacobian matrix of network function for large analog linear circuits. It is based on the use of cofactor matrices. The computational cost of the Jacobian is comparable to the cost of computing a single network function on selected frequencies. In addition, the method allows performing the reduction of Jacobian matrix based on large-change sensitivities in order to decrease the computational complexity of subsequent testability analysis. An example analysis of a frequency filter is presented.

Memristor models for SPICE simulation of extremely large memristive networks

In order to avoid non-convergence and other numerical problems associated with the simulation of extremely large memristive networks, suitable models of the individual memristors need to be developed. A circuit containing thousands of memristors for finding the shortest path in a complicated maze is a typical example of a numerically challenging simulation. A benchmark circuit for testing the applications of various complexities is used for the transient analysis. It is shown that various commonly used models, from simple behavioral to Pickett models, require special modifications for minimizing the simulation time and improving the convergence issue.