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Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on

Issue 5 • Date May 2001

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Displaying Results 1 - 18 of 18
  • Stochastic reliable control of a class of uncertain time-delay systems with unknown nonlinearities

    Publication Year: 2001 , Page(s): 646 - 650
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    This paper investigates the robust reliable control problem for a class of nonlinear time-delay stochastic systems. The system under study involves stochastics, state time-delay, parameter uncertainties, possible actuator failures and unknown nonlinear disturbances, which are often encountered in practice and the sources of instability. Our attention is focused on the design of linear state feedback memoryless controllers such that, for all admissible uncertainties as well as actuator failures occurring among a prespecified subset of actuators, the plant remains stochastically exponentially stable in mean square, independent of the time delay. Sufficient conditions are proposed to guarantee the desired robust reliable exponential stability despite possible actuator failures, which are in terms of the solutions to algebraic Riccati inequalities. An illustrative example is exploited to demonstrate the applicability of the proposed design approach View full abstract»

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  • Maximum likelihood approaches for noncoherent communications with chaotic carriers

    Publication Year: 2001 , Page(s): 533 - 542
    Cited by:  Papers (16)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    This paper deals with two problems. The first one is the noise decontamination of chaotic carriers using a maximum likelihood approach, the second is the design of communications schemes with chaotic carriers. After presenting improvements of the noise decontamination algorithms, we apply them in communication schemes. Experimental evidences show competitive capabilities of the proposed schemes with respect to the existing chaos-based modulation-demodulation techniques. In our approach we assume that the dynamics of the carriers are known in advance View full abstract»

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  • Multiplierless digital learning algorithm for cellular neural networks

    Publication Year: 2001 , Page(s): 630 - 635
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    A new learning algorithm is proposed for space-varying cellular neural networks, used to implement associative memories. The algorithm exhibits some peculiar features which make it very attractive: the finite precision of connection weights is automatically taken into account as a design constraint; no multiplication is needed for weight computation; learning can be implemented in fixed point digital hardware or simulated on a digital computer without numerical errors View full abstract»

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  • Analyzing circuits with widely separated time scales using numerical PDE methods

    Publication Year: 2001 , Page(s): 578 - 594
    Cited by:  Papers (85)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    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 View full abstract»

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  • Application of cubic constraint approximation in the recursive design of FIR filters subject to output envelope constraints

    Publication Year: 2001 , Page(s): 651 - 656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB) |  | HTML iconHTML  

    The smoothing function used in the constraint approximation plays an important role in the adaptive envelope-constrained (EC) filtering algorithms presented. In this paper, a cubic smoothing function is proposed to implement the constraint approximation and the simplified line search technique is introduced to speed up the convergence rate. It is shown that the performance of the adaptive EC filtering algorithms can be greatly improved due to the use of the cubic constraint approximation and simplified line searches. In particular, the second-order convergence is established for the Newton-Raphson type algorithm. Numerical results are included to illustrate the effectiveness of these adaptive EC filtering algorithms View full abstract»

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  • On the best quadratic approximation of nonlinear systems

    Publication Year: 2001 , Page(s): 595 - 602
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB) |  | HTML iconHTML  

    We present a new approach to the approximation of the input-output map of a nonlinear system which transforms stochastic signals. The proposed approach is based on the best approximation technique with a specific second degree operator acting on the observed input signal. We show that the obtained approximant minimizes the mean squared error between a desired output signal and the output signal of the approximating system. The strict justification of the proposed approach is provided including theorems on the error representation associated with the approximation process. Three broad extensions of the method are outlined. The simulations demonstrate the efficiency of the proposed technique with am example of its application to image processing View full abstract»

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  • On locally regular cellular neural networks

    Publication Year: 2001 , Page(s): 513 - 520
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    Since their inception, cellular neural networks (CNNs) have been divided into two classes, namely the uncoupled CNNs which do not have intercell feedback and their coupled counterparts which have feedback. The uncoupled class is fully analytically tractable and well understood, whereas the coupled class may exhibit complex dynamics prohibiting an exact analysis. In this paper, the author proposes a different dichotomy by defining the class of locally regular (LR) CNNs which comprises uncoupled and the most commonly used coupled networks. He shows that there is a unifying theory for the design and analysis of this class, and that LR CNNs meet all the requirements for a successful implementation in analog VLSI hardware. In particular, they can be made highly robust against deviations of both template parameters and cells' time constants, and they operate correctly on different classes of CNN chips, including sampled-data implementations and networks with high-gain or hardlimiting output nonlinearity. Furthermore, they can be numerically simulated very efficiently, since the integration step size may be chosen as large as the cell's time constant View full abstract»

