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Merits of PM Noise Measurement over Noise Figure: A Study at Microwave Frequencies



Archita Hati, David A. Howe, Fred L. Walls, D. Walker


This paper addresses two issues: (i) it compares the usefulness of phase-modulation (PM) noise measurements vs. noise figure (NF) measurements in characterizing the merit of an amplifier, and (ii) it reconciles a general misunderstanding in using ¿174 dBc/Hz (relative to carrier input power of 0 dBm) as thermal noise level. The residual broadband (white PM) noise is used as the basis for estimating the noise figure (NF) of an amplifier. We have observed experimentally that many amplifiers show an increase in the broadband noise of 1 to 5 dB as the signal level through the amplifier increases. This effect is linked to input power through the amplifier¿s nonlinear intermodulation distortion. Consequently, this effect is reduced as linearity is increased. It is important to note that NF is sometimes used as a selection criteria for an amplifier but yields no information about potentially important close-to-carrier 1/f noise of an amplifier, whereas PM and amplitude modulation (AM) noise measurements do. We have verified theoretically and experimentally that the single-sideband PM (and AM) noise floor due to thermal noise is ¿177 dBc/Hz, relative to a carrier input power of 0 dBm.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control


amplitude modulation noise, broadband noise, feed forward amplifier, flicker noise, noise figure, non-linear intermodulation, phase modulation noise, power spectral density


Hati, A. , Howe, D. , Walls, F. and Walker, D. (2006), Merits of PM Noise Measurement over Noise Figure: A Study at Microwave Frequencies, IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, [online], (Accessed April 15, 2024)
Created September 30, 2006, Updated October 12, 2021