Hi Yuri - And what can I say but thank you very much for your comprehensive
reply!
While I hesitate to speak for the group, I am sure that there will be others
that will benefit from
the "more details" you mention in your email.
What a coincidence that you mentioned the periodic discontinuities in the
reference plane. I ran across
a (recent) IEEE Letter in the EMC Transactions referring to the same technique.
Thank you for
your reference to the AppNotes...I am heading there now!!
Thanks
Charles Grasso
(w) 303-706-5467
-----Original Message-----
From: Yuriy Shlepnev [mailto:shlepnev@xxxxxxxxxxxxx] ;
Sent: Tuesday, August 14, 2018 1:56 PM
To: Grasso, Charles <CHARLES.GRASSO@xxxxxxxx>; leeritchey@xxxxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: IEEE Paper on a unusual technique for cross talk
reduction
This message originated outside of DISH and was sent by: shlepnev@xxxxxxxxxxxxx
Hi Charles,
It looks like almost all new FEXT reduction techniques for PCBs can be traced
back to very old directional coupler design techniques - reduction of the FEXT
in microstrips increases the directivity in backward couplers and was explored
for many years. For instance, use of the capacitors to reduce the far end
coupling can be traced back to works of G. Schaller "Optimization of microstrip
directional couplers with lumped capacitors"
(A.E.U. v. 31, 1977) and D. Kajfez "Raise coupler directivity with lumped
compensation" (Microwaves v. 27, 1978) done in 1977 and 1978. The caps
connected in parallel (at the ends or periodically) can be effectively used to
alter the odd mode phase, while not affecting the even mode.
In general, the FEXT phenomenon in microstrips and in strip lines with
non-uniform dielectric is caused by the difference in the phase velocity of the
even and odd mode. Everything that goes in and out of a 2-conductor t-line
segment is a superposition of two even and two odd modes - this is the nature
of the problem. Zero difference produces zero FEXT. Whatever reduces the
difference in velocity or difference of the phases at the end of the segment,
will reduce the FEXT. For instance, "wiggly" lines (suggested by A. Poddel in
"A high-directivity microstrip coupler technique" in 1970 at MTT Symposium!)
can be used to reduce the odd mode velocity, while not affecting the speed of
the even mode. That can be used to reduce FEXT almost to zero. The latest
re-incarnation of this technique for the PCB interconnect application are
"tabbed lines" or "stub-alternating" microstrip lines. This technique was
developed a while ago for increase of directivity of microstrip directional
couplers - see for instance analysis and overview at S. Sun, L. Zhu,
Guided-wave characteristics of periodically non-uniform coupled microstrip
lines - even and odd modes, IEEE Trans. on MTT, vol. 53, 2005, N 4, p.
1121-1227.
Periodic discontinuities in microstrips or in the reference planes (meshed or
perforated planes) can be used to equate the even and odd mode phase velocities
and the other way around - such discontinuities may increase the difference and
increase the FEXT if not properly designed. Note that such periodic structures
behave as transmission lines and the best way to simulate them as the periodic
structures - extract modal characteristic impedances and propagation constants
- see more at app notes #2018_04 (effect of meshed planes on cross-talk) and
2018_06 at http://www.simberian.com/AppNotes.php. In particular, proper ;
positioning of the traces over the meshed planes in addition to overlay
dielectric layer can be used to substantially reduce or increase the cross-talk
in flexible interconnects. Well, this is purely theoretical observation so far
- I can provide more details if someone would be interested to try it in
practice.
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, USA Office
+1-702-876-2882; Fax +1-702-482-7903 Cell +1-206-409-2368; Virtual
+1-408-627-7706
Skype: shlepnev
www.simberian.com
Simbeor - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software to Design Predictable Interconnects!
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test Finalist
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Grasso, Charles
Sent: Tuesday, August 14, 2018 8:37 AM
To: leeritchey@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: IEEE Paper on a unusual technique for cross talk
reduction
Copy that...I am puzzled to be sure..
-----Original Message-----
From: leeritchey@xxxxxxxxxxxxx [mailto:leeritchey@xxxxxxxxxxxxx] ;
Sent: Monday, August 13, 2018 4:26 PM
To: Grasso, Charles <CHARLES.GRASSO@xxxxxxxx>; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] IEEE Paper on a unusual technique for cross talk
reduction
This message originated outside of DISH and was sent by:
leeritchey@xxxxxxxxxxxxx
Sounds a bit odd to me.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Grasso, Charles
Sent: Monday, August 13, 2018 1:01 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] IEEE Paper on a unusual technique for cross talk
reduction
HI,
I ran across a paper titled: Far-End Crosstalk Noise Reduction Using
Decoupling Capacitor Authors : Bao-Ren Huang, Kuan-Chung Chen, and Chun-Long
Wang, Member, IEEE.
The paper suggests using decoupling capacitors attached between signals
first at the near end and then (for further reduction) a coupled microstrip
line using distributed decoupling capacitors (my edit: spaced along the
line) is proposed.
I am curious: Has anyone used this technique in an actual product?
Thanks
Charles Grasso
(w) 303-706-5467
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