A MULTIMODAL ANALYSIS OF THE EFFECTS OF SERIES FILTERING OVER HIGH SPEED SIGNAL PATHS

Due to the high strip density in nowadays PCB circuits, high speed signal paths are often placed next to other signal strips. These strips, commonly routed over a ground plane, generate coupled microstrip sections. If these high speed signals have high harmonic components, they can easily interfere other signal strips. In order to reduce this high harmonic content, a series impedance is sometimes placed into the signal path to filter this high harmonic content. In this paper, the effect of this series filtering is analyzed from a multimodal point of view. A multimodal analysis, very common in EMC, allows a simple interpretation of the phenomena involved in the integrity of the signals propagated through the strips. In order to test the adequacy of this multimodal approach, a PCB circuit is analyzed, circuitally simulated and measured. The good agreement between circuit simulation and measurements validates this multimodal approach.