Method of Modeling Differential Vias

Accurate, models for vias in a multilayer circuit board are necessary to predict link performance in the GHz regime. This paper describes a methodology to build a high bandwidth, scalable first approximation circuit model using simple transmission lines of long vias typically used in thick backplane designs. System architects and backplane designers for example can quickly model various interconnect topologies for what-if scenarios and to set the direction for a more detailed design evaluation. It includes necessary parameters to study and quantify the through and stub effects when effective dielectric constant and via impedance are varied. As an added benefit, this simple modeling technique also provides a means to validate and sanitize later models built with 3D field solvers when users have a limited skill set in the use of the tools.