Description

Gigabit Ethernet has established itself as the standard in the networking in office and industrial environments. However, when designing a Gigabit Ethernet interface, questions often arise about the shield connection of the cable and the design of the front end, especially with regard to the ground connections. Searches on the Internet reveal various suggestions for shield termination, often suggesting a 1-nF Y capacitor. However, the effect on the performance of the interface and the EMC behavior is not described. Würth Elektronik has therefore developed a reference design to be able to measure EMC aspects in detail. This App Note is based on the reference design and takes a detailed look at the EMC behavior of the Gigabit Ethernet interface with different shield connections and configurations.  In addition, the App Note provides design recommendations based on extensive hardware testing.

Contents:

• Gigabit Ethernet basics
• Measurements in the time domain
• EMC evaluation of the reference design
  Disturbance variables
  Interference emission
  Interference immunity
• Conclusion and design recommendations