Re: [SI-LIST] : What's your favorite Screwy SI Concept?

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From: Jon Powell (jonp@pacbell.net)
Date: Thu Jan 06 2000 - 10:49:53 PST


Just to clarify my point.
I was agreeing that this is a screwy rule and shouldn't be used "just cause it is a rule" but should be used because you understand what the 20H does and why
you want to do it. My simulations were extremely crude and the only thing I took from them was a desire to find out what was really going on.

And as Doug(S) states: Does anyone know? (cause I know people are using this)

jon

Doug Smith wrote:

> Hi Jon,
>
> I would tend to build up a test board to try something like this. I
> learned a long time ago not to trust simulators unless I could build (or
> calculate by hand if possible) a similar but simpler test case and get
> the simulator to agree with calculations or measurement. I build a lot
> of test circuits and do measurements on them. I call that "putting the
> problem on the analog computer." Many of the test boards or other
> apparatus I build eventually end up in published papers or my courses as
> demos.
>
> I have seen cases where simulation output was believable, but not
> accurate because of some problem, either an input problem (garbage in ->
> garbage out) or a problem within the simulator itself.
>
> Given the above, does anyone know of any "hard" data to support the
> simulation?
>
> DougS (as opposed to DougM who posted the original 20H item)
>
> Jon Powell wrote:
> >
> > Doug Wrote:
> > Screwy SI Concept #2: The 20H Rule
> >
> > Why It's Screwy: Highly debatable concept and it's
> > not really an SI concept at all.
> >
> > Why It's Hung Around: Easy to remember
> >
> > Jon Writes:
> > About 6 months ago I did a test to see what was going on with this "20H"
> > rule. I simulated some simple ground planes with simple sources using a
> > 3D simulator. (I am not making any claims, just telling what I saw), the
> > results: the 20H boards quickly put all of their energy into the
> > enclosure. And the regular one retained the signal (a lot longer) Now,
> > perhaps this doesn't sound like I needed a simulation to know this but
> > this is my guess:
> >
> > 1) If you have a good enclosure, (or don't care about EMI off the board)
> > th 20H rule can reduce noise on the board. (And perhaps EMI off the
> > connected cables?)
> > 2) If you don't have an enclosure, and you care about EMI off the board,
> > the 20H rule may not be a good thing.
> >
> > --
> > Jon Powell
> > Director of HSSD Consulting Services
> > Viewlogic Systems, INC.
> > 805 988 8250
> >
> > **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP.
> > si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list
> > ****
>
> --
> --------------------------------------------------------------------
> ___ _ Doug Smith
> \ / ) Manager EMC Development & Test
> ========= Auspex Systems
> _ / \ / \ _ 2300 Central Expressway
> / /\ \ ] / /\ \ Santa Clara, CA 95050-2516
> | q-----( ) | o | Phone/FAX: 408-566-2157/2020
> \ _ / ] \ _ / Email: dsmith@auspex.com
> --------------------------------------------------------------------
>
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> ****

--
Jon Powell
Director of HSSD Consulting Services
Viewlogic Systems, INC.
805 988 8250

**** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****


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