What is electromagnetic interference and which mitigation techniques are commonly used in PCB design?

• A. EMI is intentional amplification of signals; use impedance matching and phase shifting.
• B. EMI is noise from power supply only; use solder mask and thermal vias.
• C. EMI is any radiation emitted by a circuit; use shielding and power integrity optimization such as decoupling and proper grounding.
• D. EMI is unwanted coupling or radiation; use grounding/shielding and layout separation of noisy and quiet sections with decoupling capacitors.

Answer: (D)

Electromagnetic interference is unwanted coupling or radiation from a circuit that can disturb other parts of the system. It isn’t limited to emissions from a power supply; EMI can travel along traces, couple between nets, or be radiated by the board itself.

In PCB design, effective mitigation centers on keeping the local power delivery stable and controlling how currents flow. Grounding and shielding provide low-impedance return paths and block emissions from leaving the board. Separating noisy sections (like high-speed digital or switching circuitry) from quiet, sensitive analog areas reduces the opportunities for coupling. Placing decoupling capacitors close to power pins helps smooth voltage transients and lowers high-frequency impedance, which minimizes the generation and propagation of EMI. Together, these practices—grounding/shielding, layout separation, and strategic decoupling—strengthen power integrity and reduce radiated and conducted interference.