[SI-LIST] Re: strange behavior... resent after server error
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>
- Date: Wed, 11 Jan 2012 12:41:02 -0500
Gert
Can you also confirm that TDR Port 1 Cable1(rising edge) + TDR Port 2
Cable2 (falling edge) = 0. To verify that there is no asymmetry in the TDR
pulsers.
On Wed, Jan 11, 2012 at 12:32 PM, steve weir <weirsi@xxxxxxxxxx> wrote:
> Gert, so just to be clear:
>
> Set-up as TDR only:
>
> Port1 --> Cable1 --> Open
> Port2 --> Cable1 --> Open
> Port1_RoundTrip - Port2_RoundTrip = 0ps Calibration
>
> Port1 --> DUT+
> Port2 --> DUT-
> Port1_RoundTrip - Port2_RoundTrip = 16ps
>
> Port1 --> DUT-
> Port2 --> DUT+
> Port1_RoundTrip - Port2_RoundTrip = 0ps
>
> What do you get for absolute values driving single-ended:
>
> Port1 ---> DUT+
>
> Port1 ---> DUT-
>
> Port2 ---> DUT+
>
> Port2 ---> DUT-
>
> Steve
> On 1/11/2012 9:16 AM, Havermann, Gert wrote:
> > Scott,
> > the differential delay of the + and ? branch of my differential pair is
> 16ps when I feed + with TDR Port1 and ?with TDR Port 2
> > When I switch ports (- with TDR Port 1 and + with TDR Port 2) then I
> measure<1ps delay difference.
> > In addition, the latter result doesn?t change much with varying skew at
> the TDR setting, the first result does change (as expected).
> >
> > I did the same test on many Testfixtures before, and I?ve never seen
> this kind of effect. My guess is that the mix of differential and single
> ended routing is causing this behavior, but I don?t have a real explanation
> for it.
> >
> > BR
> > Gert
> >
> > Von: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]<mailto:[mailto:
> scott@xxxxxxxxxxxxx]>
> > Gesendet: Mittwoch, 11. Januar 2012 17:52
> > An: Havermann, Gert
> > Cc: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
> > Betreff: Re: [SI-LIST] AW: Re: Stange behavior in skew measurement
> >
> > Gert
> >
> > Let me ask clarifying questions. Are you saying that
> > 1. differential skew is 16 ps?
> > 2. that the difference between differential and common mode delay
> is 16ps?
> > 3. that you get different skew or delay measurements when you
> measure from different directions?
> >
> >
> > Scott
> >
> > On Wed, Jan 11, 2012 at 11:24 AM, Havermann, Gert<
> Gert.Havermann@xxxxxxxxxxx<mailto:Gert.Havermann@xxxxxxxxxxx>> wrote:
> > Steve, Jeff,
> >
> > thanks for the answer, but the cable is not the issue. I did use "cost
> effective" cable, but they are good enough for this test (and have been in
> the past). The cable was also not really moved during port switching as I
> fixed them with tape to avoid this kind of variances and the cables are
> only 5" long. We also have the phaseflex gore cables on our VNAs, and using
> them shows no difference.
> >
> > I also don't think the TDR Heads are the problem either. As I said, I
> deskewed after switching modes because I know of the timebase limitation of
> these heads.
> >
> > It must be something with the DUT that's causing this behavior. To give
> you more information, the DUT is a Test Fixture for a 25G Backplane and is
> done with FR408 flat weave material. Tracelength is 320mm, most of it
> routed single ended. Differential routed corners have deskew features
> added. The SMAs and transition to the trace shows +/-2 Ohm differential
> Impedance discontinuity and the Traces are all within 3% impedance
> tolerance. Geometrical Length matching was designed to be<1µm.
> >
> > One more information on the results: The single ended skew test (only
> one port attached the other terminated, and then difference of the signal
> runtime) showed skew<2ps, thus having a very low differential skew seems
> reasonable.
> >
> > BR
> > Gert
> >
> >
> > ----------------------------------------
> > Absender ist HARTING Electronics GmbH& Co. KG; Sitz der Gesellschaft:
> Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596;
> persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH;
> Sitz der Komplementär-GmbH: Espelkamp; Registergericht der
> Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB
> 8808; Geschäftsführer: Edgar-Peter Duening, Torsten Ratzmann, Dr. Alexander
> Rost
> >
> >
> > ---------------------------------------------------------
> >
> > Absender ist HARTING Electronics GmbH& Co. KG; Sitz der Gesellschaft:
> Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596;
> persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH;
> Sitz der Komplementär-GmbH: Espelkamp; Registergericht der
> Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB
> 8808; Geschäftsführer: Edgar-Peter Duening, Torsten Ratzmann, Dr. Alexander
> Rost
> >
> > -----Ursprüngliche Nachricht-----
> > Von: si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>
> [mailto:si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>]
> Im Auftrag von Loyer, Jeff
> > Gesendet: Mittwoch, 11. Januar 2012 17:00
> > An: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
> > Betreff: [SI-LIST] Re: Stange behavior in skew measurement
> >
> > Agreed, and just to expand a little bit on this...
