CID Signal Integrity & High-Speed Design

Question 1

What causes signal reflections in high-speed PCB traces?

Accepted Answer

Impedance mismatches

Answer

Signal reflections occur in high-speed PCB traces when there is a sudden change or discontinuity in the characteristic impedance along the transmission line. This impedance mismatch causes a portion of the signal energy to reflect back towards the source. Such reflections lead to signal integrity issues like ringing, overshoot, and undershoot, degrading signal quality.

Question 2

Which parameter affects the speed of signal propagation in a PCB trace?

Accepted Answer

Dielectric constant of the substrate

Answer

The speed of signal propagation in a PCB trace is primarily determined by the dielectric constant (Dk or Er) of the substrate material. A lower dielectric constant allows electromagnetic waves to travel faster through the material, as the signal experiences less impedance. This is a crucial factor in high-speed design for minimizing signal delay.

Question 3

What is crosstalk in high-speed design?

Accepted Answer

Signal coupling between adjacent traces

Answer

Crosstalk is an undesirable phenomenon in high-speed PCB design where a signal on one trace (the aggressor) electromagnetically induces noise or interference onto an adjacent trace (the victim). This coupling occurs due to mutual capacitance and inductance between the traces. Crosstalk degrades signal integrity, potentially causing false triggering or data errors.

Question 4

Why is controlled impedance important in high-speed PCB design?

Accepted Answer

To reduce reflections and maintain signal integrity

Answer

Controlled impedance is critical in high-speed PCB design to ensure that signals propagate without reflections. By maintaining a consistent characteristic impedance along a transmission line, designers can match the impedance of the source and load. This prevents signal reflections, thereby preserving signal integrity and preventing distortion.

Question 5

Which component is used to terminate a transmission line to prevent reflections?

Accepted Answer

Resistor matching characteristic impedance

Answer

To prevent signal reflections at the end of a transmission line, a termination resistor is used. This resistor is carefully chosen to match the characteristic impedance of the trace. By absorbing the signal energy at the load, it prevents reflections from bouncing back towards the source, thus maintaining signal integrity.

(CID) Certified Interconnect Designer Practice Test

(CID) Certified Interconnect Designer Practice Test

CID Signal Integrity & High-Speed Design