A theoretical model based on Linear Cascaded Systems (LCS) theory was developed in order to study the noise properties of a commercially available high resolution CMOS sensor (RadEye CMOS). The parameters studied were the Normalized Noise Power Spectrum (NNPS) and the Noise Transfer Function (NTF). The modeling was applied to digital mammography conditions. It considered the physical properties of the scintillator incorporated into RadEye CMOS as well as the probability of X-ray absorption directly in the photoreceptor. Furthermore it took into account the pixel pitch and the thickness of the photoreceptor. The model was compared with experimental results obtained from literature. The NTF curves were I good agreement with the experimentally determined. NNPS curves deviations were attributed to the effect of the digitization procedure as well as the non-linear behavior of CMOS detector.