[SI-LIST] Re: Routing of 12 GHz diff pairs
- From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- To: buck@xxxxxxx
- Date: Wed, 02 Apr 2003 08:04:53 -0800
Buck,
Based upon your direction and the advise you're getting from the list, I
would suggest that you go back to your customer and clarify what they
mean. Inquire about how they would like you to proceed and place the
ball back in the designers court.
If they mean edge coupled differential pairs, they need the only way to
achieve this would be to use straight connections from source to
destination. Any curve or bend will introduce delay differences at
points along the pair. If they mean broadside, then you are good to go,
but I doubt that is what is meant, since they would also need to give
you design rules for the broadside stackup. Another option is co-planar
waveguide (CPW) or grounded co-planar waveguide (GCPW) where each
differential trace is surrounded by ground. in that case, the distance
between the pairs is much larger and the pairs can easily be matched
along the way with curves. But CPW and GCPW is twitchy at these speeds
(well, in fact, all of the methods of differential pair routing are
twitchy at these speeds.) and needs some design assistance and care to
achieve good performance.
My advise, talk to the designers and ask them what their intention is,
and place the responsibility back on them.
regards,
scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
buck wrote:
>Hello,
>
> We are working with a customer that is using 12 GHz diff-pair signals.
>The customer "requires" that the time of flight across the pair
>"must" be equal at all points in time. Can any one shed any light
>on how this can be done?
>
> We are using Allegro tools any assistance is greatly appreciated.
>
>Thanks,
>Buck...
>KAW/USA
>
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