Re: Xaui jitter tolerance
The result is a zero-to-peak frequency deviation, not p-p as stated.
-__--__--__-_-_______--_-_--_--_--___-_-_-_-_-_---__-_-____
Larry DeVito
Analog Devices RSTC-121,
804 Woburn St, Wilmington MA 01887
vox= 781 937 1323 fax= 781 937 1010
email= lawrence.devito@xxxxxxxxxx
_-__-----_---_---_---_-___-_-_-_-__--__--_-_-_-_-_----_-_-
> From owner-stds-802-3-hssg@xxxxxxxx Thu Nov 30 13:21:26 2000
> Subject: Re: Xaui jitter tolerance
>
>
> Ali, to calculate the frequency change required for sinusoidal jitter:
> multiply
>
> PI * Jitter(in UIp-p) * Modulation Frequency(in Hz)
>
> The result is frequency in Hz p-p which can be converted to ppm.
>
> -Paul Wilson
> Nortel Networks
>
> -----Original Message-----
> From: Ali Ghiasi <aghiasi@xxxxxxxxxxxxx>
> To: Mike Jenkins <jenkins@xxxxxxxx>; 'richard_dugan@xxxxxxxxxxx'
> <richard_dugan@xxxxxxxxxxx>
> Cc: stds-802-3-hssg@xxxxxxxx <stds-802-3-hssg@xxxxxxxx>; Ali Ghiasi
> <aghiasi@xxxxxxxxxxxxx>
> Date: Thursday, November 30, 2000 4:52 AM
> Subject: Re: Xaui jitter tolerance
>
>
>
> HI
>
> As Rihcard and Ed mentioned most SerDes have BW at least 3 time higher
> as given by baudrate/1667. Increasing the corner frequency higher will
> help transmitter with possible clock and PS noise to pass the jitter
> specifications. Mike is also correct if we increase the corner
> frequency significantly then we will violate +/- 100 PPM clock
> specifications.
>
> The current baudrate/1667 template fits under the +/-100 PPM
> jitter assuming square wave and the jitter will change instantaneously
> from min to max, which is rare. There might be some room to
> increase the corner frequency and still not violate the +/- 100PPM.
>
> Thanks,
>
> Ali Ghiasi
> Broadcom
>
>
> Mike Jenkins wrote:
> >
> > Richard, Ed,
> >
> > I disagree with the proposal to increase the jitter corner frequency
> > higher than baudrate/1667. First, the number 1667 is tied to the
> > assumed +/-100 ppm reference frequency tolerance. I can't say it's
> > an inviolable law of physics, but 1667 does make sense. (I'll try
> > to dig up the explanation, if you want it.)
> >
> > Second, tracking jitter isn't always a good idea. One Fibre Channel
> > jitter test pattern, CJTPAT, is designed to shift edges late, then
> > early, repetitively. If the RX follows, it's jitter tolerance is
> > reduced compared to averaging out this input jitter and keeping the
> > sampling position fixed.
> >
> > If you would like more feedback on your proposal, I would suggest also
> > posting it to the Fibre Channel phy layer reflector, t11_2@xxxxxxxxxxxx
> >
> > Regards,
> > Mike
> >
> > Ed Grivna wrote:
> > >
> > > Hi Richard,
> > >
> > > 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.
> > >
> > > Regards,
> > >
> > > Ed Grivna
> > > Cypress Semiconductor
> > >
> > > > 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
> > > > possible.
> > > >
> > > > - Richard Dugan
> >
> > --
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > Mike Jenkins Phone: 408.433.7901 _____
> > LSI Logic Corp, ms/G715 Fax: 408.433.7461 LSI|LOGIC| (R)
> > 1525 McCarthy Blvd. mailto:Jenkins@xxxxxxxx | |
> > Milpitas, CA 95035 http://www.lsilogic.com |_____|
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>