Substrate coupling in mixed signal integrated circuits

Integrating digital with sensitive analog circuitry has created concerns. The fast switching digital signal creates noise that injects through the doped silicon substrate and travels through it due to its low resistivity and causes damages and bandwidth reduction. In this research work, COMSOL multiphysics was used to extract the substrate coupling parameters subsequently determining the amount of coupling in the substrate and controlling it. Several model configurations were created; such as dual and multiple contacts, which varied the separation between aggressor and victims. Also, the size of the aggressor was increased and a guard ring was added. The results show that spacing can reduce coupling between the aggressor and victim while increasing the area of the aggressor would increase coupling. Also, guard ring can be more efficient than spacing in minimizing coupling.