Efficient analytical macromodeling of large analog circuits by Transfer Function Trajectories

Abstract

Automated abstraction of large analog circuits greatly improves simulation time in custom analog design flows. Due to the high degree of variety of circuits this task is mainly a manual ad-hoc approach. This paper proposes an automated modeling approach for large scale analog circuits that produces compact expressions from a SPICE netlist. The presented method builds upon the state-of-the-art Trajectory PieceWise (TPW) approach. Because of their data-driven nature, TPW implementations generate models that require on-the-fly database interpolation during simulation, which is not embedded in a standard commercial design flow. Our approach solves this by recombining TPW samples as a surface in a mixed state space-frequency domain, revealing information about the circuit's nonlinear behavior. The resulting data, termed Transfer Function Trajectories (TFT), is fitted with a parametric vector fitting algorithm and further translated to system blocks. These are compatible with VHDL-AMS/Verilog-AMS, Matlab/Simulink or hand calculations at all design stages. The models show high accuracy and a speedup of 10×–40× against the ELDO simulator for large circuits up to 150 nodes.