Re: [SI-LIST] : Searching For Equations Governing Serpentine

Douglas McKean (dmckean@corp.auspex.com)
Mon, 18 Jan 1999 10:20:12 -0800

At the last EMC Symposium in Denver, a paper was
presented discussing serpentine traces for EMI control.

Serpentine traces I've seen are used for matching prop
delays down traces of multiple buses and was based on:

For loaded lines -

Tpd' = [L0 * (C0 + Cd)]^0.5

L0 = inductance per unit length
C0 = capacitance per unit length
Cd = Distributed or Load Capacitance

For unloaded lines -

Tpd = [L0 * C0]^0.5

L0 = inductance per unit length
C0 = capacitance per unit length

At 09:03 PM 1/17/99 -0800, you wrote:
>Dear Si-List Members,
>
> Serpentine traces are frequently employed in design of high speed
>digital PCBs to increase propagation time of certain signal lines.
>These wavy shaped tracks provide an effective means for matching trace
>lengths and flight times of various signals.
>
> I am searching for equations and rules of thumb which allow
>determination of magnitude of crosstalk and changes in signal
>propagation delay (or velocity) as a function of serpentine geometry
>(dimensions and separation of adjacent trace segments).
>
> Thank you in advance for your suggestions regarding laws or formulas
>which govern serpentine traces..
>
> Best Regards,
>
> Abe Riazi

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