PCB Design Guidelines (HSSI, EMIF, MIPI, True Differential, PDN) User Guide: Agilex™ 5 FPGAs and SoCs

ID 821801
Date 8/29/2025
Public
Document Table of Contents

3.5. Fiber Weave

The fiber weave effect happens when differing dielectric constants of the PCB fiber and resin substrate cause a phase skew in differential pair signals. The phase skew manifests as AC common mode noise at the receiver, affecting the receiver voltage and timing margin.

To mitigate the fiber weave effect, specify a dense spread instead of a sparse weave for the PCB core and prepreg materials. For example, specify 1078, 1035, 3313, or 1067 instead of 106 or 1080.