Artifacts and Errors in Cross-Spectrum Phase Noise Measurements

Grafico Rumore Segnale seminario Enrico Rubiola





Saletta Conferenze, edificio M, piano interrato 


ore 11:00 

Questo seminario vuole far luce su diverse problematiche che si riscontrano nella misurazione del rumore di fase. 

Il Prof. Enrico Rubiola darà alcuni suggerimenti per mitigare il problema. 



Prof. Enrico Rubiola 

CNRS FEMTO-ST Institute (Besançon, Francia), INRiM 



This article is intended to give a warning about: (i) the internal processing inside the phase-noise analyzers, (ii) the oscillators whose white phase noise floor seems too low, chiefly the 100-MHz OCXOs, and (iii) the need to introduce in the domain of phase-noise measurements the basic concepts of uncertainty found in the International Vocabulary of Metrology (VIM). 

 The measurement of low-noise quartz oscillators, or of other lownoise oscillators exhibiting a noise floor of the order of -180 dBc/Hz or lessrelies on the cross-spectrum method. The measurement may take long time, from hours to 1-2 days, for the number of averaged cross spectra to be sufficient to reject the background of the noise analyzer

That saidsomething anomalous is often seen in a region approximately one decade wide, located where higher-slope noise joins the white floor or the 1/f noise. The plot may be quite thick and irregular, and a dip may appearwhere the phase noise looks lower than the white noise floorSuch anomalies reveal something worse. The white region of the PM noise spectrum may be affected by gross errors and, in the not-so-rare worst case, is a total nonsense. We address the problem trough a simple experimentwhere we insert a dissipative attenuator between the oscillator and the PN analyzerSurprisingly, in some cases the attenuation results in a lower noise floorSuch erratic behavior is reproduciblehaving been observed separately in three labs with instruments from the two major brands. We provide the experimental evidence, the full theory, and suggestions to mitigate the problem.

Enrico Rubiola

Enrico Rubiola is a professor at the Université de Franche Comté and a researcher with the Department of Time and Frequency of the CNRS FEMTO-ST Institute, Besançon, France, and an associated researcher at INRiM, the Italian institute of primary metrology in Torino. Formerly, he was a professor at the Université Henri Poincaré, Nancy, France, and an assistant professor at the Politecnico di Torino. He was also a guest professor at the Università di Parma, Italy, and a guest scientist at the NASA/CALTECH Jet Propulsion Laboratory.

Ultima modifica: 25/02/2020 - 11:00