[SI-LIST] Re: Differential microstrip with coplanar ground traces ... unexpectedresults
- From: "Bob Welte" <welte@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 3 Oct 2002 09:09:09 -0400
Thanks to everyone who responded!
Based on the responses I think I would now tend to favor a stripline
structure over microstrip.
Differential microstrip requires significant spacing between pairs even
with a coplanar ground.
Microstrip structure because of its multi-mode propagation characteristics
will cause distortion (resulting in added signal jitter)
Coplanar grounds, to be effective, are required to have low impedance
(perhaps 5X width of signals),
and lots of vias ...up to 20/Wavelength. Using the 3rd harmonic, this is
a via every .075" (FR4)!
Bob Welte
IBM Microelectronics
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