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

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From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Wed Dec 15 1999 - 15:03:38 PST


Eric Goodill wrote:
> 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?

Well, a newline every 60-70 mcolumns would help :-)

Seriously, you should be able to skip the cap and just use a 100-ohm resistor.
Especially if you're running both ends of the line on a common ground.
Alternately, use a pullup pack (several 50-ohm resistors to a common pin)
and one cap. The application you're describing sounds like all of the pairs
come over a common path, so they should have pretty well-matched common-mode
potentials.

-- 
D. C. Sessions
dc.sessions@vlsi.com

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