[SI-LIST] Re: PRBS Data Pattern.
- From: Ray Anderson <reanderson@xxxxxxxxxxxxx>
- To: sjulian@xxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 12 Oct 2004 07:59:33 -0700
Simba-
An excellent question. There was a recent article published in EDN
magazine (9/2/2004) by some people at Maxim that deals with this issue
(Spectral Content of NRZ Test Patterns)
(see http://www.reed-electronics.com/ednmag/article/CA447007?industryid=2282
In summary, I'll paraphrase a few items::
K28.5+/- pattern is useful in assessing deterministic jitter in
systems using 8b10b encoding
Short random patterns such as 2^7-1 PRBS (127 bits) is useful for
testing Ethernet, Fibre Channel and digital video since it provides a
good approximation to a 8b10b encoded NRZ data stream.
A long random pattern such as 2^23-1 PRBS (~8.4MBytes) is good for
simulating scrambled or random NRZ data. The long pattern contains
considerable low frequency content which is required to stress SONET and
SDH protocol tests.
The article also provides some good analytical details on computing
the power spectrum of various patterns and the implications.
Another thing to consider though not addressed in th eabove article is
that the seed selected to generate the various PRBS patterns can have
significant effects on detrermining the ability of a long pattern to
stress maximum run length, minimum transition density, and maximum
baseline density.
For 10GB ethernet extremely long PRBS patterns 2^58 -1 are sometimes
used (or at least a portion of the pattern as the whole pattern's repeat
period is about a year) at high data rates shorter patterns (such as
2^31 -1 which would repeat in about 200msec at 10GB/s) are too short
for a lot of testing of low inidence of occurence events.
Ray Anderson
julian, simba wrote:
>Greetings fellow SI engineers,
>
>For high speed analysis of serial links, my understanding is that you would
>want to use a data pattern that would excite and replicate different ISI
>effects in simulation. Before lengthening my simulation time, or turning to
>mathematical solutions in MATLAB(or similar products), or new techniques
>such as Channel Analysis that I'm sure the list is aware of by now, I would
>like to know if there are any techniques that you use to define a
>channel/topology specific stimulus to exacerbate the majority of these ISI
>effects so that the inner and outer most contours of the eye would be
>defined even within a relatively short(or reasonable) simulation time.
>
>Specifically if you use 8b/10b encoding there is a limit on the number of 1s
>or 0s that your stimulus should have. Outside of that, is there a relation
>between channel length to Bit pattern length? Or channel length to max
>number of 1s/0s? Or bit width to pattern relationship? How about running a
>TDR type simulation on the actual channel.... is there any useful data from
>the results as it relates to derivation of an exhaustive data pattern? I
>know I'm fishing here but my gut tells me that there must be some type of
>methodology or relation that exists instead of just using this "PRBS"
>pattern that I have sitting in a file for use in all serial simulation
>cases.
>
>Thanks,
>Simba
>
>
.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
