Improving Linearity of LINC Power Amplifiers with Gain and Phase Error Calibration

In this paper the effect of imbalances between the two branches in LINC transmitters has been analyzed. Then these imbalances have been compensated in the proposed structure adaptively. Conjugate gradient algorithm has been used in the proposed structure to find optimum gain value of each branch for calibrating imbalances. These complex values changes automatically in a way to minimize phase and gain errors between two branches. In this structure power amplifiers are modeled as a complex gain which its value depends of input signal level. The final structure has been simulated using MATLAB. From simulation results, the LINC structure modified with conjugate gradient algorithm has improvement in power spectrum density in adjacent channels. One of the main advantages of the proposed structure is its high convergence speed which can make in usable in modulations with higher data transmission rate.