Re: [SI-LIST] : Physcially-small far-end LVDS terminations?

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From: Jon Powell (jonp@pacbell.net)
Date: Sat Dec 18 1999 - 09:08:31 PST


Though I could easily be wrong, I don't believe that the below is true. My understanding of LVDS is that it requires ~100 ohm termination across the differential receiver in order to generate the required signal voltage.

regards,
jon

Jim Freeman wrote:

> Hi Eric,
> Another answer would be to ensure that the differential impedance of the board between the differential pairs is 100 ohms. Then you wouldn't need the resistors. I have performed Hspice sims on this and it works fine if the stackup/trace spacing is correct.
>
> Jim Freeman
>
> Eric Goodill wrote:
>
> > Hi,
> >
> > I want to use the typical LVDS termination where you have two 50-ohm resistors in series placed between the two lines of the LVDS diff. pair and also have a cap at the junction of the resistors to ground. I have a jillion LVDS pairs to terminate at a high-pin-count ASIC, and I'm looking to squeeze more terminations per square inch. (There's no hope of putting the terminations inside the ASIC at this point.) I'm hoping some company makes a single three-pin part the has those two resistors and a cap even if not specifically for termination use.
> >
> > How about any other ideas for even higher density?
> >
> > Regards, Eric
> > --
> > Eric Goodill
> > Siara Systems, ericg@siara.com
> >
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--
Jon Powell
Director of HSSD Consulting Services
Viewlogic Systems, INC.
805 988 8250

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