FEDEVEL
Platform forum

Sniper2 , 05-06-2025, 05:58 PM

So after i route my MDI 100 OHM differential pairs into the transformer on the other side i get isolated pairs that need to be routed without a GND plane .
But how do i define their impedance?
Is routeing them as short as possible as traces ok ? well in quasi differential style
If i am to calculate self referenced differential pairs properly without a ground lane i end up with insane numbers so i think it is not that practical
We are talking about 1-2 cm here.
What would be the proper way

Sniper2 , 05-06-2025, 05:59 PM

Same question for Audio after the transformer

QDrives , 05-06-2025, 07:24 PM

You are asking the same question thousands of us are asking.
So far all I can see is remove the Gnd and use 'normal' width. Make it wider if you have space.
I have also seen plenty where the Gnd is still there.
As long as you keep it short (<25mm) you should be ok.

Sniper2 , 05-06-2025, 07:37 PM

yea about that length

Sniper2 , 05-06-2025, 07:37 PM

maybe shorter depends how it firs my backplane connector

QDrives , 05-06-2025, 07:45 PM

As always, the shorter the better.

QDrives , 05-08-2025, 03:23 PM

https://youtu.be/Rr9NBtrA4t4?t=1429

Robert Feranec , 05-14-2025, 04:17 AM

theoretically if you use no reference plane the impedance can be calculated the way that you move reference plane far away in the calculator. But you may end up with very wide tracks. Often I just try to make the tracks as short as possible, no reference plane, thickness similar to the thickness I used on the rest of the board. Not optimal solution, but I am not sure if there is something else to do about it.

Sniper2 , 05-14-2025, 04:29 AM

Thx