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Circuits and Systems, IEEE Transactions on

Issue 9 • Date Sep 1980

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Displaying Results 1 - 16 of 16
  • An abstract-symbolic description of circuit structure

    Page(s): 839 - 841
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    This report presents an alternative approach to pictorial description of circuits. A method is formulated and symbolism suggested for representing a circuit in terms of sequential, line-by-line symbolic statements. View full abstract»

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  • Signal and noise response of a spectrum expanse

    Page(s): 804 - 815
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    A spectrum expander samples an analog input signal periodically, stores these samples cyclically in a series of digital registers, and reads out these samples cyclically at a higher rate. An analysis of the signal and noise response of this device is given here. The above spectrum expander is precisely equivalent to an analog system consisting of 1) a filter-bank spectrometer, whose filter transfer functions are sine functions of frequency(sin c xequiv sin pi x/ pi x)spaced at the Nyquist interval; 2) a modulator bank that separates the filter bank outputs, spacing them equally in frequency; and 3) An adder, that sums the modulator bank outputs. Such a spectrum expander may be followed by an appropriate physical, fixed channel-bank spectrometer, and used to determine approximately the power spectrum of noise inputs with a variety of bandwidths. The input bandwidth can be accommodated to the fixed channel-bank spectrometer by adjusting the expansion ratio. Stating this another way, such a system is equivalent to a channel-bank spectrometer with variable resolution. Moreover, such a spectrum expander may be used for real-time signal processing, since it offers a digital means of dissecting a signal in the frequency domain. Each of the above applications suffers from impairments. The present analytical results permit us to evaluate the errors in various cases of interest. These include the effects of a finite number of digits in the storage registers (equivalent to quantizing the analog input) for Gaussian noise inputs. By using a weight function on the output samples, the transfer functions of the equivalent spectrometer filters described in item 1 above can be changed fromsin cfunctions of frequency to other desired characteristics. This too is amenable to treatment by extension of the present results. View full abstract»

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  • Injection locked tunable filters and amplifiers

    Page(s): 833 - 836
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    The problem of realizing coherent filters and amplifiers using injection-lock technique has been discussed in this short communication. It deals with the behavior of an injection synchronized oscillator (ISO) under different situations: i) it evaluates the locking range of an ISO in response to an FM signal corrupted with an additive random noise, ii) it finds the coherent filtering capability, and iii) it discusses its amplifying property. The experimental results have been presented in support of the theoretical approach. View full abstract»

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  • Monotone resolution sequence spaces and mappings

    Page(s): 800 - 804
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    A brief study of sequence spaces amenable to circuit and system analysis is presented. The main properties are shift and truncation operator invariance. A particularly useful class called monotone resolution space is then defined; and relations between linearity, causality, finite norm, invariance, finite gain, and boundedness of sequence mappings or these spaces are given by means of a Venn diagram. View full abstract»

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  • Parasitic pole approximation techniques for active filter design

    Page(s): 793 - 799
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    A method of approximating the parasitic poles of active filters employing one, two, or three operational amplifier(s) is presented. These approximations are good for both a single-pole and two-pole model of the operational amplifier and are useful for determining filter stability. The approximation expressions are sufficiently simple that they may be included in the active filter design process. Stability criteria for active filters employing two-pole operational amplifiers are stated in terms of the parasitic pole approximations obtained using the simpler single-pole model of the operational amplifier. The necessity of including the more accurate two-pole model of an operational amplifier in some applications is discussed. Detailed comparisons of the actual and approximate parasitic poles in two examples are made. View full abstract»

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  • An algorithm for single-row routing with prescribed street congestions

    Page(s): 765 - 772
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    The single-row routing approach for layout has attracted a great deal of interest and is in a position to become one of the fundamental routing methods for high density multilayer printed wiring boards (PWB's). A specific development has recently been accomplished on this approach [12], namely: Necessary and sufficient conditions for optimum routing have been obtained. Nonetheless, there still remains a fundamental problem to be overcome, that is, to develop an algorithm to find the optimum solution. The present paper derives an alternate set of necessary and sufficient conditions for the same problem. These are easy to check and are tailored for algorithm development. An efficient algorithm in the special cases of upper and lower street congestions up to two has been proposed. These special cases are particularly of interest in the design of practical PWB's. View full abstract»

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  • Variable digital filters

    Page(s): 836 - 838
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    IIR prototype filters cannot be used for the design of variable filters through Schüssler's all-pass transformation because of the occurrence of delay-free loops; no such problem arises with FIR prototypes. In this paper, the drawbacks of the latter type, with regard to computational efficiency and output roundoff noise, have been brought out, An approach is suggested, wherein the delay-free loops with IIR prototypes are eliminated by modifying the coefficients of the first- and second-order sections of the prototype filter. The computation of modified coefficients In this approach requires fewer multiplications as compared to an existing method. View full abstract»

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  • An efficient algorithm reduces computing time in solving a system of stiff ordinary differential equations

    Page(s): 747 - 755
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    The problem of stiff differential equations arises in many computer-aided design techniques, particularly in the transient analysis of network simulation. Special multistep methods are used to solve the first-order stiff nonlinear differential equations. Instability and a large number of steps are encountered during simulation. Different techniques such as step and order selection schemes, procedures for changing step and order, may reduce the number of steps while preserving stability. An improved algorithm is presented using BDF formulas given by Brayton et at. and leads to reducing computer time by controlling the number of integration steps, but also the number of Newton iterations, the number of Jacobian matrix evaluations and other parameters, without producing additional errors or instability phenomena. Experimental results are shown. View full abstract»

