Substrate and ground noise interactions in mixed-signal circuits

The interaction of the substrate with the inductive on-chip ground distribution network is analyzed in this paper. A transistor level approach is presented to illustrate the effects of the substrate on ground noise. The substrate can have a significant effect on ground noise due to the inductance of the ground lines. For a CMOS inverter, the substrate can reduce negative peak ground noise by 49% during the high-to-low output transition. The substrate, however, increases the positive peak ground noise by 72% during the low-to-high output transition. The effect of the substrate should therefore not be neglected if the inductance of the on-chip ground distribution network is nonnegligible. Furthermore, conventional triangle or trapezoid type current demand estimations of the nonlinear circuits are shown to be significantly inaccurate if the ground lines exhibit inductive behavior.