High speed fanout - Routing net classes where one net has series resistor?
JosephH , 03-23-2017, 08:19 PM
In the Advanced PCB Layout course, it is stated frequently that each trace within the same net class (such as DDR groups) should always be routed the same way (e.g, if one trace uses microvias from L1-L2, then L2-L3, then all traces in the group should do this).
However, what is the recommended course of action when one trace within a group has a series resistor, such as in the photo below? (see attached). In the project files for the lesson, the resistor is placed on the opposite side of the board to the trace. Is it ok to just use a throughhole via this one net, and use microvias on the other nets?
mairomaster , 03-24-2017, 02:36 AM
For such occasions it is convenient to use xSignals for the length matching:
robertferanec , 03-24-2017, 12:37 PM
The simplest way to do it is a manual addition of the two tracks (before and after the resistor) without creating any special rule. Just be aware of the total length. It is not the most precise way (as it doesn't include delay/length in the resistor), but usually the series termination resistor is in CLK signal which we normally make the longest signal of the interface.
As @mairomaster mentioned, you can also create xSignals. Some time ago I created a video about it: Altium â€“ How to use xSignals ( in Fly-By, T-Branch + Other useful things )
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