Showing papers in "IEEE Transactions on Circuits and Systems I-regular Papers in 2001"
TL;DR: Using the well-known principles in the cryptanalysis it is shown that these ciphers do not behave worse than the standard ones, opening in this way a novel approach to the design of block encryption cipher.
Abstract: This paper is devoted to the analysis of the impact of chaos-based techniques on block encryption ciphers. We present several chaos based ciphers. Using the well-known principles in the cryptanalysis we show that these ciphers do not behave worse than the standard ones, opening in this way a novel approach to the design of block encryption ciphers.
638 citations
TL;DR: This paper derives explicit formulas for the mismatch effects when all of offset, gain and timing mismatches exist together in the time-interleaved ADC system and discusses the bandwidth mismatch effect.
Abstract: A time-interleaved A-D converter (ADC) system is an effective way to implement a high-sampling-rate ADC with relatively slow circuits. In the system, several channel ADCs operate at interleaved sampling times as if they were effectively a single ADC operating at a much higher sampling rate. However, mismatches such as offset, gain mismatches among channel ADCs as well as timing skew of the clocks distributed to them degrade S/N of the ADC system as a whole. This paper analyzes the channel mismatch effects in the time-interleaved ADC system. Previous analysis showed the effect for each mismatch individually, however in this paper we derive explicit formulas for the mismatch effects when all of offset, gain and timing mismatches exist together. We have clarified that the gain and timing mismatch effects interact with each other but the offset mismatch effect is independent from them, and this can be seen clearly in frequency domain. We also discuss the bandwidth mismatch effect. The derived formulas can be used for calibration algorithms to compensate for the channel mismatch effects.
512 citations
TL;DR: In this paper, the conditions under which this effect occurs, and stability of this bias point are investigated, and verified experimentally investigating the temperature behavior of a simple voltage reference circuit realized in 0.35 /spl mu/m CMOS process.
Abstract: Mutual compensation of mobility and threshold voltage temperature variations may result in a zero temperature coefficient bias point of a MOS transistor. The conditions under which this effect occurs, and stability of this bias point are investigated. Possible applications of this effect include voltage reference circuits and temperature sensors with linear dependence of voltage versus temperature. The theory is verified experimentally investigating the temperature behavior of a simple voltage reference circuit realized in 0.35 /spl mu/m CMOS process.
504 citations
TL;DR: This study demonstrates that a careful selection of fractal dimension algorithm is required for specific applications, and the most common methods of estimating the fractaldimension of biomedical signals directly in the time domain are analyzed and compared.
Abstract: The fractal dimension of a waveform represents a powerful tool for transient detection. In particular, in analysis of electroencephalograms and electrocardiograms, this feature has been used to identify and distinguish specific states of physiologic function. A variety of algorithms are available for the computation of fractal dimension. In this study, the most common methods of estimating the fractal dimension of biomedical signals directly in the time domain (considering the time series as a geometric object) are analyzed and compared. The analysis is performed over both synthetic data and intracranial electroencephalogram data recorded during presurgical evaluation of individuals with epileptic seizures. The advantages and drawbacks of each technique are highlighted. The effects of window size, number of overlapping points, and signal-to-noise ratio are evaluated for each method. This study demonstrates that a careful selection of fractal dimension algorithm is required for specific applications.
444 citations
TL;DR: Based on the Lyapunov stability theorem as well as some facts about the positive definiteness and inequality of matrices, a new sufficient condition is presented for the existence of a unique equilibrium point and its global asymptotic stability for delayed CNNs as mentioned in this paper.
Abstract: Based on the Lyapunov stability theorem as well as some facts about the positive definiteness and inequality of matrices, a new sufficient condition is presented for the existence of a unique equilibrium point and its global asymptotic stability for delayed CNNs. This condition imposes constraints on the feedback matrices independent of the delay parameter. This condition is less restrictive than that given in earlier references.
330 citations
TL;DR: In this article, a chaotic piecewise-linear one-dimensional (PL1D) map is used as a random number generator (RNG) to find parameter values for which a generating partition is Markov and the RNG behaves as a Markov information source.
