In this article, the impact of the combination of the column-level gain and the correlated multiple sampling (CMS) on the noise of CMOS image sensor (CIS) readout chains is first analyzed. The theory is then validated experimentally with CIS readout chains embedding two different pixels, a variable gain column-level amplifier (CLA) and a passive switched-capacitor (SC) CMS circuit. The noise measurements include photon transfer curves (PTCs) for different gains and pixels and they show reasonably well that CMS reduces the 1/f noise by about 33% for order 8 as expected theoretically.