Research Of Linear Channel Amplifier Based On Predistortion

With the rapid development of wireless communication, Microwave power amplifier has a very wide range of applications in the satellite communication system and the mobile communication system. At the same time the requirement of microwave power amplifiers efficiency also raised very tall. But it is depended on the linearity of the amplifier. However, because of the existence of nonlinear distortion, there are adjacent channel emissions during transmission signals. The AM-AM and the AM-PM bring distortion, which will cause intermodulation distortion. So that the adjacent channel will has a certain degree of interference. In addition, due to the pursuit of high efficiency, the power amplifier often works in a saturation state. The higher the efficiency, the more serious of non linear distortion is. Solving nonlinear distortion of the power amplifier has become a very important issue now.Recently, there are amplifier linearization such as power back-off, feedback, LINC, feed-forward and predistortion. Power back-off is simple and easy to realize, but it has low efficiency and it constraints by PldB.Feedback reduces the gain of the amplifier. It generally used in low frequency applications. LINC has high efficiency, but it is used less because of the issue of the matching. Feed-forward has high linearity and wide frequency, but it has a high requirements of the balance degree. Predistortion is characteristic of low price and good nonlinear improvement. This paper is using the predistortion to improve the nonlinear of power amplifier.This paper first describes the basis theories of power amplifier.So that we can have a detailed understanding of power amplifier before the design of linear channel amplifier. Then it analyzes the nonlinear distortion of power amplifier such as the AM-AM and AM-PM. It also analyzes nonlinear indexes as P1dB, IP3and ACPR. This paper presents some linearization method such as power back-off, feedback, LINC, feed-forward and predistortion. After all we select predistortion to linearize the amplifier. At last this paper designs the linear channel amplifier with the research of the predistorter. This design is verified to be exactly by simulation with the ADS software. At the end of this paper, I use the Protel99SE software to design a PCB of the linear channel amplifier.