Design and experimental validation of compact common mode filter based on EBG technology

Attenuating undesired common mode signals in PCB high-speed differential interconnects is critical to reducing crosstalk and electromagnetic interference. In this paper, compact planar EBG-based common mode filters are designed and implemented using standard PCB technology without incurring any extra component cost. These filters function by converting the common mode energy propagating along a differential pair into a fundamental EBG cavity mode. The geometry of a single EBG cavity, or an array of multiple adjacent cavities, can be readily synthesized using a simple analytical procedure. Test vehicles of a common mode filter design in a 6-layer PCB were successfully manufactured and applied to differential on-board signaling with a date rate of 6.4 Gb/s. Large manufacturing variations were found to be responsible for filter performance degradation which motivated an investigation into the sensitivity of filter behavior to this variation. Precise PCB measurements for quantifying the real dielectric permittivity and the EBG dimensions coupled with experimental data with model-to-hardware correlation demonstrate that the EBG-based filters can effectively block the major undesired common mode signal harmonic associated with a high speed differential clock signal.