QUADRATURE MODULATOR

摘要

A quadrature modulator that compensates for nonlinear distortion corresponding to time-varying nonlinear characteristic and removes nonlinear distortion suitably from the transmission signal. A QAM modulator (6) in the quadrature modulator comprises a demodulator section (14) for demodulating a modulated signal y(t) passing through a nonlinear part (10). The demodulated signals yi(t) and yq(t) from the demodulator section (14) are supplied to a modeling circuit (16). The modeling circuit (16) also receives predistortion signals Pi(t) and Pq(t) from predistortion circuits (12a and 12b). The modeling circuit (16) forms an envelope model of the nonlinear part (10) according to the signal Pi(t), Pq(t), yi(t) and yq(t) to reflect the model in the predistortion performed by the predistortion circuits (12a and 12b). In this manner, nonlinear distortion is removed from transmission signals by dynamically determining a constantly changing envelope model and distorting signals based on the determined envelope model.