[SI-LIST] Re: Diff Z for asymmetric coupled striplines
- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- To: <otter30@xxxxxxxxxxxxx>, "Kotson, Michael" <mkotson@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 21 Oct 2008 12:43:25 -0600
Mike - Solvers should match each other almost exactly - with
only 10ths of an ohm difference. Especially for a stripline.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of otter30@xxxxxxxxxxxxx
Sent: Tuesday, October 21, 2008 10:10 AM
To: Kotson, Michael; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Diff Z for asymmetric coupled striplines
Hi Mike,
Thanks to you and everyone else for their suggestions.
I tried 2 open source field solvers on the same configuration. MMTL gave
a diffZ of 91.5ohms, and mdtlc gave 93.57ohms. These results seem
reasonable, and both tools were very easy to use.
Structure Parameters
---------------------
line width = 3mils
line spacing = 4mils (edge coupled)
trace thickness = .7mils (1/2 oz cu)
h1 = 3.9mils (dist to upper ref plane)
h2 = 7mils (dist to lower ref plane)
er = 4.3
Zo = 53.5ohms (obtained from a formula for a single asymmetric
stripline)
Thanks for your help,
Jim
-------------- Original message from "Kotson, Michael"
<mkotson@xxxxxxxxxxx>: --------------
> Hi Jim,
> Give MMTL a try. I have had pretty good luck with the results, and
> it's free.
>
> http://mmtl.sourceforge.net/
>
> Best of luck,
> -Mike
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of otter30@xxxxxxxxxxxxx
> Sent: Monday, October 20, 2008 10:16 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Diff Z for asymmetric coupled striplines
>
> Hello,
> I need to determine the differential impedance of pair of coupled
> stripline traces. They are edge coupled and are asymmetric in the
sense
> that the distances to the 2 reference planes are different - both
traces
> are
> 4 mils from the upper plane and 7mils from the lower.
>
> Our pcb fabricator told us that this configuration would have a diff Z
> of 100 ohms, but I have gotten a value from the cross section
calculator
> in Cadence Allegro of 79 ohms. I'd like to find another method to
settle
> this, as our board does have SI problems.
>
> The diff Z formula for this configuration isn't in any of the well
known
> SI or TL texts, although the symmetric case (H1 = H2) is. Can anyone
> either:
> 1) Point me toward the correct equation
> 2) Suggest a free field solver that would let me calculate this value?
>
> I've downloaded the student version of Ansoft Maxwell, and am trying
it
> out. If it can extract the mutual
> capacitance and inductance, is there a general method of getting the
> diff Z from these?
>
> Any help is greatly appreciated,
> Jim
>
>
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