PCB Design Guidelines: Agilex™ 3 FPGAs and SoCs

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

5.5.3. Quad Small Form-factor Pluggable and Small Form-factor Pluggable Connector Routing

Ethernet commonly uses Quad Small Form-factor Pluggable (QSFP) and Small Form-factor Pluggable (SFP) connectors.

To minimize the inductance of the ground connection, add ground vias on both sides of the connector ground pins and connect them with a short and thick ground trace. Keep the connector ground pins locally-shorted to maintain an equal potential.

Altera recommends routing the transmitter and receiver on different layers. Length matching for each pair is required. Both P and N lanes must be in phase to recover the data.

To minimize insertion loss, always use the minimum routing length from the FPGA to the connector.

Altera recommends using a 3D simulation to optimize the BGA breakout.

Try keeping the return loss lower than –15 dB at the Nyquist frequency, preferably lower than –20 dB.

Control the impedance variation of the cut out area by making the cut-out as small as possible, ideally within ±5 Ω.