Phase Noise Measurement using Cross-Correlation

Learn more about Phase Noise measurements and its use cases:
keysig.ht/p2uccz
Gregory explains how Phase Noise below the measurement setup noise-floor is measured, using two separated analyzers and cross-correlations in the frequency domain.
Some methods of Phase Noise measurement are limited by the analyzer own phase noise profile, as its own noise adds to the measured signal, corrupting its profile.
Using two separated analyzers, with uncorrelated noise profiles, it is possible to perform cross-correlation that uncouple the measured noise from the setup added phase noise.
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[@AllElectronicsChannel]

Learn more about Phase Noise measurements and its use cases:
keysig.ht/p2uccz

[@se2702]

Your knowledge and passion of the subject matter is exemplary. You present the material thoroughly yet succinctly and videos are just the right length!

[@AllElectronicsChannel]

Thanks! 🙏🏼🙏🏼🙂

[@ahmedgaafar5369]

you are really a great teacher Greg...i knew that the video will be great ....thank you...brilliant explanation for the correlation process not seen anywhere else.

[@AllElectronicsChannel]

Many thanks!

[@ahmedgaafar5369]

coming here pressing the like button before even start watching ...i am certain it will be a great video as always.

[@anameisrequired3729]

Very nice! Thank you!

[@AllElectronicsChannel]

Thank you too!

[@aduedc]

Another indirect way is to measure RMS jitter, with the help of GPSDO. Then you can calculate phase noise from jitter, using Shannon's law.
You have similar problem as jammer signal in receivers. A strong signal next to a weak signal. To increase dynamic range tune out the carrier when measuring the offset, by changing the span. You probably could use notch filter on the carrier when measuring the offset power.
Measuring anything with dynamic range of more the 90 dB is challenge.

[@AllElectronicsChannel]

Hi man! The GPSDO will reduce the phase noise of the local oscillator? I understand that it is a slow action correction loop... the oscillator needs to be very pure for low jitter measurements. Am I missing something?

[@aduedc]

@@AllElectronicsChannel For faster convergence, you might try Rubidium Frequency Standard, as the LO of the measurement device.
Also, note that your attenuator @5:41 adds phase noise.

[@erenjaeger5344]

But what if we take the cross correlation in the time domain and average?
Since jitter is the time domain equivalent of phase noise, would this reduce the jitter of the signal?

[@AllElectronicsChannel]

I don't see why it would not work!

[@user-qp2ps1bk3b]

nice!

[@electromagnetic9469]

if possible please share the code for this correlation measurement.

[@AllElectronicsChannel]

Code is available on Patreon.

[@drewwollin3462]

There are often spurs on a phase noise plot. What causes them and how can they be minimised?

[@AllElectronicsChannel]

They may be the transistor trying to oscillate at other frequencies, low frequency RF signals that are up converted, anharmonics of a crystal, some parasitic oscillation in the biasing circuit, oscillation by negative resistance with the measuring setup...

[@drewwollin3462]

Since I wrote the comment, I have heard that one of the biggest causes of spurs is intermodulation between all the frequency generators in the instrument itself, with the DUT signal. There are many clock signals in a digital device, for CPU, for ADCs, for USB drivers etc. Apparently, it is possible to write a script to take out spurs caused by known intermodulation within the analyser.
The spurs puzzled me as they appear straight away. This is because they are always present. Phase noise on the other hand is random and it takes many samples to detect it, so takes a long time.