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 > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu