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Circuits and Systems, IEEE Transactions on

Issue 11 • Date Nov. 1991

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Displaying Results 1 - 25 of 26
  • Counterexample and correction to a recent result on robust stability of a diamond of complex polynomials

    Page(s): 1370 - 1373
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (323 KB)  

    In a recent paper by N.K. Bose and K.D. Kim (see ibid., vol.36, p.1165-74, 1989), a main focal point is (strict left half plane) stability of a family of polynomials having complex coefficients with their real and imaginary parts each lying in a diamond. Subsequently, Bose and Kim provide a list of 16 distinguished edges of the diamond and claim that stability of these critical edges is both necessary and sufficient for stability of the entire family. In the present work, it is shown via counterexample that these 16-edge polynomials are wrongly selected. A different set of 16 edges that suffice is introduced.<> View full abstract»

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  • Reply to 'Counterexample and correction to a recent result on robust stability of a diamond of complex polynomials' by H. I. Kang et al. (Nov. 1991 1370-3)

    Page(s): 1397 - 1400
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    The authors show how a modification of their approach (see ibid., vol.36, p.1168-74, 1989) leads to the stability edges, correctly identified in the above-named work (see ibid., vol.38, p.1370-3, 1991) by K.I. Kang et al., for a diamond of complex polynomials. The feasibility of reduction from 32 to 16 distinguished edges is facilitated via use of Foster's (complex) reactance theorem in network theory.<> View full abstract»

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  • Comments, with reply, on "Generation of OTA-C filter structures from active RC filter structures" by R.V. Ananda Mohan

    Page(s): 1401 - 1402
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    Comments on the above-named work (see ibid., vol.37, p.656-60, 1990) are presented. For the VLSI implementations of high-frequency analog filters, reasons for, caution in the use of OTA-C (operational transconductance amplifier) filters generated from active RC filters are given. An author's reply is included.<> View full abstract»

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  • Comments on "On hidden nodes in neural nets" by G. Mirchandani and W. Cao

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (83 KB)  

    A comment on the above-named work (see ibid., vol.36, p.661-4, 1989) by G. Mirchandani and W. Cao is presented. The main contribution of that paper is a proof of a theorem showing that 'the maximum number of separable regions (M) in the input space is a function of both H and input space dimension (d),' where H is the number of hidden nodes or, equivalently, the number of hyperplanes. The commenter argues that this theorem was proven in the mid-nineteenth century by the mathematician Ludwig Schlafli.<> View full abstract»

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  • A canonical representation for piecewise-affine maps and its applications to circuit analysis

    Page(s): 1342 - 1354
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    A canonical representation for a rather general class of piecewise-affine maps has been developed. This canonical representation extends the canonical representation proposed by L.O. Chua and S.M. Hang (Proc. IEEE, vol.65, no.6, p.915-29, 1977) into PWA (piecewise-affine) partitions, which arise frequently in driving-point, transfer characteristics, and state equations. Thus, a universal canonical representation that is capable of characterizing circuit equations, state equations, and driving-point and transfer characteristics of piecewise-affine circuits in a compact global analytic form has been obtained. The canonical forms developed seem to be promising tools for computational purposes as well as for analytical studies of PWA circuits View full abstract»

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  • Design of two-dimensional zero-phase FIR filters via the generalized McClellan transform

    Page(s): 1355 - 1363
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    The authors present a design method for two-dimensional centrosymmetric zero-phase finite-impulse-response (FIR) filters, via the generalized McClellan transform. An in-depth study of the transform involved in the design method reveals a number of useful properties. These properties are used in the design method for an optimal definition of the generalized McClellan transform coefficients. The method can be applied to the design of classical 2-D FIR filters, yielding filters that are very close to the 2-D ideal specifications View full abstract»

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  • Bandpass sigma-delta analog-to-digital conversion

