[SI-LIST] Re: symmetric coupled striplines...
- From: "Lambert Simonovich" <bertsimonovich@xxxxxxxxxx>
- To: "'Ishwar Hosagrahar'" <ishwarh@xxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 31 Aug 2009 18:09:21 -0400
Ishwar,
One way to sanitize your simulations is to estimate what your results should
be using developed formulae if they exist. For example, in Eric Bogatin's
book "Signal Integrity Simplified", there are formulae to approximate total
attenuation of an interconnect due to the track and dielectric
characteristics.
A(cond)= -L*(36/(W*Zo))*sqrt(f)..........(eqn 9.65) pg 376.
A(Diel)= -2.3*f*Df*sqrt(Dk)..............(eqn 9-69) pg 378.
A(total) = A(cond)+A(Diel)
Where;
A(cond)= Attenuation of conductor
A(Diel)= Attenuation due to dielectric
A(total)= Total attenuation
W = Trace width in mils
f = freq in GHz
Zo = Characteristic impedance of single trace in ohms
Df = Dissipation factor
Dk = effective Dielectic constant
L = trace length in inches
For the 6-9-6 Nelco-4000-13SI example, I ran the geometry in my field
solver, and I assumed 1oz copper thickness. Using 53.4 ohms for Zo of a
single trace, the estimated loss (Atotal) compared to your simulated results
are as follows;
Calculated Simulated N4000-13SI
1GHz -0.15dB -0.16dB
4GHz -0.39dB -0.38dB
5GHz -0.46dB -0.43dB
10GHz -0.78dB -0.81dB
20GHz -1.35dB -1.66dB
40GHz -2.41dB -3.55dB
50GHz -2.91dB -4.46dB
As you can see, the calculation correlates fairly well (<5%)with your
simulation up to 10GHz, so I would trust your simulated results for the
Nelco-4000-13SI case. You can repeat for FR4 case.
Hope this helps.
Regards,
Bert Simonovich
Backplane Specialist and Founder,
LAMSIM Enterprises Inc.
http://lamsimenterprises.com/index.html
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Ishwar Hosagrahar
Sent: August-31-09 12:40 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: symmetric coupled striplines...
Folks,
I was pointed out that none of my attachments made it through the reflector
- apologies. I am a newbie user to the list here.
A sectional view of the HFSS model of the differential (uniform) symmetric
stripline looks like the diagram below (but a lot prettier when viewed in
the modeller view of HFSS) :-)
============================GND
8mil Dielectric Core
##SIG_P## ##SIG_N##
8mil Dielectric Core
============================GND
The Sdd21/1inch values I got were (at a few interesting frequency points).
As you can see, the loss curve is mostly linear across the frequency range
when plotted on a Y-dB X-Hz plot for both dielectrics. The plot I sent
didn't make it through either.
FR4_epoxy Nelco4000-13SI
1GHz -0.28dB -0.16dB
4GHz -0.67dB -0.38dB
5GHz -0.77dB -0.43dB
10GHz -1.53dB -0.81dB
20GHz -2.99dB -1.66dB
40GHz -6.01dB -3.55dB
50GHz -7.43dB -4.46dB
Comments appreciated.
Regards
Ishwar H
ishwarh@xxxxxxxx
> -----Original Message-----
> From: Ishwar Hosagrahar [mailto:ishwarh@xxxxxx]
> Sent: Friday, August 28, 2009 6:48 PM
> To: 'si-list@xxxxxxxxxxxxx'
> Subject: symmetric coupled striplines...
>
> Folks,
> I was pondering about PCB trace losses in general to assess the impact
> of migrating a couple of transmission lines to various dielectrics,
> and hoping that some of the experts here can provide some inputs.
>
> As a part of the pondering process, I messed about with a HFSS model
> of a symmetric differential stripline, and solved the differential
> transmission loss/1inch of two different cases :
>
> case1 : FR4_epoxy, Dk = 4.4, Er = 0.02
> case2 : Nelco-4000-13SI, Dk = 3.4, Er = 0.01
>
> (model had a 8mil thick dielectric for the symmetric stripline on the
> top and bottom, and I adjusted the (default
> copper) trace widths to get a 100ohm differential impedance for both
> cases. With a trace gap of about 9mils, the traces were between 6mils
> to 8mils wide depending on dielectric. The simplistic material
> definitions were from the default Ansoft library, ie.nothing too
> intelligent was attempted. A picture of the model is attached here)
>
> Without getting into the numerous technical details of the solver or
> the setup (choice of solution and port types, excitations, boundary
> conditions, complex dielectric definitions, surface roughness
> factors/layered impedance etc.etc.), do the HFSS results look
> believable to folks here with more experience on all this sort of
> complicated thing?
>
> My questions are :
> (a) does anyone have measured data (or an intuitive feel) to judge if
> the FR4 and Nelco4000-SI results are realistic in terms of what I'd
> get from a VNA measurement if I were able to ideally deembed any
> connections and measure the uniform symmetric stripline
> characteristics for this specific topology?
>
> (b) anyone on this list know of published data for loss/inch
> characteristics of different trace topologies (uniform symmetric
> stripline) for different dielectrics? I am looking for actual measured
> or simulated data for different dielectrics on the lines of Joel
> Goergen's qualitative comparison to the IEEE at :
> http://grouper.ieee.org/groups/802/3/ap/public/may04/goergen_0
1_0504.pdf
>
> The Sdd21 plot of my analysis is attached. I'll be happy to
> send anyone the actual Touchstone-formatted S-parameters
> [S4P] if you want to take a deeper peek at the data. (I can't
> figure out how to post the data zipfile to the si-list
> reflector submissions area, so please email me directly at this time)
>
> Thanks for inputs.
>
> Cheers,
> Ishwar Hosagrahar
> ishwarh@xxxxxxxx
>
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