Switching voltage regulator noise coupling to connector signal pins through near field radiation

In a server system, the switching voltage regulator (VR) noise coupled to the IO pins of the adjacent memory riser connector through the open air above the base board, and the link performance was impacted by the coupling. A simulation flow was developed to reproduce this EMI phenomenon. The flow first used electromagnetic field solvers to extract the VR related power network and the VR-IO coupling network, and then the di/dt and dv/dt noise sources and the induced IO noise were solved in HSpice®. The simulation revealed the underlying coupling mechanism: The high frequency current loop formed by the power MOSFET, the VR power shapes, the snubber RC circuit at the bottom layer of the board, and the stitching via acted as a transmitting loop antenna, and the radiating field propagated through the air and was picked up by another loop (receiving antenna) formed by the riser connector pins. An effective mitigation method is to use bigger snubber resistor to damp this near field radiation. Both the coupling theory and the effectiveness of the mitigation method were proved by the measurements.