Circuit model for mode conversion in grounded differential signal paths

Signal paths are often routed with their ground ones. These ground paths are usually connected through a via-hole to the ground plane. This grounded strip creates a transition: a via-hole common-to-differential mode transition. Although these transitions behave in an ideal way at low frequencies, they can show significant effects at higher frequencies, due to their multimode behavior. These effects can cause a degradation of the signal integrity. A rigorous circuit model for via-hole common-to-differential mode transitions is presented and tested. The model splits the contribution of common and differential signals (modes) into different ports, and allows the analysis of circuits that present different responses to either mode. The model is tested in several PCB configurations. The good agreement between circuit simulation and measurements validates the model and demonstrates its utility as a design tool.