Optimizing return via locations to reduce mode conversion in connector pin fields

Differential wiring is prevalent in high-speed signaling, because it provides better immunity and reduced emissions over single-ended transmission structures. These advantages are diminished when the transmitter pollutes the signal with common mode signals and when discontinuities in the channel convert some fraction of the differential mode signal to common mode. This paper focuses on the channel discontinuities, specifically the arrangement of signal and return vias. Genetic algorithms and a fast via solver are used to optimize return positions to minimize the mode conversion. Case studies of open-area via transitions are presented, as well as a pin array conforming to a common high-speed connector footprint.