Description
It is recommended to add external AC coupling capacitors given the E-tile reference clock input buffer structure.
Resolution
There are two internal 50ohm terminations that will act as 100ohm parallel termination. See the Intel® Stratix® 10 TX Signal Integrity Development Kit for an example of these capacitors.
Please refer to E-Tile Transceiver PHY User Guide Figure 64. IO Pad Ring - Transceiver Reference Clock Input Pad.