This paper presents a study of MOSFETs' linearity, exploiting a simplified version of the charge-based EKV model. It allows to deduce analytically the one-tone and two-tone harmonic distortions introduced by the nonlinear ID-VG MOSFET characteristic as a function of the inversion coefficient. The short-channel effects are included in order to address nanoscale MOSFET performance. The analysis is validated through comparisons with the BSIM6 model and measurement results from 28-nm bulk CMOS devices. By means of this model, the designer can choose the appropriate bias region for the critical devices of a circuit depending on the system requirements.