A method used in a transmitting device comprising a non-linear amplifier and a digital predistortion (DPD) circuit. The method updates real and imaginary look-up tables used by the DPD. The method comprises: i) time-aligning a complex input signal, A, and a complex output signal, E. Signal A is a scan from 0 to a maximum value comprising N discrete points and signal E also comprises N discrete points. The method comprises: ii) performing an array division of A/E=(Yr, Yi), where Yr and Yi are the real and imaginary components, respectively; and iii) computing a real curve and an imaginary curve using curve-fitting algorithms that best fit the data with coordinates (|A|, Yr) and (|A|, Yi). The method stores the real curve in a real lookup table (LUT) and the imaginary curve in an imaginary lookup table (LUT). The method iteratively updates the real LUT and the imaginary LUT.