[time-nuts] Ultra low phase noise floor measurement system forRF devices.
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Fri Mar 30 19:14:40 EDT 2007
Mike Feher wrote:
> Well, I must admit I did not read the referenced article, but, he is talking
> about dBc, or relative to the carrier and not kT. So, if the carrier power
> is high enough I suppose it could be done. Even suppose you could measure
> it, what would it take to generate such a pure carrier. That may even be
> more difficult. -
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
It actually measures the additive phase noise of components
(amplifiers, splitters, transformers etc.).
Since it uses a cross correlation technique it can easily achieve a
noise floor below the thermal noise.
Cancellation of the carrier in the interferometer/bridge allows use of a
source with a phase noise well above that of the measurement system.
In is possible to build lower phase noise oscillators using very low
phase noise sustaining amplifiers.
Such amplifiers can be implemented using feedforward correction techniques.
An RF bridge/interferometer is used to null the carrier at the input to
the low noise figure correction amplifier, so that only the phase noise
and other error components produced by the main amplifier are seen by
the correction amplifier the output of which is combined with (correct
delay and gain) the output of the main amplifier to reduce the composite
amplifier phase noise. Phase noise is absent when a carrier is not
present, so the phase noise contribution of the correction amplifier
will be very small if the interferometer/bridge is well balanced. This
technique has been used to reduce the phase noise of microwave
oscillators. In principle there's no reason it cannot be used at lower
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