[SI-LIST] Re: Touchstone for transmission lines (was Re: touchstone models)
- From: Aubrey K Sparkman <asparky@xxxxxxxxxxxxxxxxxxxxxxxx>
- To: Scott McMorrow <scott@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Oct 2011 15:42:59 -0500
Conrad,
Just to pick on Scott... :-) Hi, Scott! The "inherent problem with
using S-parameter models for long transmission line segments" is that
people forget to use sufficiently small frequency step intervals.
The thing that can get you is file/model size if you remember to include
fine enough resolution or if you don't remember, you will have accuracy
issues. As the transmission line length (or end to end delay) gets
longer, you need smaller and smaller frequency step intervals to get the
correct response.
Easy to verify. Just setup a simple transmission line, pick a line length
(ex: 1" long) sweep frequency (1GHz to 10GHz) and frequency step (0.1GHz).
S11 looks like you might expect, right? Then increase the line length
to 10"and take another look at S11. Looks weird, right Now change the
frequency step to 0.01 GHz and take another look at S11. Back to what you
might expect? As the length gets longer the file size explodes. A good
"per unit length" (accurate, passive, causal) model will save time and
disk space.
Good Luck,
Aubrey Sparkman
SparkRight Solutions
On 10/27/11 11:33 AM, "Scott McMorrow" <scott@xxxxxxxxxxxxx> wrote:
>Conrad
>
>There is no inherent problem with using S-parameter models for long
>transmission line segments. The trick is using a solver that can create
>accurate causal models (Ansoft 2D, HFSS, Simberian Simbeor, ... etc),
>with resolution that is appropriate for the maximum length of entire
>interconnect system. The disadvantage in using them is in the lack of
>scalability. However this can be resolved by some solvers, such as
>Simbeor, with length scaling at the time of touchstone file generation,
>or by creating shorter length touchstone files that can be concatenated,
>either in a network simulator, or with additional custom code. I
>routinely create sweeps with touchstone interconnect models swept from 1
>mm to multiple meters in length, in increments of 1 mm, with no loss of
>accuracy. I've published multiple papers that show our modeling match
>to measurements with extremely low error from DC to 50 GHz.
>
>Other transmission line models, such as the W-element, can be
>attractive, since they are inherently scalable. However,
>implementations from tool to tool may be different. If you use them, I
>would definitely advise correlation of your solver and your simulator
>with physical measurements.
>
>
>best regards,
>
>Scott
>
>Scott McMorrow
>Teraspeed Consulting Group LLC
>121 North River Drive
>Narragansett, RI 02882
>(401) 284-1827 Business
>(401) 284-1840 Fax
>
>http://www.teraspeed.com
>
>Teraspeed® is the registered service mark of
>Teraspeed Consulting Group LLC
>
>
>On 10/27/2011 11:42 AM, Conrad Herse wrote:
>> This thread reminded me of a discussion we had awhile back with a CAD
>> vendor (who shall remain nameless). They discouraged us from using
>> s-parameter models for long segments of traces, stating that s-parameter
>> models were better suited for small geometry discontinuities such as
>> vias, connectors, and packages. For long PCB traces they recommended use
>> of transmission line models rather than an s-parameter model.
>>
>> We had been using s-parameter models for sections of a channel when
>> modeling a full system, the s-parameter model included sections of PCB
>> routing along with vias, connectors, etc. Their recommendation was to
>> model the trace portions of the channel with transmission line models,
>> and use s-parameter models for just the vias, connectors, etc. I can't
>> remember the issue which triggered our original discussion with them but
>> I believe it was related to flight time delays (or lack there of) when
>> including a long transmission line in an s-parameter model.
>>
>> I'd be interested in hearing other's thoughts on this topic, is it bad
>> practice in general to include long transmission line segments within an
>> s-parameter model?
>>
>> Thanks,
>>
>> Conrad Herse
>>
>>
>> Carrier, Patrick wrote:
>>> Hi Megan--
>>> Others have forwarded links to some other great resources, but I
>>>wanted to let you know that there are a number of videos which discuss
>>>S-parameters up at mentor.com, the most relevant being:
>>>
>>>http://www.mentor.com/products/pcb-system-design/multimedia/s-parameters
>>>
>>> Many connector models are delivered in S-parameter format.
>>> S-parameters are also useful for comparing your total interconnect
>>>loss (including traces, vias, and connectors) against a specified loss
>>>budget.
>>> For AC power analysis, Z-parameters are most often used, which are
>>>similar. The HyperLynx Touchstone Viewer will let you convert between
>>>S-, Z-, and Y-parameters.
>>>
>>> Enjoy!
>>> --Pat
>>>
>> ------------------------------------------------------------------
>> 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
>>
>> 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
>
>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
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
