Radiated emission far-field propagation with multiple ground stitch locations within a printed circuit board

摘要

Printed circuit boards (PCB) exhibit numerous properties related to the development of common-mode currents created by digital components. When multiple devices are switching simultaneously, a complex RF field will propagate into free space from package bond wires, the silicon die itself, via implementation, poor transmission line routing, the physical board edge, interconnects, and numerous other areas generally not recognized by the designer. The majority of electromagnetic interference (EMI) is associated with a poor power distribution network (PDN). Do we really know where the EMI is coming from with a fully populated assembly and what are the effects of increasing the number of ground stitch locations to chassis ground to disrupt propagating RF? Measurement of propagated field amplitude is easy related to regulatory compliance standards. Within a complex PCB, one generally does not know the source of the EMI based on only simulation, since many second and third order parasitics are unknown to the designer. This paper investigates overall effects of disrupting the dipole antenna structure of the power distribution network in the far field using numerous source stimuli versus a simple single source stimulus along with simple transmission line routing to a simple end termination.