[SI-LIST] Re: PRBS7 vs PRBS15
- From: Vinu Arumugham <vinu@xxxxxxxxx>
- To: "Sharma, Rajeev" <rajeevsh@xxxxxxxxxxxxxxxx>
- Date: Fri, 22 Feb 2013 13:12:56 -0800
If you look at the bit stream, say 20 bits at a time, there will be a
lot more bit combinations with PRBS15 than with PRBS7 (both 8B10B
encoded). Looking at a 20 bit long pulse response, one can compute the
bit sequence that produces the worst jitter.
With more 20 bit combinations in PRBS15, there is a higher probability
that the worst case jitter sequence will occur.
Thanks,
Vinu
On 02/22/2013 12:49 PM, Sharma, Rajeev wrote:
>
> That is exactly where I have the problem. In both cases run length is
> determined by 8B/10B encoding and so probably they should have same DDJ.
>
> Is there any advantage of testing a CDR with 8b/10B encoded PRBS 15
> over PRBS 7?
>
> *From:*Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
> *Sent:* Friday, February 22, 2013 12:46 PM
> *To:* vinu@xxxxxxxxx
> *Cc:* Sharma, Rajeev; Joseph.Schachner@xxxxxxxxxxxxxxxxxx;
> si-list@xxxxxxxxxxxxx
> *Subject:* Re: [SI-LIST] Re: PRBS7 vs PRBS15
>
> I may be wrong, but if a PRBS7 or a PRBS15 is passed through an 8B10B
> encoder, the run length is still limited to 5, which ultimately limits
> the bounds of DDJ. What changes is the spectral distribution within
> this truncated spectrum, and the time that it will take to create a
> statistically significant sample of data to analyze to your target BER
>
> Scott
>
> On Fri, Feb 22, 2013 at 3:38 PM, Vinu Arumugham <vinu@xxxxxxxxx
> <mailto:vinu@xxxxxxxxx>> wrote:
>
> Even though the CDR is not affected, the extra DDJ means more stress
> that the receiver as a whole needs to handle. So the pattern can affect
> the outcome of a Jitter Tolerance test. There are patterns such as XAUI
> CJPAT that will specifically stress the CDR.
>
> Please see discussion here:
> //www.freelists.org/post/si-list/Majic-Fbaud1667-for-CDR-bandwidth,12
>
> Thanks,
> Vinu
>
>
> On 02/22/2013 11:42 AM, Sharma, Rajeev wrote:
> > Though the 8B10B encoded PRBS7 and PRBS15 will have different
> repeat lengths...but isn't that both the patterns will still have same
> length of long 0's and 1's[I believe 5 due to 8B10B encoding].
> > And since CDR performance is determined by the Long sequence of 1's
> or 0's it can track, CDR performance will be same for both these
> Patterns(with 8B/10B encoded)?
> >
> > Thx,
> > Rajeev
> >
> > -----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
> Joseph.Schachner@xxxxxxxxxxxxxxxxxx
> <mailto:Joseph.Schachner@xxxxxxxxxxxxxxxxxx>
> > Sent: Friday, February 22, 2013 11:10 AM
> > To: vinu@xxxxxxxxx <mailto:vinu@xxxxxxxxx>
> > Cc: si-list@xxxxxxxxxxxxx <mailto:si-list@xxxxxxxxxxxxx>
> > Subject: [SI-LIST] Re: PRBS7 vs PRBS15
> >
> > minor correction: if PRBS-15 is 8B10B coded the result will repeat
> every every 2^15 * 10/8 bits, that's 25% more than 2^15.
> > Similarly, 8B10B coded PRBS-7 is 25% longer than 2&7 bits.
> >
> > I would say it can still make a difference by adding to the tails of
> the jitter distribution. 8B10B coding should hold down the DDJ. As
> was recently presented at design con, longer tails in the jitter
> distribution is likely to be indistinguishable from Rj, even though
> it's actually just long pattern DDj. PRBS-15 will have more of that
> effect than PRBS-7.
> >
> > --- Joe S.
> >
> >
> >
> > From: Vinu Arumugham <vinu@xxxxxxxxx <mailto:vinu@xxxxxxxxx>>
> > To: si-list@xxxxxxxxxxxxx <mailto:si-list@xxxxxxxxxxxxx>
> > Date: 02/22/2013 01:06 PM
> > Subject: [SI-LIST] Re: PRBS7 vs PRBS15
> > Sent by: si-list-bounce@xxxxxxxxxxxxx
> <mailto:si-list-bounce@xxxxxxxxxxxxx>
> >
> >
> >
> > 8B/10B will limit the run length to 5 bits. 8B/10B encoded PRBS15
> will still have patterns that repeat every 2^15 bits.
> >
> > 8B/10B encoded PRBS7 on the other hand will not have patterns
> repeating at any rate lower than 2^7 bits.
> >
> > So it will make a difference for Jitter Tolerance by increasing the
> DDJ (exciting the "tail" of the pulse response).
> >
> > Thanks,
> > Vinu
> >
> > On 02/21/2013 08:51 PM, Sharma, Rajeev wrote:
> >> Steve,
> >> But in case we encode the PRBS15 with 8B/10B Encoding, wouldn't that
> > limit the signal band as compared to pure PRBS15?
> >> -----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: Thursday, February 21, 2013 8:34 PM
> >> To: si-list@xxxxxxxxxxxxx <mailto:si-list@xxxxxxxxxxxxx>
> >> Subject: [SI-LIST] Re: PRBS7 vs PRBS15
> >>
> >> Yes, the signal band is wider for PRBS15 and will exhibit more DDJ due
> > to non-uniform frequency response.
> >> Steve.
> >> On 2/21/2013 6:28 PM, Sharma, Rajeev wrote:
> >>> Hi,
> >>> Is there any difference between "8B/10B Encoded" PRBS7 and PRBS15
> >>> for
> > Receiver Jitter Tolerance?
> >>> I mean both the PRBS patterns are 8B/10B encoded and so they will
> >>> have
> > equivalent sequence of long 1's or 0's. Is this understanding correct?
> >>> Thx.
> >>> Rajeev
> >>>
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