Impact of Via Stub Position on High Speed Serial Links

While designing any interface, the impact of channel components like vias, trace, materials, stack-up, connectors, cables, transmitter/receiver packages, and other parasitic effects need to be considered. This paper discusses the impact of via and more importantly the impact of via stub position and length on high speed serial links. Via stub resonance impacts high speed signals but in this paper it is shown that their position also has an impact. Depending on where the via stubs are located on a high speed channel, sometimes their effect could be insignificant (no eye degradation) and sometimes their impact could be significant (major eye degradation). High speed analysis is performed at 16Gbps and 20Gbps to demonstrate the margin loss due to various positions of via stubs.