AN 766: Intel® Stratix® 10 Devices, High Speed Signal Interface Layout Design Guideline

ID 683132
Date 3/12/2019
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Sweeping Void Width Only on the First GND Plane under the Capacitor

Keeping the via anti-pad radius fixed while adjusting the void width on the first GND plane under the AC capacitors also impacts the structure's impedance.

Figure 42. Differential Return Loss and TDR Impedance Performances for 0402 AC Capacitors by Various GND Cutout Widths

Changing the void width from 60 mil to 90 mil impacts the structure's impedance and return loss. A 90 mil void width is the optimum solution for this case and results in the least mismatching.