An apparatus for compensating the phase rotation in the feedback loop of a cartesian feedback power amplifier in a final transmitter stage for quadrature modulation of the complex difference signal between a complex input signal and the corresponding complex feedback signal with a complex modulation...http://www.google.de/patents/US5483681?utm_source=gb-gplus-sharePatent US5483681 - Apparatus for compensating of phase rotation in a final amplifier stage
