New methods for adaptation of quadrature modulators and demodulators in amplifier linearization circuits

Imperfections in analog quadrature modulators (QMs) and demodulators-gain and phase imbalance and DC offset-have a devastating effect on amplifier linearization circuits. Correction circuits have a simple structure, but their parameters must be adjusted adaptively. This paper introduces two new methods for such an adaptation. The first is based on a training sequence consisting of a tone at one or more amplitudes, and the second needs no training sequence at all. They are faster and more robust than previously published methods