[PCB_FORUM] Re: DGND/AGND merge point
- From: Mike Golding <Mike.Golding@xxxxxxxxxx>
- To: "'icu-pcb-forum@xxxxxxxxxxxxx'" <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Fri, 22 Apr 2005 02:23:58 -0500
So it sounds like the only good answer that would satisfy the problem is the
0 ohm resistor. I've done a lot of the suggestions from this thread in the
past and personally like the 0 ohm solution the best.
Pros
It doesn't cause DRCs, it's driven by the schematic, no manual alterations.
Cons
Takes up board space(there's always room for one more!), added item(s) to
the BOM
-Mike
(Feel free to deprecate)
-----Original Message-----
From: Budathoki, Trilok (GE Consumer & Industrial)
[mailto:trilok.budathoki@xxxxxx]
Sent: Friday, April 22, 2005 3:14 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Cc: Paul Bradshaw
Subject: [PCB_FORUM] Re: DGND/AGND merge point
Paul,
With Due respect, I disagree with you. We talking about shorting two nets
AGND & DGND. The method you suggesting just clears DRC but it leaves serious
question unanswered.
1> How will you differentiate AGND & DGND nets.
2> Component Placement, deciding on split Gnd planes is difficult. This is
gray area where you can go wrong.
3> If your board has only one net AGND/DGND, Signal Integrity Analysis
3> for entire design is not possible.
4> At PCB vendor's end,it might not pass BBT.
Trilok Budathoki
G.E- India Business Center
Email : trilok.budathoki@xxxxxx
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of Paul Bradshaw
Sent: Thursday, April 21, 2005 8:57 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: DGND/AGND merge point
If you short together two signals in ConceptHDL, it picks the alphabetically
first one. So in this case, as far as Allegro is concerned, everything
becomes AGND. But this method does work. It's what we do.
Paul Bradshaw
Symbol Technologies, Inc
6480 Via Del Oro Drive
Mail Stop 14
San Jose, CA 95119
(408) 528-2606
>>> gary.macindoe@xxxxxxx 04/21/05 08:15AM >>>
William,
Quite a few responses, all of them basically workarounds, for good reason.
You want to short together two differently named nets, YOU ARE NOT SUPPOSE
TO DO THAT!! No matter how you choose to short the two nets together (and
there are lots of ways to do it), you are more or less tricking the system.
When we have gnd and gndaud (audio ground), we create the separate planes,
and have a 0603 resistor to tie them together. This way gives you the most
flexibility: you can just put in a zero ohm to short them, you can put in
any value of resistance, short the 0603 pads with a wire or solder blob etc.
Ok, here's another way, a little bit different. Throughout your schematic,
you have lots of GND and AGND connections (probably two different ground
symbols). Somewhere in your schematics, put a resistor with GND on one side
and AGND on the other. After the design is placed/routed and you are ready
to create planes, define the separation between the two grounds with anti
etch (if your plane will be negative) or a reference line.
Next, in the schematics, remove the resistor between the two different
ground symbols and connect them together with just a wire. Since GND
probably has more connections than AGND (at least in our designs it does)
Concept will put all of the AGND connections on the GND net. Now you create
your GND plane leaving about a 50 mil or so gap somewhere along the
separation line. It is quite easy to undo if you want, just put the
resistor back in between the two ground symbols and you are back to GND and
AGND nets.
Good luck!
Gary E. MacIndoe
PCB Design Engineer
Advanced Micro Devices, Inc.
Longmont, Colorado
U2 at the Denver Pepsi Center were incredible!
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of William Billereau
Sent: Thursday, April 21, 2005 2:33 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] DGND/AGND merge point
Hello All.
Quite often, a board contains both AGND and DGND and the customer asks us
to connect them together on a single point on the board, like GND pin of a
connector.
Does anybody know how to do it in Allegro without generating DRCs errors?
Thanks in advance.
William.
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