Using Superposition Principle with Noise Sources
When multiple sources of noise are present, their contributions add in proportion to their
noise powers, not the noise voltages. Uncorrelated noise adds by the sum of the individual
noise powers. This is easy when working with power, but usually we work with voltages or
currents, so we square the values. For example, given uncorrelated voltage noise sources
e1, e2 ... en, the total noise, et, is given by the square root of the sum of the squares of the voltages.