Implementation of pole-zero analysis in SPICE based on the MD method

The modification-decomposition (MD) method for finding the poles and zeros of a general circuit has been implemented in SPICE 3c1. The method is based on finding the eigenvalues of the time constant matrix, and convergence is guaranteed as long as the circuit has a DC solution. The method requires no complex operations and only one LU decomposition. It fits in very conveniently with the framework used in SPICE. Special elements like transcapacitances and transfer function blocks are taken care of in the implementation. Apart from a standard filter application involving RC elements and op amps, an ECL (emitter coupled logic) ring oscillator and root locus of a switching mode power supply are given as examples.<
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