Errors present in the output of an amplifier (10) are compared with the amplifier input in a control unit (24) to derive corrected coefficients for a look-up table used by predistorter (12) to eliminate distortion in the output of the amplifier (10). Depending on the format of the predistorter (12), at least some of the coefficients are corrected using measured errors that have been rendered independent of the input signal's amplitude.