If we are going to check the accuracy of the .W model, I wish to make the
suggestion that we use measurements as well for verification. Most field
solvers do not account for losses in copper or dielectric to as correct an
extent that I would deem acceptable. Does anybody have a set of test board
that they would volunteer?
Dr. Dmitri Kuznetsov's comments in a recent si-list communication see
(7/29/99) are very relevant. The behavior of the skin effect and
dielectric formulas in the frequency domain, when transformed back into the
time domain involve functions that have very special properties.
The losses which are proportional to frequency, namely the dielectric
losses can be shown to be related to the unit capacitance and the loss
tangent of the material, Equation (8) for small losses.
See "OC-48/2.5 Gbps Interconnect Design Rules", Sayre, Chen and Baxter;
DesignCon99 Proceedings. (Available on NESA's web site). Use of equation
(8) together with the .W model has been found to be very satisfactory when
the simulation results are compared to measurements.
Lastly, just as recently mentioned by Scott McMorrow, we too have also seen
small differences with respect to the same problem solved by two recent
versions of HSPICE. I do not think the way to resolve this is through the
use of field solver predictions.
Sincerely,
ed sayre
However,
At 07:51 AM 8/2/99 -0700, you wrote:
>Apparently the W element model uses a pseudo-propagation function with the
>following form.
>
>P(f)= exp{-sqrt[ (G0+f*Gd+j*2*pi*f*C)*(R0+sqrt(f)(1+j)Rs+j*2*pi*f*L) ]*len }
>
>(From HSPICE application note "Boosting Accuracy of W Element
>for Transmission Lines with Nonzero Rs or Gd Values")
>
>Let's assume that this is valid for some conditions. It would be nice to
>know what the assumptions are.(geometry, frequency, etc.) We can talk about
>the validity of the above in another thread.
>
>I would like to make a proposal. I would like to know what various field
>solvers report in regards to the above propagation function. Let's start
>with a microstrip first (and only look at skin effect). The geometry
>follows.
>
> Height over ground: 0.004"
> Width of conductor: 0.006"
> Thickness of conductor: 0.001"
>
> Conductivity: 0.58E8 mho/meter
>
>Let's all use the same units for Rs. Say:
> Ohms/(sqrt(Hz)*meter)
>
>Now, A colleague of mine has supplied a formula that is used in microwave
>design. I have attached a PDF file with details. (Too tough for text, TTFT
>:-)), I remember foobar)
>
>The answer, using the closed form formula for Rs is:
> 1.806E-03 ohms/(sqrt(Hz)*meter)
>
>If this is the magnitude of complex Rs, then Re(Rs) would be
> 1.277E-03 ohms/(sqrt(Hz)*meter)
>
>I have received sidebar results from some of you folks, but I don't want to
>post other people answers. However I will compile a table of posted
>results. There are issues of complex number involved. Remember I'm looking
>for the Rs for the above propagation formula.
>
>Step 2 will be to do same for a strip line geometry where:
>
> Height over ground: 0.005"
> Width of conductor: 0.0025"
> Thickness of conductor: 0.0005"
> Distance between ground planes: 0.0105
>
>
>It would be appreciated if we could find out what "tricks" people are using
>to get Rs from their field solvers.
>
>Regards,
>Richard Mellitz
>Intel
>
> <<Mathcad - ms_loss_eq.pdf>>
>
>Attachment Converted: "C:\TEMP\attachments\Mathcad - ms_loss_eq.pdf"
>
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