EMC PCB Layout Notes

  • Implicit RLC (potentially filters) and antennas formed by traces
  • Large ground/voltage planes serves as EMI shield, low impedance path current sink
  • True differential signals can be generated by current sources
  • Decouple with ferrite beads if radiation inevitable by geometry/placement
  • Avoid / minimize large current swings on analog plane (e.g. buffer digital signals)
  • Star ground when splitting sections: don’t let heavy digital current sink through analog ground by cascading the grounds.
  • Don’t really need to split planes as long as large digital current’s preferred return paths are localized and far away from the analog section.
  • AGND/DGND refers to the grounds responsible for different sections of a mixed-signal IC. Has nothing to do with which actual ground to tie to. (e.g. DGND pin in ADC chips still goes to analog ground plane as it has low switching current)

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