If CI test failures are still observed after trying the steps above, the issue is most likely on the DUT side. Here are some recommendations to further improve CI test performance:

• Check the CI failing frequency:
  • If CI tests are failing at lower frequency ranges, check the power lines, power plane, and power supplies on the boards near the connector ground or MDI lines. Also verify the power supply is not close to any noise sources
  • If CI tests are failing around the clock frequency, check the clock trace or clock source on the board. Verify they are not close to the connector ground or MDI lines
  • If CI frequency failing around 10MHz to 80MHz, normal PHY operating frequency, please try the following recommendations below
• Solid earth ground path on the connector ground of DUT
• Remove bob smith terminations on unused pairs to help with CI tests
  • Having a bob smith termination on the unused pair can provide a smaller impedance path to earth ground. This can result in higher common mode noise flowing on the unused pair, further coupling noise to the used pair
  • On the used pair, common mode impedance is generally large due to the common choke
    
• Verify there is ground separation between the connector ground and digital ground to prevent any noise injected directly into the system. This can reduce the ground bounce effect on the system
• No shorted center taps on the transformer
  • Reduces crosstalk
  • Reduces chance of mode conversion
• Discrete magnetics and RJ45 connector helps reduce the injection area of ESD noise and improve the performance of the transformer during ESD tests
• Optimize the layout of MDI lines to reduce the common mode noise picked up from surroundings, ground bounce, and other signals on the PCB.
• Optimize the PCB connector ground to provide a better ground path and minimize the effect coupled to the MDI lines