A new predistortion linearizer using envelope-feedback technique for PCS high power amplifier application

A predistortion linearizing method using an envelope-feedback technique is proposed and implemented. This linearizer compensates the gain and phase nonlinearity of the power amplifier at the same time by controlling both variable attenuator and phase shifter with the feedback of only the difference signal between the input and output envelopes. Also a new way to achieve signal cancellation is presented with the combination of a minimization circuit, log detector and vector modulator. A two-tone test for a class-A power amplifier at 1.855 GHz with a frequency spacing of 1 MHz showed an IMD reduction of 16 dB maximum and stable operation over 5 dB output power variation up to 4 dB back-off. The proposed linearizer is also applicable to class-AB and class-B power amplifiers without any special adjustments. The adaptation algorithm is fully implemented with analog ICs, which can further extend its applicability with the integration technology.