Abstract: This paper and its companion (Part II) are devoted to the analysis of the application of a chaotic piecewise-linear one-dimensional (PL1D) map as random number generator (RNG). Piecewise linearity of the map enables us to mathematically find parameter values for which a generating partition is Markov and the RNG behaves as a Markov information source, and then to mathematically analyze the information generation process and the RNG. In the companion paper we discuss practical aspects of our chaos-based RNGs.
329 citations
TL;DR: Frequency-compensation techniques of single-, two- and three-stage amplifiers based on Miller pole splitting and pole-zero cancellation are re-analyzed and several proposed methods to improve the published topologies are given.
Abstract: Frequency-compensation techniques of single-, two- and three-stage amplifiers based on Miller pole splitting and pole-zero cancellation are re-analyzed. The assumptions made, transfer functions, stability criteria, bandwidths, and important design issues of most of the reported topologies are included. Several proposed methods to improve the published topologies are given. In addition, simulations and experimental results are provided to verify the analysis and to prove the effectiveness of the proposed methods.
315 citations
TL;DR: The authors present their opinion and research results collected during the last ten years on the conjunction of chaos and cryptography and provide some pointers to a comprehensive and careful evaluation of the cryptographical properties of chaotic systems.
Abstract: In this paper, the authors present their opinion and research results collected during the last ten years on the conjunction of chaos and cryptography. Special consideration is taken to show some general critical points and limitations of this approach and to provide some pointers to a comprehensive and careful evaluation of the cryptographical properties of chaotic systems.
310 citations
TL;DR: This paper finds optimum parameters that give an RNG with lowest redundancy and maximum margin against parasitic attractors, and estimates that the output bit rate of the RNG is substantially higher than the outputbit rate of RNGs available on the market.
Abstract: This paper and its companion (see ibid., vol. 48, p. 281-88, 2001) are devoted to to the analysis of the application of a chaotic piecewise-linear one-dimensional (PL1D) map as Random Number Generator (RNG). In Part I, me have mathematically analyzed the information generation process of a class of PL1D maps. In this paper, we find optimum parameters that give an RNG with lowest redundancy and maximum margin against parasitic attractors. Further, the map is implemented in a 0.8 /spl mu/m standard CMOS process utilizing switched current techniques. Post-layout circuit simulations of the RNG indicate no periodic attractors over variations in temperature, power supply and process conditions, and maximum redundancy of 0.4%. We estimate that the output bit rate of our RNG is 1 Mbit/s, which is substantially higher than the output bit rate of RNGs available on the market.
298 citations
TL;DR: In this article, it is demonstrated that n-scroll attractors can be generated using a simple sine or cosine function and a guideline is given so that a different number of scrolls can be designed easily by modifying two variables in the function.
Abstract: A new approach for generating n-scroll attractors is introduced. It is demonstrated that n-scroll attractors can be generated using a simple sine or cosine function. A guideline is given so that a different number of scrolls can be designed easily by modifying two variables in the function. An electronic circuit is also designed for the implementation and the observation of a 9-scroll attractor is reported for the first time.
289 citations
TL;DR: In this paper, a two-phase voltage doubler and a multiphase voltage multiplier are discussed and design guidelines for the desired voltage and power levels are discussed, as well as the area requirements, the voltage gain, and the power level.
Abstract: A novel organization of switched capacitor charge pump circuits based on voltage doubler structures is presented in this paper. Each voltage doubler takes a dc input and outputs a doubled dc voltage. By cascading n voltage doublers the output voltage increases up to 2/sup n/ times. A two-phase voltage doubler and a multiphase voltage doubler (MPVD) structures are discussed and design considerations are presented. A simulator working in the Q-V realm was used for simplified circuit level simulation. In order to evaluate the power delivered by a charge pump, a resistive load is attached to the output of the charge pump and an equivalent capacitance is evaluated. A comparison of the voltage doubler circuits with Dickson charge pump and Makowski's voltage multiplier is presented in terms of the area requirements, the voltage gain, and the power level. This paper also identifies optimum loading conditions for different configurations of the charge pumps. Design guidelines for the desired voltage and power levels are discussed. A two-stage MPVD was fabricated using MOSIS 2.0-/spl mu/m CMOS technology. It was designed with internal frequency regulation to reduce power consumption under no load condition.
