[SI-LIST] Re: AW: Re: strange behavior... resent after server error
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- Date: Thu, 12 Jan 2012 08:16:54 -0800
Gert I have to run off to customer meetings that will consume most of
the day. I'll take a look at this when I get back to the office.
Steve.
On 1/12/2012 8:07 AM, Havermann, Gert wrote:
> Scott, Steve
>
> I just doublechecked my driver and receiver deskew settings (twice) to be
> sure I'm not measuring wrong.
> Rising and falling edge is deskewed to<0.1ps right at the DUT's SMA (open).
> I again measured 3 ports . Results are in your text below (a negative number
> is when the edge arises at C2 first).
>
> I didn't capture the absolute timing single ended. I alsways measure one leg
> single ended, save the waveform and then attach the other leg and measuring
> the skew at the centre of the rising edge (I'm using rho instead of voltage
> to see both edges rising).
> The Single ended Skew is DUT1: -11ps; DUT2: 6.5ps; DUT3 -24.2ps
> I also tested DUT 3 again with the other TDR port, and with -24.0ps I think
> that's a fit.
>
> Any suggestions? (Maybe we can do a "Hands On" at the Tek Booth at DesignCon?)
>
> 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
>
> -----Ursprüngliche Nachricht-----
> Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
> Auftrag von Scott McMorrow
> Gesendet: Mittwoch, 11. Januar 2012 18:41
> An: steve weir
> Cc: si-list@xxxxxxxxxxxxx
> Betreff: [SI-LIST] Re: strange behavior... resent after server error
>
> 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 --> Correct
>>
>> Port1 --> DUT+
>> Port2 --> DUT-
>> Port1_RoundTrip - Port2_RoundTrip = 16ps --> New reults: DUT1: -3.5ps;
>> DUT2: 9.7ps; DUT3: -18.0ps
>>
>> Port1 --> DUT-
>> Port2 --> DUT+
>> Port1_RoundTrip - Port2_RoundTrip = 0ps --> New reults: DUT1: 11.0ps; DUT2:
>> -3.0ps; DUT3: 25.5ps
>>
>> 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@xxxxxxxxxxx
>> rg>]
>> 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@xxxxxxxxxxx
>> rg>]
>> 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
>>> 150 N. Center St. #211
>>> Reno, NV 89501
>>> www.ipblox.com<http://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.
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>> notify the sender.
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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/>
>>>
>>> Teraspeed® is the registered service mark of Teraspeed Consulting
>>> Group LLC
>>>
>>>
>>>
>>>
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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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>
> --
>
> 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
>
> Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC
>
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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
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This e-mail may contain confidential material.
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