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

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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