    Page(s): 1406 - 1409
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    The traditional low-pass sigma-delta (ΣΔ) analog-to-digital converter is extended to the bandpass case. For input signals with small relative bandwidths, bandpass ΣΔ converters offer high signal-to-noise ratios at significantly lower sampling rates than are required for low-pass ΣΔ converters. A sixth-order single-ended switched-capacitor circuit, clocked at 3 MHz, is designed to convert bandpass signals centered at 455 kHz with 20-kHz bandwidth. Time-domain circuit simulations show that this modulator realizes a 94-dB signal-to-noise ratio for a half-scale input, giving roughly 16-b performance View full abstract»

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  • The effect of integrator leak in Σ-Δ modulation

    Page(s): 1293 - 1305
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    A method is presented which makes it possible to determine exactly the effect of integrator leak on the performance of the single-loop Σ-Δ modulator with DC input. Theory from the field of nonlinear dynamics is used to provide an analytical description of the behavior of the single-loop modulator with leaky integrators. Integrator leak is inevitable in any practical circuit implementation due to finite op-amp gain. The results obtained make it possible to discuss in quantitative rather than qualitative terms the robustness of the sigma-delta system to this circuit imperfection View full abstract»

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  • Real lossless functions of continuous- and discrete-type orthogonal polynomials on the real line, and polynomial stability tests

    Page(s): 1314 - 1321
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    The authors deal with the problem of verifying whether a given antisymmetric function is lossless (in the discrete sense), which is closely related to the polynomial stability problem. The proposed approach is based on some simple correspondences between the class of discrete-type lossless functions and the subclass of continuous-type lossless functions having all their finite poles and zeros in a fixed interval of the imaginary axis. They make it possible to derive a collection of discrete-type losslessness tests by a mere translation of suitable refinements of the classical Cauer criteria. The underlying recurrence relations are shown to have interesting interpretations in the classical framework of real line orthogonal polynomial theory View full abstract»

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  • On the root structures of weighted median filters

    Page(s): 1402 - 1404
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    A class of weighted median filters (WMFs) is considered whose weights are symmetric about and nondecreasing upon going to the window center. It is shown that the structure of root signals of these WMFs can be sharply different from those of the standard median filter. The root signal may contain three parts: edges that are defined in the same way as that of the median filter; constant neighborhoods which, compared to that of the median filter, can have a shorter minimum-length; and a third part that exhibits an oscillatory behavior View full abstract»

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  • An alternate cascade factorization for para-unitary matrices

    Page(s): 1373 - 1376
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A cascade factorization procedure is derived for paraunitary matrices, resulting in a structure consisting of constant unitary matrices and diagonal matrices of scalar all-pass functions. The factorization is canonic in the number of internal states and includes FIR (finite-impulse-response) lattice and wave lattice filters as particular instances. The procedure exploits the special pole-zero properties of paraunitary matrices and gives greater insight into the structure of such matrices View full abstract»

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  • A cautionary aspect of stationary random processes

    Page(s): 1409 - 1410
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    A problem associated with determining the stationarity of a random process from discrete time samples is noted View full abstract»

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  • An analytic method for designing simple cellular neural networks

    Page(s): 1332 - 1341
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    A method is proposed for synthesizing cellular neural networks (CNNs) designed for simple applications. Based on the comparison principle for ordinary differential equations, this method leads to a set of inequalities that must be satisfied by the parameters of the cloning template defining the cellular neural network in order to guarantee correct operation for the network. The authors review the architecture of CNNs, compute the bounds of the state and output of a cell, and illustrate how to use this technique to design CNNs for shadowing, motion detection, and hole filling View full abstract»

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  • An output-whitening approach to adaptive active noise cancellation

    Page(s): 1306 - 1313
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    An approach to adaptive active noise cancellation that is based on adaptive control principles is described. The approach aims at creating a physical noise-reduced environment in the vicinity of noisy machinery, for stochastic machine noise. The system described uses a single microphone, in contrast to previously described two-microphone systems. Computed results on two types of recorded industrial noise are presented to support the theoretical design. In one case, a reduction of the sample variance of noise by a factor of 500, i.e. about 54 dB, occurred; in the second case, a reduction factor of 17, i.e. about 25 dB, was achieved View full abstract»

