Re: 8b/10b and EMI
a good source of data onthis can be found in the IEEE 1394b development
archives. Since 1394b maskes use of 8B/10B encoding, and they spend
a lot of effort on EMI reduction, there should be a significant number
of papers/presentations available on the subject.
As a background on what I remember, it is definately possible to
create "hot spots" in the radiated emission spectrum if you keep
repeating a short sequence of characters. This occurs in Fibre Channel
systems with their 4-character Idle sequence. To get around this,
1394b added a level of scrambling to both the source data cahracters
AND to the command characters used, prior to sending them through the
8B/10B encoder. By doing this they were able to achieve some dramatic
(sorry, I can't remember the number of dB) reduction in radiated
The 8B/10B code, when sending random data, has a fairly wide emissions
spectrum (which is what you want), but if you sit on the same
character or small group of characters, you can see the discrete
spectral peaks quite clearly.
> I would like to raise the issue of EM emissions with 8b/10b
> vs. scrambling (spectrum comparisions can be found in the SLP presentation
> or in Joel Goergen's presentation). My impression is that component vendors
> are leaving this problem for the system integrators to solve.
> Has anyone looked into the issue of EMI/EMC within the context of system
> cost and time-to-market?
> While system integration and implementation are
> beyond the scope of the standard, it would be grossly negligent to ignore
> these issues, as ultimately the goal is to get product out the door that
> satisfies FCC/ETSI regulations.