10.1.2 High-Speed PCB Trace Routing and Coupling
Observe the following general high-speed recommendations for high-speed trace routing:
- For differential pairs, maintain a uniform width and gap for each differential pair where possible. When traces must diverge (for example, due to AC-coupling capacitors), ensure that the traces branch out or merge uniformly.
- To prevent reflections due to trace routing, ensure that trace bends are at most 45°. Right angle bends should be implemented with at least two 45° corners. Radial bends are ideal.
- Avoid using signal vias. If signal vias must be used, a return path (GND) via must be placed near the signal via to provide a consistent ground reference and minimize impedance discontinuities.
- Avoid via stubs by back-drilling as necessary.
SDI_OUT1± and SDI_OUT2±:
- Use an uncoupled trace with 75-Ω single-ended impedance for signal routing to SDI_OUT1± and SDI_OUT2±.
- The trace width is typically 8 to 10 mils with reference to a Layer-3 ground plane.
IN0± and OUT0±:
- Use coupled traces with 100-Ω differential impedance for signal routing to IN0± and OUT0±.
- The trace width is typically 5 to 8 mils with reference to a Layer-2 ground plane.