Brian Kirk, Signal Integrity Engineer, Amphenol TCS
Jason Chan, Signal Integrity Engineer, Amphenol TCS
Tom Cohen, Principal Development Engineer, Amphenol TCS
Jose Paniagua, Signal Integrity Engineer, Amphenol TCS

Conventional interconnect analysis techniques, including those cited in the IEEE 802.3ap standard, emphasize the evaluation of channel performance with respect to pure differential mode propagation while discounting the undesirable effects of common-mode and mode-converted energy. Maintaining a differentially balanced system is becoming practically infeasible with increasing data rates and manufacturing process imperfections, thus leading to higher amounts of common-mode energy in differential systems. This paper investigates the common-mode characteristics of different structures such as plated-through-holes, backplane connectors, and twinax cables, with a focus on signal integrity and EMI issues.