[time-nuts] Ultra low phase noise floor measurement system forRF devices.
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Fri Mar 30 19:55:33 EDT 2007
> 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
Use of the cross correlation technique and cancellation of the carrier in the interferometer/bridge allows use of a
source with a phase noise well above that of the measurement system.
The test signal phase noise is common to both correlator inputs and is
rejected by the cross correlation technique.
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