Re: [SI-LIST] : MECL System Design Handbook

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Tue Jun 05 2001 - 17:04:08 PDT


Lee,

As to whether a corner discontinuity for a "realistic" trace can be
measured with a TDR, the answer to this question is closed.

It can.

Whether the "effect" matters is a different animal altogether
and depends upon the application and the margins within a
particular design.

Gus Panella of Molex and myself have provided a preliminary
paper to the si-list on the "perturbations" of right angle bends and measurement
of same with a TDR. These measurements of 12.5 mil low loss stripline
traces are consistent with Tom Dagostino's experience. A number of
days back, I copied you on this paper.

With the impedance of a trace held as a constant, the discontinuity seen by an
edge passing a corner should remain consistent across a very wide range
of trace widths. Why? Because the important dimension W/h remains
constant with size scaling. Since W/h is constant (to achieve the same impedance)
Eeff is also constant. With Eeff constant for varying trace widths (and associated
adjustment of the trace height above the plane for impedance) the trace velocity will be
identical.
Since the trace velocity is identical, the distributed L and C is exactly the
same for any length of trace or size of feature. This means that as the
trace width, corner, and trace height above the plane are scaled geometrically.
the effect of the corner discontinuity remains the same.

Now, there are limits to this analysis.

1) TEM mode propagation is assumed.
2) Corner feature length is less 1/10 risetime.

As the trace width decreases, there is also a different limit. Skin effect losses
will eventually attenuate the edge harmonics and limit the risetime that
reaches the corner. But, when this is the case, we really aren't transmitting
any really interesting signals anyway.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

Ritchey Lee wrote:

