Re: [SI-LIST] : Question on propagation delay........

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From: Steve Corey (steve@tdasystems.com)
Date: Mon Apr 17 2000 - 11:53:04 PDT


Also, narrower traces see more conductor loss and therefore more DC losses and skin effect losses, which tend to increase delay.

Intuitively, it seems like wider traces would see greater dielectric loss which would offset the above to some degree, especially at higher frequencies, but I've never looked very deep into it. I'm sure
some microwave designers on this list have, though.

-------------------------------------------
Steven D. Corey, Ph.D.
Time Domain Analysis Systems, Inc.
"The Interconnect Modeling Company."
http://www.tdasystems.com

email: steve@tdasystems.com
phone: (503) 246-2272
-------------------------------------------

Istvan Novak - Board Design Technology wrote:

> Michael,
>
> In stripline, if nothing else is connected to the traces, the propagation delay
> is a function only of length of trace and dielectric constant, it does not
> depend on the trace cross sectional dimensions or dielectric layer height. When
> you add discontinuities, such as via capacitances, their effect will depend on
> the ratio of via capacitance to inherent trace capacitance. The approximate
> correction factor for the delay is sqrt(1+Cload/C).
>
> If your three traces with different trace widths come with proportionally
> adjusted dielectric layer height, so that the unloaded trace impedance is the
> same for all three traces, the effect of vias (assuming identical via
> capacitance on all three traces) will be the same. However, if the different
> trace widths are used to set intentionally different trace impedances, the
> effect (of identical) vias will be less on lower-impedance traces (higher
> inherent trace capacitance) and will be higher on higher-impedance traces (less
> inherent trace capacitance).
>
> Istvan Novak Sun Microsystems, Inc.
> Istvan.Novak@Sun.Com Workgroup Servers, BDT Group,
> One Network Drive, Burlington, MA 01803
> Phone: (781) 442 0340
>
>
> From: "Greim, Michael" <mgreim@mc.com>
> To: "'si-list@silab.eng.sun.com'" <si-list@silab.eng.sun.com>
> Subject: [SI-LIST] : Question on propagation delay........
> Date: Mon, 17 Apr 2000 13:14:56 -0400
> MIME-Version: 1.0
>
> Hi everyone,
>
> Here is what I thought was a simple question but
> has turned into a discussion of some debate. Three
> nets are routed on a pwb as stripline structure. They
> are driven by the same type of driver and have the same
> type of receiver. There is one driver and one receiver per
> net. They contain the same number of vias in the same
> location on the nets with the same padstack. The only
> topological difference of the nets is that they are routed
> as different widths. That being said, what is the flight
> time of these topologies as a function of length. Is it
> strictly a function of the dielectric? What is the relative
> effect of varying number (say difference of no more than
> a handful) of vias on the nets.
>
> Whaddya think?
> >
>
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