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Haythemjls , 05-23-2025, 03:58 PM

How do we choose between Length Units and Delay Units when performing length matching for high-speed signals in Altium?

QDrives , 05-23-2025, 07:29 PM

Length tuning is the easy one -- just measure the length of the traces.
Delay tuning is the 'correct' one. Vias have delays. Pins of the IC have delays. Traces on different layers have different delays (with the same length).
So if you keep the 'groups' to the same layers, equal amount of vias and ignore the pin delays, then you can use length matching.
If the rise time is low enough, you can do length matching.

Haythemjls , 05-26-2025, 10:52 AM

Sorry, Ididn't understand, could you explaine to me by exampls ?

QDrives , 05-26-2025, 03:26 PM

If you did not understand, better stick to length tuning and keep all signal groups on the same layer.

Robert Feranec , 05-27-2025, 05:40 AM

The goal of tuning is to be sure the signals in multiple tracks will arrive at the same time to the chip. So, delay tuning is the ultimate goal - for example you know how long it takes signal to travel from processor to memory pin.

However, delay tuning depends on many factor e.g. any changes in your PCB stackup or wrong calculations will influence the result.

So often length tuning is used, as it is much simpler approach, but you need to be careful and route all the signals that have to be length matched together, you need to route them the same way so they all travel through the same environment and then they all will have same delay if they have the same length.

Haythemjls , 05-27-2025, 01:32 PM

For exampe if I have MIPI interface which will be routed in multi layers, which one I choose ?