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  • Stability analysis of 2-D digital filters described by the Fornasini-Marchesini second model using overflow nonlinearities

    Publication Year: 2001 , Page(s): 612 - 617
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB) |  | HTML iconHTML  

    This paper discusses new criteria for the global asymptotic stability of two-dimensional (2-D) digital filters described by the Fernasini-Marchesini second local state-space model subject to overflow nonlinearities. For saturation and triangular arithmetics, the presented approach will always lead to a larger overflow stability region in the parameter-space, as compared to a recent criterion due to Liu; for other overflow nonlinearities, new criteria may generally provide results as supplement to those obtainable from Liu's criterion. The approach leads to a more relaxed saturation overflow stability condition, as compared to a recent criterion due to Hinamoto. Finally, the approach is extended to the situations involving quantization nonlinearities View full abstract»

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  • Generating chaos via x|x|

    Publication Year: 2001 , Page(s): 636 - 641
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    This paper investigates the role of the function x|x| as a chaos generator in nonautonomous systems. A Duffing-like nonautonomous oscillator is used for illustration. It is rigorously proven via the Melnikov function method that this particular quadratic function induces Smale horseshoes to the Duffing-like system. Moreover, its physical meaning as an energy function is demonstrated, which provides a critical value for the emergence of chaos. Simulations with bifurcation analysis are given for better understanding of the underlying dynamics View full abstract»

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  • Design and realization of an FPGA-based generator for chaotic frequency hopping sequences

    Publication Year: 2001 , Page(s): 521 - 532
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    Chaos-based pseudonoise (PN) sequences for spread spectrum (SS) communications ranks amongst the most promising applications of chaos to communications. This paper deals with the design and realization of a chaotic frequency hopping (FH) sequence generator that is compatible with current FH/SS technologies. A simplistic generator architecture adopting nonlinear auto-regressive (AR) filter structures is proposed, which is based on the random sequence model and the metric entropy criterion for generation of random sequences. Conventional PN sequences are employed to perturb the generator such that the resulted sequences fulfil the FH requirements on period and family size. In addition, a chaos-based FH sequence generator prototype is realized in field programmable gate arrays (FPGAs) and various tests are performed. The generator produces long period FH sequences with uniform distribution over the available bandwidth, large linear complexity as well as suboptimal Hamming correlation properties. Bit error rate (BER) performance of the chaos-based asynchronous FH/CDMA system is evaluated by means of computer simulation. These results suggest that the cost-effective and well-performing generator has the potential to be incorporated into existing FH systems View full abstract»

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  • A geometrical interpretation of the Chinese remainder theorem and its applications to MD signal processing

    Publication Year: 2001 , Page(s): 603 - 605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    This work introduces a geometrical interpretation of the Chinese remainder theorem (CRT) which is novel and which can be profitably used in the field of multidimensional signal processing. The practical application of the proposed result in some multidimensional signal processing procedures is demonstrated View full abstract»

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  • Current-feedback amplifiers versus voltage operational amplifiers

    Publication Year: 2001 , Page(s): 617 - 623
    Cited by:  Papers (40)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    This paper compares the main performance parameters of the current feedback opamp (CFOA) with those of a conventional voltage opamp (VOA). To make the comparison effective, a folded cascode VOA is considered (which is characterized by similar features and topology) and the same power consumption was assumed for both amplifiers. The work confirms that the CFOA can provide higher bandwidth, albeit at the expense of reduced loop gain. Noise performance is also analyzed. Input-referred noise generators are determined and some peculiar CFOA features, having no equivalence in conventional opamps, have been highlighted. It is shown that the CFOA has slightly lower noise voltage, but a larger noise current. Simulations are given which are in very good agreement with expected results View full abstract»

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  • On consistent initial conditions for circuit's DAEs with higher index

