Re: Xaui jitter tolerance
I agree with your viewpoint. Many/most RX PLLs for this speed have
BW in the 10+ MHz range, which is what you want to allow fast pull-in
and tracking of jitter in high noise environments. The low BW is
generally a carry over from SONET environments where the
repeater functions (and the jitter gain in some parts of the PLL transfer
function) can cause problems. As far qas I know, these implementations
are all re-timed to a local reference so jitter gain is not an issue.
> Since XAUI jitter will likely be addressed in a separate meeting at Austin,
> I would like to raise the issue of modifying the jitter tolerance frequency
> "break point" from the standard baudrate/1667 (used in MJS) to something
> significantly higher.
> For Xaui, the baudrate/1667 would give us a tolerance break point at 1.875
> MHz. My feeling is that there is nothing magical about the baudrate/1667
> and that it doesn't accurately reflect typical receiver operation in today's
> monolithic PLL's. (Perhaps in early telecom days SAW filter applications
> required this, but today's receiver designs (at least in XAUI) will not be
> using such costly techniques.) Moving the jitter tolerance break point out
> to ~5 MHz or so would allow us to track more of the jitter components and
> perhaps even make the Tx design easier (smaller capacitors, etc.).
> Soo, would there be any objections to moving the tolerance break point out?
> I'd like to get some feedback on this before the Austin meeting if
> - Richard Dugan