Correlated Multiple Sampling (CMS), which is an extension of Correlated Double Sampling (CDS), is a very popular noise reduction technique used in the readout chain of image sensors. It has been analyzed in the literature, showing that, with an increasingly number M of samples, the
total noise tends to a limit value dominated by the pixel 1/f noise. Nevertheless, this approach fails to explain why, in some cases, the total noise measurement may reach a minimum before, against all odds, finally growing with M. This paper shows that an explanation can be found if the pixel
noise Power Spectral Density (PSD) varies in 1/fE with a frequency exponent E > 1 instead of E=1.