[time-nuts] What is a Time-Nut grade Zero Crossing Circuit?
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Jul 31 12:02:15 EDT 2008
Hello Bruce,
I believe a driver for an FPGA running at 350MHz was the initial query, 6GHz
BW and crystal filters are probably overkill.
bye,
Said
In a message dated 7/31/2008 01:59:34 Pacific Daylight Time,
bruce.griffiths at xtra.co.nz writes:
Yes, however it is quieter and adding duty cycle stabilisation feedback
fixes that problem.
For even lower noise, bandpass filter the OCXO output (a crystal filter
is particularly effective).
Its not too difficult to drop the noise floor to a few tens of femtosec.
The drawbacks being the cost, and the need to regulate the bandpass
filter temperature to minimise phase shift variations with ambient
temperature.
You would also need to use a quieter clock driver.
It may even be necessary to use a well designed bandpass limiter to
increase the signal zero crossing slew rate before using a 6GHz
bandwidth clock driver.
However the cost and complexity probably isnt justified when driving an
FPGA which may have tens of picoseconds of jitter.
Bruce
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