Crosstalk Problem

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p3rd1x
Posts: 1
Joined: 13 Mar 2021, 13:09

Crosstalk Problem

#1 Post by p3rd1x » 13 Mar 2021, 14:37

I a a total beginner to PCB design. I just designed my first 2-layer board with diptrace but unfortunately my design did not work due to what i think is crosstalk.

In the attached screenshots you can see the lanes which i think are the aggressor and the victim lane. I thought crosstalk woldn't be much of an issue to me, because the frequencies are not really high(300Hz max), and the lanes are not that close to each other either. But after some research i found that because of the short rise and fall times of modern chips crosstalk can be an issue anyway. The victim lane is a asynchronous reset and resets every time the aggressor lane rises to high.

A potential fix to this problem could be a ground pour on both layers. Will a ground pour fix my problem? What other solutions could there be? What diptrace tools are there to help me with this?

The logic voltage level is 9V.
A thing that surprised me is that every time i touch a contact to one of the two lanes with my finger or a screwdriver, it works perfectly fine and no crosstalk occurred. Why is that so?

Thanks <3
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DevilMKD
Posts: 23
Joined: 09 Dec 2013, 08:12
Location: Macedonia

Re: Crosstalk Problem

#2 Post by DevilMKD » 15 Mar 2021, 03:37

Ground plane should minimize the issue you have, also a good way would be to include pull-up/ pull-down resistors, if there is the possibility for that, so the pins are not left floating.
Did you made any measurements to confirm that you have crosstalk ?
A good practice is to include capacitors next to the power pins of the IC, they will minimize the noise in the power lines if there is something, also dont forget to include vias for connecting the two layers of the ground planes, and remove any unconnected ground plane islands.

I usually go with a clearance of 0.4mm, line width 0.1mm and line spacing 0.3mm, if its a larger boards switch the thermals from direct to 4 spoke or it will be hard to solder the ground pins of the parts.
PCB designs and Product development are my everyday life.

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