[SI-LIST] Re: Right Angle Bends

  • From: Doug Brooks <dbrooks9@xxxxxxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Fri, 15 Jul 2011 13:49:24 -0700

Well, as Eric points out, with a 50 psec rise time (equating to the 
rise time of about a 6 GHz sine wave) a square corner might introduce 
a 5% transient impedance mismatch.
If you can make a corner that square....
If you can measure the resulting reflection coefficient from that 
impedance mismatch....
If the timing on the circuit is that critical.....
If the critical length conditions are right.....

In our experience, if this is the worst problem you have, you're home free!

Doug



At 01:32 PM 7/15/2011, Mick zhou wrote:
>Maybe it is not a simple YES or NO although in most SI work it is NO.  We
>may want to think about electrical dimensions and what/how they are
>connected. I think this is well-documented in papers and books. The problem
>is some enginners may misunderstand the conclusions in the way they like. We
>like tips/points to remember etc but forget the conditions.
>There are measured data showing bends matter in certain configurations.  For
>example, section 8.16 in Signal Integrity--simplified presents an example.
>A serpentine line is another extreme example.
>Regards,
>On Fri, Jul 15, 2011 at 1:43 PM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>wrote:
>
> > None of these calculations are substantiated by actual measurements.
> >
> > There are several published works with actual testing out to 20+ GHz
> > measuring signal traces that show there is no detectable effect on signal
> > quality.
> >
> > I have a half dozen test PCBs which have been used to make the same
> > measurements and I have published the results as well as shown them to
> > 8000+
> > students in my public and private classes.
> >
> > Our industry has a problem with people doing simulations from which
> > conclusions are drawn without validating the simulations.  Often, as in the
> > case of right angle bends, much time and money is spent by designers making
> > something go away that is of no consequence.
> >
> > Simulations without validation can be very dangerous.
> >
> > Lee Ritchey
> >
> >
> >
> > --------------------------------------------------
> > From: "Zabinski, Patrick" <zabinski.patrick@xxxxxxxx>
> > Sent: Friday, July 15, 2011 9:46 AM
> > To: <si-list@xxxxxxxxxxxxx>
> > Subject: [SI-LIST] Re: Right Angle Bends
> >
> > > Here are a few of the earlier references on the topic.
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE Calculation of Microstrip Bends and Y-Junctions With Arbitrary
> > > Angle
> > > AUTHOR Reza Mehran
> > > SOURCE IEEE Transactions on MTT, MTT-26
> > > DATE June, 1978
> > > PAGES 400-405
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE   Microstrip - A New Transmission Technique for the Kilomegacycle
> > > Range
> > > AUTHOR  D. D. Grieg & H. F. Engelmann
> > > SOURCE  Proceedings of the IRE
> > > VOLUME  40
> > > DATE    December, 1952
> > > PAGES   1644-1650
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >
> > > These offer related info.
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE Equivalent Circuit Modeling of Interconnects From Time-Domain
> > > Measurements
> > > AUTHOR Jyh-Ming Jong, Bozidar Janko, and Vijai Tripathi
> > > SOURCE IEEE Trans. on CHMT
> > > VOLUME 16
> > > NUMBER 1
> > > DATE February, 1993
> > > PAGES 119-126
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE Equivalent Circuits for Discontinuities in Balanced Transmission
> > > Strip Lines
> > > AUTHOR Arthur A. Oliner
> > > SOURCE IRE Trans Micorwave Theory & Techniques
> > > VOLUME MTT-3
> > > DATE March, 1955
> > > PAGES 134-143
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE Experimental Determination of the Properties of Microstrip
> > > Components
> > > AUTHOR Maurice Ardit
> > > SOURCE Electrical Communication
> > > VOLUME 30
> > > DATE December, 1953
> > > PAGES 283-293
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > TITLE Time-Domain Characterization of Interconnect Discontinuities in
> > > High-Speed Circuits
> > > AUTHOR Jyh-Ming Jong and Vijai K. Tripathi
> > > SOURCE IEEE Trans on CHMT
> > > VOLUME 15
> > > NUMBER 4
> > > DATE August, 1992
> > > PAGES 497-504
> > >
> > > ~~~~~~~~~~~~<done>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >
> > > Enjoy,
> > > Pat Zabinski
> > > Mayo Clinic
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > > On Behalf Of Lee Ritchey
> > > Sent: Friday, July 15, 2011 11:33 AM
> > > To: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Re: Right Angle Bends
> > >
> > > Does anyone know the origin of the myth that right angle bends cause
> > > signal integrity problems?
> > >
> > > I though this myth had died a long time ago, but had a conversation last
> > > week with a well known fabricator who was told by a customer that right
> > > angle bends were a no no.
> > >
> > > This was a customer who should know better.
> > >
> > > Lee Ritchey
> > > Speeding Edge
> > >
> > >
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