Study of PM Noise and Noise Figure in Low Noise Amplifiers Working under Small and Large Signal Conditions

A study of the noise performance of low noise amplifiers (LNAs) working under different operating regimes is presented. The LNAs have been characterized through the measurement of phase modulation (PM) noise power spectral density as a function of carrier power level. The degradation of the amplifier noise figure (NF) due to input power is obtained from the residual PM white noise. Measurements show that the LNA NF can increase dramatically with the gain compression level. The growth of NF in nonlinear operating conditions can be explained due to the gain compression itself and the increasing level of the internal noise added by the amplifier. The flicker PM noise behavior introduced by the amplifier is also discussed.