[SI-LIST] Re: Diff Z for asymmetric coupled striplines

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: 
> http://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: 
> http://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:
http://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:     
                http://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:
http://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:     
                http://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: