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

From: Larry Miller ([email protected])
Date: Thu Nov 30 2000 - 07:54:18 PST

Wider traces also have less skin effect loss, nu?

> -----Original Message-----
> From: Doug Hopperstad [SMTP:[email protected]]
> Sent: Thursday, November 30, 2000 7:24 AM
> To: 'Loyer, Jeff W'; [email protected]
> Subject: RE: [SI-LIST] : D/W vs. S/H
>
> Jeff,
> Thanks for your comments regarding my question. The ratio of the trace to
> plane (H) to the trace-to-trace spacing (D) is the fundamental factors in
> determining the crosstalk. Yes there are other considerations but the most
> popular formula regarding crosstalk is the listed in the Howard Johnson's
> book. The formula is: 1/(1+(D/H)^2). This formula will provide the
> crosstalk
> coefficient. I try to keep the value between 0.015 - 0.03. The other
> ratio,
> D/H, should be kept to at least a 4:1 ratio. By using these values, the
> amount of crosstalk will generally be small enough for most applications.
>
> Your question regarding why you don't want to use S/H vs. D/W can be
> answered this way: the closer you keep the trace to the ground plane the
> better the coupling you will achieve. Try to keep the trace as wide as you
> can. There are a few reasons for keeping the trace wide: 1. With a wider
> trace, the effects of manufacturing tolerances and board trace edging will
> be minimized, 2. The wider trace provides more coupling area to the ground
> plane.
>
> QLogic Corporation
> [email protected]
>
>
>
>
> -----Original Message-----
> From: Loyer, Jeff W [mailto:[email protected]]
> Sent: Wednesday, November 29, 2000 2:55 PM
> To: [email protected]
> Subject: [SI-LIST] : D/W vs. S/H
>
>
> 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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