From: Scott McMorrow (firstname.lastname@example.org)
Date: Tue Oct 31 2000 - 15:13:59 PST
There is nothing wrong with your idea. A driver which drives two 70 ohm
traces will see a 35 ohm impedance. There are some other issues which
you will want to look at carefully.
First, assuming that this is a reflected wave circuit, you will need to
make sure that the trace delay for both traces is close to equal. Otherwise,
you will get a nasty little ledge in the middle of the signal transition, the
duration of which will be equal to the difference in delay between the two
Second, you need only provide ground stitch vias near the layer
change vias for the traces. This provides a place for the AC fields to
follow as the signal changes layers.
Otherwise, your design should work just fine.
-- Scott McMorrow Principal Engineer SiQual, Signal Quality Engineering 18735 SW Boones Ferry Road Tualatin, OR 97062-3090 (503) 885-1231 http://www.siqual.com
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