[SI-LIST] Re: TDR vs. VNA? Which to purchase?

Paul-

I think the problem manifests itself as non-passivity when the model is
utilized in a transient simulation. That is why people go to the trouble
of checking for passivity and doing passivity enforcement on their
s-parameter data. A non-passive model can cause convergence issues among
other things.

-Ray Anderson
Xilinx Inc.


> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Paul Levin
> Sent: Sunday, February 24, 2008 11:40 AM
> To: ron@xxxxxxxxxxx
> Cc: art_porter@xxxxxxxxxxx; kuifeng@xxxxxxxxx;
tom_cip_11551@xxxxxxxxx;
> si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: TDR vs. VNA? Which to purchase?
>=20
> Dear Ron,
>=20
> Values in excess of 1.00 aren't necessarily fatal. S-parameters and
> transient
> responses estimated from them work just fine for my +26 dB gain
> amplifiers.
>=20
> Tiny errors at very low frequencies may not matter much for high-speed
> data
> transmission anyway. With almost any encoding scheme in use today, it
is
> hard to get much energy into very low frequencies.
>=20
> Regards,
>=20
> Paul Levin
> Senior Principal Engineer
> Xyratex
> _________________
>=20
> ron@xxxxxxxxxxx wrote:
> > Guys
> > The S-Parameter measurements are very accurate, but have a problem
in
> > that close to DC, minor
> > noise usually corrupts the data with the values exceeding 1.00 even
by a
> > microvolt which then cannot
> > converge when used as a model in used in time domain simulations.
> >
> > It is necessary to remove any value that exceeds 1.00
> >
> > Also, it is necessary to add a DC line.
> >
> > However, S-Parameters derived  from TDR measurements will not have
these
> > two problems and
> > can be used directly.
> >
> > ...............Just another reason for the TDR
approach................
> >
> > BTW   Both TEK and Agilent  TDR works well if the DUT is brought
clost
> > to the TDR head so short 3" semirigid cables can be used.
> >        Both instrument have umbilicals to remote the head to the
bench
> > or in the air.
> >         However, TEK TDR head is smaller, lighter and easier to
handle
> > when remoted to the test area or benchtop.
> >
> > Ron Miller
> >
> > art_porter@xxxxxxxxxxx wrote:
> >
> >
> >> Just a note: "3rd party SW" is not required for time-domain to =3D
> >> S-parameter conversion on the Agilent TDR. The option 202 for the
> 86100C =3D
> >> provides this capability in the instrument. =3D
> >> http://cp.literature.agilent.com/litweb/pdf/5989-3110EN.pdf
> >>
> >> Note: Not intended as an advertisement, just to make sure the =3D
> >> information out there is correct and complete.=3D20
> >>
> >> Art Porter
> >> Agilent Technologies=3D20
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-
> bounce@xxxxxxxxxxxxx] =3D
> >> On Behalf Of kuifeng hu
> >> Sent: Tuesday, February 19, 2008 12:14 PM
> >> To: tom_cip_11551@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> >> Subject: [SI-LIST] Re: TDR vs. VNA? Which to purchase?
> >>
> >> Hi, Tom
> >> For your question:
> >>
> >> TDR Pros:
> >> Live trace ;Intuitive user interface ;Excess reactance ;TDR
> >> normalization; Quick and easy
> >>
> >> VNA pros:
> >> Most accurate measurement
> >> Complete characterization
> >> Excellent SNR
> >> RLCG model extraction
> >> Eye diagrams w/o sig gen
> >>
> >> TDR cons
> >> Need 3rd party software to do conversion, Agilent PLTS vs Tek
Iconnect
> >> Complete characterization is time consuming
> >> Need sig gen for eye diagrams
> >>
> >> VNA cons
> >> Expensive solution (today)
> >> Complex user interface
> >>
> >> Use TDR if  Data rate < 3 Gb/s Intuitive tool wanted
> >> Quick set-up Easy measurements Simple calibration 1st order models
okay
> >> used for all general applications
> >>
> >> Use VNA if Data rate > 3 Gb/s High SNR required
> >> DUT Xtalk < 1% DUT has low insertion loss DUT sensitive to EMI
> >> Post data analysis needed Ultimate precision required
> >>
> >> Kuifeng (Clifford)
> >>
> >>
> >>
> >>
> >>
> >>
> >> On 2/19/08, art_porter@xxxxxxxxxxx <art_porter@xxxxxxxxxxx> wrote:
> >>
> >>
> >>
> >>> If you can only purchase one, one question to ask yourself is:
Will I
> =3D
> >>>
