[SI-LIST] Re: Random Jitter Value varies with Data pattern
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 31 Jan 2013 23:10:15 -0800
Vinod, an 80 sample to 200 sample windows is very small to try and
extract meaningful Rj data from a RTS. If you want good Rj information
the recorded and processed data must contain a statistically significant
number of points. 200 points is not very significant. There should be
information about this in the oscilloscope's manual.
Steve.
On 1/31/2013 10:16 PM, vinod ah wrote:
> Hi All,
> Sorry for not mentioning few details. My mistake. Below are the same.
>
> Scope: Real time
> BW: 12.5GHz
> Sampling rate : 100Gs/s
> Record length used: 1M
> Time base setting: 1us/div
> Signal fed: PRBS 11 and 2.5GHz clock
>
> Below are the few observation which i could make in last 2 days in process
> of finding out dependency of Rj on data pattern.
>
> 1) In Jitter decomposition software, when i set the Pattern type
> as Arbitrary (when capturing PRBS pattern) and Window length as 2UI, i see
> that the Rj value is very near to Rj value measured with clock pattern. I
> understand that the technique used to separate Rj Dj is different if we set
> Pattern type as Arbitrary or Repeating. Does it mean that algorithm used
> for Arbitrary pattern converges to Repeating pattern algorithm when we set
> the window length as 2UI?
>
> 2) As i increase the window length for arbitrary pattern setting from 2UI
> to 5UI, the Rj vaule keeps increasing dramatically. But Dj value seems to
> be pretty much constant. Dj not increasing implies ISI is fully captured,
> but Rj increasing not sure !!!
>
> 3) As the number of samples considered (Record length) increases, both Rj
> Dj increases. Most of measurements are taken with Record length of 1M, but
> if i make it 10M with all other settings remaining same, i see that Rj and
> Dj both give very high readings.
> Is there any rule which says what should be the record length for certain
> type of jitter measurement?
>
> 4) I see minor difference in readings of Rj Dj when using Real time
> sampling compared to Interpolated real time sampling. Is this expected?
>
> Regards
> Vinod A H
>
> On Wed, Jan 30, 2013 at 4:35 AM, T.K. Jeon <tkjeon@xxxxxxxxxxx> wrote:
>
>> Hi Vinod,
>>
>> Most of jitter software use the jitter spectrum in order to separate RJ
>> and PJ. In general, any spectral peak is considered as PJ and RJ would be
>> obtained by averaging the rest of the power spectrum.
>>
>> As Steve mentioned, RJ should be independent of the pattern in the ideal
>> case. However, in reality, RJ could be affected by both the pattern length
>> and the data acquisition memory. Let me show you an example.
>>
>> Assuming that your scope has 1M of acquisition memory with 40GSa/s for
>> 5Gb/s signal, I get the number of samples like 1M/(40G/5G)=125K. The
>> samples will contain 61 times of your PRBS11 pattern (125K/(2^11-1)), while
>> 62500 times of your clock pattern(125K/2). You will see significant
>> difference in terms of the jitter samples covering the whole data pattern.
>> This difference could cause RJ discrepancy after power spectrum average.
>>
>> Best Regards,
>> TK
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of vinod ah
>> Sent: Monday, January 28, 2013 1:24 AM
>> To: weirsi@xxxxxxxxxx
>> Cc: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Random Jitter Value varies with Data pattern
>>
>> DUT itself is signal generator which generates either PRBS pattern or clock
>> pattern based on certain register settings. The DUT is connected to an
>> oscilloscope where a jitter decomposition software runs.
>> On Mon, Jan 28, 2013 at 2:15 PM, steve weir <weirsi@xxxxxxxxxx> wrote:
>>
>>> Truly random jitter is independent of the data pattern. Do you see this
>>> jitter going straight from a pattern generator into a signal analyzer,
>>> or only when your DUT is in the path?
>>>
>>> Steve
>>>
>>> On 1/27/2013 10:57 PM, vinod ah wrote:
>>>> Hi All,
>>>> On a 5Gb/s USB3 serial link, i see that there is variation in Random
>>> jitter
>>>> value when i use CP0 pattern (PRBS 11 pattern) when compared to CP1
>>> pattern
>>>> (Clock pattern 2.5GHz).
>>>>
>>>> I also see a variation in deterministic jitter, but that is more
>>>> understandable as ISI effects are dominant with PRBS pattern and it is
>>>> pretty much constant with clock pattern.
>>>>
>>>> Is Random jitter varying with data pattern is expected?. The difference
>>> in
>>>> readings is 2ps (Rj with PRBS is 5ps mean, while Rj with clock pattern
>> is
>>>> 3ps mean)
>>>>
>>>> Note: The measurements are not dual-dirac model based measurements.
>>>>
>>>> Regards
>>>> Vinod A H
>>>>
>>>>
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>>>
>>> --
>>> Steve Weir
>>> IPBLOX, LLC
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>>
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>
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--
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV 89523-9998
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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