[SI-LIST] Flight time skew due to Dk varation
- From: "Perry Qu" <perry.qu@xxxxxxxxxxx>
- To: "si-list" <si-list@xxxxxxxxxxxxx>
- Date: 17 Jan 2003 16:14:12 -0500
Hi,
I'm dealing with a design where timing is extremely tight and our
theoretical analysis shows that we are failing the spec. One of the big
contribution to skew is PCB flight time variation. The length of track
is about 48" and it is a single stripline configuration on GETEK
material. There are many pairs so they are distributed on a few routing
layers through the stackup. According to material vendor, the variation
of Dk is from 3.8 to 4.0, which translate to a worst case skew of around
50 ps/foot. This will result in 200ps skew for 4 feet long track. Such
estimation seems a bit too pessimistic and I wonder whether there is a
better approach.
The measurement in the lab shows that total skew from chip to chip is
between 100 - 200 ps. The analysis above, however, is to try to get some
data for worst case due to process variation.
Thanks
Perry
--
Perry Qu
SDN D & Q | 600 March Road
Alcatel Canada | Ottawa, ON K2K 2E6, Canada
DID: (613) 7846720 | FAX: (613) 5993642
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