From: Lee Ritchey ([email protected])
Date: Thu Dec 23 1999 - 09:38:45 PST
Use Thevenin Equivalents.
Bruce Rosenquist wrote:
> I was skimming the latest SI news, and your final comment caught my interest.
> I am new to high-speed issues and controlling board impedances, and working
> on a design which contains a lot of parallel termination for LVPECL signals.
> This requires a termination voltage, which must, as you say, both sink and source current.
>
> How do the pros typically do this? Are there any DC-DC converters that are made
> specifically for this function? What are some of the nasties you speak of ?
> What are the tricks ?
>
> Bruce Rosenquist, Designer
> DesignPRO Inc.
> 35 Stafford Rd., Unit 1
> Nepean, Ontario
> K2H 8V8 CANADA
>
> http://www.designpro.org
>
> [email protected]
>
> phone: (613) 596-5030 fax: (613) 596-5163
>
> D. C. Sessions wrote:
>
> > With the year wrapping up and my inbox filling with
> > "Out of Office Autoresponse" messages, I thought I'd
> > kick off something more interesting than the joys of LVDS.
> >
> > In particular, what would we use for signaling if we could
> > start with a totally clean sheet of paper? Rather than
> > immediately jump to a solution, I'm looking for some criteria:
> >
> > * It has to be scalable. Given silicon technology trends, it
> > should migrate gracefully to lower-voltages and less
> > voltage-stress-tolerant semiconductors.
> >
> > * It has to be SI clean. Output impedance should be matched
> > (stringency variable) to the line across the switching range.
> > Inputs switchpoints should be symmetrical and well-defined
> > (ie differential receivers). Power plane proliferation
> > leads to bad SI and wasted money, so separate termination
> > supplies are a Bad Thing.
> >
> > * It has to be versatile. Single-ended, balanced single-ended, or
> > differential; multidrop or point-to-point; uni- or bidirectional;
> > all should be minor variations on the same system.
> >
> > * It should be economical. Wasted power is a Bad Thing, so low
> > swing is a must. Padrings are some of the most expensive real
> > estate around, so pincount should be minimized. Line termination
> > can dominate a PWB so KISS is the rule. Power supplies (esp.
> > ones that can both sink and source current) are expensive and
> > nasty to deal with, so do without (both for termination and
> > funny analog functions in the I/O circuits.)
> >
> > What can we add to the list? Remove? Priorities? (This is
> > engineering, we make tradeoffs.) Where does this take us?
> >
> > --
> > D. C. Sessions
> > [email protected]
> >
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