    Publication Year: 2001 , Page(s): 606 - 612
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In this paper, we study efficient numerical methods for obtaining consistent initial conditions for systems of differential-algebraic equations (DAEs) with higher index arising e.g., from electronic circuits. We show that the class of Gear's backward differentiation formulas, unlike other multi-step techniques, are useful means for obtaining consistent initial conditions when carefully implemented. The new method does not employ burdensome techniques such as the QR factorization or singular value decomposition which require the order of ns operations, where n is the size of the system. Therefore, these techniques are prohibitive for large circuits. The numerical experiments suggest that the method works reliably even for index-3 DAEs. Furthermore, the method is not only restricted to initial value problems for DAEs but can also be applied to solvers for boundary value problems based on shooting techniques View full abstract»

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  • On the poles and zeros of linear, time-varying systems

    Publication Year: 2001 , Page(s): 565 - 577
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Definition of poles and zeros are presented for continuous-time, linear, time-varying systems. For a linear, time-varying state equation, a set of time-varying poles defines a stability-preserving variable change relating the original state equation to an upper triangular state equation. A zero is a function of time corresponding to an exponential input whose transmission to the output is blocked. Both definitions are shown to be generalizations of existing definitions of poles and zeros for linear, time-varying systems and are consistent with the definitions for linear, time-invariant systems. A computation procedure is presented using a QR decomposition of the transition matrix for the state equation. A numerical example is given to illustrate this procedure View full abstract»

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  • Making a continuous-time minimum-phase system chaotic by using time-delay feedback

    Publication Year: 2001 , Page(s): 641 - 645
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    A time-delay feedback control approach is developed for making a continuous-time minimum-phase system chaotic. The approach is based on the geometric control theory and a suitable approximate relationship between a time-delay differential equation and a discrete map. If the original system has an exponentially stable equilibrium point, then a simple time-delay output-feedback controller with arbitrarily small amplitude can drive the system chaotic. Two different types of simulation examples are included for demonstration View full abstract»

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  • Tools for designing chaotic systems for secure random number generation

    Publication Year: 2001 , Page(s): 552 - 564
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB) |  | HTML iconHTML  

    It is well known that the output of chaotic systems can be completely predicted from the exert knowledge of the initial conditions. However, their extreme sensitivity to initial conditions lends itself to being exploited for generation of random numbers. This work explores this possibility and gives a simple circuit arrangement, together with the tools necessary to assess the random characteristics of its output. The fact that the statistical characteristics of a chaotic system can be determined through spectral analysis of an evolution operator is shown. Numerical techniques for practical estimation of this operator are presented. Special attention is paid to robustness both with respect to numerical approximation and circuit tolerances. Error bounds of practical significance are given. One example of the proposed method and results is given. The results presented are valid for generic sampled chaotic systems and can also be used for applications other than random number generation, e.g., chaotic communications View full abstract»

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  • Energy-based control of numerical errors in time-domain simulation of dynamic circuits

    Publication Year: 2001 , Page(s): 543 - 551
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    In this paper, we consider the accuracy of integration algorithms such as the implicit Euler and the trapezoidal methods, which are largely employed in the time domain circuit analysis. These algorithms require one to make hypotheses on the intersample shape and on the “energy content” of the sampled waveforms. For example, the implicit Euler algorithm supposes functions to be piecewise constant, When these hypotheses are violated, some errors are introduced by the integration process into the solution waveform. We consider the energy of the sampled functions, and through energy balance equations, estimate the accuracy of the integration algorithm. Furthermore, we propose an implicit algorithm to determine an adequate integration time step during numerical time domain analysis. This algorithm is based on a global energy balance equation and not on the conventional estimation of the local truncation error. It avoids the “cut and try” mechanism used in SPICE to determine the time step that satisfies the desired error tolerance View full abstract»

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  • Reconstructing the keystream from a chaotic encryption scheme

    Publication Year: 2001 , Page(s): 624 - 630
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    A new technique of secure communication was developed which uses a synchronizing chaotic communication channel to transmit an encrypted message. The important feature of this system is that the keystream used in the encryption stage is not transmitted but may be dynamically reconstructed by the intended receiver. Since an additional level of encryption is employed, it was claimed that an eavesdropper may have limited success using nonlinear dynamic (NLD) forecasting techniques to extract the message. In this paper we show that there may be sufficient geometric information in the transmission to extract an estimate of the keystream (although it could require a difficult search) as well as characteristics of the encrypting function. Consequently, it may be possible to recover the hidden message with good accuracy View full abstract»

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