Re: [SI-LIST] : Plane Capacitance

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From: David Instone (david_instone@uk.xyratex.com)
Date: Thu Nov 11 1999 - 13:14:33 PST


Just a thought, If, as has been stated in this thread, a 'wavefront'
travels out from the points drawing power then will not the signal
layers between the two planes get this coupled into them?
Dave Instone

Joel Jorgenson wrote:
>
> I've designed a number of six layer circuit
> cards that had the planes on layers 2 and 5.
> This created two layers of stripline circuitry,
> although it decreased the innerplane capacitance.
>
> The circuit cards could then be designed such
> that all signal layers (1, 3, 4, and 6) have approximately
> equal characteristic impedances.
>
> If I kept the design to six layers, but placed the planes
> as close as possible (layers 3 and 4), I would sacrifice
> the stripline construction as well as matched impedances
> between layers.
>
> I wasn't worried about "too much" capacitance, but rather
> I worried if I had "enough" capacitance. In my case, separating
> the planes still provided enough capacitance.
>
> Joel Jorgenson
>
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-- 
Regards

Dave Instone Test Systems, MP24/22 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. Tel +44 (0)1705 486363 ext 3071 or +44 (0)1705 443071 (direct line) Fax +44 (0)1705 499315 http://www.xyratex.com

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