Impedance calculations not matching carrier board stack up documentation

Hello,

I’m looking into design a carrier board for the Jetson Nano and I’m setting up my board stack up and impedance controlled trace dimensions. I wanted to replicate the dimensions of the development board as close as possible, however when I input the trace dimensions into online impedance calculators the differential impedance it outputs doesn’t match the impedance given in the P3449_B01_PCB_stackup document. Perhaps I have made an error with units or dimensions, so it would be good to understand why the calculations don’t match. I believe all units are in mm as stated at the bottom of the document.

Below I have input the the 85ohm edge coupled differential impedance trace dimensions into the calculator provided by EEWeb.

I notice that the single ended 50ohm trace dimensions do give ~50ohms impedance when input into the calculator.

I have tried different differential edge coupling calculators and get similar results which don’t match the stack up documentation. I’ve tried varying the copper thickness to account for differences in how plating is accounted for and varying Er within reason but can’t get the values close.

Any thoughts on the discrepancy would be appreciated. I’d like to understand where the error is before proceeding and including it in my design.

We’re checking this issue, will do the update once clarified.

Thanks

Hi, if you plan to replicate layout of devkit carrier board, please just follow the stack up doc in the carrier board docs package. That has been validated. We have no suggestion on the online tools.

Ok, thanks for getting back to me.

Is it possible to get the trace dimensions used for the Ethernet 100ohm differential impedance traces? Those dimensions aren’t listed in the stack up document

Please refer to the product design guide of nano in DLC for that.