Lengths matching home work!

[robertferanec]

In case of using the waves to match the length of tracks, how can we guarantee that space between two adjacent track is x3 times of width of track (for preventing crosstalk).

Altium is not good in fitting the waves into small space. So very often I do the waves manually e.g. I create one and then copy and paste it ... or I just draw it. When you draw the waves, you will get the idea what the space between the tracks should look like (you can also measure it). If you use interactive length tuning, then set "Gap" to be 3x track width (often I route 50OHMs by 0.1mm, so I use space 0.3mm)

[robertferanec]

Interesting that I made DRC check on OpenRex board and get same error!!

Can you attach screenshots?

[zagrosmega]

Altium is not good in fitting the waves into small space. So very often I do the waves manually...

so i think that in OpenRex pcb(imx6) many signal traces like ddr3 data line and address line are routed with this method ok?and does it means that (length matching rules) in altium designer cannot be useful in some cases ,because altium uses standard wave shape for length tuning .

[robertferanec]

- yes, waves in OpenRex are done manually
- wave shape doesn't influence length matching and it is still useful to setup the rules. Maybe this can help: https://www.fedevel.com/welldoneblog...useful-things/

[Via]

[Via]

Sorry for delay , here is errors from your projects

[robertferanec]

This is uncoupled length. We set it intentionally low, so Altium then highlights all the segments which have the uncoupled length (the places where space between tracks is different as specified by stackup and impedance). It is not length matching.

[Via]

Yes I know, How we can setup a rules for them? I had idea to define the room in area that we make space for length matching in Diff but doesn't work!

[robertferanec]

Please could you be more specific? I am not sure what rules you would like to set for what.
PS: You can always have a look at our open source designs to check how we set them up: http://www.imx6rex.com/

[Via]

The area like this. I need update the the max gap in Diff rules or there is another way to solve this problem?

[robertferanec]

This is called uncoupled length. You can set higher tolerance for it. Go to Design -> Rules -> Routing -> Differential pair routing: select your differential pair rule: set "Max Uncoupled Length" to higher number (you can check the longest uncoupled length in DRC report, so set it to be a little bit longer ... just be sure you are ok with all the uncoupled length). See the screenshot below: