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

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From: Scott McMorrow (scott@vasthorizons.com)
Date: Tue Feb 29 2000 - 08:55:07 PST


Aubrey,

Baseband would be a signal which has the possibility
of having a frequency range that extends from 0Hz to xxxxxMhz
Digital signals on real boards. It seems to me that unless the
accuracy of the instruments and resolution of the numerics
is extreme, there is always some amount of error in the Frequency
domain measurement which translates into an absolute
pulse timing error.

What I am interested is in the accuracy of the delay function.

regards,

scott

Aubrey_Sparkman@Dell.com wrote:

> Scott,
>
> I'm not sure what you mean by "baseband". If you are asking about
> correlating frequency domain (VNA) measurements with time domain
> measurements (TDR) that has been done for semiconductor packages where the
> longest connection was short with respect to the wave length of the highest
> frequency of interest. This should also apply to connectors that are
> electrically short
> Look at the work of the JEDEC JC-15 committee circa 1992-1994. A Tektronix
> 11801 TDR was compared to a Hewlett Packard 8753 (along with other
> instruments). Most correlation issues were traced to setup and fixture
> differences. These results were also compared to a couple of field
> simulators. But in that situation VNAs needed to capture lower frequencies
> (hence 8753 which starts at 300KHz VS 8510 which started ~100MHz) and TDRs
> needed to capture longer (time) waveforms. FFT equivalence again. And
> neither handle DC very well. But DC measurements are done with other
> instruments.
>
> Hope this helps,
> Aubrey Sparkman
> Signal Integrity
> Aubrey_Sparkman@Dell.com
> (512) 723-3592
>
> > -----Original Message-----
> > From: Scott McMorrow [mailto:scott@vasthorizons.com]
> > Sent: Monday, February 28, 2000 9:47 PM
> > To: si-list@silab.eng.sun.com
> > Subject: Re: [SI-LIST] : Frequency or time domain for component
> > characterization
> >
> >
> > 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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> >

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****


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