Re: [SI-LIST] : differential pairs

Andy Ingraham (ingraham@wrksys.ENET.dec.com)
Thu, 18 Sep 97 08:12:31 EDT

> I would like to get some opinions on how to layout differential pairs for
> high speed (1 Gbit/s) data signals. I am not quite sure if it is preferable
> to use broad side or edge side coupled differential pairs?

Where do these signals come from / go to?

Diff. pairs have both differential-mode and common-mode impedances.
Ideally, both should be matched to load and maybe source. If these
signals interface directly with a cable, I'd be concerned about that.

Also, what is the common-mode impedance of your termination network?

If these diff. pairs go from IC to IC (which tend to look electrically
like single-ended sources and loads), and each line is terminated,
then maybe you'd want to stick with coplanar edge coupled pairs with
not much coupling.

Regards,
Andy