SLAAE45 September   2021 TMUXHS4412

 

  1.   Trademarks
  2. 1Introduction
  3. 2Practical PCB Design Rules
    1. 2.1 PCIe® Specific Standard
    2. 2.2 PCIe® High-Speed Signal Layout Guidelines
    3. 2.3 Vias, Stub, and ESD/EMI Layout Guidelines
    4. 2.4 Power and Grounding Layout Guidelines
  4. 3Layout Examples
  5. 4Summary
  6. 5References

2.1 PCIe® Specific Standard

There are many differences in the various high-speed standards that need to be taken into account when designing the layout of a system. These differences include parameters like data-rates/frequency, AC coupling capacitors, inter-pair skew, intra-pair skew and trace impedance. Table 2-1 lists the standard values for PCIe standard.

Table 2-1 Parameters of PCIe® Standard
Parameter Value
Frequency PCIe® Gen 1: 1.25 GHz (2.5 Gbps)
PCIe® Gen 2: 2.5 GHz ( 5 Gbps)
PCIe® Gen 3: 4 GHz (8 Gbps)
PCIe® Gen 4: 8 GHz (16 Gbps)
AC Coupling Capacitors AC capacitors required:
75 nF–220 nF
Polarity Reversal Allowed
Max Intra-Pair Skew 5 mils
Max Inter-Pair Skew No Inter-pair specification
Trace Impedance PCIe® Gen 1 and 2:100 Ω ±5% differential; 50 Ω ±5% single ended
PCIe® Gen 3 and 4: 85 Ω ±5% differential; 42.5 Ω ±5% single ended