CID Electromagnetic Compatibility & EMI Control 3

Question 1

What is the purpose of an ESD (Electrostatic Discharge) protection device placed at a PCB connector interface?

Accepted Answer

To clamp transient voltage spikes to safe levels before they damage internal ICs

Answer

ESD protection devices such as TVS diodes clamp fast, high-energy transients at the board edge to voltages safe for downstream ICs, preventing latch-up or permanent damage.

Question 2

In the context of EMC pre-compliance testing, what is the advantage of using a near-field probe rather than waiting for a full OATS or semi-anechoic chamber test?

Accepted Answer

Near-field probes allow rapid identification and localization of noise sources on the PCB during development

Answer

Near-field probes are used iteratively during development to pinpoint EMI hotspots on the PCB, enabling design fixes before the costly and time-constrained formal chamber test.

Question 3

A PCB designer notices that a clock signal's return current is being forced around a plane slot. The most appropriate corrective action is:

Accepted Answer

Reroute the signal over a continuous reference plane or add a ground stitching bridge across the slot

Answer

Rerouting the clock trace over a continuous reference plane or bridging the slot with a bypass capacitor or solid copper connection restores a direct return path and eliminates the high-emission loop.

Question 4

Which statement about differential signaling (e.g., LVDS) and EMI is most accurate?

Accepted Answer

Tightly coupled differential pairs cancel most magnetic fields when the coupling is ideal, reducing radiated emissions

Answer

When a differential pair is tightly coupled and well-matched, the equal and opposite currents produce nearly canceling magnetic fields, dramatically reducing net radiated emissions compared to single-ended signaling.

Question 5

For a board operating above 1 GHz, which via structure modification best reduces the parasitic inductance and capacitance that cause signal integrity and EMI issues?

Accepted Answer

Using a back-drilled (counter-bored) via to remove unused via stub

Answer

Back-drilling removes the via stub below the last used layer, eliminating the transmission line stub resonance that causes insertion loss and radiates EMI at high frequencies.

(CID) Certified Interconnect Designer Practice Test

(CID) Certified Interconnect Designer Practice Test

CID Electromagnetic Compatibility & EMI Control 3