Electromagnetic Compatibility & EMI Control Flashcards

Which PCB stackup strategy most effectively reduces common-mode EMI radiation from high-speed traces?

Answer: Placing each signal layer adjacent to a continuous reference plane

Placing signal layers adjacent to a continuous reference plane minimizes the loop area of the return current path, directly reducing radiated EMI.

What is the primary purpose of a ground guard trace placed alongside a high-speed signal trace?

Answer: To reduce crosstalk and contain the electromagnetic field

Guard traces shielded to ground contain the electromagnetic field around the signal trace, reducing crosstalk and EMI coupling to adjacent circuits.

In EMC design, a 'stitching via' near a signal via that crosses reference plane layers primarily serves to:

Answer: Provide a low-inductance return current path across the plane split

Stitching vias placed near signal vias give return currents a direct, low-inductance path when transitioning between reference planes, preventing loop area expansion and EMI.

The 20-H rule in PCB design recommends that power planes be set back from the board edge by 20 times the distance between the power and ground planes. What does this primarily reduce?

Answer: Fringe field radiation at board edges

The 20-H rule reduces fringe electric fields that extend beyond the board edge by setting back the power plane, limiting edge radiation that contributes to EMI.

Which decoupling capacitor placement practice best minimizes high-frequency EMI from an IC power pin?

Answer: Placing the capacitor as close as possible to the IC power pin with short, direct connections to power and ground vias

Placing decoupling capacitors with minimal lead inductance directly at the IC power pin provides the lowest impedance path and fastest charge delivery for noise suppression.

What is the typical effect of a split in the ground plane beneath a high-speed signal trace?

Answer: It forces return current to detour around the split, increasing loop area and radiated emissions

A ground plane split forces the return current to take a longer path around the gap, greatly increasing the effective loop area and thus radiated emissions.

Which shielding technique is most appropriate for containing EMI generated by a local high-frequency oscillator on a PCB?

Answer: A metal shield can soldered to the PCB ground plane around the oscillator

A metal shield can bonded to the PCB ground plane provides a Faraday enclosure that attenuates near-field EMI radiation from the oscillator to surrounding circuitry and external environments.