ABSTRACT
Noise, from a variety of sources, distorts signals of interest, setting a lower bound on the minimum detectable signal. The intrinsic transistor noise sources include thermal noise, a white band noise source with a constant value spectral density, and flicker noise, which varies inversely with the frequency, gate current noise, and shot noise. For any mixed signal, multi-stage system, including amplifiers, the voltage noise at the input is more important to consider than the output noise. The noise at the input node of any stage is determined from the gain of the output signal with respect to the input signal. Amplifier noise is measured at the output directly using the spectrum analyzer and a voltage buffering circuit to prevent the analyzer from loading the amplifier. The noise efficiency factor is a popular metric for characterizing noise and power of a system.
