A method for the improved accuracy of LO phase adjustment in the feedback circuit of a Cartesian amplifier

摘要

Separate test signals are applied to the I and Q channels of a Cartesian amplifier to provide separate estimates of the phase shift setting for the LO phase shifter 442 in the feedback circuit. The average of the two phase shift settings is applied to the phase shifter, giving improved loop IQ phase balance in comparison with calibration using only one test signal. Reduced tolerance 90 degree LO phase shifters 436,422 can be used. Loop stability and wideband noise performance are improved. Test signals may be applied to determine amplitude imbalance. The technique may also be applied to linearized amplifier systems using predistortion.