SPRAAR7J November   2018  – February 2023 66AK2G12 , AM1806 , AM1808 , AM2431 , AM2432 , AM2434 , AM3351 , AM3352 , AM3354 , AM3356 , AM3357 , AM3358 , AM3358-EP , AM3359 , AM3871 , AM3874 , AM3892 , AM3894 , AM4376 , AM4377 , AM4378 , AM4379 , AM5706 , AM5708 , AM5716 , AM5718 , AM5726 , AM5728 , AM5729 , AM5746 , AM5748 , AM5749 , AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP , AM62A3 , AM62A3-Q1 , AM62A7 , AM62A7-Q1 , AM62P , AM62P-Q1 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442 , AM6526 , AM6528 , AM6546 , AM6548 , BQ24392-Q1 , HD3SS6126 , LP8727 , OMAP-L137 , OMAP5912 , TMS320C6745 , TMS320DM335 , TMS320DM355 , TMS320DM365 , TMS320DM368 , TMS320DM369 , TMS320DM6441 , TMS320DM6443 , TMS320DM6446 , TMS320DM6467 , TMS320DM8127 , TMS320DM8147 , TMS320DM8148 , TMS320DM8165 , TMS320DM8167 , TMS320DM8168 , TMS320VC5506 , TMS320VC5507 , TMS320VC5509A , TS3USB221A-Q1 , TS3USBA225 , TSU5611 , TSU6111 , TSU6111A , TSU6721 , TSU8111

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Scope
    2. 1.2 Critical Signals
  4. 2General High-Speed Signal Routing
    1. 2.1 PCB Fiber Weave Mitigation
    2. 2.2 High-Speed Signal Trace Lengths
    3. 2.3 High-Speed Signal Trace Length Matching
    4. 2.4 High-Speed Signal Reference Planes
  5. 3High-Speed Differential Signal Routing
    1. 3.1  Differential Signal Spacing
    2. 3.2  High-Speed Differential Signal Rules
    3. 3.3  Symmetry in the Differential Pairs
    4. 3.4  Crosstalk Between the Differential Signal Pairs
    5. 3.5  Connectors and Receptacles
    6. 3.6  Via Discontinuity Mitigation
    7. 3.7  Back-Drill Stubs
    8. 3.8  Increase Via Anti-Pad Diameter
    9. 3.9  Equalize Via Count
    10. 3.10 Surface-Mount Device Pad Discontinuity Mitigation
    11. 3.11 Signal Bending
    12. 3.12 Suggested PCB Stackups
    13. 3.13 ESD/EMI Considerations
    14. 3.14 ESD/EMI Layout Rules
  6. 4References
  7.   A Device Layout Parameters
  8.   Revision History

3.1 Differential Signal Spacing

To minimize crosstalk in high-speed interface implementations, the spacing between the signal pairs must be a minimum of 5 times the width of the trace. This spacing is referred to as the 5W rule. A PCB design with a calculated trace width of 6 mils requires a minimum of 30 mils spacing between high-speed differential pairs. Also, maintain a minimum keep-out area of 30 mils to any other signal throughout the length of the trace. Where the high-speed differential pairs abut a clock or a periodic signal, increase this keep-out to a minimum of 50 mils to ensure proper isolation. For examples of high-speed differential signal spacing, see #SPRAAR76242 and #SPRAAR79659.

GUID-5BCD5A0F-7EDF-4D28-821D-7238AD5C8733-low.gif Figure 3-1 USB3/SATA/PCIe/HDMI/SGMII/CSI Differential Signal Spacing (mils)
GUID-9EF8B4C4-BE3B-4166-B1A1-3FFEC276D7C2-low.gif Figure 3-2 USB2 Differential Signal Spacing (mils)