In this paper, starting from an accurate MOSFET model, new expressions for calculating the harmonic distortion coefficients of active-loaded CMOS amplifier are derived. The accuracy of derived expressions is demonstrated on a circuit example. The proposed expressions are especially suitable for investigation of the harmonic distortion properties of CMOS amplifiers. The results are not obtainable with conventional SPICE simulation, therefore derived expressions provide the possibility of completing the simulation with hand calculations in the design of low-distortion and low-cost CMOS operational amplifiers. (C) 1997 Elsevier Science Ltd.