[SI-LIST] Re: purpose of 8b/10b encoding

  • From: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Mon, 10 Sep 2001 19:30:39 -0500


Thanks for the feedback.

Looking at the spectrum of an un-encoded/raw data stream versus
an 8b/10b-encoded data stream, I can see how the power
spectral density will be increased at a frequency
equal to the data rate/2, which would provide more
information for a PLL to synch onto.

If this is the case, is there a way of analyzing exactly how
much better a PLL can synch when using 8b/10b vs when
not using 8b/10b?  If there is, can the analysis be
generalized to allowing me to determine how often
transitions need to be in order for a PLL to lock?


> # What's the purpose of 8b/10b encoding?
> Generally as I understand, it is to be able to recover the clock by
> ensuring some number of transitions per period (8 per 10?). 
> Clocks change
> period frequently when working at high speeds, due to 
> temperature, etc... not
> to meantion the fact that otherwise the sending clock would 
> inevitably be
> out of phase, plus period, of your receiver's clock.
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