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  • Finite impulse response switched-capacitor filters for the delta-sigma modulator D/A interface

    Page(s): 1391 - 1397
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    Switched-capacitor finite-impulse-response (FIR) low-pass filters that can act as the first stage of the noise filter for a delta-sigma-modulation-based digital-to-analog converter are presented. The output of the filter can be generated at a reduced sampling rate without increasing the noise in the baseband. The lower output sampling rate relaxes the settling requirements of the operational amplifier. The filters have the properties that the coefficients are symmetric and take only integer values. These properties make them especially suitable for MOS switched-capacitor implementation. A symmetric implementation that has low sensitivity to capacitor mismatch is presented. The authors focus on the decimation filter for a second-order delta-sigma modulator, although extension to other order loops is possible View full abstract»

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  • Automatic tuning of continuous-time integrated filters using an adaptive filter technique

    Page(s): 1241 - 1248
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    An adaptive filter technique for tuning continuous-time integrated filters is presented. This technique is based on the model-matching configuration and tunes both the poles and zeros of the transfer function. Circuit details of an experimental prototype are given. The experimental prototype consists of an integrated third-order filter that is automatically tuned by off-chip circuitry realizing the adaptive tuning system. Both experimental and simulation results are presented to confirm the viability of the proposed approach View full abstract»

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  • Exact simulation of feedback circuit parameters

    Page(s): 1382 - 1389
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    Techniques for finding the important parameters of a single-loop feedback circuit at the closed-loop DC operating point are presented. The main advantage of these techniques is that they allow exact computer simulation of feedback parameters with a circuit simulator such as SPICE. Maintaining the closed-loop DC bias point in all test circuits makes it possible for the circuit simulator to compute the small-signal models for all nonlinear elements correctly. The methods presented for simulating loop transmission are particularly valuable since they can be used to accurately determine gain and phase margin using frequency-domain analysis, which is faster and more efficient than simulating step response via transient analysis. The equations behind the two methods for calculating loop transmission are presented as background. Examples are included to demonstrate the techniques View full abstract»

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  • A bound involving n-dimensional instantaneous frequency

    Page(s): 1389 - 1390
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    The author states and proves an integral inequality that bounds the absolute difference ε(x)=|m(x) -mˆ(x)| where m(x) is the response of a modulated n-dimensional real linear filter w to a complex exponential signal with n-dimensional instantaneous frequency Δu(x) and m(x)=|Wu(x)-u 0]| where W is the Fourier transform of w . The quantity of ε(x) provides an estimate of the error incurred by using mˆ(x) as an estimate of m(x), e.g., if Δu(x) is unknown. Such estimates may be applied to the problem of measuring the n-dimensional instantaneous frequency of certain nonstationary phase-modulated signals View full abstract»

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  • A novel capacitance assignment procedure for the design of sensitivity- and noise-optimized SC-filters

    Page(s): 1255 - 1268
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    A procedure for determining the capacitor values for a given integrator-based SC (switched capacitor) network with given capacitor ratios is presented. A limited capacitance area is optimally distributed among the individual circuit capacitors by minimizing the overall capacitor spread while simultaneously minimizing either sensitivity or noise. Noise in SC circuits is a function of ideal SC design parameters such as capacitor ratios and capacitance levels and of the technology-dependent parameters describing the switches and amplifiers. In the description of the noise performance, a characteristic point was found which is only a function of SC design parameters and can thus serve as a measure for the noise performance. For its description a closed-form expression that has the same form as the corresponding sensitivity measure is used. With these expressions an efficient capacitance assignment optimization procedure is derived. It is implemented in the computer-aided design and optimization program package SCSYN View full abstract»

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  • Switched-capacitor equalizers with digitally programmable tuning characteristics

