PCB Signal Integrity & EMC

Question 1

What is the industry-standard characteristic impedance target for most controlled-impedance PCB traces?

Accepted Answer

50 ohms

Answer

50 ohms is the industry-standard characteristic impedance used to match source and load impedances, minimizing reflections on high-speed traces.

Question 2

What phenomenon occurs when a high-speed signal travels down a transmission line and encounters an impedance discontinuity?

Accepted Answer

Signal reflection

Answer

Reflections occur at impedance discontinuities because signal energy that cannot pass through the mismatch is sent back toward the source.

Question 3

Which termination method places a resistor matching the trace's characteristic impedance between the signal line and ground at the far end of the trace?

Accepted Answer

Parallel (shunt) termination

Answer

Parallel termination places a resistor equal to the characteristic impedance to ground at the load end, absorbing reflected energy and preventing signal bounce.

Question 4

At what fraction of signal wavelength does a PCB trace typically need to be treated as a transmission line requiring controlled impedance?

Accepted Answer

λ/10

Answer

Traces longer than 1/10 of the signal wavelength (or equivalent rise-time length) must be treated as transmission lines to avoid signal integrity problems.

Question 5

In a stripline PCB layer configuration, where is the signal trace located within the stackup?

Accepted Answer

Between two reference planes

Answer

Stripline traces are embedded between two ground or power reference planes, providing shielding on both sides and superior EMI performance compared to microstrip.

PCB - Design Practice Test

PCB - Design Practice Test

PCB Signal Integrity & EMC