An adaptive digital method of imbalances cancellation in LINC transmitters

The linear amplification using nonlinear components (LINC) technique is a well-known power amplifier linearization method to reduce adjacent channel interference in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method is described which corrects any gain and phase imbalances in LINC transmitters mainly due to the unmatching of the two amplifier paths. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficient to adjust gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator imbalances and loop delay. A computer simulation has been carried out to verify the method functionality.