PCB Design Guidelines (HSSI, EMIF, MIPI, True Differential, PDN) User Guide: Agilex™ 5 FPGAs and SoCs
6.1.2. DRAM Break Out in Layout Routing
For discrete DRAM components on PCB, you can use the dog-bone or via in pad at DRAM for the signal transition from inner layer to DRAM. If you use dog-bone via transition, Altera recommends a larger pitch separation to avoid crosstalk between signal vias.
Symmetrical routing of differential signals (DQS/CLK) in the DRAM pin area is limited because of a very small pitch. Altera recommends routing the differential signals as single-ended signals within the DRAM pin field, ensuring to keep the same impedance while changing from differential to single-ended configuration. You must also keep the same routing length for single-ended lane P and N single-ended lane within the DRAM pin field. Applying the skew matching between P and N lanes before reaching the DRAM pin field improves performance.