PCB Design Guidelines: Agilex™ 3 FPGAs and SoCs

ID 853726
Date 8/20/2025
Public
Document Table of Contents

5.5.1. Channel Recommendations

  • Evaluate the maximum PCB routing lengths based on specific stack-up and standards.
  • Follow the pair-to-pair stripline spacing rules, where 'H' is the distance from the signal layer to the closest reference layer:
    • 5× H for transmitter–to–transmitter and receiver–to–receiver.
    • 9× H for transmitter–to–receiver.
  • For microstrip routing, use a larger spacing such as 6× H for receiver-to-receiver on Agilex™ 5 SoM board.
  • Keep insertion loss within IEEE specifications.
  • Make the N/P routing as symmetrical as possible.
  • Ensure that the ground plane fully surrounds the HSSI traces.
Informative:
  • Target differential impedance—90 Ω~100 Ω
  • Differential return loss—lower than –15 dB from 0 to Nyquist frequency