Many high-volume, high-speed printed circuit boards distribute clock signals with a differential clock driver. Previous work by the Missouri S&T EMC Laboratory has shown that differential clock signals usually contribute very little to the overall radiated emissions. For this reason, the current expert system algorithms discount differential clock traces when calculating most types of common-mode-source EMI. Nevertheless, some products with differential clocks do radiate significantly at harmonics of the clock frequency. The goal of this project is to fully characterize a variety of clock drivers and clock trace routing schemes to understand how and why some differential clock drivers create EMI problems.