CID Electromagnetic Compatibility & EMI Control

Question 1

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

Accepted Answer

Placing each signal layer adjacent to a continuous reference plane

Answer

Routing all high-speed signals on outer layers

Answer

Increasing the distance between signal and ground planes

Answer

Using thicker copper on signal layers

Question 2

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

Accepted Answer

To reduce crosstalk and contain the electromagnetic field

Answer

To increase the characteristic impedance of the signal trace

Answer

To improve the thermal dissipation of the PCB

Answer

To increase the current-carrying capacity of the trace

Question 3

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

Accepted Answer

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

Answer

Increase the impedance discontinuity at layer transitions

Answer

Block high-frequency currents from the power plane

Answer

Reduce the via capacitance to improve signal rise time

Question 4

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?

Accepted Answer

Fringe field radiation at board edges

Answer

Differential-mode radiation from power traces

Answer

Thermal gradients across the power plane

Answer

Signal reflection at the plane boundary

Question 5

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

Accepted Answer

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

Answer

Placing the capacitor at the board edge to shorten the loop to the power supply

Answer

Using long traces between the IC and capacitor to distribute the bypass effect

Answer

Mounting the capacitor on the opposite side of the board beneath the IC

Question 6

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

Accepted Answer

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

Answer

It improves impedance matching for the signal

Answer

It reduces the capacitance between the signal and ground plane

Answer

It provides isolation between two different signal domains

Question 7

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

Accepted Answer

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

Answer

A copper pour on the same layer as the oscillator with no vias

Answer

A thin solder mask opening over the oscillator area

Answer

Increasing trace width of the oscillator output to reduce impedance