[SI-LIST] Re: Differential S-parameters
- From: "databits" <databits@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 10 Jan 2002 21:35:22 -0600
Getting a bunch of single-ended s-parameter that have been to differential
s-parameters is a neat mathematical system that allows _close_ correlation
to _simulators_ (like ADS, Serenade, others?) when the "ports" component is
used.
In the simplest (most common) common simulation configurations, and using 4
ports, both of these systems use a perfect ground (i.e. node 0 reference) on
both sides (i.e. at each port) of the device being measured. "Accurate"
can be a word used to describe this comparison.
I can not say that "accurate" is incorrect. Measuring what is being modeled
and vice versa is a good thing.... however, for the measurements or the
model have anything to do with system performance, the currents should
return through the same path as is in the real system.
I have been trying to understand a better way of creating a differential
s-parameter measurement/simulation that is more indicative of SYSTEM
performance. What I am struggling with is the same things as stated by
Mick, Patrick and Chuck.
Random Thought from the empirical perspective....
I like the baluns concept.... but these usually only have a very limited
bandwidth. A different way (notice I did not say better) to approach the
problem may be to only measure differential "s11". Basically, connect
port1 from 2 VNAs to two terminals on one side of the DUT (shifting the
phase of one of the VNAs 180, I wonder what the best way is to do that?).
Then terminating the far end TO THE RETURN PATH through the device (yes, we
will have to have a "known termination")... look at the return loss for each
port.... then some math to get the results, The test may then need to get
repeated with the DUT flipped ( s22'ish )... and on and on and on and
on.... Yuck... I will break the equipment budget with this one. :)
|-------|
| P1|---------|
|VNA1 | |
| P2| |
|-------| | |-----|
| -----> | | ---/
| DUT | \ Far End
|-------| | -----> | | ---/
| P1|---------| (inv) |-----|
|VNA2 |
| P2|
|-------|
In this diagram at least all the currents will return through the device
back to the source through a return path similar to that of the application.
Boy this sure would be messy... There is probably a better way to do this in
simulation... How about using multiport single ended measurements to fully
"port-wise" characterize" devices... confirm these results to a model....
Then take advantage of the simulator, install an empirically confirmed
models... Is it possible to create non-ground referenced (i.e. amplifier to
be referenced to a lossy return path) differential amplifier models?
Depending on how they work, those "no-ground" ports could come in handy
here!
Too many random thoughts.... [richochet_rabbit_mode=off]
_gus
How many of you will be at DesignConn??? How about a pizza, beer, and
differential s-parameters evening (or two) to set up a plan to figure this
out?
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Gary Otonari
Sent: Thursday, January 10, 2002 4:15 PM
To: xlzhou@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Differential S-parameters
There is no "true" differential VNA that we know of today, but at GigaTest,
we have been using the Agilent Multiport for Mixed-mode (common and
differential) S-parameter measurements, with good results. We have done
several correlation experiments to verify that direct TDR measurements
agree with the differential S-parameters (via simulation in ADS). For a
clear, well written App. Note on the subject of single-ended and
differential S-parameters, which references the Blockelman paper, see
Maxim's App Note #HFAN-510:
http://pdfserv.maxim-ic.com/arpdf/AppNotes/4hfan510.pdf
We'll be discussing differential measurements, including the Agilent 4-port
VNA, several times in public during the month of January. I'll send a
separate note to the list, with our upcoming schedule of events....
-- Gary
======================
"Zhou, Xingling (Mick)" wrote:
> Dennis,
>
> Sorry for the errors. It should be
>
> MTT-Vol.45,No.7,1997,pp.1071-1077.
>
> The title is "Pure-Mode Network Analyzer for On-Wafer Measurements of
> Mixed-Mode S-Parameters of Differential Circuits" by David E. Blockelman
> etc.
>
> Thanks for pointing it out.
>
> Mick
>
> -----Original Message-----
> From: Dennis Rehm [mailto:drehm@xxxxxxxx]
> Sent: Thursday, January 10, 2002 2:32 PM
> To: xlzhou@xxxxxxxxx
> Subject: Re: [SI-LIST] Re: Differential S-parameters
>
> I looked on the MTT web site and did not find the article that you
> mentioned below. The pages in No. 1 start at 1, the july issue has pages
> in the 1000 to 1100 range but no article starting on page 1071. What is
> the title of the paper?
>
> Thanks
>
> Dennis
>
> "Zhou, Xingling (Mick)" wrote:
>
> > Hi,
> >
> > We have exactly the same concern.
> >
> > I use the formulas published in MTT-Vol47,No.1,1999,pp.1071-1077. The
> > authors proposed PMVNA system. I do not know any commericial one.
> >
> > Furthermore, how does the "Network Analyzer with Ungrounded Ports
> > (SP_Diff.)" in Agilent ADS
> > work in this case? I mean, are the definitions consistent?
> >
> > Mick
> >
> > -----Original Message-----
> > From: Zabinski, Patrick J. [mailto:zabinski.patrick@xxxxxxxx]
> > Sent: Thursday, January 10, 2002 9:23 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Differential S-parameters
> >
> > In the past few years, we've seen a tremendous surge
> > in the application of differential signaling, and we
> > do not expect the trend to end anytime soon.
> >
> > In our lab, we like to characterize our devices, both
> > active and passive, with S-parameters. We feel S-parameters
> > give us MUCH useful information.
> >
> > However, making differential S-parameter measurements
> > takes us a considerable amount of effort, requiring
> > a series of baluns, switches, etc., all manually
> > controlled/installed.
> >
> > Is there a commercial piece of equipment on the market
> > (or being developed) that makes truly differential S-parameters.
> >
> > I am aware of the ATN/Agilent system that takes single-ended
> > measurements and mathematically converts the results to
> > differential, but for active/non-linear devices, I believe
> > we really need a truly-differential capability. Does such
> > a beast exist?
> >
> > Thanks,
> > Pat
> >
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