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Length Matching in Lesson 4 of Advanced PCB Layout

Tom Yunghans , 05-19-2020, 07:33 AM
Hi Robert,

I'm working on the length matching activities of Lesson 4 of Advanced PCB Layout. I am not having much success in manually adjusting the tracks to get the desired lengths while still maintaining the desired wave shapes. For example, I generate a nice wave using 45 degree angles, but when I try to adjust it, to add or subtract a little, I end up with an undesirable shape (e.g. 90 degree angles or non-symmetrical wave) or the wave I created totally collapses. Is there a trick to doing this? I played a little with the "routing gloss" feature, but that didn't seem to help much.

I am using a new version of Altium (20.1.8). There seems to be a lot of discussion in the Altium documentation about using the "interactive length turning", the "interactive diff pair length tuning" and the "equalize net length" commands. I am thinking that using these commands to generate accordians may be a better way to go than trying to manipulate these tracks manually. In your course you didn't really demonstrate these commands; maybe they weren't available at that time?

I don't want to spend the time researching the use of these commands if they are not the way to go. Please advise...
Seriez , 05-19-2020, 08:12 AM
Hello Tom,

Maybe I can help

To make nice length controlled Tracks, Differential or not I first make sure I know the exact length +- error margin and establish a Rule High Speed/High Speed Matched for the specific nets.
Then using Route -> Interactive length Length Tuning I press left click on the area where I want the "wave" to start and press again where I want it to end. (The "Box" this creates can be adjusted later as well.

I find length matching a bit "Dangerous" in Altium as I feel it can be prone to error if one is not careful with the routed tracks... even with the rules in place... that is why I lock critical tracks once I am done with them.

This Document explains it better then I can do:

If you are planning to do any Impedance Controlled Design I can recommend spending the time researching as it will save you the big headache in the Future.

Edit: Also I like to have the "PCB" Panel open showing me the routed length of the Nets.
Tom Yunghans , 05-19-2020, 09:27 PM
Hi Seriez,

Thanks for the input. It's good to hear that you use the accordians successfully. I played with them a few months ago, but didn't spend too much time researching their use, and I had a lot of trouble getting them to work properly.

Do you believe that using them is superior to adjusting the tracks manually? As I stated above, I have had a lot of trouble with the manual approach also, as Altium is continuously trying to optimize the routing, sometimes removing the extra track segments I added to match the length.

I was wondering if Robert didn't discuss the accordian approach in the course because he prefers the manual approach or if it was just because the accordian feature didn't exist when he created the course. Hopefully he will respond with his thoughts.

robertferanec , 05-20-2020, 12:38 AM
I often hold CTRL during routing to disable hot spots snapping. That will help you to move cursor more smoothly instead of jumping around.

Length tuning - I will be testing it soon in AD20. Let's see if they improved it.

This may help:
- Altium - How to use xSignals (in Fly-By, T-Branch + Other useful things) https://youtu.be/jpk-hfsFaqA
- Length Matching in Altium https://youtu.be/bzRDfcJIlgA
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