TL;DR: In this paper, the authors make a qualitative study of the dynamics of a network of diffusively coupled identical systems and derive conditions on the systems and on the coupling strength between the systems that guarantee the global synchronization of the systems.
Abstract: In this paper, we make a qualitative study of the dynamics of a network of diffusively coupled identical systems. In particular, we derive conditions on the systems and on the coupling strength between the systems that guarantee the global synchronization of the systems. It is shown that the notion of "minimum phaseness" of the individual systems involved is essential in ensuring synchronous behavior in the network when the coupling exceeds a certain computable threshold. On the other hand, it is shown that oscillatory behavior may arise in a network of identical globally asymptotically stable systems in case the isolated systems are nonminimum phase. In addition, we analyze the synchronization or nonsynchronization of the network in terms of its topology; that is, what happens if either the number of couplings and/or systems increases? The results are illustrated by computer simulations of coupled chaotic systems like the Rossler system and the Lorenz system.
TL;DR: In this paper, two generic classes of chaotic oscillators comprising four different configurations are constructed based on the simplest possible abstract models of generic second-order RC sinusoidal oscillators that satisfy the basic condition for oscillation and the frequency of oscillation formulas.
Abstract: Two generic classes of chaotic oscillators comprising four different configurations are constructed. The proposed structures are based on the simplest possible abstract models of generic second-order RC sinusoidal oscillators that satisfy the basic condition for oscillation and the frequency of oscillation formulas. By linking these sinusoidal oscillator engines to simple passive first-order or second-order nonlinear composites, chaos is generated and the evolution of the two-dimensional sinusoidal oscillator dynamics into a higher dimensional state space is clearly recognized. We further discuss three architectures into which autonomous chaotic oscillators can be decomposed. Based on one of these architectures we classify a large number of the available chaotic oscillators and propose a novel reconstruction of the classical Chua's circuit. The well-known Lorenz system of equations is also studied and a simplified model with equivalent dynamics, but containing no multipliers, is introduced.
TL;DR: In this article, some novel criteria for the global robust stability of a class of interval Hopfield neural networks with constant delays are given, based on several new Lyapunov functionals.
Abstract: In this paper, some novel criteria for the global robust stability of a class of interval Hopfield neural networks with constant delays are given. Based on several new Lyapunov functionals, delay-independent criteria are provided to guarantee the global robust stability of such systems. For conventional Hopfield neural networks with constant delays, some new criteria for their global asymptotic stability are also easily obtained. All the results obtained are generalizations of some recent results reported in the literature for neural networks with constant delays. Numerical examples are also given to show the correctness of the analysis.
TL;DR: These criteria are of theoretical and applicable important significance in signal processing, especially in speed detection of moving objects, processing of moving images and the design of networks since they possess infinitely adjustable real parameters.
Abstract: This work presents a set of criteria on the global asymptotic stability of delayed cellular neural networks (DCNN) by constructing suitable Lyapunov functionals, introducing ingeniously real parameters w/sub i/>0, /spl alpha//sup *//sub ij/, /spl beta//sup *//sub ij/, /spl eta//sup *//sub ij/, /spl zeta//sup *//sub ij/, /spl alpha//sub ij/, /spl beta//sub ij/, /spl eta//sub ij/, /spl zeta//sub ij//spl isin/R with /spl alpha//sup *//sub ij/+/spl beta//sup *//sub ij/=1, /spl alpha//sub ij/+/spl beta//sub ij/=1, /spl eta//sup *//sub ij/+/spl zeta//sup *//sub ij/=1, /spl eta//sub ij/+/spl zeta//sub ij/=1(i, j=1, 2, ..., n) and combining with elementary inequality technique 2ab/spl les/a/sup 2/+b/sup 2/. These criteria are of theoretical and applicable important significance in signal processing, especially in speed detection of moving objects, processing of moving images and the design of networks since they possess infinitely adjustable real parameters. This result is also discussed from the point of view of its relationship to earlier results.
