[SI-LIST] Re: Effect of Pwr-Gnd plane pairing vs. non-paired planes on signal return currents
- From: "George Peterson" <George_Peterson@xxxxxxxxx>
- To: Aubrey_Sparkman@xxxxxxxx, vinu@xxxxxxxxx
- Date: Thu, 16 Feb 2006 15:40:58 -0500
Aubrey,
Look again, your original premise is wrong. Top to bottom is a PWR to
GND transition on both stackups.
George Peterson
Sr. Signal Integrity Engineer
Jabil Circuit, Inc.
(727) 803-3743
george_peterson@xxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Aubrey_Sparkman@xxxxxxxx
Sent: Thursday, February 16, 2006 3:29 PM
To: vinu@xxxxxxxxx
Cc: alexh1@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Effect of Pwr-Gnd plane pairing vs. non-paired
planes on signal return currents
Vinu,
I don't disagree; my point was a hint that I didn't think Alex was
asking about the biggest performance limiting feature.
Aubrey Sparkman=3D20
Enterprise Engineering Signal Integrity Team
Dell, Inc.=3D20
Aubrey_Sparkman@xxxxxxxx=3D20
(512) 723-3592
-----Original Message-----
From: Vinu Arumugham [mailto:vinu@xxxxxxxxx]=3D20
Sent: Thursday, February 16, 2006 2:20 PM
To: Sparkman, Aubrey
Cc: alexh1@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: Effect of Pwr-Gnd plane pairing vs.
non-paired planes on signal return currents
If there are no ground vias nearby, a ground reference to ground
reference switch would behave the same as a ground reference to a power
reference switch.
I expect the two stack-ups to behave the same.
Thanks,
Vinu
Aubrey_Sparkman@xxxxxxxx wrote:
>Alex,
>The thing that caught my attention is that your signal switched =
from=3D20
>ground reference on top to power referenced on bottom, not that =
you=3D20
>removed a couple of reference planes....=3D3D20
>
>But that's just my quick gut reaction....
>
>Aubrey Sparkman=3D3D20
>Enterprise Engineering Signal Integrity Team Dell, Inc.=3D3D20=3D20
>Aubrey_Sparkman@xxxxxxxx=3D3D20
>(512) 723-3592
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx=3D20
>[mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of Alex Horvath
>Sent: Thursday, February 16, 2006 1:45 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Effect of Pwr-Gnd plane pairing vs. non-paired=3D20
>planes on signal return currents
>
>Normally, when I design a multi layer stackup I always try to alternate
>and pair Pwr-Gnd planes to maximize inter-plane capacitance. For=3D20
>example, a 16 layer stackup might look like-
> =3D3D20
> =3D3D20
> Sig - - - - - - -=3D3D20
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd---------------
> Pwr ---------------
> Sig - - - - - - -=3D3D20
> =3D3D20
> For cost reasons I might be forced into a stackup with the same=3D20
>number of signal layers but with 2 power planes removed (14 =
layers,=3D20
>same dielectric thickness) -
> =3D3D20
> Sig - - - - - - -=3D3D20
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd---------------
> Pwr ---------------
> Sig - - - - - - -=3D3D20
> =3D3D20
> =3D3D20
> Let's assume a signal traverses from the top signal layer to the=3D20
>bottom layer in both stackups. Let us also assume as a worst case
that=3D20
>there are no nearby vias or decoup caps and the signal edge rate =
is=3D20
>approximately 10 times the via length (about 200 psec). Is there a=3D20
>significant difference in the expected signal quality when =
comparing=3D20
>these 2 stackups?
> =3D3D20
> My gut feel is that all else being equal the primary factor=3D20
>determining signal quality is the spacing of the planes. The DC=3D20
>assignment of the planes has (again ignoring effect of gnd or pwr vias)
>little effect and thus the signal quality in the above cases would
be=3D20
>virtually identical.
> =3D3D20
> Since I hate to bet my designs on a gut feel hopefully someone =
can=3D20
>confirm or deny my assumptions.
> =3D3D20
>
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