Return Path Discontinuities: The Silent Killer of Signal Integrity

The return current path for any signal always has a return path even when disruptions occur in the return current path like when there is a split ground plane or there is a gap between different planes. If there is a disruption in the return path, the current will take a longer different route than it normally would and this will cause an increase in EMI, noise and loop area. Therefore, now you have turned your clean signal into a small FM transmitter. Keeping return paths continuous and below the traces is extremely important with high-speed signals. Do not run traces across plane splits and do not use stitching vias to change layers to maintain continuity of a path back to its source. Good integrity of a signal source is based not only on the physical characteristics of the trace itself but also on the physical characteristics of the physical return path to the source.