TL;DR: A multilevel version of the differential chaos shift keying (DCSK) telecommunication system, based upon the generation of an orthogonal basis of chaotic functions, that is characterized by an increased data rate with respect to DCSK, with the same bandwidth occupation.
Abstract: In this brief, we propose a multilevel version of the differential chaos shift keying (DCSK) telecommunication system. The scheme, that we call quadrature chaos shift keying (QCSK), is based upon the generation of an orthogonal basis of chaotic functions. QCSK is characterized by an increased data rate with respect to DCSK, with the same bandwidth occupation. The price for the performance enhancement is the increased complexity of both the transmitter and the receiver.
TL;DR: Some of the less known aspects of sampling are presented, with special emphasis on non bandlimited signals, pointwise stability of reconstruction, and reconstruction from nonuniform samples.
Abstract: The sampling theorem is one of the most basic and fascinating topics in engineering sciences. The most well-known form is Shannon's uniform-sampling theorem for bandlimited signals. Extensions of this to bandpass signals and multiband signals, and to nonuniform sampling are also well-known. The connection between such extensions and the theory of filter banks in DSP has been well established. This paper presents some of the less known aspects of sampling, with special emphasis on non bandlimited signals, pointwise stability of reconstruction, and reconstruction from nonuniform samples. Applications in multiresolution computation and in digital spline interpolation are also reviewed.
TL;DR: In this article, the authors present a mathematical formulation and numerical methods for analyzing a broad class of such circuits or systems, where the key idea is to use multiple time variables, which enable signals with widely separated rates of variation to be represented efficiently.
Abstract: Widely separated time scales arise in many kinds of circuits, e,g., switched-capacitor filters, mixers, switching power converters, etc. Numerical solution of such circuits is often difficult, especially when strong nonlinearities are present. In this paper, the author presents a mathematical formulation and numerical methods for analyzing a broad class of such circuits or systems. The key idea is to use multiple time variables, which enable signals with widely separated rates of variation to be represented efficiently. This results in the transformation of differential equation descriptions of a system to partial differential ones, in effect decoupling different rates of variation from each other. Numerical methods can then be used to solve the partial differential equations (PDEs). In particular, time-domain methods can be used to handle the hitherto difficult case of strong nonlinearities together with widely separated rates of signal variation. The author examines methods for obtaining quasiperiodic and envelope solutions, and describes how the PDE formulation unifies existing techniques for separated-time-constant problems. Several applications are described. Significant computation and memory savings result from using the new numerical techniques, which also scale gracefully with problem size.
TL;DR: In this article, the optimal power flow with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF.
Abstract: The computation of an optimal operation point in power systems is a nonlinear optimization problem in functional space, which is not easy to deal with precisely, even for small-scale power systems. On the other hand, the emergence of competitive power markets makes optimal power flow (OPF) with transient stability constraints increasingly important because the conventionally heuristic evaluation for the operation point can produce a discrimination among market players in the deregulated power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large-scale power systems with a large number of transient stability constraints. This paper also derives the Jacobian matrices of the transient stability constraints and gives two computation algorithms based on the relaxation scheme. The numerical simulation verified the effectiveness of the proposed approach.
TL;DR: In this work, a finite difference formulation is used to simulate large networks and several orders of magnitude in speedup over matrix-based methods are obtained.
Abstract: In this work, a finite difference formulation is used to simulate large networks. The method makes use or introduces reactive latency in all branches and nodes of a circuit to generate update algorithms for the voltage and current quantities. A criterion is established that guarantees the stability of the algorithm for specified choices of the time step. Because of its linear numerical complexity, several orders of magnitude in speedup over matrix-based methods are obtained. Nonlinear networks can also be simulated by the formulation. Several comparisons are made with standard simulators in order to evaluate the accuracy and efficiency of the algorithm. In all cases that satisfy the stability criterion, good agreements with established techniques are obtained.
TL;DR: In this article, a one-dimensional iterative chaotic map with infinite collapses within a symmetrical region was proposed, and the stability of fixed points and that around the singular point were analyzed.
