Analysis of return path discontinuities in multilayer PCBs and their impact on the signal and power integrity

This paper investigates the impact of return path discontinuities on both signal and power integrity of high speed interconnects. A test board is built for the purpose and 4 different configurations are analyzed and correlation between measurements and simulations (coming from a full wave 3D EM field simulator) results is also presented. Both time and frequency domain results are analyzed and design guidelines are provided. It is observed that return path discontinuities have a sensible impact on ground bounce in single-ended signals; however the differential signaling can drastically reduces it. Discontinuities from gaps in return paths (e.g. plane splits) and connectors impact the differential signals on both insertion loss and cross talk. The real value of return/grounding vias is to reduce the common signal noise.