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PM-AM Correlation Measurements and Analysis



David A. Howe, Archita Hati, Craig W. Nelson, Danielle G. Lirette


We measure and analyze effects of nonlinear mixing of phase-noise modulation (PM) and amplitude-noise modulation (AM) in an oscillating signal by real-time correlations measured in the cross power spectral density (CPSD). We outline sensitive measurements of PM-AM correlation coefficients by means of a time-averaged CPSD measurement technique. Separate but simultaneous PM and AM measurements using a two-channel cross-correlation spectrum analyzer, quantifies the relevant effects of intermodulation mixing with excellent sensitivity compared to traditional 3IM measurements and the scatter-plot correlation technique. Time-averaged cross-spectrum measurements provide good estimates of correlation coefficients as a function of Fourier frequency (f). We use normalized PM-AM CPSD measurements of a 645 MHz quartz-MEMs oscillator as an example and find that 1/f PM-AM CPSD is exactly correlated, even for very widely differing levels of PM and AM noise, in which individual PSDs of PM and AM differ by >40 Db (or, greater than a factor of 10,000). We also verify that white-PM noise has uncorrelated PM-AM CPSD.
Proceedings Title
Proceedings of the 2012 IEEE International Frequency Control Symposium
Conference Dates
May 22-24, 2012
Conference Location
Baltimore, MD
Conference Title
2012 IEEE International Frequency Control Symposium


3IM, Amplitude noise, Correlation, Cross-spectrum, Digital AM measurement, Digital PM measurement, Duffing, IM3, Intercept, MEMS, Nonlinear, Phase noise, Resonator


Howe, D. , Hati, A. , Nelson, C. and Lirette, D. (2012), PM-AM Correlation Measurements and Analysis, Proceedings of the 2012 IEEE International Frequency Control Symposium, Baltimore, MD (Accessed December 6, 2023)
Created May 24, 2012, Updated February 19, 2017