[SI-LIST] Re: Guard traces for differetial pairs

Well stated, Scott. Beginners should definitely heed the cautions noted in 
Scott's posting.
For reference, I have routinely achieved 6-8 dB crosstalk improvements in 
microstrip traces using properly grounded guard traces, and occasionally as 
high 
as 14 dB improvements. Also, the radiated emissions of these PCBs were reduced 
by 21-30 dB from their previously un-guarded designs.

Lee Ritchey has often commented negatively on the need for guard traces; 
however, I strongly suspect that the many other field control techniques and 
good 
design practices he uses reduces the necessity for this added complication. 
Since many vias (and their associated clearance holes in power planes and 
routing impacts on other signal layers) are required for proper implementation 
of 
guard traces, and when other good layout practices are in place, there is a 
point of diminishing returns that can yield degradation (not improvement) when 
guard traces are employed.

Electromagnetic fields and waves in different PCB layups, dimensions, shapes, 
and frequency ranges is a very complex and inter-related area of expertise. 
How often have you seen that no two different PCB designs exhibit the same EMC 
performance? 

Good luck in your designs, I'm edging futher into retirement...going trout 
fishing now.

Mike

Michael L. Conn
Owner/Principal Consultant
Mikon Consulting

*** Serving Your Needs with Technical Excellence ***


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: