In high-speed digital channel design, vias are everywhere and are becoming very crucial elements to the channel performance. Especially with the higher data rate requirements in mobile, networking, and data center applications, the effect of vias in a design is very noticeable. Design engineers have traditionally used time domain reflectometry (TDR) as a tool to characterize and optimize via designs, yet the TDR approach comes with shortcomings such as demanding shorter rise-time step signal or larger bandwidth S-parameters, and inaccurate read-out on the via impedance.
In this article, we propose a simple and effective Z-input impedance method that augments the traditional TDR method for characterizing and optimizing via designs in much faster speed systems.