[SI-LIST] Re: Speed Limit for dual stripline diff pairs?
- From: Martyn Gaudion <martyn.gaudion@xxxxxxxxxxxxxxxxxxxx>
- To: patricko@xxxxxxxxxxxxxxxxx
- Date: Thu, 04 Jul 2002 00:08:45 +0100
Hi Patrick,
Not really sure about your question.. could you describe further?
Certainly the propagation velocity is faster on a surface trace
as: Vp = c / square root Er effective, (on surface traces a percentage of
the field is in air ) ~0.65 c compared to 0.5 the speed of light
on a stripline configuration in FR4 .
This will mean a surface trace can be somewhat longer before you need
to take transmission line effects into account. However surface traces are
harder to control accurately for impedance purposes so the answer is really
going to depend on what you need to achieve..
Kind regards
Martyn Gaudion
P.S. The PCB industry often use the term dual stripline to refer to
two uncoupled striplines usually running at 90 degrees to each other.
Usually differential structures will be referred to as either edge coupled
striplines for diff pairs coupled on the same layer, or broadside coupled
if the pair is coupled across a core.
This application note is a handy reference:
www.polarinstruments.com/support/cits/AP152.pdf (1.9Mb)
At 14:15 03/07/2002 -0700, you wrote:
>Gents,
>
>What is the speed threshold for the use of a dual stripline config on a
>copper interconnect <12"? Can you achieve a higher speed with a microstrip,
>or dual stripline structure, or does it really matter?
>
>Patrick
>
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