[SI-LIST] Fw: Re: Random Jitter Value varies with Data pattern
- From: Marty Miller <martym777@xxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 4 Feb 2013 11:16:21 -0800 (PST)
----- Forwarded Message -----
From: Marty Miller <martym777@xxxxxxxxx>
To: "ah.vinod@xxxxxxxxx" <ah.vinod@xxxxxxxxx>
Sent: Monday, February 4, 2013 1:28 PM
Subject: Re: [SI-LIST] Re: Random Jitter Value varies with Data pattern
Vinod, I'd like to offer some advice, but first I would ask what
Clock-Data-Recovery are you using?
The behavior you describe is easily achievable by having a slight error in
frequency (bit rate). For whichever
method you use repeating or arbitrary, you will get the same behavior for such
a case.
I presented a paper at DesignCon last week on precisely the subject of
increasing Rj with increasing PRBS
lengths. That paper concerns much longer test patterns than you are using.
________________________________
From: vinod ah <ah.vinod@xxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Sent: Friday, February 1, 2013 1:16 AM
Subject: [SI-LIST] Re: Random Jitter Value varies with Data pattern
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)5K. 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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