Measurement, Analysis and Estimation of the Noise Figure of an AGC Amplifier

The front end of a radio receiver contains an AGC amplifier so as to maintain the specified performance over a wide input dynamic range of the receiver. The carrier to noise ratio or the bit energy to noise density ratio at the demodulator input is directly proportional to the noise figure of its front-end AGC amplifier. Hence, it is important to estimate the noise figure of an AGC amplifier over its input dynamic range or AGC range while designing such radio reception systems. The paper describes an analytical method to estimate the noise figure of an AGC amplifier and also an experimental method (called the gain method) to measure its noise figure practically. Using the analytical method, the noise figures of a 70 MHz double-stage AGC amplifier have been estimated. The comparison between the estimated values and the measured values is also presented in the paper.