We did a version of this at my last job. Placed a 0 ohmer and added a line/shape between the pads that was not on a metal layer but was included in the gerber. It allowed us to have the part and everything worked ok but we did not need to place the part. The software did not complain and the schematic made sense (we used a "do not place" part). Still got a call from the board house because of a short, but after a few times they came to understand it was intended.
Kevin McCowan Sr. PCB Designer TSI Telsys
-----------------------------------------------------------I agree. No DRC's, and you don't have to explain that you have two nets shorted on the Gerber that are not connected in the netlist. Less confusion for the downstream process.
Nolan
-----Original Message----- From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Mike Golding Sent: Friday, April 22, 2005 2:24 AM To: 'icu-pcb-forum@xxxxxxxxxxxxx' Subject: [PCB_FORUM] Re: DGND/AGND merge point
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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