Miniaturization of Common Mode Filter Based on EBG Patch Resonance

"High Speed differential signals have become common place in the computer industry. While the use of differential signaling can significantly improve the signal integrity, it does not eliminate EMC concerns. Small amounts of asymmetry between the differential pair can create significant amounts of common mode signals, which, in turn, cause EMI emissions. Previous work to create common mode filters on printed circuit boards (PCB) based on the resonant behavior of Electromagnetic Band Gap (EBG) structure (as sequence of isolated patches) for high speed differential signal lines required significant PCB real estate. While effective as common mode filters, their use on dense PCB structures was limited. This recent miniaturization work, which consists of each patch based on the EBG geometry, without changing the electrical properties (i.e. dielectric permittivity) of the PCB substrate, has reduced the required PCB area to less than 20% of the previous real estate requirements, making them much more attractive for use in dense PCBs."