Q: What is proper grounding strategy to minimize EMI in mixed-signal PCB designs?
Answer
Grounding principles for EMC: (1) Single-point vs multi-point ground: low-frequency (<1 MHz) circuits use single-point star ground; high-frequency (>1 MHz) use multi-point ground with ground planes. (2) Never mix ground returns: digital return current stays in digital ground; analog return stays in analog ground; power return stays in power ground. (3) Connect analog and digital grounds at a single point near the power supply – usually star connection at the LDO or filter. (4) Ground planes: always better than ground traces for RF and high-speed signals. (5) Use guard rings around high-impedance analog nodes (ADC inputs op-amp inputs) connected to analog ground. (6) Chassis ground: connect metal enclosure to board ground at one point to prevent ground loops. (7) Return path: always route signal traces adjacent to their ground return path to minimize loop area. Never route a signal over a split in the ground plane.
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