Re: [SI-LIST] : Frequency or time domain for component characterization

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Mon Feb 28 2000 - 19:47:26 PST


What are the issues if you would like to characterize a
circuit at baseband, when using a VNWA? Seems to me that
there are significant issues in dealing with the DC and low
frequency components.

Anyone have experience in correlating frequency domain measurements
with baseband pulse performance?

regards,

scott

c deibele wrote:

> Kai,
>
> If you can correctly characterize your TDR head, and your
> connectors/cables to connect to your DUT, then either measurement
> technique will work well.
>
> In my opinion, it is easier to get accurate measurement using frequency
> domain. This is a result of several assumptions.
>
> a) a VNWA can be calibrated to extract extraneous effects that are
> difficult to extract in the time domain. These effects are connectors,
> cables, gain slope of the VNWA, etc.
>
> b) the VNWA can run a relatively pure sinusoid. This means that the
> effective bandwidth is very low, and therefore noise becomes a
> nonissue. The only way to combat this in the time domain is to sample
> your result for a very "long time". This is of course not true if what
> you are measuring is a very high Q and then resonances can be missed
> because of a poor choice of frequency sampling.
>
> I've gotten excellent results using circa 12 psec pulseheads to get
> relatively good results out to 30 GHz. I compared these results with
> calibrated VNWA results and observed the time domain results are simply
> more noisy. additionally, depending on the impedance of the DUT
> compared to your measurement system, reflection and/or transmission
> measurements in the time domain can be next to impossible because of the
> noise considerations in b)
>
> Of course, if you wish to characterize your results using some microwave
> tools (like touchstone or ADS or other simulator), then you'll most
> likely have to go to the frequency domain.
>
> Regards,
>
> Craig Deibele
>
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--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

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