How to Find Return Path Discontinuities the Keysight Way
Chun-Ting "Tim" Wang Lee, PhD
SI Application Scientist at Keysight Technologies
You are walking down the sidewalk merrily, humming your favorite tune. As you take the next step, you find a void beneath your right foot. It was too late to take your foot back, you fell into an endless dark abyss.
"Wow, that was scary." You woke up in cold sweats, thanking the deities that it was only a dream. Unfortunately, in PCB designs, return path void under a signal trace is no dream. It is a reality that must be dealt with.
Return path discontinuity creates a change in the instantaneous impedance the signal sees as it travels down the line. This impedance difference results in the reflection of the signal.
Because there is definitely more than 1 impedance discontinuity in a real channel, this reflected signal will reach the receiver and contribute to inter-symbol-interference (ISI), degrading the signal integrity of the channel. If you are not looking for these discontinuities in your designs, you are in for some cold sweats.
To empower the PCB designers with the knowledge of the location of the return path discontinuities, Keysight Technologies pioneered the return path discontinuity detection in Electrical Performance Scan (EP-Scan). As shown in below figure, the return path discontinuities are detected and reported in a systematic manner.
Try the EP-Scan 2023 using below links.
Leave a comment below if you want to be in on the exclusive first look of EP-Scan 2023 Update 1!
In the meantime, remember to anticipate before you measure and simulate.