Q: What are the techniques for reducing EMI from microstrip and printed circuit board traces?
Answer
PCB trace EMI reduction: (1) Keep traces short: radiation is proportional to loop area – minimize. (2) Ground plane: route high-speed signals on top/bottom layer over solid ground plane. (3) Terminate properly: unmatched transmission lines cause reflections (ringing) which radiate. Use series termination (source series resistor) for point-to-point connections. (4) Avoid 90-degree bends: use 45-degree mitered corners or rounded bends. (5) Differential pairs: maintain tight coupling (matched spacing) throughout the trace. (6) Staggered via usage: if vias are unavoidable stagger them to minimize discontinuity. (7) Guard traces: route guard traces (grounded) on both sides of critical high-frequency signals. (8) Anti-pad clearance: maintain clearance around through-hole vias for high-speed signals to reduce parasitic capacitance. (9) Reduce edge rates: add 10-33 Ohm series resistor at driver output to slow edge rates for non-critical high-speed signals.
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