Q: How to design PCB layout for EMC compliance (CISPR 22/EN 55022)?
Answer
PCB EMC design for CISPR 22 compliance: (1) Partition: separate analog/digital/power sections physically. (2) Ground plane: full unbroken ground plane on layer 2 is mandatory. (3) Critical signals: keep clock and high-speed data traces short with ground reference. (4) Power filtering: bulk cap + 100 nF ceramic as close as possible to IC power pin. (5) Ferrite beads on power rails to isolate digital noise from analog. (6) Via stitching: ground vias every 1/20th of the wavelength of the highest frequency (e.g. every 3 mm for 1 GHz). (7) Crystal oscillator: keep within 5 mm of MCU with guard ring around the crystal. (8) Connector EMC: place filter components at the connector not on the PCB interior. (9) Slot antennas: avoid slots that span more than lambda/20 on ground planes. Use pre-scan with near-field probe (30 MHz-1 GHz) during design.
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