Abstract: A one-dimensional iterative chaotic map with infinite collapses within symmetrical region [-1, O)/spl cup/(O, +1] is proposed. The stability of fixed points and that around the singular point are analyzed. Higher Lyapunov exponents of proposed map show stronger chaotic characteristics than some iterative and continuous chaotic models usually used. There exist inverse bifurcation phenomena and special main periodic windows at certain positions shown in the bifurcation diagram, which can explain the generation mechanism of chaos. The chaotic model with good properties can be generated if choosing the parameter of the map properly. Stronger inner pseudorandom characteristics can also be observed through /spl chi//sup 2/ test on the supposition of even distribution. This chaotic model may have many advantages in practical use.
TL;DR: A more general model of CNNs with unbounded delay is proposed, which may have potential applications in processing such motion related phenomena as moving images, and global convergence properties of this model are studied.
Abstract: Cellular neural networks (CNNs) have been successfully applied in many areas such as classification of patterns, image processing, associative memories, etc. Since they are inherently local in nature, they can be easily implemented in very large scale integration. In the processing of static images, CNNs without delay are often applied whereas in the processing of moving images, CNNs with delay have been found more suitable. This paper proposes a more general model of CNNs with unbounded delay, which may have potential applications in processing such motion related phenomena as moving images, and studies global convergence properties of this model. The dynamic behaviors of CNNs, especially their convergence properties, play important roles in applications. This paper: (1) introduces a class of CNNs with unbounded delay; (2) gives some interesting properties of a network's output function; (3) establishes relationships between a network's state stability and its output stability; and (4) obtains simple and easily checkable conditions for global convergence by functional differential equation methods.
TL;DR: It is shown that MEMS alone can be used to build a sophisticated information processing system (U.S. provisional patent 60/178,654) and a theoretical possibility of using MEMS oscillators to build an oscillatory neurocomputer having autocorrelative associative memory is investigated.
Abstract: We combine here two well-known and established concepts: microelectromechanical systems (MEMS) and neurocomputing. First, we consider MEMS oscillators having low amplitude activity and we derive a simple mathematical model that describes nonlinear phase-locking dynamics in them. Then, we investigate a theoretical possibility of using MEMS oscillators to build an oscillatory neurocomputer having autocorrelative associative memory. The neurocomputer stores and retrieves complex oscillatory patterns in the form of synchronized states with appropriate phase relations between the oscillators. Thus, we show that MEMS alone can be used to build a sophisticated information processing system (U.S. provisional patent 60/178,654).
TL;DR: A pseudo-chaotic modulation suitable for ultrawide-bandwidth impulse-radio communication systems, based upon controlling the symbolic dynamics of a chaotic map for encoding the digital information to be transmitted.
Abstract: In this paper, we propose a pseudo-chaotic modulation suitable for ultrawide-bandwidth impulse-radio communication systems. The coding scheme is based upon controlling the symbolic dynamics of a chaotic map for encoding the digital information to be transmitted. The pseudo-chaotic time hopping enhances the spread-spectrum characteristics of the system, by removing most periodic components from the transmitted signal. A maximum-likelihood detector for the proposed scheme is presented and its scalability features are illustrated. Finally, theoretical performance bounds for both soft and hard Viterbi decoding are derived and compared with the simulation results.
TL;DR: In this article, the stability of boost and buck-boost DC-DC power converters under proportional plus integral (PI) control is discussed and a novel PI control configuration is proposed, which reveals the effect that the right-hand side zero has on PI control stability.
Abstract: The stability of boost and buck-boost DC-DC power converters under proportional plus integral (PI) control is discussed in this paper. A novel PI control configuration is proposed, which reveals the effect that the right-hand-side zero has on PI control stability. Tuning rules in terms of the converter parameters are derived and illustrated via numerical and experimental simulations.
TL;DR: In this paper, the authors proposed a new mechanism for interarea electric power system oscillations in which two oscillatory modes interact near a strong resonance to cause one of the modes to subsequently become unstable.
Abstract: We suggest a new mechanism for interarea electric power system oscillations in which two oscillatory modes interact near a strong resonance to cause one of the modes to subsequently become unstable. The possibility of this mechanism for oscillations is shown by theory and computational examples. Theory suggests that passing near strong resonance can be expected in general power system models. The mechanism for oscillations is illustrated in 3- and 9-bus examples with detailed generator models.
