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Circuits and Systems, IEEE Transactions on

Issue 10 • Date Oct 1991

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Displaying Results 1 - 16 of 16
  • On minimal realization of 2-D systems

    Page(s): 1228 - 1233
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    An algorithm to obtain possibly absolutely minimal realizations of a given 2-D transfer function is developed. It is algebraic in nature and requires only 1-D realization theory and basic knowledge of linear algebra. Hence, the algorithm is simple and easy to program. The algorithm is guaranteed to yield absolutely minimal realizations for 2-D transfer functions having separable numerators and may also be applicable to general 2-D systems satisfying a certain consistency condition. An example is used to illustrate the effectiveness of the algorithm View full abstract»

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  • Resolution-to-noise trade-off in linear image restoration

    Page(s): 1206 - 1212
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    The incorporation of both spatial and spectral adaptivity in a linear restoration algorithm is addressed. The formulation of a combined criterion is proposed, involving the minimum-mean-square-error (MMSE) and the least-mean-square-error (LMSE) criteria, in portions controlled by an indicator of the spatial signal activity. The incorporation of spectral adaptivity is achieved through the use of a decorrelating matrix in each individual criterion. The restoration algorithm derived, called the resolution-to-noise trade-off (RNT) algorithm, offers the flexibility of applying either linear MMSE (Wiener) filtering, inverse filtering, or no filtering at all, depending on the indicator of the spatial signal activity and the decorrelating matrices. The relationship of the RNT algorithm to other linear noniterative restoration approaches is discussed. it is indicated that the RNT filter forms a generalization of restoration filters that involve the point-spread function (psf) in a linear fashion View full abstract»

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  • Class E low dv/dt synchronous rectifier with controlled duty ratio and output voltage

    Page(s): 1165 - 1172
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    A class-E high-frequency low-dv/dt synchronous rectifier/DC regulator is analyzed. The circuit is derived from a class-E rectifier by replacing a diode with a controllable switch. It can then both rectify and regulate the rectified output against variations in DC load and amplitude of the AC input voltage. The switch consists of a transistor and an antiparallel diode or a series diode. The DC output voltage of the rectifier is regulated by varying the ON duty ratio of the switch. The AC input voltage can be at a constant or varying frequency. The controllable switch turns on and off at zero voltage with low dv/dt, reducing switching losses, stresses, and noise. Equations governing the circuit operation are derived. Experimental results at 0.5 MHz were in good agreement with the theoretical predictions. The rectifier can be used in high-frequency-power-density multiple-output power supplies, all of whose outputs are regulated. The frequency need not be varied to regulate the DC output View full abstract»

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  • A model of op-amp circuits

    Page(s): 1233 - 1235
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    In stability analysis, op-amp circuits are often modeled as single-loop feedback systems, as shown with a finite open-loop gain A in the forward path and β in the feedback path. The author proposes a different model that has two feedback loops. The model is useful in stability of op-amp circuits and in determining the oscillation conditions of Wien-bridge oscillators. The model has one positive feedback loop and one negative loop. The model is easy to develop and offers better insight into op-amp circuits than the single-loop model View full abstract»

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  • A substrate-referenced data-conversion architecture

    Page(s): 1212 - 1217
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    A substrate-referenced (SR) data-conversion architecture that operates with widely varying single polarity and or bipolar power supplies has been developed. By using well-established analog circuit design techniques and a novel substrate-referenced level-shifting scheme, digital switching noise on the noisiest power supply (V dd in p-well CMOS) appears to the analog subsystem as a common-mode signal that is substantially rejected. Substrate-referenced successive-approximation weighted-capacitor analog-to-digital (A/D) converters have been implemented in p-well CMOS technology for several VLSI mixed-mode applications. A conventional ground-referenced converter was also integrated in the same technology for one specific application. With identical static logic circuitry on both chips, the SR architecture exhibited significantly higher accuracy than the conventional architecture View full abstract»

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  • Design methodology of decimation filters for oversampled ADC based on quadratic programming

    Page(s): 1121 - 1132
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    A design methodology for oversampled analog-to-digital converter decimation filters is presented. The methodology tackles the finite-impulse-response (FIR) filter design problem by formulating a quadratic programming problem that minimizes the integral of the aliased noise subject to the passband and stopband constraints. The approach offers a design whose response is optimized to meet arbitrary quantization noise power spectral density and anti-alias requirements. Because the projected Hessian matrix of the objective function is positive definite, the quadratic function has a unique minimum. The methodology is applied to design filters for different requirements and the performance is compared to conventional approaches View full abstract»

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  • A continuous-time current-mode integrator

    Page(s): 1236 - 1238
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    The authors propose a continuous-time current-mode integrator that offers potential advantages for both higher frequency and lower power monolithic filtering applications. Owing to the small voltage swings inherent in current-mode circuits, the integrator time constant is determined by a small-signal transconductance and an additional MOSFET gate capacitance, while good linearity is maintained using a standard 2-μm digital CMOS technology. Simulation results predict passband cutoff frequencies exceeding 30 MHz for a five-pole low-pass filter dissipating as little as 2 mW/pole with a 5-V power supply View full abstract»

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  • Resonator-based filter-banks for frequency-domain applications

    Page(s): 1145 - 1159
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    The filter-bank structure proposed is based on a digital simulation of a singly terminated ladder filter. This filter bank can also be arrived at from a filter described by G Peceli (1989) and represents an extremely hardware efficient structure, having a complexity of O(N). The main application examined is adaptive line enhancement. The filter-bank-based line enhancer is shown to have the necessary conditions for global convergence and to yield uncorrelated sinusoidal enhanced outputs that are undistorted versions of the corresponding frequency components of the input. A number of additional possible applications for the filter-bank are described. These include the tracking of periodic signals, subband coding, frequency-domain adaptive noise-cancellation, and frequency-domain processing of signals from phased arrays View full abstract»

