Addressing Substrate Coupling in Mixed-Mode IC’s: Simulation and Power Distribution Synthesis

This paper describes new techniques for the simulation and power distribution synthesis of mixed analogldigital integrated circuits considering the parasitic coupling of noise through the common substrate. By spatially discretizing a simplified form of Maxwell’s equations, a three-dimensional linear mesh model of the substrate is developed. For simulation, a macromodel of the fine substrate mesh is formulated and a modified version of SPICE3 is used to simulate the electrical circuit coupled with the macromodel. For synthesis, a coarse substrate mesh, and interconnect models are used to couple linear macromodels of circuit functional blocks. Asymptotic Waveform Evaluation (AWE) is used to evaluate the electrical behavior of the network at every iteration in the synthesis process. Macromodel simulations are significantly faster than device level simulations and compare accurately to measured results. Synthesis results demonstrate the critical need to constrain substrate noise and simultaneously optimize power bus geometry and pad assignment to meet performance targets.