[time-nuts] Comparison of Logic Standards for Clock Distribution
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Mon Oct 30 20:01:29 EST 2006
Stephan Sandenbergh wrote:
> Hi Bruce,
>> Whilst there are many books available of clock distribution within
>> digital systems (eg http://cva.stanford.edu/books/dig_sys_engr/) and
>> within VLSI chips, there is little specific info published in book form
>> on precision clock/frequency standard distribution on the larger scale
>> such as within or between buildings.
> What could the reason for this lack of information be? Is the topic just not
> interesting, or is the distribution of accurate clock signals not a big
> issue? I can't really imagine that either of these are the case.
>> The difficulties associated with high speed clock distribution in
>> silicon VLSI chips currently limits the maximum clock speed of such
>> chips to around 4GHz or so.
>> Simply using higher resolution lithography to produce smaller
>> transistors doesn't help much. Optical techniques for clock distribution
>> on chip are being investigated.
>> One can glean some idea of how this may best be done by looking at how
>> NIST, USNO, NIST, PTB, etc pipe the standard frequencies from their
>> various atomic standards around. Current designs for modern radio
>> telescope arrays such as the Atacama millimeter array and upgrades of
>> various existing instruments give a good indication of current best
>> practice for such instruments that require state of the art timing
> It is strange that these guys know how it is done and not publishing it. I
> guess there are a few papers available on this issue. Could you maybe point
> me to some of them?
> Thanks for the help,
> Stephan Sandenbergh
> time-nuts mailing list
> time-nuts at febo.com
The audience for such books is probably considered too small to justify
the publication costs.
The techniques and issues involved have been known for decades.
Using local RF and DC feedback in distribution amplifiers to minimise
flicker phase noise.
Mitigating the effect of the variation in the phase shift of filters and
tuned circuits with time and temperature.
Shielding and grounding issues.
Cable propagation delay stability.
Stabilisation of optical fibre propagation delays.
Most of these issues have been addressed in papers published decades ago.
Slightly off topic the following paper provides a more comprehensive
theory of oscillator phase noise than the familiar Leeson model which
too many (including Ulrich Rohde in one notable example) have blindly
applied to calculation of the phase noise floor even when the
assumptions made in the model are not satisfied.
Papers/web pages of frequency standard distribution systems:
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