The effect of quadrature modulator and demodulator errors on adaptive digital predistorters for amplifier linearization

Imperfections in quadrature modulators and demodulators-gain and phase imbalance and de offset--have a crippling effect on amplifier linearization circuits, a fact that has previously been noted experimentally. This paper is the first analysis of these effects on an adaptive predistorter. The primary result is an expression that provides an explicit tradeoff among intermodulation power, accuracy of the quadrature modulator and demodulator, and speed of adaptation, Another useful result is a simple and easily measured error Figure for quadrature modulators and demodulators.