Study On RF Feedforward Power Amplifier

As the number of global wireless useres increasing rapidly, the frequency source becomes more and more crowded. At the same time, the new linear modulation techniques with varying envelop, such as the QAM and QPSK, are emphasized in recent years, which bring forward much more strict linearization target to the RF system. Feedforward has been developing and becomes the most popular linearization technology due to its many merits, such as high stability, wide bandwidth, good cancellation efficiency.Through the research and analysis about many papers of feedforward amplifier system, this paper proposed the basic knowledge of the nonlinear, the characteristics of the nonlinear distortion and the principium of usual linearization technologies in the paper. The traditional feedforward amplifier has been developed for a long time, but there are still some problems needing be solved now. For example: the output power attenuation, the strict demands for the error amplifier and the complicated adjustment.In response to these issues, this paper indicates that one of the important causes that affect the output power and linear based on the traditional feedforward circuit is the consume and the nonlinear distortion of componentes. First, there is a lower signal power in Loop1 which is distorted easily by the output noise. This small signal after the synthesizer 1 is a challenge for the adaptive control. This paper proposes an idea that the principal signal and error signal maintain in the input signals of error amplifier at the same time. Secondly, the paper analyzes the relation that the loss and nonlinear of device against amplitude-mismatch and phase-mismatch based Loop1 and Loop2. The expression was proposed which can display the conection. In the end, the paper design a feedforward power amplifier system with a principal wave amplifier. In the developed amplifier sysrem, the output power has a great improvement; the gain of error amplifier has been decreased effectively; the system has a lower nonlinear distortion and makes a flexible regulation of feedforward system.