Recai Kiliç

A SC-CNN-Based Chaotic Masking System with Feedback

A secure transmission application of the State Controlled Cellular Neural Network (SC–CNN)-based circuit is presented. Since the SC–CNN-based circuit has feedback connections between the cells, it is potentially very suitable for realizing a chaotic masking system with feedback algorithm. So, we have constructed a chaotic masking system with feedback using the SC–CNN-based circuit. PSpice simulation experiments verify that the proposed SC–CNN-based secure communication system exhibits a good performance for a wide range of amplitude and spectral characteristics of the information signal.

IMPROVED REALIZATION OF MIXED-MODE CHAOTIC CIRCUIT

An improved realization of mixed-mode chaotic circuit which has both autonomous and nonautonomous chaotic dynamics is proposed. Central to this study is inductorless realization of mixed-mode chaotic circuit using FTFN-based inductance simulator. FTFN-based topology used in this realization enables the simulation of ideal floating and grounded inductance. This modification provides an alternative solution to the integration problem of not only mixed-mode chaotic circuit but also other chaotic circuits in the literature using CMOS VLSI technologies. In addition to this major improvement, CFOA-based nonlinear resistor was used in the new realization of mixed-mode chaotic circuit. The usage of CFOA-based nonlinear resistor in the circuits structure reduces the component count and provides buffered and isolated output.

A Comparative Study on Realization of Chua's Circuit: Hybrid Realizations of Chua's Circuit Combining the Circuit Topologies Proposed for Chua's Diode and Inductor Elements

Several realizations of Chuas circuit have been proposed in the literature. The methodologies used in these realizations can be divided into two basic categories. In the first approach, a variety of circuit topologies have been considered for realizing the nonlinear resistor, NR in Chuas circuit. The main idea in the second approach related to the implementation of the circuit is an inductorless realization of Chuas circuit. For this purpose, several circuit topologies serving as a synthetic inductor, i.e. inductance simulator, are used instead of the inductor element in Chuas circuit. In this study, after comparing the circuit topologies proposed for Chuas diode and the inductor element in the circuit, we will present six alternative hybrid realizations of Chuas circuit combining circuit topologies proposed for the nonlinear resistor and the inductor element in the literature. The PSpice simulation experiments confirm that the six alternative hybrid realizations of the circuit exhibit the original chaotic behavior of Chuas circuit.

A Simple CMOS-Based Membership Function Circuit

In this study, design and analysis of a voltage-input current-output simple CMOS-based Membership Function Circuit (MFC) is presented. The proposed MFC is based on simple OTA structure and current-mode maximum circuits. This MFC implements basic four membership functions (trapezoidal, triangle, Z-shape and S-shape). The characteristics (width, height, slope and position) of the implemented membership functions are easily adjustable and it is suitable for current-mode fuzzy hardware. While the circuits membership function characteristics have been confirmed by PSPICE-DC simulations, the circuits transient response has been analyzed applying up to 10 MHz input signals in continuous time by PSPICE Transient simulations.

MIXED-MODE CHAOTIC CIRCUIT AND ITS APPLICATION TO CHAOTIC COMMUNICATION FOR TRANSMISSION OF ANALOG SIGNALS

We present a mixed-mode chaotic circuit which has both autonomous and nonautonomous chaotic circuit dynamics and we show how this mixed-mode chaotic circuit can be utilized in a chaotic communication system for transmitting analog signals. The investigation of static and dynamic analyses of the proposed circuit has been carried out and its chaotic behavior was verified by PSpice simulation experiments. For the transmission of analog signals via mixed-mode chaotic circuit, a well-known chaotic communication system introduced by Itoh et al. was chosen.

A NEW WAY OF GENERATING N-SCROLL ATTRACTORS VIA TRIGONOMETRIC FUNCTION

In this work, a way of generating n-scroll attractors in State Controlled-Cellular Neural Network (SC-CNN) using a trigonometric function is introduced. In spite of the studies on generation of n-scrolls cited in literature, there is no need to add break points in the nonlinear function of the system. Also, wide number of scrolls can be generated by modifying only one variable.

RECONFIGURABLE IMPLEMENTATIONS OF CHUA'S CIRCUIT

Chuas circuit is very suitable as a programmable chaos generator because of its robust nonlinearity. In addition to exhibiting a rich variety of bifurcation and chaos phenomenon, this circuit can be modeled and realized with a fixed main system block and many different nonlinear function blocks such as piecewise-linear function, cubic-like function, piecewise-quadratic function and other trigonometric functions. This paper presents a FPAA (Field Programmable Analog Array) based programmable implementation of Chuas circuit. Nonlinear function blocks used in Chuas circuit are modeled with an FPAA and hence a model can be rapidly changed for realization of other nonlinear functions. In this study, four FPAA-based reconfigurable implementations of Chuas circuit have been realized. Experimental results agree with numerical simulation and results obtained from discrete electronic implementations of Chuas circuit.

TWO IMPULSIVE SYNCHRONIZATION STUDIES USING SC-CNN-BASED CIRCUIT AND CHUA'S CIRCUIT

The impulsive synchronization method has been applied to several well-known chaotic circuits and systems such as Chuas circuit, Lorenz system and hyperchaotic circuit in the literature. In this paper, we also present two impulsive synchronization studies using SC-CNN-based circuit and Chuas circuit. In the first study, we have investigated the impulsive synchronization between two SC-CNN-based circuits. Pspice simulation results show that two SC-CNN-based circuits can be synchronized impulsively via x1 and x2 cell dynamics for different impulse width and impulse period values. And in the second study, we have investigated the impulsive synchronization between SC-CNN-based circuit and Chuas circuit. Pspice simulation results verify that two chaotic circuits, which have identical dynamical systems via appropriate parameter transformations but having quite different hardware implementations, can be synchronized impulsively for different impulse width and impulse period values.

EXPERIMENTAL STUDY OF CFOA-BASED INDUCTORLESS CHUA'S CIRCUIT

The current feedback op amps (CFOAs), with some significant advantages over the conventional op amps, have been used instead of voltage op amps (VOAs) in new implementations of Chuas circuit. In our previous study, after providing a comparative investigation of CFOA-based realizations of Chuas circuit in the literature, we have also presented an alternative inductorless CFOA-based realization of Chuas circuit, and the circuits chaotic behavior by Pspice simulations. In this paper, we investigate CFOA-based Chuas circuit by constructing an experimental setup, and testing the performance of the proposed implementation at different frequencies. Its excellent high frequency performance was experimentally verified.

Cycle Lengths and Correlation Properties of Finite Precision Chaotic Maps

This paper investigates cycle and transient lengths of spatially discretized chaotic maps with respect to different initial condition values. By investigating cycle lengths and their correlation properties using fixed point arithmetic, it is observed that for different initial condition values only a limited number of cycles occur for each resolution and rounding type. Additionally, it is seen that cycles with the same length are actually identical due to intersections between pseudo trajectories. The drawbacks of this situation are demonstrated for chaos based cryptosystems that use initial conditions as key. It is shown that highly correlated outputs for different initial conditions cause serious security vulnerabilities, although the statistical tests indicate otherwise. Finally, correlations in the perturbed systems are discussed.