In a message dated 10/27/2003 2:04:45 AM Eastern Standard Time, 
[EMAIL PROTECTED] writes:


> We have a pcb that has both analog and digital circuits and consequently we 
> have assigned a ground to each type (AGND and DGND). I need to join both of 
> these to a common point on the pcb which is the power supply circuit common 
> (GND). How do I join these three nets without using a wire link or other 
> connecting component - ie I would like to tie all three nets together on the 
> schematic and pcb.
> 

The easiest way within P99SE has been called on this forum, the "Lomax 
virtual short". You can search the archives, but in essnce it involves building a 
tiny gap, much too small to be fabricated, and adding a design rule to allow the 
tiny gap to pass DRC. Personally, I have a component called "TIE" in my 
footprint library. This component is essentially an 0603 footprint, but I've added 
a "pad" which lies between the two pads, the width of my usual traces, and 
coming within 0.001 mils (yes, 0.000001") of the pads on each end. The pad 
designator is set to "SHORT", and I add a design rule to the design allowing any pad 
named "SHORT" to have a clearance of 0.001" to any other object. By having 
this named pad in between other, bigger pads, I can mostly protect it from 
becoming an erroneous short to other objects. The trickiest part of the whole thing 
is remembering to tell the PCB fabricator not to be "helpful" and enlarge the 
gaps to make them fabricatable, just in case they happen to spot it.

Steve Hendrix


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