> TOm, > > I have such PCBs and have launched edges as fast as 60 pSEC into them with no detectable perterbation. My objective is to see how > PCB features affect logic signals, none of which have edges faster than 60 pSEC by the time they reach the PCB. All of us who are > looked to for technical guidance should be doing the same. > > It might be possible to "see" a 90 corner at some very high frequency, some use numbers like 40 GHz, or at some bery large > geometry, like 100 mil wide traces, but these cases aren't germain to what our community works with day to day. The stuff of 10 > mil traces ans thinner and edges of 60 pSEC and slower are of interest. That's the reagon where we should be sure our advice has > meaning. > > Lee > > Dagostino, Tom wrote: > >> I agree that this board is not the latest technology, that is why I qualified my offer, but it does have real square corners and >> the traces of interest are fairly isolated. If you can send me a test board that has good square corners that are isolated and >> that I can get a clean launch into I will measure that and publish those results too.I now have the GPIB system working on my >> scope again and will make some measurements on the test board I have. Tom Dagostino >> Modeling Manager >> Mentor Graphics Corp. >> SAE >> tom_dagostino@mentor.com >> 503-685-1613 >> >> -----Original Message----- >> From: Ritchey Lee [mailto:leeritchey@earthlink.net] >> Sent: Friday, June 01, 2001 10:10 AM >> To: Dagostino, Tom >> Cc: 'Dr. Edward P. Sayre'; Rich Peyton; Roehrner Wolfgang; si-list@silab.eng.sun.com >> Subject: Re: [SI-LIST] : MECL System Design Handbook >> Wolfgang, >> >> The test board you cite doesn't relfect how real logic PCBs are built. No one uses 100 mil wide traces. Also, no >> one builds PCBs with such thick dielectrics. It would be misleading to suggest that what you measure with the >> structures you have apply to the structures that appear in logic PCBs, unless you show that the scaling is >> appropriate. >> >> Lee >> >> Dagostino, Tom wrote: >> >> > >> > >> > I have a board that demostrates this very nicely. As soon as I get my scope/extraction system working again I will >> > publish some results. The board is two layers with ground on one side and 50 Ohm traces on the other. Yes, these >> > traces are quite wide, on the order of 0.100". There are several right angel bends with square corners. The corners >> > are quite visible. >> > >> > Tom Dagostino >> > Modeling Manger >> > Mentor Graphics Corp. >> > SAE >> > tom_dagostino@mentor.com >> > 503-685-1613 >> > >> > -----Original Message----- >> > From: Dr. Edward P. Sayre [mailto:esayre@nesa.com] >> > Sent: Thursday, May 17, 2001 6:47 PM >> > To: Ritchey Lee; Rich Peyton >> > Cc: Roehrner Wolfgang; si-list@silab.eng.sun.com >> > Subject: Re: [SI-LIST] : MECL System Design Handbook >> > >> > Lee and others: >> > >> > I don't know what kind of TDR or fixturing you might have used, but the >> > excess capacitance is very real and can be seen. It is also illustrated in >> > a number of microwave books. If your fixturing caused a significant loss (> >> > 100 ps) of risetime of the step out of the TDR, then the capacitance effect >> > will be washed out. >> > >> > Sincerely, >> > >> > ed sayre >> > ========================== >> > At 08:36 AM 5/10/01 -0700, Ritchey Lee wrote: >> > >Any of you who want to know how the myth about right angle bends got >> > >started, look >> > >at figure 7.17 on page 155. This alleges that right angle bends can be >> > >seen by a >> > >TDR. I've done this measurement dozens of times and coiuld never see a right >> > >angle bend. >> > > >> > >A few years ago, I called Mr. Blood the author of the book and asked >> > >about the >> > >diagram. His reply was that he knew the diagram was flawed, but there >> > >wasn't time >> > >to fix it before the book went to press. >> > > >> > >As a result, thousands of engineers have spend countless time worrying >> > >about right >> > >angle bends. >> > > >> > >When we publish technical information such as this, it is important to >> > >insure it >> > >is accurate. >> > >This applies especially to applications notes, whic often contain entirely >> > >false >> > >data. >> > > >> > >Lee >> > > >> > >Rich Peyton wrote: >> > > >> > > > FYI, >> > > > >> > > > The hard copy can be ordered free of charge. >> > > > >> > > > Rich >> > > > >> > > > Roehrner Wolfgang wrote: >> > > > >> > > > > http://www.onsemi.com/home <http://www.onsemi.com/home> >> > > > > >> > > > > In the Menu-tree go to: >> > > > > >> > > > > Technical Documents >> > > > > CD/Document Ordering >> > > > > General Search >> > > > > >> > > > > search for document number: hb205 >> > > > > download it as pdf (or order!). >> > > > > >> > > > > regards, >> > > > > Wolfgang >> > > > > >> > > > > -----Original Message----- >> > > > > From: Ashok Babu K [mailto:k.ashokbabu@gdatech.co.in] >> > > > > Sent: Tuesday, April 10, 2001 12:39 PM >> > > > > To: si-list@silab.eng.sun.com >> > > > > Subject: [SI-LIST] : MECL System Design Handbook >> > > > > >> > > > > Hi all, >> > > > > I see that a good resource for general high speed termination design and >> > > > > especially ECL/PECL termination is Motorola's MECL System Design >> > > Handbook by >> > > > > Blood Jr., and William R. Many articles and papers specify the same as a >> > > > > good resource. Unfortunately I could not get the soft copy of the MECL >> > > > > System Design Handbook. I could not get it from the ON Semiconductor >> > > > > website. If any of you have the PDF file of the same or know where it >> > > can be >> > > > > obtained, please inform me. Any suggestions of other resources are highly >> > > > > welcome. >> > > > > Regards, >> > > > > Ashok. >> > > > > >> > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to >> > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE >> > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. >> > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu >> > > > > **** >> > > > >> > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to >> > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE >> > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. >> > > > si-list archives are accessible at http://www.qsl.net/wb6tpu >> > > > **** >> > > >> > > >> > > >> > > >> > >**** To unsubscribe from si-list or si-list-digest: send e-mail to >> > >majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE >> > >si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. >> > >si-list archives are accessible at http://www.qsl.net/wb6tpu >> > >**** >> > >> > >> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ >> > | NORTH EAST SYSTEMS ASSOCIATES, INC. | >> > | ------------------------------------- | >> > | "High Performance Engineering & Design" | >> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ >> > | Dr. Ed Sayre e-mail: esayre@nesa.com | >> > | NESA, Inc. http://www.nesa.com/ | >> > | Primrose Park Tel +1.978.392-8787 | >> > | 5 LAN Drive, Ste 200 Fax +1.978.392-8686 | >> > | Westford, MA 01886 | >> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ >> > >> > **** To unsubscribe from si-list or si-list-digest: send e-mail to >> > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE >> > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. >> > si-list archives are accessible at http://www.qsl.net/wb6tpu >> > **** >> -- Scott McMorrow Principal Engineer SiQual, Signal Quality Engineering 18735 SW Boones Ferry Road Tualatin, OR 97062-3090 (503) 885-1231 http://www.siqual.com

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