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  • The colored branch theorem and its applications in circuit theory

    Page(s): 816 - 825
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    The colored branch theorem (Minty 1960 [1]) is a result in graph theory, which essentially says that the existence (resp., nonexistence) of a certain loop immediately implies the nonexistence (resp., existence) of a certain cutset. Its relevance and use in circuit theory, however, has only recently been recognized. Since it is expected that many more applications in circuit theory will follow, the theorem is interpreted and proved in a network setting. Many graph-theoretic corollaries are derived, which may facilitate later use. It is illustrated that many results in circuit theory can he simplified or given a simpler proof using this theorem and its corollaries. View full abstract»

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  • A variance minimization approach to tolerance design

    Page(s): 737 - 747
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    This paper describes the development of a variance minimization strategy for the tolerancing of linear circuits and systems. The technique is conceptually simple and can be implemented through commonly available optimization routines. The applicability of the approach is illustrated through standard numerical examples. In addition the paper also derives a new expression for the variance of a system performance index. View full abstract»

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  • Multiple solutions of nonlinear equations: Roots of polynomials

    Page(s): 825 - 832
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    A search method is presented for obtaining multiple solutions of a system ofnnonlinear equations whose first(n- 1)equations do not necessarily define a unique space curve. In particular, the approach is used to find all the roots of a complex polynomial. Singularities on the space curve are analyzed and properly classified according to their high-order derivatives. Depending on the nature of singularities, the rules for a sign change in the algorithm are determined so that the root-finding procedure can be continued. View full abstract»

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  • On the inadequacies of loop gain in broad-band, multiloop feedback amplifiers

    Page(s): 843 - 848
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    Experience in communications engineering has repeatedly shown that loop gain can be an unreliable basis for the assessment of stability margins in feedback amplifiers. There are both theoretical and practical reasons for this. A simple identity provides a sounder theoretical basis, and provides a novel way of looking at old problems. The presence of any unstable modes of the closed-loop amplifier can be predicted with more assurance from open-loop measurements by examining a product of functions derived from the identity rather than a single-loop gain. Further improvements in stability assessment are possible by using the data base of the embedding network method [1]. The loop gains computed from the data base can be compared with those derived directly from two-port s-parameter measurements at the corresponding nodes, thus avoiding the use of circuit diagrams. Results on several practical amplifiers are quoted, which show that plots of loop gains can fail to predict closed-loop instability. In another actual case, a loop gain failed to predict conditional stability. The correct predictions in each case were obtained using the method described in [1]. View full abstract»

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  • Yield maximization and worst-case design with arbitrary statistical distributions

    Page(s): 756 - 764
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    We describe a method by which a variety of statistical design problems can be solved by a linear program. We describe three key aspects of this approach. 1) The correspondence between the level contours of a given probability density function and a particular norm, which we shall call a pdf-norm. 2) The expression of distance in this norm from a given set of hyperplanes in terms of the dual of the pdf-norm. 3) The use of a linear program to inscribe a maximal pdf-norm-body into a simplicial approximation to the feasible region of a given statistical design problem. This work thus extends the applicability of a previously published algorithm, to the case of arbitrary pdf-norms and consequently to a wide variety of statistical design problems including the common mixed worstcase-yield maximization problem. View full abstract»

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  • Stability domains for second-order recursive digital filters in normal form with 'matrix power' feedback

    Page(s): 841 - 843
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    The allowable pole locations that will provide guaranteed immunity from finite-word limit cycles are derived for a class of secondorder normal digital filters. View full abstract»

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  • Canonic structures for lossless one-ports

    Page(s): 772 - 778
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    Necessary and sufficient topological conditions for a lossless 1-port to be canonic have been discovered and proved. All the currently known canonic structures, comprising the classical Foster and Cauer forms and the five more recently discovered networks, are special cases of the general class of canonic 1-ports described here. View full abstract»

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  • Improved methods of assessing feedback in wide-band multiloop amplifiers

    Page(s): 779 - 792
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    A pressing problem in modern, wide-band feedback amplifiers is to obtain reliable information on margins against self-oscillation. The application of Bode's general and exact theory of feedback to practical circuits of considerable complexity, such as a complete repeater, has been achieved by a new method based upon measurements over a very wide band of frequencies. Transistor models and circuit diagrams are not required above the traffic band. The theory of the method is presented in nodal analysis terms. The principal result is a set of relationships between determinants of a 4-node matrix derived from measurements and corresponding determinants of a hypothetical, multinode matrix of the complete circuit. Extensive software was developed to translate the theoretical results and insights into algorithms. These have been applied to several practical amplifiers with outstanding results. Apart from stability assessment, feedback also affects sensitivities and some results due to Bode are extended to cover large changes. Return ratios and related quantities have been evaluated for transistors in practical amplifiers over the range 1-1300 MHz, with accuracies comparable with those of the basics-parameters. Reliable gain and phase margins, and values of total feedback and sensitivities, have been computed without the need to split a node as required for loop gain. More information, greater assurance in circuit design, and a potential tool in amplifier development have been achieved. View full abstract»

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