[SI-LIST] Re: S parameter to time domain signal

Hi Cody,

It seems there are two methods you could use to turn measured S11 data into
TDR-like data:

1 - Directly translate the S11 data (frequency-domain) to a time-domain
representation
2 - Simulate a transient waveform interacting with the S11 data block in a
circuit simulator

The first method is usually a built-in function found in VNAs or
EM-extraction programs. The fundamental procedure used is an inverse fast
fourier transform (IFFT). Application of the IFFT to the frequency-domain
data can yield a time-domain step-response and even a TDR-waveform. Given
complex s-parameter data, an IFFT-based procedure can also be implemented in
standard mathematical packages like Matlab. 

The second method is to perform a transient circuit simulation with the
measured S-parameter block. Here you can define a step-source and series
resistance connected to the s-parameter block, run the simulation, then
calculate and plot the TDR response. The pitfalls here include passivity
issues (yes, measured s-parameters can sometimes come over as
"non-passive"), implementation method (pole-zero or convolution),
DC-extrapolation, and high-frequency content. The transient simulation of
s-parameters seems to be what some of the other posts refer to - this is
where you'll see the differences between technologies that the EDA industry
offers.

If all you require is a TDR waveform from the measured S-parameter block
alone, then method 1 above is probably sufficient. However, if other circuit
elements, models or stimuli are to be included (as in a channel or system),
then you're probably going to be looking at method 2. 

If you'd like to talk more about what Ansoft offers with respect to either
of these methods, please feel free to contact me offline and I'd be glad to
help. 

Regards,
Andrew Byers
abyers@xxxxxxxxxx




 
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of codymiller@xxxxxxxxxx
Sent: Wednesday, December 19, 2007 10:15 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] S parameter to time domain signal

All,

Does anyone in the group know of any available software packages that
can take post measurement S11 data and convert it to a time domain
reflected signal?

Thanks,
Cody Miller
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