I’m working on a PCB design in KiCad and need to match the lengths of two traces that form a differential pair. I referred to a blog from Sierra Circuits on differential signal design in KiCad that mentioned the “Tune Differential Pair Skew” tool can be used to adjust the length of the shorter trace to match the longer one.
Can someone explain the correct steps to use this tool? Specifically, how do I select the traces, and how does KiCad automatically adjust the lengths? Any kind of help is appreciated
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Thanks, I referred to this blog to create differential pairs, but I’m having trouble matching the length of the pairs and I’m facing a challenge here
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First of all set the rules for differential pair skew in board setup → Design rules → length tuning patterns → default properties for differential pair skews. This will set the default settings, use spacing as 3 times the differential pair trace width, amplitude and radius can be adjusted as per requirement. Next it is a good idea to set a custom rule for differential pair skew to make sure it is checked during final design rule checks. Kindly check the attached images. Generally skew for differential pair traces is 5 mils which means the maximum difference between the two traces of a diff pair should be 5 mils. After routing the differential pair, go to route → tune skew of a differential pair, click on any one of the two traces of a diff pair and check which trace shows skew in negative number and the number should be greater then 5. negative number means the trace is smaller then the other trace. After clicking on any one of the trace right click and select length tuning settings. A window will open, set target skew as 5 mils, rest will be taken from default settings. Click okay and then move the cursor such that the trace is pulled out and check if skew becomes less than or equal to 5. Once it is achieved click on the screen and you are done.
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Make sure not to pull the extension too much, after extending the spacing between the two traces should be maximum 2S to 3S where S is the differential pair spacing. If not possible to match skew by maintaining 2S to 3S spacing then use multiple such extensions.
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