[SI-LIST] Re: PRBS Data Pattern.
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: "julian, simba" <sjulian@xxxxxxx>, "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 12 Oct 2004 13:08:54 -0400 (EDT)
Hi Simba,
I didn't know that the king of the jungle is also an SI engineer ;-) Sorry for
the joke.
I speak Swahili, and "simba" is the Swahili word for "lion".
Jokes aside, you've asked a very good question. A short answer: Yes, there
exist known
data patterns that can give rise to maximum ISI. But maximum ISI doesn?t imply
maximum
deterministic jitter (DJ) at the end of the channel, which I think you?re
ultimately
interested in. In other words, the pattern that gives you maximum ISI does not
necessarily give you the maximum DJ ? unless considered in isolation.
In any practical channel, there are other DJ components that are not
pattern-dependent.
For example, crosstalk, channel attenuation, reflection loss, etc. The jitter
you read
on the output eye diagram is actually a function of all those ?jitter factors?.
It may
so happen that the data pattern for maximum ISI, combined with the channel
attenuation
characteristics, gives rise to less DJ at the end of the channel than with
other data
patterns on the same channel.
I?m sure you know about various equalization techniques used to reduce output
jitter
(increase output eye-opening). You see, all the equalization does is to add
another ?jitter factor? that reverses effects of the other ?jitter factors?
including
ISI.
Best regards.
Hassan.
On Oct 12, "julian, simba" <sjulian@xxxxxxx> 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
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