Intel® Agilex™ Device Family High-Speed Serial Interface Signal Integrity Design Guidelines

ID 683864
Date 9/26/2022
Public
Document Table of Contents

1.4.1.4. AC Coupling Capacitor

The layout design of AC coupling capacitors can impact high-speed channel performance.
  • Use a 0402 or 0201 size capacitor for a smaller parasitic and smaller footprint.
  • Place the AC coupling capacitors at the device end or connector end. Do not place them in the middle of the trace routing.
  • Keep the placement of the AC coupling capacitors on the two lines of a differential pair symmetrical, make sure that the fan-in and fan-out routing of the capacitors is symmetric, and make sure the line lengths on both sides of the capacitors are matched.
  • Similar to the connector landing pad, optimize the cut-out size under the capacitor pad using a 3D EM simulation tool for your specific stackup and capacitor pad size. Cut the direct, next-layer ground plane of the capacitor pad.
Figure 14. AC Coupling Capacitor Layout

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