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

4.6.1. GTS Transceiver Channel Recommendations

  • Minimum two inches of PCB Route length to a maximum four inches for SoM and carrier board together. Evaluate the maximum and minimum routing lengths based on specific PCB stack-up and standards.
  • Follow the pair-to-pair spacing rules:
    • 5×H 2 for transmitter-to-transmitter and receiver-to-receiver stripline routing
    • 9×H2for transmitter-to-receiver, transmitter-to-others, and receiver-to-others stripline routing
    • 6×H or larger spacing for microstrip routing and for receiver-to-receiver on SoM board
  • Keep total insertion loss, skew, and other requirements within the PCIe* 4.0 specifications.
  • Place the AC coupling capacitors on the FPGA transmitter paths close to the FPGA or connector. Do not place the AC coupling capacitors in the middle of the trace routing. Run a simulation to optimize the cut-out size of AC capacitors, as demonstrated in the General Design Considerations section.

Informative:

  • Target Differential Impedance: 85 Ω
  • Differential return loss better than -15 dB from 0 to 8 GHz
2 'H' is referenced to the thinner dielectric side