Low Loss Skip Layer Transmission Lines With Common Mode Filtering for Packages

To address the increasing bandwidth demand in chip-to-chip communication, data rates of high-speed serial input–output (I/O) interfaces have been aggressively increasing, which tightens the available packaging electrical budgets for channel loss and noise. Enabling a cost-effective and high-volume manufacturing compatible solution to improve these metrics is of great importance. In this article, we expand on the recently introduced skip-layer-based transmission line (TL) technology with simultaneous common mode (CM) filtering properties, which can address both of these challenges simultaneously. The TL is composed of periodic repetitions of narrow and wide sections, which generates a CM impedance contrast to filter out the CM noise, while differential impedance is kept constant by locally voiding the planes below and above the wide trace sections. Because of the wider sections, the loss is also smaller. We provide a theoretical discussion of the CM filtering using Bloch’s Theory on periodic structures. We also provide an analytical formulation, which utilizes quasi-static assumption, for crosstalk control. Finally, we demonstrate the electrical performance of this new TL technology with both numerical and experimental data in frequency and time domains and provide design guidelines to address some of the practical aspects of real-world applications.