[SI-LIST] Re: Losses - 2.5Gbps on FR4

Scott:

Could you elaborate a bit how do you do the calibration with test PCB ? THe best
option I think is to use coplanar probes with a probe station/cal kit, but there
is no way we can afford that. Any other alternatives ? I saw designs using SMA
connector but always wonder how one will do the calibration accurately,
especially in GHz range.

THanks

Perry

Scott McMorrow wrote:

> Just as a point of reference, we see a consistent loss tangent of .0215
> for FR-4 from one of our fabricators using Polyclad materials.  But it
> is something that should be measured for your particular fab process and
> stackup (it will change with different glass/resin ratios and process
> impurities).  Be sure to have a good launch into your board in order to
> make this measurement.  A bad launch will distort the loss measurement.
> And perform some comparision measurements across a few traces or
> structures of different sizes to be sure that all measurement artifacts
> have been removed.
>
> best regards,
>
> scott
>
> --
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 2926 SE Yamhill St.
> Portland, OR 97214
> (503) 239-5536
> http://www.teraspeed.com
>
> Raymond W. Waugh wrote:
>
> >A loss tangent of 0.030 may sound lossy when compared to more expensive PCB
> >materials (such as the Teflon-based materials used at X-Band and higher by
> >we microwave geeks), but it is pretty typical for FR4.  I have measured
> >several six inch test lines over a wide range of frequencies, and have found
> >that FR4 comes in at 0.030 almost every time, and over a range of frequency
> >from 1 to 6 GHz.
> >
> >I also agree with Jeff - ten hours of simulation to obtain losses is
> >excessive.  You can fabricate and test a microstrip line in less time...
> >
> >Ray Waugh
> >Volcano Microwave
> >
> >----- Original Message -----
> >From: <jeff_latourrette@xxxxxxxxxxx>
> >To: <dorin.oprea@xxxxxxxxxxx>
> >Cc: <si-list@xxxxxxxxxxxxx>
> >Sent: Tuesday, July 29, 2003 9:01 AM
> >Subject: [SI-LIST] Re: Losses - 2.5Gbps on FR4
> >
> >
> >Dorin:
> >Sounds real to me, tand = 0.03 is pretty lossy material.
> >
> >Based on information provided, I also ran your scenario (in msec) on
> >Linecalc, part of Agilent's ADS, and got 5.5 dB power loss (for just the 30"
> >line) at 1.25 GHz ("fundamental" of switching frequency).  Loss was 9.9 dB
> >at 2nd harmonic and 18.4 dB at 4th, which sounds very high, but seems to
> >compare well with Geoff's results.
> >
> >You shouldn't have to run 10 hours of simulation just to get losses,
> >although I'm sure there are other things you are after.  You could simulate
> >(& measure to compare) an inch or two of FR-4 to get dB/inch.
> >
> >Experimental boards allowing different connector types and run lengths are
> >invaluable for this type of work.
> >
> >Some colleagues of mine at Agilent wrote a great paper on this at ONIDS 2002
> >.....
> >
> >The Path to 10 Gb/s:Connector and Backplane Capabilities for High-Speed
> >Applications
> >
> >http://literature.agilent.com/litweb/pdf/5988-7053EN.pdf
> >
> >
> >Enjoy,
> >
> >Jeff LaT.
> >
> >
> >-----Original Message-----
> >From: Dorin [mailto:dorin.oprea@xxxxxxxxxxx]
> >Sent: Tuesday, July 29, 2003 7:47 AM
> >To: si-list
> >Subject: [SI-LIST] Losses - 2.5Gbps on FR4
> >
> >
> >Hi,
> >The simulation I did shows 5dB voltage loss on 30" long interconnect on
> >FR4 (tan loss 0.03) which includes 0.005" traces 0.5 oz. copper, one
> >NexLev and two Metral connectors. Two pulses P/N, 2V with 50 ohm series
> >were applied to the circuit and one 100 ohm resistor as a termination.
> >Is this loss real? If not, can you tell what is the approximate
> >deviation, just to get a feeling?
> >I was told that hspice simulated losses are too optimistic and
> >therefore, long traces should be chopped; if so, what would be the
> >optimum segment length recommended for the loss simulation so that the
> >simulation time is not excessively long (now I need over 10 hours on
> >Linux LSF server).
> >
> >Thanks,
> >Dorin
> >
> >
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--
Perry Qu

Design & Qualification       |      600 March Road
Alcatel Canada               |      Ottawa, ON K2K 2E6, Canada

DID: (613) 7846720           |      FAX: (613) 5993642


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