Anticipating EMI from coupling between high-speed digital and I/O lines

The increasing speed of digital circuit design as well as the density of printed circuit board (PCB) layouts often result in more challenging electromagnetic interference (EMI) problems. The coupling between a high-speed digital line and an I/O line can be a primary EMI coupling path, and the attached cable a dominant radiator. This mechanism is studied and modeled herein in a multi-stage modeling fashion. EMI modeling is developed for coupling between the transmission lines, and the attached cable as the EMI antenna. Finally, the EMI is calculated for the coupled noise driving the attached cable. The agreement between the modeled and measured results demonstrates that the modeling method is suitable for estimating the EMI due to high-frequency coupling to I/O lines.