Circuit model for common-to-differential mode PCB transitions

Common-to-differential mode PCB transitions are present in most PCB implementations. Although they 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. In this paper, a rigorous circuit model for common-to-differential mode PCB transitions is presented and tested. The model splits the contribution of common and differential signals (modes) ports, and allows 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.