Design Guideline Glossary
Jetson AGX Xavier Series Product DG-09840-001_v2.5 | 138
• Breakout Spacing
Possible exception to board trace spacing where different spacing rules are allowed
under module connector pin in order to escape from the pin array. Outside device
boundary, normal spacing rules apply.
ï‚„ Reference Return
• Ground Reference Return Via and Via proximity (signal to reference)
> Signals changing layers and reference GND planes need similar return current
path.
> Accomplished by adding via, tying both GND layers together.
• Via proximity (signal to refeference) is distance between signal and reference return
vias.
> GND reference via for Differential Pair.
> Where a differential pair changes GND reference layers, return via should be
placed close to and between signal vias (example to right).
• Signal to return via ratio
Number of Ground Return vias per Signal vias. For critical IFs, ratio is usually 1:1. For
less critical IFs, several trace vias can share fewer return vias (i.e. 3:2 – 3 trace vias
and 2 return vias).
• Slots in Ground Reference Layer
> When traces cross slots in adjacent power or ground plane.
> Return current has longer path around slot.
> Longer slots result in larger loop areas.
> Avoid slots in GND planes or do not route across them.
• Routing over Split Power Layer Reference Layers
> When traces cross different power areas on power plane.
− Return current must find longer path - usually a distant bypass cap.
− If possible, route traces with solid plane (GND or PWR) or keep routes across
single area.
> If traces must cross two or more power areas, use stitching capacitors.
− Placing one cap across two PWR areas near where traces cross area
boundaries provides high-frequency path for return current.
− Cap value typically 0.1uF and should ideally be within 0.1" of crossing.
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