EMI resulting from signal via transitions through the DC power bus

Signal routing with layer changes through via transitions are common in multi-layer printed circuit board (PCB) design. For high-speed signals that transition through the internal parallel planes comprising the DC power bus, the return current has to switch from one reference plane to another reference plane. The return current discontinuity at the via excites the DC power bus and can result in a power bus noise problem, as well as an EMI problem. EMI resulting from the signal transitions through a DC power bus is studied herein. Measurements were made on an experimental board, and numerical modeling was used to study the EMI resulting from the excited DC power bus. The effects of local and global decoupling as an EMI mitigation approach were also studied. In addition, noise coupled to I/O lines, and EMI were studied for a test board with varying layer thickness between the power and ground planes.