[SI-LIST] Re: approximating Trise when extracting t-parameters from an s-parmaeter model
- From: Peter.Pupalaikis@xxxxxxxxxx
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 9 Aug 2011 14:19:51 -0400
Hi Michael:
When you inverse FFT the s-parameters, your sample rate is twice your end
frequency. If you have lots of frequency content up at your end frequency,
you will potential have lots of "Gibbs phenomena" due to the implied brick
wall filtering of the s-parameter data. You can avoid this with a model
fit, taking higher frequency data, etc. So, if you wanted to look at
time-domain data like step response, impulse response, impedance vs. time,
etc., it would be good to employ a risetime increasing filter (like
convolution with a gaussian) to smooth out your time domain data -
unfortunately, that is the same as filtering in the frequency domain.
of course your sample rate of your time domain data does not necessarily
mean you get that resolution on the data. You can zero pad your
s-parameter data to increase time-domain sample rate, which would be the
same as interpolation, but this would not increase your risetime or
resolution.
There seems to be quite a bit of divergent opinions on this resolution,
some of it based on detection of features and total isolation of features
(you need less resolution to see a feature, but more resolution to totally
isolate it). Resolution translates to bandwidth (end frequency) which
corresponds to risetime as well.
Agilent and Tekronix have some application notes to this effect - I'd look
there for numeric calculation of this - but I'd go with a rule of thumb
like risetime*bandwidth = 0.5 or thereabouts for brick-wall filters, so
1/(2*Fe) would be my estimate.
Pete
|------------>
| From: |
|------------>
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|"Rose, Michael" <mrose@xxxxxxxxxxxxxxxxx>
|
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| To: |
|------------>
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|"si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
|
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Date: |
|------------>
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|08/09/2011 02:01 PM
|
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Subject: |
|------------>
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|[SI-LIST] approximating Trise when extracting t-parameters from an
s-parmaeter model |
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|------------>
| Sent by: |
|------------>
>--------------------------------------------------------------------------------------------------------------------------------------------------|
|si-list-bounce@xxxxxxxxxxxxx
|
>--------------------------------------------------------------------------------------------------------------------------------------------------|
I like to understand the relationship between rise-time of a TDR excitation
source and the corresponding frequency range of an s-parameter frequency
domain sweep which is post-processed (inverse FFT) to convert to
t-parameters (impedance). Is it essentally Tr = 1/fmax? Will applied
windowing affect the relationship significantly?
Many thanks, Mike
_______________________________________________________________________
This e-mail and any files transmitted with it are proprietary and intended
solely for the use of the individual or entity to whom they are addressed.
If you have reason to believe that you have received this e-mail in error,
please notify the sender and destroy this email and any attached files.
Please note that any views or opinions presented in this e-mail are solely
those of the author and do not necessarily represent those of the
Curtiss-Wright Corporation or any of its subsidiaries. Documents attached
hereto may contain technology subject to government export regulations.
Recipient is solely responsible for ensuring that any re-export, transfer
or disclosure of this information is in accordance with applicable
government export regulations. The recipient should check this e-mail and
any attachments for the presence of viruses. Curtiss-Wright Corporation and
its subsidiaries accept no liability for any damage caused by any virus
transmitted by this e-mail.
------------------------------------------------------------------
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:
