An iterative calibration technique for LINC transmitter

The linear amplification using nonlinear components (LINC) is one of the most promising techniques that can simultaneously provide high efficiency and high linearity. However, it is sensitive to in-phase/quadrature imbalances in quadrature modulators (QMs), and to gain/phase mismatches between two PA paths. In this paper, we present an iterative calibration technique to compensate for the imbalances and mismatches, based on the observation that when the I/Q imbalances in the QM are ideally calibrated, the PA input signal has constant envelope, which allows the PA to be characterized as a linear gain model. It allows us to estimate the calibration parameters without modeling the nonlinear characteristics of the PAs. An adaptive implementation scheme is given. Simulation results demonstrate that the proposed technique accurately determines the calibration parameters, yielding significant performance improvement of the LINC transmitter.