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3.6.3. QSFP Connector Routing
Ethernet commonly uses QSFP connectors, however the SOM and carrier board do not have any QSFP connectors. Add ground vias on both sides of the connector ground pins and connect them with short, thick ground trace to minimize the inductance of the ground connection. Keep the connector ground pins locally shorted to maintain an equal potential. Altera suggests routing Tx and Rx on different layers. Length matching for each pair is required. Both P and N lanes must be in phase to recover the data. For breakout design, refer to the following figures. Always use the minimum routing length from the FPGA to the connector to minimize insertion loss. Altera recommends to use a 3D simulation to optimize the BGA breakout. Try to make return loss lower than -15 dB at Nyquist frequency (lower than -20 dB is better) and control the impedance changing of cut-out area by making it as small as possible (ideally within ±5 ohm).