ONLY one ref multiplier?: PMA clock reference
Your proposal sounds good,i.e. to have only a single clock multiple
(1/4 division) for the reference clock, but I am not sure if this is wise.
a lower rate frequency clock autmatically implies worse jitter performance for
the PLL's. This is not as much of an issue for the WDM case as it is for
but every psec (or even sub-ps) counts for the serial versions. So I would opt
to be NOT too restrictive in saying only 155-156Mhz xtal osc are allowed.
Note that the present community of OC192 people use the higher clock rate
for the reference. Are there any that uses the 155MHz as a reference for
OC192? Having said all this ... are there readily available
644.53125MHz xtal osc.?
In a message dated 6/16/00 1:03:26 AM Pacific Daylight Time,
> Sorry about the confusion. I did mention in my note that there would have
> two optional clock references specified in the XBI, one for the LAN PHY
> other for the WAN PHY.
> What I should have said is that only one clock MULTIPLE be specified. For
> example, 161.1328125 MHz is 1/4 of 644.53125 MHz and 155.52 MHz is 1/4 of
> MHz. One fourth is a good multiple to use. This means that other multiples
> should not be required anywhere in the standard, even optionally (i.e.
> 1/16, 1/1, etc.)
> Best Regards,
> "Lysdal, Henning" wrote:
> > Rich,
> > I don't see how you can avoid having separate reference clocks for LAN
> > WAN (with realistic PLL design).
> > In the LAN case there are several options
> > 156.25 MHz (seems to be prefered among serial folks)
> > 161.1328125 MHz
> > 644.53125 MHz
> > In the WAN case the OIF specifies 622.08 MHz. I know of a lot of people
> > also like 155.52 MHz
> > Now the problem is: how do you synthesize 9.95328 GHz and 10.3125 GHz
> > the same reference. If you use a 10 kHz reference, it's easy, but you
> > most likely have problems with transmit jitter.
> > So I haven't been discussing the WAN case at all, since I was under the
> > impression that WAN PHYs will use existing SONET SerDes using 622.08 MHz
> > refck.
> > Regards,
> > Henning