[SI-LIST] Re: Current Return Path

Ken,
If you have a near field H-probe, you should check how does the change 
affect the radiated emissions from the card.  This is more of an EMI issue 
than Signal Integrity.  If you return loop is bigger, it will have 
noticeable impact on the card EMI.
Regards, Ravinder
Server PCB and Flex Development
Hitachi Global Storage Technologies

Email: Ravinder.Ajmani@xxxxxxxx






kfrobinson@xxxxxxxxxx
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06/26/2003 08:43 AM
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All,
I was recently evaluating a board design and noticed that some signals =
were referenced to a power plane(VTERM) and some nets were referenced to =
ground.  This is a very large board 13" x 22" and there are bypass caps =
between the power plane and ground plane around the perimeter of the =
board.  I thought I would see if I could destroy the current return path =
by removing all the bypass caps between the power plane and ground plane =
except from the far end of the board furthest from the driver.  I then =
looked at the signals that were referenced to the power plane and they =
were identical to what they had been before the removal of caps.   I =
took scope shots at multiple locations before and after the cap removal. =
The net in question runs the length(22") of the board right down the =
center.  I had expected to see a pronounced change, but did not see one. =
 Any thoughts?

Stack up
s
vterm
s
s
vcc
gnd
vcc
gnd
s
s
gnd
s

Ken Robinson
kfrobinson@xxxxxxxxxx


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