    Page(s): 1322 - 1331
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    A digitally programmable switched-capacitor equalization filter is presented. The proposed structure uses only two nonoverlapping clock phases and is fully programmable through the use of three independent capacitor arrays. Effects of the finite gain of the operational amplifiers are investigated in detail, and simulation results are presented, verifying the models involved in the analysis. Also shown is a comparison of the performance of the proposed equalizer with that of other equalizers reported in the literature. Experimental results obtained from a prototype circuit built with discrete components are also included View full abstract»

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  • Fast computation of real discrete Fourier transform for any number of data points

    Page(s): 1280 - 1292
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    In many applications, it is desirable to have a fast algorithm (RFFT) for the computation of the real discrete Fourier transform (RDFT) for any number of data points N. To achieve this, the two-factor Cooley-Tukey decimation-in-time and decimation-in-frequency RFFT algorithms are first developed and expressed in terms of matrix factorization using Kronecker products. This is generalized to any number of factors with arbitrary radices. Each factor M involves the computation of the size-M RDFT, which is carried out by the best size-M RFFT algorithm available. The RFFT algorithm for the case where M is a prime number is also developed. The RFFT algorithms are more efficient in the number of operations when the factors are arranged in a certain order, unlike the Cooley-Tukey complex FFT algorithms. which have the same number of operations for any order of the factors View full abstract»

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  • A new fast method for ladder networks characterization

    Page(s): 1377 - 1382
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    The authors present a method for writing directly, from both a numerical and a symbolic point of view, some of the main electrical characteristics (such as the node voltages, the branch currents, and the input and output impedances) of a ladder network formed from a cascade of n identical elementary cells, once the type of cell impedances and the number of cells are known. These characteristics can be written in terms of the coefficients of two numerical triangles. Then, voltages, currents, and impedances are determined in the case of real and unit series to shunt impedance ratio and for the significant case of a semi-infinite-length ladder network View full abstract»

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  • Sensing and measurement of DC current using a transformer and RL-multivibrator

    Page(s): 1366 - 1370
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    A circuit for sensing and measurement of DC current using a transformer and RL-multivibrator is proposed. The bridge multivibrator circuit is obtained, connecting the primary coil of a nonlinear transformer to an operational amplifier. The DC current that has to be measured is applied to the secondary of the transformer. It is shown that the DC voltage measured at the inverting node of the operational amplifier gives the information on polarity and value of DC current in the secondary. The transfer characteristic of such a DC current sensor is linear for small values of the measured DC current View full abstract»

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  • An approximate noise computation for general integrator-based SC filters

    Page(s): 1249 - 1254
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    An approximate measure for the noise performance of integrator-based SC (switched capacitor) filters of general order n is developed. The measure is dependent on SC-design parameters such as capacitor ratios and capacitance levels, but not on technology-dependent parameters describing the switches and amplifiers. A simple and explicit closed-form expression for this approximate noise measure is derived and compared with more complex-and accurate-measures. The comparison demonstrates extraordinary accuracy for the approximate noise computation presented. An important application for this noise measure is in the optimization of integrator-based SC filters; it is used in the computer-aided design of sensitivity- and noise-optimized SC filters View full abstract»

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  • Spectral analysis of double-sampling switched-capacitor filters

    Page(s): 1269 - 1279
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    The double-sampling scheme (DSS) design technique is suitable for the realization of high-frequency switched-capacitor (SC) filters. This design technique effectively doubles the applicable frequency range of standard bi-phase SC filters. In practice, the particular nonideal properties of the double-sampling scheme result mainly in parasitic sidebands in the output spectrum. The DSS design technique is described, and a spectral analysis of double-sampling SC filters, including the nonideal properties, is given. With these results, the precise specifications for the pre- (anti-aliasing) and postfilter are derived. An excellent match between the analytical description and experimental results is found for a linear fifth-order elliptic double-sampling SC low-pass filter designed for video frequency applications View full abstract»

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