A practical algorithm for DC operating‐point analysis of large‐scale circuits

Abstract SPICE‐type general‐purpose circuit simulators are used widely as a support tool for circuit design. It often happens, however, that the do operating‐point analysis does not converge. To cope with such a situation, various approaches have been proposed based on continuation methods with the global convergence property, but these have yet to come to the stage of practical application to large‐scale circuits. This paper proposes a practical algorithm which can be implemented on the general‐purpose circuit simulators with modified nodal formulation, for determining the de operating‐point of large‐scale circuits. As the first step, the concept of “modified cut‐set analysis” is introduced and some properties of the modified nodal equation are presented. Then it is shown, in practical circuits, that the convergence of the algorithm is theoretically guaranteed. The proposed algorithm is then implemented on an existing general‐purpose circuit simulator and applied to a bipolar analog LSI to demonstrate its effectiveness. For the LSI circuit formulated in 18, 553 modified nodal equations, the de operating point was determined in 270 minutes using an IBM RS6000‐550.