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 stripline implementation
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magent1900

United Kingdom
3 Posts

Posted - Jun 11 2015 :  11:18:29  Show Profile  Reply with Quote
Dear colleagues
I have recently known about fastcap and fasthenry, where i need to implement stripline in 90nm tech.
i need your help to get started with this software, where my job is on two stage, firstly get the parasitic of the stripline alone and secondly with coupled one. my work dimensions w=4um, t=1um, and l=10mm
in the center of two gnd plats in the top layers where the dielectric thickness 4um, and Er=3.9.
are there any ready codes or the way to determine the units to implement like this work? I ask you for help as you could
thanks in advance.

moh

Enrico

410 Posts

Posted - Jun 14 2015 :  00:41:57  Show Profile  Reply with Quote
If you need to model a stripline, I strongy suggest you to use FasterCap in 2D mode. Actually, FasterCap / FastCap2 and FastHenry2 are quasi-static simulators. This means that the results are valid if the dimension of the structure is small with respect to the minimum wavelength of interest. Now, this is usually not true for a stripline or a transmission line in general, as you are interested in the signal propagating along the line. However, if the cross-section of the transmission line is small w.r.t. the wavelength of the maximum frequency of interest, can still use quasi-static simulators to extract the parameters per-unit-length of the structure.

Said that, since you are interested in the cross-section, you should assume that you have an infinitely long line. This is why FasterCap in 2D mode is the perfect way to extract these parameters.

You can check any of the examples in the 'Samples->2D' directory of the FasterCap installation. Please be sure to read the comments inside the files, and possibly the papers referenced there.

Best Regards,
Enrico
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magent1900

United Kingdom
3 Posts

Posted - Jun 16 2015 :  10:44:13  Show Profile  Reply with Quote
Error: Generic error, program execution stopped!

I have this message when i tried to execute the following code

*

C microstrip_top_4um.txt 4.2 0.0 0.0000015 +
C microstrip_bottom_4um.txt 4.2 0.0 0.0000015

D diel_microstrips_4um.txt 4.2 0.0 0.000004

C gnd_plane_n.txt 4.2 0.0 0.0 +
C gnd_plane_n.txt 4.2 0.0 0.000004

could any one help me to know what is the problem?

best regards
moh

Edited by - magent1900 on Jun 16 2015 10:45:39
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Enrico

410 Posts

Posted - Jun 18 2015 :  12:17:11  Show Profile  Reply with Quote
As explained in the embedded help, in case of 2D simulation, the first line should start with

* 2D


otherwise FasterCap will assume you are running a 3D simulation; however as the input files will be invalid (they are 2D), they will eventually lead to an invalid solution, with consequent error.

Best Regards,
Enrico
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magent1900

United Kingdom
3 Posts

Posted - Jun 19 2015 :  18:05:45  Show Profile  Reply with Quote
many thanks, it's working.
but what if i want to find the inductance (L) for the same stripline, should i write a new code in fasthenry or what?


moh

Edited by - magent1900 on Jun 19 2015 18:15:19
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Enrico

410 Posts

Posted - Jun 22 2015 :  23:47:36  Show Profile  Reply with Quote
quote:
but what if i want to find the inductance (L) for the same stripline, should i write a new code in fasthenry or what?


Actually you could do both: i.e. either perform a FastHenry2 simulation, or use again FasterCap.

The reason for the former, i.e. using FastHenry2, is straightforward I think. However, unless you are interested in the behavior of the line in a low frequency range i.e. when skin effect is not so pronounced, you can avoid using a 3D simulation to extract 2D parameters. On this topic you can read the parallel thread under the FastHenry forum with the title "impact of length on per-unit-length calculation".

The reason for the latter, i.e. using FasterCap again, is not so straightforward, but if you read the articles I pointed you to, you should have some clues about it. Actually if you read the paper from A. R. Djordjevic, T. K. Sarkar, "Closed-Form Formulas for Frequency-Dependent Resistance and Inductance per Unit Length of Microstrip and Strip Transmission Lines" IEEE Trans. on Microwave Theory and Techniques, vol. 42, no. 2, February 1994, you will understand that L and C per unit length in a transmission line are related by the speed of light. So you can derive the value of L (at high frequency) from the C extracted when no dielectric is present. You already know C when there is dielectric medium (your first FasterCap simulation), so you have all your data for using the resulting values in, say, a Spice simulation.

Best Regards,
Enrico
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