FEDEVEL
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Astral Master , 11-15-2025, 09:35 AM

SPI trace length < 9mm



SPI Via size 0.3mm x 0.6mm



Stitching Ground Via Size 0.2mm x 0.4mm



I'm estimating .5ns or 500ps rise time



Frequency estimate 2-3 GHZ



I did the best I can I don't know if there is something I could be doing better.

I would like to reduce noise as much as possible.

very sensitive EEG signal electrode traces 10H distance away. 10H = 10x distance from spi trace to ground plane.

I heard Rick Hartley say 20H was necessary

QDrives , 11-15-2025, 04:44 PM

Why the two different sizes in vias?
What makes you think the rise time is 500ps?
What data rates do you need?
If noise is important, why not add a series terminating resistor as well?

Astral Master , 11-16-2025, 06:13 AM

I need about 40kb/s. The ads1299 ibis model said 500ps I will be adding 22 ohm series resistors and the different via sizes are because those small ones are stitching vias

QDrives , 11-16-2025, 05:15 PM

So slow.
https://www.tina.com/ibis-simulation/
But why have bigger vias?

Astral Master , 11-17-2025, 09:34 AM

i dont understand why have bigger vias? and yea its eeg so i only really nees 500 sps at 24 bits so ill be good

QDrives , 11-17-2025, 03:18 PM

For SI the best vias have a via barrel of 0.2mm.
Do note that the pad size (often) needs to be bigger to comply to the annular ring rules (>= 0.15mm).