[SI-LIST] Touchstone for transmission lines (was Re: touchstone models)
- From: Conrad Herse <conrad.herse@xxxxxxxxxxxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 27 Oct 2011 10:42:19 -0500
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
>
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