[time-nuts] Distributed DDS
Florian E. Teply
usenet at teply.info
Mon Feb 7 07:32:51 UTC 2011
On Sun, 30 Jan 2011 23:47:10 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> On 30/01/11 23:08, ehydra wrote:
> > I'm not sure if I overview the problem correctly. Hm, why not run
> > the cable back and measure the round time? Half this time und you
> > know the delay of one way. Then you can shift this with a PLL away.
> > A similar scheme is used in almost all modern PC clock distribution
> > chips. A bunch of PLLs on the chip. Severals are available. For
> > example Cypress Semi.
> The LHC at Cern and associated accelerators build up cable distance.
> They also have a myriad of different timing requirements. Essentially
> they try to do away with them once and for all. I'm not convinced
> they can do all of them in this round... but can't blame them for
> trying. Only then they will learn the real requirements and problem
Another Problem they have at CERN is that basically anything that goes
into the vicinity of the detectors has to radiation-hard to some
very high levels, roughly up to a few hundred MegaRads and 1e15
neutrons/cm^2 for the next upgrade in order to survive for the planned
time spans. Have no idea whether this also goes for the clock
distribution. But this limits the choice of vendors quite a bit.
Just my 2 Cents,
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