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Susano , 12-31-2025, 04:29 PM

In philip salmony mixed signal course the lecture routing he did mention two things that seem contradicting to me now that I need clarifying
at first he mentioned that stubs are bad idea for EMI and SI because they expand the field and variate the impedance matching of the trace which is understandable
but later in the same lecture he created a T connection for VCOM and 3.3V connection and mentioned that T connections should be okay and there's no proven problem with them although I understand those are DC traces anyway

I'm wondering how are both of those things different ? a T connection is still an impedance imbalance to my understanding if not for the fact that this is a DC trace of course

QDrives , 01-02-2026, 04:36 PM

In part a stub is a T-connection.
The 'difference' is the length of the 'stub' compared to the length of the 'through' line.
More importantly, the length of the stub compared to the length of the wave (rise time).
With 'DC', that wave length is in kilometers, so no trace on a board will cause an issue.

Robert Feranec , 01-04-2026, 11:18 AM

in T connection you may want to keep the length of branches the same, have a look here: https://youtu.be/CDJn-35W8sg?si=RHf4ntDAmaCy6-lP

Susano , 01-12-2026, 05:19 AM

thanks for your response

So my intuition was generally right the only thing this T connection was okay was the fact that this a DC signal

when going with high enough frequency this T connection will be a problematic stub

Susano , 01-12-2026, 07:21 AM

wow thanks for the dense information what I understood so far is that branching is still a problem but having different lengths is making the problem worse and uncontrolled since the branches form a behaviour of what I might call it an LC-Tank Like behaviour the signal is bouncing between the two branches like an LC tank would and not reflecting back to the proberly matched end for dissipation did I get that right ?

QDrives , 01-12-2026, 03:54 PM

"*...bouncing...*" -- in regards to rise time, yes.