An adaptive direct conversion transmitter

An adaptive direct conversion transmitter in which adjacent channel power measurements are used to simultaneously compensate for both power amplifier (PA) nonlinearity and quadrature modulator (QM) errors is presented. The measured results are presented to identify the sensitivity of the quadrature modulator´s parameters (gain and phase imbalance, DC offsets) to temperature and the local oscillator frequency. An analysis of the system is given which details the relationship between the adjacent channel power and the PA nonlinearity and the QM errors; this result explains how a simple algorithm may be used to adjust the parameters based on a scalar measurement of the adjacent channel power. Simulation and measured results of a system using offset QPSK modulation with adaptive PD and QM correction are given