Analysis of inter-bundle crosstalk in multimode signaling for high-density interconnects

While the increasing demand for smaller packages and low-cost platforms aggressively drives the interconnect density per unit area, crosstalk noise due to capacitive and inductive coupling limits the achievable interconnect density. As an alternative, we investigate multimode signaling where n signals are transmitted by exciting all fundamental modes on a group of n closely coupled lines called a bundle. Even though crosstalk is ideally zero in a single bundle, practical implementation of this idea for a typical input/output (IO) bus requires multiple closely-placed bundles. Thus, inter-bundle crosstalk may be an issue. In this paper, we analyze the inter-bundle crosstalk starting with the analytical expressions for the modal conversion from one bundle to another. Frequency domain simulations for both frequency-dependent and frequency-independent terminations are performed to compare performance vs. density benefits of multi-bundle multi-mode interconnects to those provided by conventional single-ended and differential signaling.