SNLA426 june   2023 DS320PR1601 , DS320PR410

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 PCIe Gen3, Gen4, and Gen5 Loss Budget
  6. 3 Minimum Eye Width
  7. 4 Cross Talk Mitigation
  8. 5 Humidity and Temperature Insertion Loss
  9. 6 Critical Signals
  10. 7 General High-Speed Signal Routing
  11. 8 PCB Grain and Fiber Weave Selection
  12. 9 PCB Material Loss Budget
  13. 10High-Speed Signal Trace Impedance
  14. 11High-Speed Signal Trace Length Matching
  15. 12Differential Trace Routing Guidelines
  16. 13Differential-Inter-Pair Matching
  17. 14Intra-pair Length Matching
  18. 15Trace Bends
  19. 16Minimum Differential Trace-To-Trace Distance
  20. 17Serpentine Guidelines
  21. 18High-Speed Differential Signal Quick Rules
  22. 19High-Speed Differential Pair Reference Plane
  23. 20Via Staggering
  24. 21Via Stubs
  25. 22Via Pads
  26. 23Via Discontinuity Mitigation
  27. 24Back-Drill Stubs
  28. 25AC Coupling Capacitors Placement
  29. 26AC Coupling Capacitor Physical Placement
  30. 27Auxiliary Signal AC Match Termination
  31. 28Suggested PCB Stack-ups
  32. 29Summary
  33. 30References

4 Cross Talk Mitigation

PCIe Gen5 cross talk needs to be mitigated, meaning there is a total channel loss that needs to be considered. We must allow at least 4 to 5 dB increased signal strength versus total system loss. This mitigation can be achieved by reducing differential signal loss insertion loss (SDD21) or improving cross talk. This 4 to 5 dB of signal strength improves the signal to noise ratio and thus improves the targeted BER (1E-12). To reduce the effect of cross-talk, maximize pair-to pair spacing, ground stitching, and the optimization of via anti-pads – more details about the listed topics are discussed in later paragraphs. Typically, it is advised to use closely coupled strip line to reduce the effect of cross-talk . However, vias and anti-pads need to be designed carefully. The DS320PR1601 TI EVM is designed using a co-planar GND reference waveguide, which reduces the effects of cross-talk.