Analysis of Electromagnetic Interference Problems Caused by Split Reference Plane on High-Speed Multilayer Boards

Digital/Analog ground partitioning has been used to isolate noisy digital and power current from sensitive analog currents in high-speed multiplayer printed circuit boards. This design, however, breaks the current return path for signal traces that cross the two separated grounds, which causes undesired effects such as signal distortion and radiated emission. Electromagnetic mechanism associated with them needs to be understood to control and suppress these undesired effects. In this paper, equivalent circuit diagrams are presented to explain the current path in a practical camera device with the separated ground. Finally, optimal stitching via locations is determined to provide a good return current path and thus suppress the radiated emission. Numerical simulations are conducted for validation in frequency ranges from 10MHz to 2GHz.