TL;DR: In this paper, the authors describe the bifurcation phenomena of a system of parallel-connected dc/dc buck converters and provide useful information for the design of stable current sharing in a master-slave configuration.
Abstract: This paper describes the bifurcation phenomena of a system of parallel-connected dc/dc buck converters. The results provide useful information for the design of stable current sharing in a master-slave configuration. Computer simulations are performed to capture the effects of variation of some chosen parameters on the qualitative behavior of the system. These are summarized in a series of bifurcation diagrams. In particular, it is found that while variation of the voltage feedback gains leads to standard period-doubling bifurcation, variation of the current sharing ratio leads to border collision bifurcation. Analysis is presented to establish the possibility of the bifurcation phenomena and to locate the current sharing ratio at which border collision occurs.
TL;DR: A new approach to communication with chaotic signals, which demonstrates good performance in the presence of channel distortions, and the possibilities of multiuser communication using CPPM and its advantages over standard communication techniques are discussed.
Abstract: Utilization of chaotic signals for covert communications remains a very promising practical application. Multiple studies indicate that the major shortcoming of recently proposed chaos-based communication schemes is their susceptibility to noise and distortions in communication channels. In this paper, we review a new approach to communication with chaotic signals, which demonstrates good performance in the presence of channel distortions. This communication scheme is based upon chaotic signals in the form of pulse trains where intervals between the pulses are determined by chaotic dynamics of a pulse generator. The pulse train with chaotic inter-pulse intervals is used as a carrier. Binary information is modulated onto this carrier by the pulse position modulation method, such that each pulse is either left unchanged or delayed by a certain time, depending on whether "0" or "1" is transmitted. By synchronizing the receiver to the chaotic-pulse train we can anticipate the timing of pulses corresponding to "0" and "1" and thus can decode the transmitted information. Based on the results of theoretical and experimental studies we discuss the basic design principles for the chaotic-pulse generator, its synchronization, and the performance of the chaotic-pulse communication scheme in the presence of channel noise and filtering. We also discuss the possibilities of multiuser communication using CPPM and its advantages over standard communication techniques.
IBM1
TL;DR: In this article, it has been shown that synchronization can be improved by using nonlocal connections or introducing random connections in arbitrary coupled arrays of nonlinear systems, and several well-known stability conditions to obtain synchronization criteria in arbitrarily coupled arrays: the passivity criterion, the circle criterion and a result on observer design of Lipschitz nonlinear system.
Abstract: It has been shown that synchronization between two nonlinear systems can be studied as a control-theory problem. We show that this relationship can he extended to synchronization in arbitrary coupled arrays of nonlinear systems. In particular, we use several well-known stability conditions to obtain synchronization criteria in arbitrarily coupled arrays: the passivity criterion, the circle criterion and a result on observer design of Lipschitz nonlinear systems. We also study how these synchronization criteria depend on the topology of the coupled networks. In particular, we show that synchronization is improved by using nonlocal connections or introducing random connections.
TL;DR: By factorizing the WDFT matrix, this paper proposes an exact computation scheme for finite sequences using less number of operations than a direct computation.
Abstract: In this paper, we advance the concept of warped discrete-Fourier transform (WDFT), which is the evaluation of frequency samples of the z-transform of a finite-length sequence at nonuniformly spaced points on the unit circle obtained by a frequency transformation using an allpass warping function. By factorizing the WDFT matrix, we propose an exact computation scheme for finite sequences using less number of operations than a direct computation. We discuss various properties of WDFT and the structure of the factoring matrices. Examples of WDFT for first- and second-order allpass functions is also presented. Applications of WDFT included are spectral analysis, design of tunable FIR filters, and design of perfect reconstruction filterbanks with nonuniformly spaced passbands of filters in the bank. WDFT is efficient to resolve closely spaced sinusoids. Tunable FIR filters may be designed from FIR prototypes using WDFT. In yet another application, warped PR filterbanks are designed using WDFT and are applied for signal compression.