A predistortion linearizer using envelope-feedback technique with simplified carrier cancellation scheme for class-A and class-AB power amplifiers

A predistortion linearization method using an envelope-feedback technique i s proposed and implemented in this paper. This linearizer compensates the g ain and phase nonlinearity of power amplifier (PA) simultaneously by contro lling both variable attenuator and phase shifter with the feedback of only the difference signal between input and output envelopes, A new carrier can cellation scheme composed of a minimization circuit, log detector, and vect or modulator is also presented, This circuit achieves adaptive control of t he linearizer by enabling direct measurement of out-of-band power. It is we ll suited to a multichannel system where the allocated channels are time va riant, The principle of the proposed linearizer is described and simple AM- AM distortion analysis is presented analytically and graphically based on t he conceptual schematic diagram. A two-tone test for a class-a PA at 1.855 GHz with frequency spacing of 1 MHz showed intermodulation-distortion reduc tion of maximum 16 dB and stable operation over 5-dB output power variation up to 4-dB backoff from the saturation power level. The proposed linearize r is also applicable to class-AB PA's without further special adjustments. The adaptation circuit is fully implemented with analog integrated circuits , which can further extend its applicability with the integration technolog y.