Addressing substrate coupling in mixed-mode ICs: simulation and power distribution synthesis

Abstract

Abstract-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.

Dominant Substrate Noise Coupling Mechanism for Multiple Switching Gates

“…The extraction and simulation of large scale circuits to determine the dominant noise generation mechanism is not feasible due to the high computational requirements since the logic gates, power/ground network, and substrate must all be considered together [10], [11], [12]. A sufficiently accurate model which considers the effects of multiple parameters on the dominant noise is therefore required.…”

Contact merging algorithm for efficient substrate noise analysis in large scale circuits

“…The first class includes those techniques that discretize the substrate into a 3-D R(C) mesh to determine the impedances such as the finite difference method (FDM) [1], [2] and the boundary element method (BEM) [3], [4]. The substrate volume can be discretized in differential form using FDM, resulting in a huge, sparse matrix.…”

Compact substrate models for efficient noise coupling and signal isolation analysis

“…Current approaches to model the substrate can typically be divided into two classes. The first class includes those techniques that discretize the substrate into a 3-D R(C) mesh to determine the impedances such as the finite difference method (FDM) [2], [3] and the boundary element method (BEM) [4], [5]. Although highly accurate, the primary limitation of these approaches is the increase in computational complexity with the size of the circuit, prohibiting the efficient analysis of large scale mixed-signal circuits [6].…”