L.M. Vidigal

Massachusetts Institute of Technology, Cambridge, MA, United States

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Publications (6)2.19 Total impact

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    ABSTRACT: The stability and accuracy properties of exponentially fit integration algorithms applied to the test problem x &dot;=- Ax are compared with the more standard backward-Euler and semi-implicit methods. For the analysis, A∈ IR <sup>n×n</sup> is assumed to be connectedly diagonally dominant with positive diagonals, as this models the equations resulting from the way MOS transistors and interconnect parasitics are treated in circuit-level timing simulation programs. Examples are used to demonstrate that all the exponential-fitting methods, and the semi-implicit methods, are much less accurate than backward-Euler for tightly coupled stiff problems, and an example is given which destabilizes one of the exponential-fitting methods. It is then proved that in the limit of large time steps, the more stable exponential-fitting methods become equivalent to a semi-implicit algorithm. It is shown that the backward-Euler, semi-implicit, and certain exponentially fit algorithms are multirate A -stable
    IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems 06/1992; · 1.09 Impact Factor
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    ABSTRACT: In this paper, we present our results on the stability and accuracy properties of exponentially-fit integration algorithms, and demonstrate these properties on some test examples. We consider the multivariate test problem = -Ax where A "x" and is assumed to be irreducibly diagonally-dominant with positive diagonals, as this models the equations resulting from the way MOS circuits are treated in timing simulation programs. It is shown that for these problems, the CINNAMON exponentially-fit algorithm is A-stable, and an example is given where the algorithm in XPSim is unstable. A semiimplicit version of the XPSim algorithm is then described, and it is shown that this semi-implicit algorithm is A-stable. Examination of examples demonstrate that neither the stabilized XPSim algorithm nor the CINNAMON algorithm produces satisfactory results for very large timesteps. The effect of ordering on the accuracy and stability of the integration methods is also examined, and it is shown that ordering always enhances accuracy, though not significantly for large timesteps, and that the XPSim algorithm can be made more stable with a carefully chosen ordering.
    IEEE Trans. on CAD of Integrated Circuits and Systems. 01/1992; 11:566-574.
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    ABSTRACT: Some of the theoretical and practical aspects of using exponential fitting for MOS digital circuit timing analysis are described. The multivariate test problem x &dot;=- Ax where A ∈ R <sup>n×n</sup> and is assumed to be irreducibly diagonally dominant with positive diagonals is considered, as this models the equations resulting from the way MOS circuits are treated in timing simulation programs. It is shown that for these problems, the Cinnamon exponentially fit algorithm is A -stable, and an example is given where the algorithm is XPSim is unstable. A semi-implicit version of the XPSim algorithm is described, and it is shown that this semi-implicit algorithm is A -stable. Examination of examples demonstrates that neither the stabilized XPSim algorithm nor the Cinnamon algorithm produces satisfactory results for very large timesteps. The effect of ordering on the accuracy and stability of the integration methods is also examined, and it is shown that ordering always enhances accuracy, though not significantly for large timesteps, and that the XPSim algorithm can be made more stable with a carefully chosen ordering
    Circuits and Systems, 1990., IEEE International Symposium on; 06/1990
  • H.C. Neto, L.M. Vidigal
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    ABSTRACT: A new multirate algorithm for circuit simulation that combines the efficiency of event-driven techniques with the simplicity of explicit integration to successfully decrease the overall run-times, is described. The method uses discretization in the voltage axis and exponentially fitted integration formulas to avoid stability problems inherent to traditional explicit integration schemes, and uses a new and effective step control algorithm to take full advantage of the multirate behaviour of large circuits and further increase the performance of the simulation
    Circuit Theory and Design, 1989., European Conference on; 10/1989
  • L.M. Vidigal, S.R. Nassif, S.W. Director
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    ABSTRACT: The use of simulation tools to verify the behavior of integrated circuits is a well established technique for circuit design. This paper describes a novel approach for circuit simulation that promises a significant improvement over conventional methods. The algorithm involves an explicit event driven technique that seems stable even when the accuracy of the solution is relaxed, and is able to perform automatic and dynamic partitioning of the network, thus allowing the full exploitation of latency in large digital networks. Although the basic method could be generalized for any type of circuit, in this paper the scope is limited to MOS integrated circuits.
    Design Automation, 1986. 23rd Conference on; 07/1986
  • L.M. Vidigal, S.W. Director
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    ABSTRACT: Random variations inherent in any fabrication process may result in very low production yield. This is especially true in the fabrication of integrated circuits. Several methods have been proposed to help the circuit designer minimize the influence of these random variations. Most of these methods are deterministic and try to maximize yield by centering the nominal value of the designable parameters in the so-called region of acceptability. However, these design centering techniques require an assumption of convexity which is not valid in many real design situations. To overcome this problem a new convergent method is proposed which is based on the sequential solution of subproblems for which the convexity assumption is valid. A practical implementation of the algorithm is shown by examples to be computationally efficient.
    IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems 02/1982; · 1.09 Impact Factor

Publication Stats

45 Citations
2.19 Total Impact Points

Institutions

  • 1990–1992
    • Massachusetts Institute of Technology
      • Department of Electrical Engineering and Computer Science
      Cambridge, MA, United States
  • 1986
    • Carnegie Mellon University
      • Department of Electrical and Computer Engineering
      Pittsburgh, PA, United States