FreeLists / si-list / [SI-LIST] Re: PRBS Data patterns

[Pierre-Luc Cantin <plcantin@xxxxxxxxxxxxx>]

Dear Bob,

If I understand corectly, with PRBS 2^23 you have no errors. 
But with PRBS 2^31 you have some errors, which leads to BER 2.88e-11.

Assuming the above, this makes sense to me. With PRBS 2^31 you will have
longer streams of "0" (or "1") than with PRBS 2^23. What happens is with
longer streams of "0" the line will discharge to a lower level (DC level
will drift lower) therefore in order to charge back up to "1" it will take
more time. This can be seen as increased amount of jitter since the time of
arrival of a "edge" as been mis-positionned by the data-pattern
(determinstic jitter (DJ), data-dependant jitter, (DDJ)).

More jitter therefore more errors. The receiver jitter-tolerance is specifed
usually at BER 10^-12. Is is the amount of peak-to-peak jitter at the input
of a CDR that produce a 10^-12 BER.

Hope this help.

Pierre-Luc Cantin
Hyperchip

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Bob Patel
Sent: December 5, 2001 1:11 PM
To: si_list
Subject: [SI-LIST] PRBS Data patterns



Hi! I had a question regarding PRBS data patterns
being sent through a system. I am sending PRBS data at
a fixed frequency of 2.488GHz and varying the pattern
from 2^10-1 to 2^31-1 through a system and measuring
the received BER.
I see that when I use PRBS 2^31-1 I get BER of
2.88e-11 which is quite low but there and 0 BER when
using 2^23-1. Now, if I understand correctly PRBS
2^31-1 is just a longer string length then PRBS 2^23-1
and since the frequency of the data remains constant,
I don't see where the BER is coming from.
I would appreciate any help in this matter.
Thanks in advance
Bob Patel 

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