# RE: [SI-LIST] : D/W vs. S/H

From: Larry Miller ([email protected])
Date: Thu Nov 30 2000 - 12:09:25 PST

....unless, of course, you are setting up a differential edge-coupled pair,
in which case the cetroids of the fields will get pulled off the centerlines
of the traces.

vasthorizons, eh? that must be a cocktail party conversation grabber....
<grin>

Larry

> -----Original Message-----
> From: Scott McMorrow [SMTP:[email protected]]
> Sent: Thursday, November 30, 2000 9:00 AM
> To: Loyer, Jeff W
> Cc: [email protected]
> Subject: Re: [SI-LIST] : D/W vs. S/H
>
> Jeff,
>
> You are correct. As you and Larry Miller
> have pointed out, it is the ratio of S/H that is
> critical parameter for crosstalk. However, in order to
> execute the layout, the SI engineer will want to
> translate this into a minimum S for use by the
> layout team.
>
> And actually, to be more correct, the ratio that is
> truly important is D/H. That is, the center
> to center spacing of the traces divided by the distance
> to the plane. The center of the trace is the center
> of moment of the created fields. A rule of thumb
> based upon D will more accurately scale across
> various trace widths.
>
> scott
>
>
>
> "Loyer, Jeff W" wrote:
>
> > Doug's query brought up a related question to my feeble mind...
> >
> > Is there any reason to specify distance between traces relative to their
> > width? As far as I know, the most critical dimensions to consider are:
> 1)
> > distance between the edges of two traces, relative to 2) distance
> between
> > the trace and its ground plane(s). The width of the conductor is not a
> > significant factor, unless you're using center-to-center separation,
> where
> > you'll have to take into account the width. I don't understand why we
> > wouldn't specify S/H instead of D/W (see below).
> >
> > ______________________________________________________ GND
> > ^
> > |
> > (H)
> > |
> > v
> > ___________ <--- (S) ---> ___________ Signals traces
> > <-- (W) -->
> > <---------- (D) ---------->
> >
> > Jeff Loyer
> > (253) 371-8093
> >
> > -----Original Message-----
> > From: Doug Hopperstad [mailto:[email protected]]
> > Sent: Wednesday, November 29, 2000 12:27 PM
> > To: [email protected]
> > Subject: [SI-LIST] : RE: Crosstalk Bus spacing
> >
> > When determining the minimum spacing between traces on a digital bus, is
> it
> > best to setup the three traces as follows:(The design is using a
> stripline)
> >
> > "A": Aggressor trace
> > "V": Victim trace
> > "A": Aggressor trace
> >
> > ------------------------------------------------------- Ground Plane
> layer
> > ------(A)------ ------(V)------ ------(A)------ Trace layer, 0.5
> > ounce.
> > ------------------------------------------------------- Ground Plane
> layer
> >
> > Should both Aggressors be in-phase with each other or should one of them
> be
> > inverted to get the worst case crosstalk. I am simulating with both
> > applications and getting much more crosstalk on the victim trace when
> both
> > aggressors are in-phase.
> >
> > The clock edge rate is 950pS and the trace width is set at w = 5 mils.
> The
> > Plane to trace layer spacing is 6.5 mils. This provides a nice 50 ohm
> trace
> > impedance.
> > The distance between traces is set at 5 mils (1w). I have been playing
> with
> > 2w in the simulations as well.
> >
> > Is it traditional to set the trace-to-trace spacing on the bus traces,
> i.e.
> > bits(0:x) for example, at 1w the trace width. The bus-to-adjacent traces
> > have been set for 2w spacing. The clock spacing is set for a 3w minimum.
> >
> >
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> --
> Scott McMorrow
> Principal Engineer
> SiQual, Signal Quality Engineering
> 18735 SW Boones Ferry Road
> Tualatin, OR 97062-3090
> (503) 885-1231
> http://www.siqual.com
>
>
>
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