Digital compensation of branches imbalance effects in LINC transmitters

A study of the branch complex gain imbalance effects, as a distortion source, in term of adjacent channel power ratio and signal dynamic range is carried out in this paper. Although a linearity improvement is achieved using a digital predistortion when considering the imbalanced LINC transmitter as a memoryless nonlinear system, this method suffers from a limited dynamic range restitution at the output of the LINC transmitters. The inappropriateness of this technique was demonstrated for highly imbalanced branches in the context of 3G signal excitation. Alternately, a mixed DSP/FPGA implementation of an enhanced LINC transmitter capable of minimizing and correcting RF impairments effects is proposed in this paper.