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 Post subject: Re: Multiple power and ground net issue
PostPosted: 20 Sep 2015, 00:17 
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Joined: 20 Jan 2012, 10:50
Posts: 116
Well, DerekG, since you asked... ;)

First of all, FWIW, a big thumbs-up to all who are participating in this thread. I hope others will join in as well and together we can keep this issue at the forefront.


About the star ground:

Yes, best practices often dictate that multiple ground paths eventually merge at a common point in a star ground fashion as Tomg has so clearly illustrated above and that is the primary reason for this thread. Nice work, BTW.

But there are other times that a ground or power 'bus' may have branches along the way and each one of these branches may be a ground or power path of a differnt purpose. As I noted in a previous post, I've seen professional audio equipment that has up to 5 different ground branches in a single high-gain audio preamp section each servicing it's own particular stage alone not to mention the rest of the power amplifier and chassis. Those grounds split off along the way and eventually they all return back to the main star ground (envision a tree branch). This method ensures the quietest possible grounding scheme. Another application might be a differential amplifier sensing current across a PCB trace. What would you do if you wanted to sense current across that trace segment? And a simpler issue might be how do you handle planar inductors? And then there's buried grounds in a multi-layer PCB.

But here's the problem that I see:

Tomg's illustration requires a special component to make this connection and it appears at this point, that would indicate that this special component has a corresponding special pattern (i.e. pad) attached to it. That would mean that one would have to place several of these special patterns on the pcb and route to them. Due to the nature of Diptrace, that would mean that 'one size fits all' is probably not going to happen in every application and therefore one would wind up with an array of special components with different shaped and sized patterns, one for each instance as it arises. This is probably the biggest problem with the Diptrace Pattern Library currently, in that you wind up with way too many minor revision of a pattern just to customize it to the current need. For example, a header or IC footprint, one with silk screen and the same pattern without silk screen. In this case, it would be better if there were only one pattern and one had the option of simply enabling or disabling the silkscreen on a per part basis and not the whole PCB... but I digress.

So, just to clarify, this was my thought process in proposing the ability to connect those 'Net Groups' (for the lack of a proper adopted name) to each other not only at one star ground location, but anywhere else along the way. This gives one the option to join these group members not only at one common point/pad but branch anywhere one deems necessary. So, you see, not all ground or power branches are exactly a star so that might not be exactly the best term to use as it could be construed as to be ambiguous. i.e. not all branches are exactly stars but a star would be made of branches.

Yeah... well anyway, this is the reason that I'm really not crazy about a special component/pattern to get it done.

And remember, this would be benificial not only for ground paths, but any power bus as well.

Well, anyway, I do hope others will join in to this discussion and maybe, just maybe we can get something done about this... whatever the solution turns out to be.

jeff


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 Post subject: Re: Multiple power and ground net issue
PostPosted: 21 Sep 2015, 08:54 
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Joined: 18 Mar 2014, 08:06
Posts: 41
Location: Norfolk Island
Thanks Jeff for your very explicit explanation.. I agree it is not an easy one.

I have added 0R resistor links between the differing earths in the past.

I do all the routing & the design rules are happy.

I then remove the 0R links just before production. I do not run another design rule check as errors will now be thrown up.

I place an outline of the SMD 0R resistors on a mechanical layer so that I know where to place them again should I revise the board at a later date.

With the new beta now pushed to ver 2.9 it looks like the final version will be 3.x

This means an upgrade will be required.

Please keep in touch.

Best regards,

Derek.

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 Post subject: Re: Multiple power and ground net issue
PostPosted: 21 Sep 2015, 10:57 
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Joined: 20 Jun 2015, 14:39
Posts: 934
Well, for what it's worth, here is another "variation on a theme"...
Add a new Net Type called STAR> that would allow other standard Nets to connect to it without any of these connecting Nets merging, losing their own unique identities/names/types or causing ERC/DRC errors. Care would have to be taken to connect the standard Nets at different locations on the STAR> Net in the Schematic to prevent conflicts between standard Nets. However, all of the standard Nets connected to a specific STAR> Net designated in the Schematic would be allowed to physically connect to the STAR> Net at the same location in the PCB Editor if so desired. Below is a step-by-step example of how this might be handled in the Schematic Editor...

-- 22 Sep 2015, 06:58 --

In the Schematic Editor, a STAR Net will be indicated by a special line made up of asterisks, making its function obvious...


You do not have the required permissions to view the files attached to this post.

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 Post subject: Re: Multiple power and ground net issue
PostPosted: 24 Sep 2015, 14:19 
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Joined: 26 Mar 2015, 15:27
Posts: 87
I really think Altium's "Net Tie" is the best, most logical solution.


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 Post subject: Re: Multiple power and ground net issue
PostPosted: 11 May 2017, 18:47 
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Joined: 19 May 2016, 10:18
Posts: 2
I find this post when Googling for the answer to this problem. I am very disappointed to find there is no solution (I added a 0 ohm resistor). I (a Diptrace owner) am adding my vote for a solution to this problem. How hard can it be???


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