[SI-LIST] Re: PRBS Data patterns
- From: "Greim, Michael" <mgreim@xxxxxxxxxxxx>
- To: "'whizplayer@xxxxxxxxx'" <whizplayer@xxxxxxxxx>,m.randol@xxxxxxxxxxxx, si_list <si-list@xxxxxxxxxxxxx>
- Date: Thu, 6 Dec 2001 09:11:42 -0500
Hi,
The increase in jitter with the longer string
is expected behavior due to the increase in freq
content and the bandwidth of the interconnect,
otherwise known as inter-symbol interference or
ISI jitter. The fact that you see errors in low
to high transition rather than the high to low,
may be a function of asymetric drive of your driver.
best regards,
Michael Greim
-----Original Message-----
From: Bob Patel [mailto:whizplayer@xxxxxxxxx]
Sent: Wednesday, December 05, 2001 10:03 PM
To: m.randol@xxxxxxxxxxxx; si_list
Subject: [SI-LIST] Re: PRBS Data patterns
Hi! Mark, Greimm and Vinu, I ran the experiment
further and over an interval of 10minutes I find that
with PRBS 2^31-1 the BER is 1.873e-11. This error
ratio is when 0 is transitioning to 1 and the error
ratio is 0 for 1-->0. So I think when there is long
run of zero's in the pattern and then the data bit
switches to 1 there is an error. I will try to look at
the pattern on the scope and see if I can see the
error happening. In the EYE mode I think the pk-pk
jitter goes up with the longer string.
Thanks
Bob
--- Mark Randol <m.randol@xxxxxxxxxxxx> wrote:
>
> Bob Patel wrote:
> >
> > 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.
>
> To paraphrase Michael a little, the longer the
> sequence, the longer a
> cluster of just 0's or 1's that occur during the
> sequence. IIRC, the
> averaged frequency content will remain the same, but
> for the period the
> longer clusters of 0's and ones occur, the frequency
> content of the
> signal will be lower than "normal".
>
> It's another example of time and frequency being
> duals of each other.
> You have to understand both in digital
> communications systems. :)
> --
> Mark Randol, RF Evaluation Engineer
> Motorola SPS, Inc.
> M/S EL536
> 2100 E. Elliot Road
> Tempe, AZ 85284
> (480)413-8052 Voice
> (480)413-8690 FAX
> m.randol@xxxxxxxxxxxx
>
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