[SI-LIST] Re: Diff Z for asymmetric coupled striplines
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <otter30@xxxxxxxxxxxxx>, "'Kotson, Michael'" <mkotson@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 21 Oct 2008 12:20:15 -0700
Hi Jim,
Here are some results for your configuration obtained with another field
solver.
Electro-static analysis (similar to MMTL and mdtlc): Zd=91.35 Ohm
Full-wave electromagnetic analysis (extraction from 3D analysis of a line
segment with DK=4.3 and LT=0.02 at 1 GHz, wide-band Debye dielectric model,
no roughness):
Zd=105.2 Ohm at 10 MHz
Zd=96.83 Ohm at 100 MHz
Zd=95.3 Ohm at 1 GHz
Zd=96.08 at 40 GHz
You can see that the impedance varies with the frequency, though it stays
relatively flat at the frequencies important for a multi-gigabit signal. If
your PCB fabricator uses TDR to verify the impedance, it may actually show
something closer to 100 Ohm (depends on the measurement setup and
post-processing). A frequency-domain verification and material parameters
extraction may be better alternative to TDR-based procedure in that case.
Another important parameter to take a look is propagation constant for the
differential mode. In your case the effective dielectric constant may change
from 5.1 at 10 MHz to 4.1 at 40 GHz (about 25%). It must be accounted during
the simulation.
Best regards,
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of otter30@xxxxxxxxxxxxx
Sent: Tuesday, October 21, 2008 9:10 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
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
> *****************************************************************
> *************
>
> CONFIDENTIAL NOTE: This e-mail and any attachments may be
> confidential and protected by legal privilege. If you are not
> the intended recipient, be aware that you are hereby notified
> that any unauthorized review, use, disclosure, dissemination,
> distribution, or copying of this communication, or any of its
> contents, is strictly prohibited. If you have received this
> email in error, please notify us immediately by replying to the
> sender and deleting this copy and the reply from your system.
> Thank you for your cooperation.
>
> EXPORT CONTROLLED DOCUMENT
> This document may contain information whose export is restricted
> by the Arms Export Control Act (Title 22, U.S.C., Sec 2751 Et
> Seq.) or the International Traffic in Arms Regulation (ITAR)
> under the Export Administration Act of 1979, as amended, (Title
> 50, U.S.C., App. 2401, Et. Seq.). Violations to these
> export laws are subject to severe criminal penalties.
>
> All technical data forwarded by VT Miltope to its suppliers is
> EXPORT CONTROLLED. Suppliers shall not disclose technical data
> in any form to a Foreign Person (including foreign persons
> employed by the Supplier), or export the technical data from
> the United States without U.S. Government authority and the
> written authorization of VT Miltope.
>
> *****************************************************************
> *************
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