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  • Coherent parametric echoes in nonlinear resonator ensembles

    Page(s): 1217 - 1221
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    Use is made of the concept of nonuniform (incommensurate) resonator spacings in order to minimize the linear echo problem. The circuit domain simulation of a general class of parametric coherent echoes, previously modeled by means of uniformly spaced nonlinear resonators, is reexamined. This is accomplished by introducing nonuniform (incommensurate) resonator spacings to represent more closely an actual physical system. The effects of this approach in both nonlinearly coupled and anharmonic resonator ensemble models are investigated View full abstract»

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  • A learning and forgetting algorithm in associative memories: results involving pseudo-inverses

    Page(s): 1193 - 1205
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    The authors develop a design technique for associative memories with learning and forgetting abilities via artificial feedback neural networks. The method utilizes the theory of large-scale interconnected dynamical systems, instead of the usual energy methods. Networks synthesized by this design method are capable of learning new patterns as well as forgetting old patterns without recomputing the entire interconnection matrix. The method, in which the properties of pseudo-inverse matrices are used to iteratively solve systems of linear equations, provides significant improvements over the outer product method and the projection learning rule. Several specific examples are given to illustrate the strengths and weaknesses of the methodology View full abstract»

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  • Exponential stability and trajectory bounds of neural networks under structural variations

    Page(s): 1182 - 1192
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    The dynamic behavior of neural networks under arbitrary unknown structural perturbations depends essentially on the compatibility/incompatibility of input variables in these networks. Estimates of the upper bounds of the motions of neural networks of either type and exponential stability of compatible neural networks are established by using three different forms of Lyapunov functions. Conditions for the maximum possible estimate of the domain of structural exponential stability are determined. All new concepts such as compatible/incompatible neural networks and structural exponential stability are defined. All the conditions are stated in simple algebraic forms. Their applications are straightforward View full abstract»

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  • An analysis methodology to identify dominant noise sources in D/A and A/D converters

    Page(s): 1133 - 1144
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    The authors describe a methodology by which noise sources in converters can be modeled using SPICE. Two converter topologies were used to illustrate the noise analysis methodology. SPICE input files constitute a noise model of a particular converter topology whose noise parameters may be changed to match actual converter noise behavior more closely. SPICE simulations are used to verify the analytical results and to examine typical noise levels in all of the circuits. The SPICE noise models allow easy identification of dominant noise sources within a given topology for a given set of noise parameters. The effects of changing the parameters of the dominant noise sources (e.g., using components designed for low noise) are examined to address design implications of the noise analysis. The effects of all noise sources on an analog-to-digital-to-analog converter system are examined View full abstract»

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  • Frequency-domain design of 2-D digital filters using the iterative singular value decomposition

    Page(s): 1225 - 1228
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    The authors propose a technique for designing 2-D digital filters (2DDFs) with specified magnitude and constant group delay characteristics. The method is based on the iterative singular value decomposition (ISVD) of a 2-D magnitude specification matrix. The ISVD guarantees all its decomposition results to be always nonnegative. By using the ISVD, 2-D magnitude specifications can be decomposed into a pair of 1-D ones, and thus the problem of designing a 2DDF can be reduced to the one of designing a pair of 1DDFs or even only one 1DDF. A design example shows that this technique can be used to design 2DDFs with a higher degree of precision but needs less computational effort View full abstract»

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  • Time-domain analysis of lossy transmission lines with arbitrary terminal networks

    Page(s): 1160 - 1164
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    A numerical method based on traveling wave theory is presented for the transient analysis of lossy transmission lines with arbitrary terminal networks. The method is well suited to computer programming. By introducing the imaginary transmission line, the network is portioned into two parts. An approach by the S-matrix and the z-transform is applied to the arbitrary terminal networks and time convolution is applied to the lossy transmission lines. The time domain S-matrix required for the convolution is obtained by the use of a fast inversion of a Laplace transform. A time-domain wave flow for the network is considered. The voltage waves at the lumped part are obtained by the S-z method, and the time-domain S -matrix is convolved with the voltage waves on the imaginary and lossy transmission lines to obtain a time-stepping solution. Three numerical examples are presented to illustrate the application of the method View full abstract»

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  • Enhancement of image quality for low bit rate video coding

    Page(s): 1221 - 1225
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    The authors propose a number of improvements based on the RM8 algorithm aimed at enhancing the visual quality of the reconstructed images, especially at the low rates of 64 and 128 kb/s. RM8 is a novel approach to defining a coding standard for video communications at p ×64 kb/s. Methods studied include reducing the quantizer step size, randomized scanning of the macroblock, and/or nonuniform quantization of the transform coefficients. Reducing the quantizer step size did improve the codec performance, but only marginally. Nonuniform quantization coupled with randomized scanning of the macroblocks was found to be effective in improving the image quality, both objectively and subjectively. Improvement is particularly marked in the initial 20 frames of a sequence View full abstract»

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  • A general relationship between amplifier parameters, and its application to PSRR improvement

    Page(s): 1173 - 1181
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    A general relationship between the gains of multiterminal amplifiers is derived. This approach generates a constraint for the simultaneous improvement of the common-mode and the power-supply rejection ratio of the simple operational amplifier. This constraint can be relaxed by either adding a supplementary input terminal to the amplifier circuit or using a fully differential design. The method can be used to improve the power-supply rejection ratios in operational amplifiers. Several implementations of a two-stage operational amplifier illustrate this technique View full abstract»

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