FreeLists / si-list / [SI-LIST] Re: Split Plane Routing

["Peterson, James F (FL51)" <james.f.peterson@xxxxxxxxxxxxx>]

Pat,

I think a lot of us have had to deal with this same problem. Henry Ott's
article on this subject made a lot of sense to me. Check it out if you get a
chance.

the link is : http://www.hottconsultants.com/papers.html
the name of the article is "Partitioning and Layout of a Mixed Signal PCB".

regards,
Jim



-----Original Message-----
From: Pat Sharkey [mailto:psharkey@xxxxxxxxxxx]
Sent: Friday, February 01, 2002 12:12 PM
To: Ken Cantrell; Si-List@Freelists. Org
Subject: [SI-LIST] Re: Split Plane Routing 



Ken,

My dilemna is regarding a mixed-signal design with an FPGA interfacing to
16-bit ADCs and DACs. Would I simply be better off not isolating the analog
ground
(which will be connected at some point anyway) and put barriers on the
signal layers
so I don't have any high-speed signals next to the precious analog?

With good placement the two worlds are partitioned with the exception of the
serial data/control between the FPGA and the analog converters. Here's where
the
temptation is to spilt the ground planes to block switching currents from
entering
the analog ground.

Pat


-----Original Message-----
From: Ken Cantrell [mailto:Ken.Cantrell@xxxxxxxxxxx]
Sent: Friday, February 01, 2002 10:10 AM
To: psharkey@xxxxxxxxxxx; Si-List@Freelists. Org
Subject: RE: [SI-LIST] Split Plane Routing


Pat,
Other than NEVER(personal opinion)splitting the ground plane:
1 - S1
2 - pwr1 (lowest voltage)
3 - S2
4 - gnd
5 - pwr2 (highest voltage)
6 - S3
7 - gnd
8 - S4
would work.  If emissions are still an issue, flood the top and bottom.
That may not fix your emissions, but it will reduce it.  The way the board
is tied to the chassis is just as critical as the board emissions
themselves.  There are times when you have to split the ground plane, but
you should, in general, resist any push to do this.  If it is a "must do",
then minimize the number of traces crossing the split, and confine the type
of traces to slow and/or aperiodic signals.
Ken

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Pat Sharkey
Sent: Friday, February 01, 2002 7:10 AM
To: Si-List@Freelists. Org
Subject: [SI-LIST] Split Plane Routing



Hello all,

Given the following stackup with planes split in different areas -

1 - S1
2 - GND (SPLIT 1)
3 - S2
4 - GND(SPLIT 2)
5 - POWER(SPLIT 3)
6 - S3
7 - GND (SPLIT 4)
8 - S4.

For a signal which originates on layer 8, should the signal only be
routed on layers 6 & 8? Or, can layers 1 and 3 also be used to cross
a plane split on layer 7, assuming layers 2 and 4 are not split in the
same place (z axis)?

Thanks in advance,
Pat

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