From: Scott McMorrow (firstname.lastname@example.org)
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
Anyone have experience in correlating frequency domain measurements
with baseband pulse performance?
c deibele wrote:
> 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.
> 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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