Q: How to design robust power plane splitting for mixed analog/digital PCB?
Answer
Split planes can isolate analog from digital grounds but improper splitting causes more problems than it solves. Rule 1: NEVER split the ground plane beneath a high-speed signal – the return current must have a complete path. Better approach: use a single solid ground plane and separate analog circuits physically on the board with digital ground connected at the power supply star point. If you must split: use a single-point bridge (narrow trace) at the star point. For ADC reference (VREF) use an analog power plane island isolated from digital switching noise. Route ADC inputs with guard rings (ground trace on both sides of the analog input trace).
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