[SI-LIST] Re: plane-to-plane decoupling

  • From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
  • To: "Michael Rose" <mrose@xxxxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 15 Sep 2008 10:52:58 -0700

Michael,

There are no capacitors that work at 3.125 Gb/S for decoupling.  The way to
provide this path is by placing the planes close to each other.  I use 3
mils all of the time for this purpose.  Works greast!

Lee Ritchey
Speeding Edge


> [Original Message]
> From: Michael Rose <mrose@xxxxxxxxxxxx>
> To: SI-List <si-list@xxxxxxxxxxxxx>
> Date: 9/15/2008 10:01:17 AM
> Subject: [SI-LIST] plane-to-plane decoupling
>
> I looking for some suggestions regarding decoupling between co-planar
> plane splits. I'm working on a backplane with a number of 3.125Gbps diff
> pairs. I've specified a dual stripline stackup assigned as follows:
>
> 1 - P
> 2 - G
> 3 - S
> 4 - S
> 5 - P
> 6 - G
> and so on
>
> Some diff pairs on L4 will cross power plane splits (actual different
> power sources and loads) and I wanted to provide an effective AC path
> for any common-mode return currents. I was thinking about placing some
> nearby decoupling caps from plane-to-plane across the split. Do you
> think it would be better to decouple from plane-to-ground on both sides
> to steer the current through the L6 ground layer? L5 and L6 are already
> coupled through the inter-plane capacitance (they're about 4mils apart).
> Which will provide a lower inductance path?
>
> Mike
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