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Cross-spectrum Measurement of Thermal-noise Limited Oscillators



Archita Hati, Craig W. Nelson, David A. Howe


Cross-spectrum analysis is a commonly-used technique for the detection of phase and amplitude noise of a signal in the presence of interfering noise. It extracts the desired correlated noise from two time series which also contain uncorrelated interfering noise. Recently, we demonstrated that the phase-inversion (anti-correlation) effect due to AM noise leakage can cause complete or partial collapse of the cross-spectral function. In this paper, we discuss the newly discovered effect of anti-correlated thermal noise that originates from the common-mode power divider (splitter), an essential component in a cross-spectrum noise measurement system. We studied this effect for different power splitters and discuss its influence on the measurement of thermal-noise limited oscillators. An oscillator whose thermal noise is primarily set by the 50 ohm source resistance is referred to as a thermally-limited oscillator. We provide theory, simulation and experimental results. In addition, we expand this study to reveal how the presence of ferrite-isolators and amplifiers at the output ports of the power splitters can affect the oscillator noise measurements. Finally, we discuss a possible solution to overcome this problem.
Review of Scientific Instruments


anti-correlation, cross-spectrum, collapse, isolators, oscillator, phase inversion, power spectral density, thermal noise


Hati, A. , Nelson, C. and Howe, D. (2016), Cross-spectrum Measurement of Thermal-noise Limited Oscillators, Review of Scientific Instruments (Accessed April 13, 2024)
Created March 1, 2016, Updated February 19, 2017