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Subject: Re: [geda-user] Net attributes
From: John Doty <jpd AT noqsi DOT com>
In-Reply-To: <55A7D999.5020101@ecosensory.com>
Date: Thu, 16 Jul 2015 11:34:24 -0600
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On Jul 16, 2015, at 10:19 AM, John Griessen <john AT ecosensory DOT com> wrote:

> On 07/16/2015 02:37 AM, Roland Lutz wrote:
>> I can currently come up with the following:
>>   - managing voltage drop, oscillation, and heat by
>>     - keeping trace resistance low and
>>     - keeping common trace segments short, and
>>   - improving signal quality in differential pairs by minimizing signal
>>     run time differences
>> 
>> I'm not an electronics engineer, though
> 
> The differential pair attribs that can help also include
> 1.  smoothness of board material,
> 	since the waveguide smoothness affects how much mismatch there is and so reflections and in a short
> 	transmission line in a system, standing wave patterns on the transmission line (differential pair).
> 2. definition and smoothness of the trace width
> 	so it does not have blips or sharp edges
> 
> For some frequencies, (pcb antennas and feed lines), corners matter, so
> 3. min radius spec on a trace edge
> 
> 4a. 4b. 4c. Power decoupling caps needed near a pin  -- three type ranges
> 
> 5.  attrib category of keep away by X distance.  Add it and a unique name to two nets to keep them apart.
> 
> 
> 
> 
> 

Yup. It can get quite elaborate. The attributes above are requirements, but then there are also specs derived from layout.

Gschem has the capacity to handle attributes of net segments, but I wonder if this is just too much metadata to burden a schematic with in many cases. DJ¢s database of attributes idea continues to grow on me.

For requirements, I would add that printed circuit traces also have a thermal function. Sometimes you want a net segment to carry away the heat, and sometimes you want one that conducts as little heat as possible.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com