[SI-LIST] Re: purpose of 8b/10b encoding
- From: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 13 Sep 2001 20:02:22 -0500
Raja,
If you'd like to 'see' the difference between a
truly-random and an 8b10-encoded bit stream, I
recommend using a pseudo-random pattern generator
and spectrum analyzer. Note: the pattern generator
and spec-an can be either real test-lab hardware or
can be in software (via matlab or other).
* Looking at random digital signal
Generate a serial bit stream using a pseudo-random
generator with a long-length. Most bit error rate
testers have 2^32-1 code (which allow up to 32 consecutive
1's or 0's), or you can generate one in code.
Pump the bit stream into a spectrum analyzer.
* Looking at 8b10b-encoded signal
For comparison sake, use the same exact pseudo-random
pattern generator with the same settings. Put that
into a deserializer (i.e., 1:8 demux), put that into
an 8b10-encoder, then put the 10 bits into a serializer
(i.e., 10:1 mux).
Put the resulting serial bit stream into a spec-an.
If all goes well, you should be able to 'see' two
distinctive differences:
1) the fundamental frequency of the 8b10-encoded
stream should be 25% higher than the raw
pseudo-random stream (note the frequency locations
of the peaks/valleys); and
2) the magnitude of the spectrum at the lower frequencies
of the 8b10-encoded stream is lower.
Hope this helps.
Sorry, I do not have plots to share. If you are
able to produce some through C/MatLab, I'd appreciate
getting a copy.
Pat
>
> Okay the que is:
> If I am to write a C/Matlab code for converting a *raw* data
> to 8b10b encoded data what exactly I need to do? or in other
> words, Pat how did you
> *look at* the spetrum of raw and encoded data.
> How did you generate both the streams?
> I hope C/Matlab are sufficient to get a feel for it.
> or was is it back-of-the-envelope calculation.
>
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