> >>>
> >>>
> >> =3D3D
> >>
> >>
> >>
> >>> need the scope for other measurements as well?=3D3D20
> >>>
> >>> Art Porter
> >>> Agilent Technologies
> >>>
> >>> -----Original Message-----
> >>> From: si-list-bounce@xxxxxxxxxxxxx =3D
> >>>
> >>>
> >>>
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx] =3D3D
> >>
> >>
> >>
> >>> On Behalf Of Lars Juul
> >>> Sent: Tuesday, February 19, 2008 8:22 AM
> >>> To: si-list@xxxxxxxxxxxxx
> >>> Subject: [SI-LIST] Re: TDR vs. VNA? Which to purchase?
> >>>
> >>> Hi Tom.
> >>> For characterization and validation of new board designs, I'd =3D
> >>>
> >>>
> >>>
> >> personally =3D3D
> >>
> >>
> >>
> >>> go
> >>> for the TDR, as the hunt for discontinuities and other impedance
=3D3D
> >>> mismatches
> >>> on a board is far more easy in the time domain. I believe some
models
> =3D
> >>>
> >>>
> >>>
> >> =3D3D
> >>
> >>
> >>
> >>> also
> >>> show the excess capacitance/inductance.
> >>>
> >>> But again, there are exceptions, depending on the interface you
want =3D
> >>>
> >>>
> >>>
> >> to
> >>
> >>
> >>
> >>> characterize. Take the XFP interface for instance. It has some of
the
> >>> electrical interconnect parameters defined in terms of DS11, DS21.
If
> =3D
> >>>
> >>>
> >>>
> >> =3D3D
> >>
> >>
> >>
> >>> you
> >>> want to demonstrate compliance you really do need a VNA to measure
it.
> >>>
> >>> For video applications, I'm not sure what the requirements are,
but I
> =3D
> >>>
> >>>
> >>>
> >> =3D3D
> >>
> >>
> >>
> >>> doubt
> >>> a VNA is the answer to your questions, unless RF is involved.
> >>>
> >>> Hope this helps.
> >>>
> >>> Lars
> >>>
> >>> 2008/2/19, Tom Cipollone <tom_cip_11551@xxxxxxxxx>:
> >>>
> >>>
> >>>
> >>>> Hi,
> >>>>
> >>>>  I realize that this thread has been done before, but as we all =
=3D
> >>>>
> >>>>
> >>>>
> >> know,
> >>
> >>
> >>
> >>>> technology changes pretty fast, and what might have been true a
year
> =3D
> >>>>
> >>>>
> >>>>
> >> =3D3D
> >>
> >>
> >>
> >>> or two
> >>>
> >>>
> >>>
> >>>> ago, may not still be true today.
> >>>>
> >>>>  I am ready to make a large investment in signal integrity test
=3D3D
> >>>>
> >>>>
> >>>>
> >>> equipment
> >>>
> >>>
> >>>
> >>>> for my company. I'm probably no more than a week away from the
=3D3D
> >>>>
> >>>>
> >>>>
> >>> decision. As
> >>>
> >>>
> >>>
> >>>> some of you will no doubt suggest to get both, let me just say
that =3D
> >>>>
> >>>>
> >>>>
> >> I =3D3D
> >>
> >>
> >>
> >>> can
> >>>
> >>>
> >>>
> >>>> not afford both. I will have one or the other.
> >>>>
> >>>>  I have had the demos and seen the equipment.
> >>>>
> >>>>  What I do for a living is design boards for digital video, that
=3D
> >>>>
> >>>>
> >>>>
> >> are
> >>
> >>
> >>
> >>>> comprised of many differential pairs, routed closely together. =
=3D
> >>>>
> >>>>
> >>>>
> >> Rising =3D3D
> >>
> >>
> >>
> >>> edges
> >>>
> >>>
> >>>
> >>>> are in the neighborhood of 100 ps. I want to be able to find and
=3D3D
> >>>>
> >>>>
> >>>>
> >>> modify
> >>>
> >>>
> >>>
> >>>> discontinuities (either capacitive or inductive), determine =3D
> >>>>
> >>>>
> >>>>
> >> crosstalk
> >>
> >>
> >>
> >>>> between the pairs and measusre jitter (yes, I will need a signal
=3D3D
> >>>>
> >>>>
> >>>>
> >>> source for
> >>>
> >>>
> >>>
> >>>> that).
> >>>>
> >>>>  If this were as little as two years ago I would have believed
that =3D
> >>>>
> >>>>
> >>>>
> >> =3D3D
> >>
> >>
> >>
> >>> the
> >>>
> >>>
> >>>
> >>>> VNA solution would have been the most versatile. However,
Tektronix =3D
> >>>>
> >>>>
> >>>>
> >> =3D3D
> >>
> >>
> >>
> >>> has made
> >>>
> >>>
> >>>
> >>>> a lot of progress with their TDR equipment and with their
"Iconnect"
> >>>> software. Also, there is a big difference in price between the
TDR =3D
> >>>>
> >>>>
> >>>>
> >> =3D3D
> >>
> >>
> >>
> >>> solution
> >>>
> >>>
> >>>
> >>>> and the VNA solution.
> >>>>
> >>>>  In appealing to the SI group for opinions I am trying to go
beyond =3D
> >>>>
> >>>>
> >>>>
> >> =3D3D
> >>
> >>
> >>
> >>> my
> >>>
> >>>
> >>>
> >>>> own predjudice and the marketing hype.
> >>>>
> >>>>  Thank You
> >>>>  Tom
> >>>>
> >>>>
> >>>>
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