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

摘要

With the increasing importance of spectral efficiency in mobilencommunications, the power amplifier linearity has become a criticalndesign issue for nonconstant envelope modulation. Imperfections innquadrature modulators and demodulators-gain and phase imbalance and DCnoffset-have a crippling effect on amplifier linearization circuits, anfact that has previously been noted experimentally. This paper is thenfirst analysis of these effects on an adaptive predistorter. The primarynresult is an expression that provides an explicit tradeoff amongnintermodulation power, accuracy of the quadrature modulator andndemodulator, and speed of adaptation. Another useful result is a simplenand easily measured error figure for quadrature modulators andndemodulators