Novel Periodic-Aperiodic Routing to Mitigate Floquet Mode Resonances in Crosstalk Transfer Function Due to Periodically Routed Structures

Reducing cost in printed circuit board (PCB) layout has pushed designers to use broadside coupled layers to reduce the layer count. The traces are generally routed at an angle in zig-zag fashion to eliminate fiber-weave impact on the insertion loss (THRU) of the channel. If the zig-zag routing is periodic, then it can increase the crosstalk due to Floquet mode resonances. The Floquet resonances aggravate near-end crosstalk (NEXT) and degrade the insertion loss (THRU) profiles. Creating any random structure will not mitigate the Floquet mode resonance. The aperiodic topology created by making the each unitcell different in length did not mitigate the resonances observed in periodic structure but instead created additional resonances in the frequency range of interest. The other challenge for the layout engineers is to route the aperiodic topology that contains different unit cell blocks with different lengths and angles on a real board. In this paper, the proposed solution relies on "periodic-aperiodicity" to eliminate these resonances. The topology reuses the unitcell from periodic routing that have same lengths but only vary the spacing between each unitcell to create the aperiodicity. The proposed topology is easy to route as layout engineers can reuse the periodic routing and space them with aperiodic uncoupled segments.