Return via location optimization to minimize mode conversion in differential via transitions

Differential signaling is used predominantly for its lower radiated emissions and better susceptibility. Mode conversion, however, can negate these benefits. Mode conversion can be caused by many channel features. This paper focuses on via transitions, specifically the position of the return vias relative to the signal vias and each other. Genetic algorithms and a fast via solver are used to optimize return via positions to minimize mode conversion. Both simple and complex cases are presented, including a QSFP connector footprint design.