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by foofie
887 days ago
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> I guess a few elements in the connector (USB and Ethernet) are differential pairs. So okay, you need to know a bit about transmission line theory. But as far as actually running differential pairs with matched-impedances, its just a matter of knowing what a "dielectric constant" is and plugging that into the calculator, so that you know how thick the PCB-trace should be in a stripline. You understand that none of this is doable by anyone without a background in EE, don't you? |
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You don't need an EE degree to look at your PCB-manufacturer's specifications. Lets run a brief example:
https://www.digikey.com/-/media/Images/Marketing/Resources/D...
Lets go for Edge Coupled Microstrip. Solve for Trace Width.
I believe Ethernet is 100 Ohms differential impedance. Set the top to 100.
Trace Thickness as per DKRed is 0.5 oz/ft^2. This value might be 1 on different manufacturers.
Height is 7.04 mil. Just steal it from the specsheet above.
Spacing is whatever you plan to do. Lets say 8-mil.
Dielectric Constant is 4.01: https://www.digikey.com/-/media/Images/Marketing/Resources/D.... See "Dk", Dielectric Constant.
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Bam. Now 9.814 mil thickness for differential pair Ethernet routes.
Yeah, it will take you some study. But I literally laid everything out in front of you with my post above. It shouldn't take you any more than like 30 minutes of studying at this point now that I put everything in just a few posts for you.
An EE Degree will help. But... there's not much to this particular issue. You need to understand that different manufacturers have different thicknesses, dielectric-constants and other such measurements. But its all plug-and-play once you know how to read a spec-sheet.
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If that's too hard, just don't route Ethernet or USB I guess? There aren't very many differential-pair lines or impedance-matched lines on the Rasp. Pi4 CM as far as I can tell.