[SI-LIST] Re: is 8b/10b too much or too little?
- From: tim stroud <tim.stroud@xxxxxxxxxx>
- To: zabinski.patrick@xxxxxxxx
- Date: Tue, 11 Sep 2001 13:35:50 -0400
Pat,
This is from Dally and Poulton Digital Systems Engineering
Max number of bit cells between transitions is given by
N = tpd
___
dF * tc^2
tpd = timing margin budgeted to drift
dF = maximum frequency difference (Function of PLL)
tc = bit cell time
The maximum frequency difference is a function of PLL bandwidth. A wider
bandwidth allows more drift
between pump cycles, but allow the pll to lock into frequency changes
faster. So, your question has to be taken
in the context of the pll filters. If you want to be able to track faster
changes (i.e. more jitter tolerance)
you need more edges. If you are certain your system doesn't jitter too
much, then you can get away with
lower edge rates.
Is this the kind of stuff you are looking for? Let me know and I will dig
up what I can.
Tim
"Zabinski, Patrick J." wrote:
> Thanks to all for responding to my posting on 8b/10b encoding.
>
> Summarizing what I received from folks:
>
> 8b/10b encoding:
> * ensures no more than five consecutive 1's or 0's
> * provides DC-free code, which allows for AC-coupling
> * reduces spectrum, thus easing constraints placed on equalizers
> * increases the number of transitions, thus makes it
> easier for PLLs to recover a clock
>
> Of these, the last issue is of my concern/interest to me.
> I can understand qualitatively that PLLs can more easily (i.e.,
> reliably) lock onto 8b/10b-encoded serial data streams
> than truly-random non-return to zero (NRZ) data streams.
>
> However, can anyone provide quantitative information? Specifically,
> how many transitions does a PLL really need in order to
> reliably recover a clock from a serial data stream? If
> 8b/10b works, will 99b/100b suffice? Or, do we really
> need 1b/2b (Manchester) coding?
>
> Can anyone offer analytics to support the claims of
> using 8b/10b encoding for clock recovery?
>
> Thanks
> Pat
>
> P.S. Don't bother with CNN.com, NBC.com, etc.; they are all over-loaded
> with the Trade Center news. I tried my local paper, TV, and radio
> web sites, and they all had news/photos on the attacks.
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
--
-------------------------------------------
Analog Devices "Enjoy yourself -
7910 Triad Center Dr it is later than you think"
Greensboro, NC
336-605-4317
tim.stroud@xxxxxxxxxx
-------------------------------------------
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
