Using the Allan variance and power spectral density to characterize DC nanovoltmeters

When analyzing nanovoltmeter measurements, stochastic serial correlations are often ignored and the experimental standard deviation of the mean is assumed to be the experimental standard deviation of a single observation divided by the square root of the number of observations, This is justified only for white noise. This paper demonstrates the use of the power spectrum and the Allan variance to analyze data, identify the regimes of white noise, and characterize the performance of digital and analog de nanovoltmeters. Limits imposed by temperature variations, 1/f noise and source resistance are investigated.