[SI-LIST] Re: Power - Ground Swap in PCB

If you have any PLL circuits or other circuits that have performance
determining components like A/D or D/A converters, it is advisable to make
the first plane below those components logic ground to avoid noise coupling
from Vdd to those parts.  Most of us have such circuits.  

Once you make that choice, the next one is how to get ground and Vdd planes
close enough to create a reasonable plane capacitor for support of the fast
switching transients related to driving address and data lines.  The
choices are to add two more planes or to fill the unused space in the
signal layers with the copper attached to the appropriate power rails as I
do for PCMCIA class PCBs.

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just took the energy it took to be angry and wrote some blues.
Count Basie


> [Original Message]
> From: steve weir <weirsp@xxxxxxxxxx>
> To: <msalami@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 4/25/2004 8:20:39 PM
> Subject: [SI-LIST] Re: Power - Ground Swap in PCB
>
> Mehrdad, it depends on your goals.  Ground near the bottom of a six layer 
> stack-up has the advantage that you likely have more free real estate on 
> the bottom layer to route with.  If you use Lee's trick of a capped
design, 
> ( quasi eight layer ), then you have two well controlled impedance layers 
> both referenced to ground, like they should be.  The more signals that
you 
> reference against ground versus a power layer, generally, the easier your 
> life will be.  It also means that higher speed signals are pushed down in 
> the stack and see less of a via stub.  OTOH, ground near the top can be 
> better for EMI.
>
> Regards,
>
> Steve.
> At 12:03 PM 4/26/2004 +1000, Mehrdad Salami wrote:
> >Hello All,
> >
> >I have a question about layer stack in PCBs. For a simple six layer like
> >(configuration 1)
> >
> >Top (Signal1)
> >Ground
> >Signal2
> >Signal3
> >Power
> >Bottom (Signal4)
> >
> >What would be the effect if the Ground and Power planes are swapped
> >(configuration 2)
> >
> >Top (Signal1)
> >Power
> >Signal2
> >Signal3
> >Ground
> >Bottom (Signal4)
> >
> >Assuming the same distance between Power or Ground to signal layers and
> >also the same track routing on the signal layers.
> >
> >
> >Regards
> >
> >
> >
> >Sal
> >
> >==========================================
> >Mehrdad Salami
> >Hardware Design Engineer
> >
> >Colour Vision Systems
> >11 - Park St - Bacchus Marsh
> >Victoria - 3340 - Australia
> >
> >
> >
> >------------------------------------------------------------------
> >To unsubscribe from si-list:
> >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> >or to administer your membership from a web page, go to:
> >http://www.freelists.org/webpage/si-list
> >
> >For help:
> >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >List FAQ wiki page is located at:
> >                 http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> >
> >List technical documents are available at:
> >                 http://www.si-list.org
> >
> >List archives are viewable at:
> >                 http://www.freelists.org/archives/si-list
> >or at our remote archives:
> >                 http://groups.yahoo.com/group/si-list/messages
> >Old (prior to June 6, 2001) list archives are viewable at:
> >                 http://www.qsl.net/wb6tpu
> >
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
>                 http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
>                 http://www.si-list.org
>
> List archives are viewable at:     
>               http://www.freelists.org/archives/si-list
> or at our remote archives:
>               http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>               http://www.qsl.net/wb6tpu
>   



------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: