xSignals and Delay Calculations
brs , 01-22-2022, 08:21 AM
Hi, I'm trying to understand delay matched routing and xSignals. I tried some situations and I have four questions.
- Altium calculates different delays for tracks which are on same layer and have same length but different widths. Why width has effect on delay?
- How can I calculate via delays?
- I'm trying to route nets between CPU and LPDDR4. Should I use length matching or delay matching. Tracks of different lenghts can give same delay.
- I'm trying to implement xSignals on Altium. I created a test project with 2 ICs and a capacitor. I routed basic tracks between 2 IC pads and a capacitor pad. Net's total delay is 193ps and delay between IC pads is 113.9 ps. Lets say it must be 150ps so I created an xSignal between IC pads with min 149ps, max 150ps rule. When I'm trying to tune tracks in NetC1_1_PP1 xSignal with interactive length tuning tool, Altium says "Target Delay Smaller Than Old Delay". Probably it uses total net delay (193ps) instead of xsignal delay. How can I resolve this issue. Please see attached screenshot.
WhoKnewKnows , 01-22-2022, 05:54 PM
Delay is a function of some amount of trace impedance and trace length. Trace width affects trace impedance. I think this should help you with your first question. Perhaps others can help you with the other questions.
robertferanec , 01-25-2022, 10:38 PM
1. can you attach screenshots?
2. I don't know. Normally I route all the signals in group the same way, so it cancels effect of vias. Also, when using xSignals, I think altium now includes delay in VIA
3. It's always delay matching. However many tools can't calculate delay precisely, so length matching is used instead.
4. I don't know why it doesn't work
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