> > I've found it useful to monitor the open TDR waveform while putting my
> cables through some contortions. Cables which are not "phase-stable" stick
> out like a sore thumb - you'll see timing shifts and variations in the
> rising edge of the pulse as you wiggle them around.
> >
> > Well behaved cables will appear rock-solid, and you can rest assured
> they will remain so as you move between reference and various DUT
> measurements. Cables which are not phase-stable will cause you all kinds
> of grief.
> >
> > This should be done periodically to all your cables, whether you're
> making TDR or VNA measurements, IMHO. Label the "bad" cables and only use
> them for non-phase-critical measurements (or throw them away). It may save
> you hours of consternation.
> >
> > And yes, you'll see a huge difference between the costly cables (Gore,
> Rosenberger) and cheap ones.
> >
> > Jeff Loyer
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>
> [mailto:si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>]
> On Behalf Of steve weir
> > Sent: Wednesday, January 11, 2012 7:45 AM
> > To: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
> > Subject: [SI-LIST] Re: Stange behavior in skew measurement
> >
> > An 8200 with 80E04 heads is capable of consistent and accurate
> measurements. The only thing that Ihave seen with the 8000's and 8200's is
> that you have to be careful that the internal temperature stays within the
> calibrated range. Assuming that you have then I would look at the cables.
> How long are your cables, and how good are your cables?
> > Consistency is a good reason to spend the money on a good set of WL Gore
> > cables. And even with Gore cables you want to avoid tight radii, and
> > variations in bend from the time you calibrate to the time you are done
> measuring your DUT.
> >
> > You can try switching cables, and/or using semi-rigid, and/or keeping
> the cables in a very straight and uniform orientation to see if they are
> the main contributor.
> >
> > Steve.
> >
> >
> > On 1/11/2012 7:12 AM, Havermann, Gert wrote:
> >> Hello SI-Fellows,
> >> can someone explain to me the following effect I found in a skew
> measurement:
> >>
> >> I use Tek TDS8200 with 80E04 TDR Sampling Heads. I usually make 5
> separate measurements: 2xdifferential, 2xcommon and 1xsingle ended. For
> diff and common I make a separate deskew up front, due to the non
> synchronized timebase when switching modes. After deskew I measure the skew
> at the open end of the DUT (I know its not the most accureat way, but it is
> quick and served my needs very well in the past).
> >>
> >> For the two common and differential measurements I always switch dut
> ports to check my deskew. Usually both measurements show about the same
> value regardless of the port assignment. This time I had 16ps difference,
> and in addition, one measurement showed just a few fs skew, and the other
> 16ps. Just for sanity check I deskewed a bit more, and still one
> measurement showed just fs while the other changed.
> >>
> >> Any Ideas or hints?
> >>
> >> BR
> >> Gert
> >>
> >>
> >>
> >> ---------------------------------------------------------
> >>
> >> Absender ist HARTING Electronics GmbH& Co. KG; Sitz der Gesellschaft:
> >> Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596;
> >> persönlich haftende Gesellschafterin: HARTING Electronics Management
> >> GmbH; Sitz der Komplementär-GmbH: Espelkamp; Registergericht der
> >> Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH:
> >> HRB 8808; Geschäftsführer: Edgar-Peter Duening, Torsten Ratzmann, Dr.
> >> Alexander Rost
> >>
> >>
> >>
> >>
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> >
> > --
> > Steve Weir
> > IPBLOX, LLC
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> > --
> > Scott McMorrow
> > Teraspeed Consulting Group LLC
> > 121 North River Drive
> > Narragansett, RI 02882
> > (401) 284-1827 Business
> > (401) 284-1840 Fax
> >
> > http://www.teraspeed.com<http://www.teraspeed.com/>
> >
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>
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
> All contents Copyright (c)2012 IPBLOX, LLC. All Rights Reserved.
> This e-mail may contain confidential material.
> If you are not the intended recipient, please destroy all records
> and notify the sender.
>
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(401) 284-1827 Business
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Teraspeed® is the registered service mark of
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