FEDEVEL
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Michael , 03-04-2025, 06:36 AM

Hello
i have a question that is facing the problem of EMI.
What is the better way to route a CLK-signal especially when the focus is on the distance to the refering GND?
From the videos i saw so far i catched that the distance between CLK and other signals shall be min. twice the width.
But what about the refering GND e.g. when the layer is flooded ?
In this case i have a 8 layer board, 2nd layer is GND
Would it be better like shown in the first picture ( red flood = GND; 0.5mm = 500mic ) or
is the solution in the 2nd picture better ?
Thank you for your answers.

Denis , 03-04-2025, 12:03 PM

Hi Michael, I'm trying to follow application notes and guidelines since I dont have enough experience. In all examples I saw, the crystal oscillator is close to the IC.
In attached screenshot is a page from STM application notes as example

Robert Feranec , 03-04-2025, 12:07 PM

it will influence impedance of the track, I am not sure what is your target impedance. btw if you have GND plane under the track you may not need to do that. I recommend to watch this: https://youtu.be/9lEtkysFGGg

Robert Feranec , 03-04-2025, 12:08 PM

I almost never do copper pour

Robert Feranec , 03-04-2025, 12:09 PM

also maybe watch this: https://youtu.be/52fxuRGifLU

QDrives , 03-04-2025, 04:34 PM

In your first picture you have a co-planer waveguide together with a reference plane. That will lower the impedance of the trace.
For ease of calculation use the second.
Make sure that the trace impedance is 50 ohm and add a series termination at the source to match 50 ohm together with the impedance of the output.