Linearized Doherty amplifier using a new digital predistorter compensating frequency-dependent intermodulation distortion for mobile radio

A linearized Doherty amplifier is proposed that employs a digital predistorter to compensate the frequency-dependent intermodulation distortion, the so-called memory effect. This scheme effectively reduces intermodulation distortion and makes it possible for the Doherty amplifier to operate near its saturation output power. A 2-GHz band 1-W class linear amplifier is investigated that has a Doherty amplifier with Class-F operation and a digital predistorter designed to cancel third-order intermodulation distortion. In an experiment, the drain efficiency and the third-order intermodulation distortion at 3-dB output back-off from saturation output power are improved to 55% and less than -60 dB, respectively. The proposed technique can be extended to cover higher-order intermodulation distortion and will minimize the power consumption of the base station amplifiers in cellular communications systems.