[SI-LIST] FEXT reduction by very small spacings
- From: Hermann Ruckerbauer <hermann.ruckerbauer@xxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sun, 16 Aug 2009 19:40:45 +0200
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: 7bit
Hello all,
for a training I wanted to show some simulation with FEXT and NEXT
comparison. So I did some simulation sweeps with different spacings.
On a normal Microstrip trace I saw, that going to wider spacing it took
a quite large spacing to reduce FEXT (as expected). But when reducing
the spacing below 100um the FEXT got smaller quite fast. Based on the
waveform my guess was, that the capacitive coupling got larger quite
fast and compensated the inductive coupling, which is normally causing
the neg. peak (for a rising edge) at the far end of the line. So far I
have not seen this effect in literature, but from Agilent support I got
a hint to an IEEE Paper which shows this behavior:
IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 43, NO. 4,
NOVEMBER 2001
Far-End Crosstalk Reduction in Double-Layered Dielectric Interconnects
Talgat R. Gazizov, Member, IEEE
The author closes with the statement, that he hopes the paper can be
used to find a way how to utilize this effect. And that's my question
too. Has somebody tried to cancel out the FEXT by reduction of the spacing?
The biggest issue I see is the NEXT. It is getting quite large with this
small spacings, so even when your system is only reacting on FEXT,
because you have e. g. a parallel memory bus you need a good source
termination to ensure, that the reflected NEXT is not hitting the
receiver after it's reflected at the driver.
Additionally it might be necessary to exactly control the routing for
each trace seperatly. In simulation it is easy to "route" two signals
side by side with always the same distance, but for a real system this
will be a real problem, and it might be necessary to separately control
the routing for each from the 64/72 bits of the memory bus.
I guess it might be difficult to use this effect, but it should be
doable ... what is your opinion?
regards
Hermann
EKH - EyeKnowHow
Hermann Ruckerbauer
www.eyeknowhow.de
hermann.ruckerbauer@xxxxxxxxxxxxx
Veilchenstrasse 1
94554 Moos
Tel.: +49 (0)9938 / 902 083
Mobile: +49 (0)176 / 787 787 77
Fax: +49 (0)721 / 151 258 230
------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//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:
