RE: [SI-LIST] : RE: 2.5 GHz in FR4

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From: Degerstrom, Michael J. (degerstrom.michael@mayo.edu)
Date: Tue Apr 03 2001 - 14:49:44 PDT


Larry,

Can you share with us what kind of loss you see for 12"
of .01" wide stripline for your 3.125Gbps signals? I.e.,
if you had a 1V signal swing without loss then what is the
remaining swing for a one-zero repeating pattern through
your 12" path?

Is the pre-emphasis then a requirement to maintain
good signal transmission?

Mike

_______________________________________________________________
Mike Degerstrom Email: degerstrom.michael@mayo.edu
Mayo Clinic; 200 1st Street SW ; Rochester, MN 55905
Phone: (507) 538-5462 FAX: (507) 284-9171
WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html
_______________________________________________________________

> -----Original Message-----
> From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
> Sent: Tuesday, April 03, 2001 2:04 PM
> To: 'Michael Nudelman'; si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4
>
>
> Not at all masochistic.
>
> This was an extremely easy board to route. AMP, Erni and
> Teledyne (in no
> particular order) have expended great amounts of research for
> high speed
> back/mid planes using differential pairs for the telecomm and
> networking
> industries and have reduced it down to a turn-the-crank
> operation. (The app
> notes are readily available on their websites.)
>
> Plus, the quotes we have regularly gotten from
> backplane/midplane vendors
> show the cost for Getek to be about 1.8X that of FR-4, and
> the more exotic
> ones like the Rodgers materials go up exponentially.
>
> Thirdly, the other materials (Getek and up) have comparative
> availability
> problems when you are using slabs that are 17" or 21" wide by
> 24" or more
> high.
>
> Lastly, for serial backplanes, the SERDES manufacturers have
> fitted their
> chips up with pre-emphasis logic to hugely reduce the
> data-dependent jitter
> (DDJ) caused by the roll-off vs. frequency of FR-4.
>
> If anyone from Tyco or other such fabricators is listening,
> please chime in.
>
> Larry Miller
>
> -----Original Message-----
> From: Michael Nudelman [mailto:mnudelman@tellium.com]
> Sent: Tuesday, April 03, 2001 10:20 AM
> To: si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4
>
>
> This is quite masochistic. Do you have to do it to yourselves
> and use FR4,
> unless you are running couple of inches of hi-speed wires?
>
> -----Original Message-----
> From: Larry Miller [mailto:ldmiller@rhapsodynetworks.com]
> Sent: Tuesday, April 03, 2001 12:57
> To: 'Gaboian, Jerry'; 'Zabinski, Patrick J.';
> si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4
>
>
> I, too, must take issue with practically every statement made by Mr.
> Zabinski.
>
> We are using stripline. We do not have vias except the
> connector pins (AMP
> HS-3).
>
> We are using 10-mil stripline traces on the backplane, 5-mil
> stripline on
> the plug-in boards (have to, the boards get too thick
> otherwise). Yes, the
> 5-mil sections are lossy because of skin effect; luckily,
> these are short.
>
> We have backplane traces that are over 12" long (can't help it).
>
> In spite of all this, our system happily percolates along at
> 3.125 GHz (2.5
> GHz with 8B/10B coding).
>
> Larry Miller
>
> -----Original Message-----
> From: Gaboian, Jerry [mailto:j-gaboian@ti.com]
> Sent: Tuesday, April 03, 2001 5:00 AM
> To: 'Zabinski, Patrick J.'; si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : RE: 2.5 GHz in FR4
>
>
> Check out this site from AMP.....
>
> It will surprise you on how long of a trace one can use.....
> They also compare other materials, widths act.....
>
> http://www.amp.com/simulation/files/papers/dc99cmdh.pdf
>
> Regards,
> Jerry
>
> -----Original Message-----
> From: Zabinski, Patrick J. [mailto:zabinski.patrick@mayo.edu]
> Sent: Tuesday, April 03, 2001 6:24 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : RE: 2.5 GHz in FR4
>
>
>
> Sreejith,
>
> It is possible to use common FR4 in 2.5 GHz systems, but you
> need to follow a few design constraints:
>
> * Do not use stripline. The discontinuities presented by
> the vias are most often killers. Avoid all vias in the high
> speed nets and use microstrip (i.e., top-surface only).
>
> * Use wide traces. FR4 is lossy at 2.5 GHz, so try to compensate
> for the high dielectric loss by decreasing the metal loss. Use
> wider traces which will reduce the resistive losses in the metal.
>
> * Use short traces. If you need to route 2.5 GHz signals
> on nets that are 10 inches (25 cm) long, I doubt if your
> system will function. Keep the traces *short* (say, less
> than 1 inch [2.5 cm]).
>
> Hope this helps,
> Pat
>
> > HI All,
> >
> > i am doing a 2.5Ghz PCB design. i was wondering whether FR4
> material
> > is sufficient for such high speed signals? or i should look at some
> > other material for these desings? and if FR4 is sufficient is
> > there any
> > special care i have to take (other than impedance matching
> > and differential
> > routings)
> >
> > thanks in advance,
> > Sreejith
> > Paxonet Comm. (I) Ltd.
> > Blore, India
>
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