[SI-LIST] Re: Effect of Pwr-Gnd plane pairing vs. non-paired planes on signal return currents
- From: Vinu Arumugham <vinu@xxxxxxxxx>
- To: Aubrey_Sparkman@xxxxxxxx
- Date: Thu, 16 Feb 2006 12:20:02 -0800
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
>ground reference on top to power referenced on bottom, not that you
>removed a couple of reference planes....=20
>
>But that's just my quick gut reaction....
>
>Aubrey Sparkman=20
>Enterprise Engineering Signal Integrity Team
>Dell, Inc.=20
>Aubrey_Sparkman@xxxxxxxx=20
>(512) 723-3592
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [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 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
>example, a 16 layer stackup might look like-
> =20
> =20
> Sig - - - - - - -=20
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd---------------
> Pwr ---------------
> Sig - - - - - - -=20
> =20
> For cost reasons I might be forced into a stackup with the same number
>of signal layers but with 2 power planes removed (14 layers, same
>dielectric thickness) -
> =20
> Sig - - - - - - -=20
> Gnd --------------
> Pwr --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd --------------
> Sig - - - - - - - -
> Sig - - - - - - - -
> Gnd---------------
> Pwr ---------------
> Sig - - - - - - -=20
> =20
> =20
> Let's assume a signal traverses from the top signal layer to the
>bottom layer in both stackups. Let us also assume as a worst case that
>there are no nearby vias or decoup caps and the signal edge rate is
>approximately 10 times the via length (about 200 psec). Is there a
>significant difference in the expected signal quality when comparing
>these 2 stackups?
> =20
> My gut feel is that all else being equal the primary factor
>determining signal quality is the spacing of the planes. The DC
>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
>virtually identical.
> =20
> Since I hate to bet my designs on a gut feel hopefully someone can
>confirm or deny my assumptions.
> =20
>
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