[SI-LIST] Re: Question about split gnd planes/"tools to predict Radiated Emissions"

Howdy,
In response to one of the questions that I received off-line;

>> do u think its good that the tool allows
>> the merging of two nets without a DRC error

No, I believe using a net short capability in any package is bad design 
practice 
and I strongly urge and suggest other ways to work around it.  Though in the 
end, it is the customer or more senior design engineer at my current employer 
who makes the final decision because I want all of us to be pleased with the 
product.
If I must short the nets, I will put a note in the readme file with the 
offending object's X:Y coordinates included with the manufacturing files. 
Thanks goes to the Cadence forum as well as this list that I did not have to 
learn this issue the hard way.

Cheers!
Drew

----- Original Message ----- 
From: Sol Tatlow
To: drew3rdof3@xxxxxxxxxxxx ; si-list@xxxxxxxxxxxxx
Sent: Sunday, May 28, 2006 2:58 PM
Subject: Re: Question about split gnd planes/"tools to predict Radiated 
Emissions"


As Drew states, there are possibilities with at least these 2 (and as per my 
experience at least 5 other tools) that allow this to be done in one way or 
another - certainly a specific CAD system need in no way be a reason for only 
realising one system or another, if the CAD operator even half-way knows his 
stuf ...

As the significant amount of often contradictory evidence might suggest, I 
believe there is no one blanket solution for all cases. However, one can 
perhaps 
(underline 'perhaps') make the blanket statement that single-plane gnd systems 
are at least better for EMC (EMV) reasons, and in some cases (again, underline 
'some', although here, in particular, I can support this with my own layout 
experiences in high quality analog audio system designs!) even for audio 
reasons.

I also believe that this overlaps, to a large degree, the subject of "tools to 
predict Radiated Emissions" - here, I have to say, that, IMHO, software tools 
are way off resembling even simple real-life situations, where tolerances with 
regards to manufacturing and assembling 'simple' cable assemblies are not even 
close to being represented (although they must have a really significant effect 
with regards to phase related radiations). Would that the situation was 
different ... and, of course, it should all cost nothing!!

On the upside, I guess we can only expect things to get better (at least with 
respects to the long term development of the quality of the actual results 
:)!!).
____________________________________
Sol Tatlow, M.Eng. (Oxon)
Pro Design Electronic GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062/808-302
Fax:   +49 (0) 8062/808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________

-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Andrew W. Riley III
Gesendet: Freitag, 26. Mai 2006 21:35
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Re: Question about split gnd planes


Just a note,
>> As per I know no tool will allow you
>> to connect the AGND and DGND directly

Allegro and the Altium package that I am now forced to deal with have this
capability.  And I can't imagine that no others have the same capability.

Cheers!
Drew


----- Original Message ----- 
From: Ayan Bhattacharyya
To: weirsi@xxxxxxxxxx ; Manickavelu M. ; istvan.novak@xxxxxxxxxxx ; Ed Troy ;
si-list@xxxxxxxxxxxxx
Sent: Friday, May 26, 2006 4:32 AM
Subject: [SI-LIST] Re: Question about split gnd planes


Hi,
 As per I know no tool will allow you to connect the AGND and DGND 
directly....u 
can connect them through CAPs also... Else in same ground plane u can maintain 
less noise interference by making bottle-necks in the layout for the different 
noise sources. "Istvan Novak"'s approach is a good one...ground guard signals 
also help a lot ...specially for clock signals...around crystals. Regards Ayan 
Bhattacharyya.


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of steve weir
Sent: Friday, May 26, 2006 4:47 PM
To: Manickavelu M.; istvan.novak@xxxxxxxxxxx; Ed Troy; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about split gnd planes

Manix, no.  There are many misconceptions out there about the myth of ground 
and 
its relation to noise isolation.  Those myths get propagated into misguided 
applications of moats and such.  Think in fields and the misconceptions go away.

Steve.
At 09:50 PM 5/25/2006, Manickavelu M. wrote:
>Istan,
>Is it not that the analog and digital grounds planes can not be
>connected together anywhere but only under the chip that sources the
>analog signals? Also that while coupling these two planes we should not
>use direct Cu plane connection but couple them via inductors?
>
>Manix,
>MindTree.
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of
>istvan.novak@xxxxxxxxxxx
>Sent: Friday, May 26, 2006 6:26 AM
>To: Ed Troy; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Question about split gnd planes
>
>Ed,
>
>Splitting more than one ground plane in the stackup requires a lot of
>consideration, and mostly it is not necessary.  Isolating a sensitive
circuit
>(e.g., analog input, low-jitter oscillator) may be a good idea, but
>instead of cutting a large solid ground plane, you may want to try
>first to put the circuit to be isolated on a grounded patch on a
>'non-ground' layer.  You can make ground surface patches under and
>around your circuit to be isolated, or you can put the patch on a
>signal layer.
>
>Regards,
>
>Istvan Novak
>SUN Microsystems
>
>
>From: Ed Troy <etroy@xxxxxxxxxxxxxxx>
>Date: Thu May 25 15:38:33 CDT 2006
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Question about split gnd planes
>
>If you have a circuit board that requires a split gnd  plane over a
>small section of the board, and you have several ground planes, should
>only one have the split (the one nearest the side containing the
>components that require analog ground)  while the rest of the ground
>planes are continuous, or should the split section be on all ground
>layers? I would think that you should only have it on one layer. Also,
>if it should only be on one layer, I would imagine it would be best to
>connect it to the digital ground with one, and only one, via. Is that
>generally correct? What are some good references for layer stackups,
>etc? I know I saw one, once, but can't remember where.
>
>Ed
>
>


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