The Design Of A Predistortion Power Amplifier Based On Improved DGS

With the increasing demand for the mobile communication services in modern society, the radio frequency resources inevitable is not sufficient, severely limit the rapid development of mobile communications. High data rate and high efficient of the radio frequency resources are the effective way to solve the problem. So the modern communication systems mainly use the modulating signal with high rate,amplitude fluctuation within a large range and high PAPR, which demands higher for the radio frequencies section of mobile communications system, especially have a challenge to the design of more sensitive radio frequencies power amplifier. Power amplifier often uses the back-off technology in many systems, the linearity is improved, but the efficiency will seriously deteriorate, so designing the RF power amplifiers with high efficiency and high linearity is necessary.Due to lack of large signal parameters of power transistor, the design of RF power amplifier has always been a difficult problem in circuit design. This article researches on some design methods of basis RF power amplifier, and designs a radio frequencies power amplifier system with three stages using Load-pull test bed. The test results indicate that the performance of RF power amplifier system satisfy the requirement of the design. Compared with other methods, the testing system can accurately measure many important indicators of RF power amplifier in big-signal state, such as the input and output impedance, etc. It provides Large-signal parameters used in the design of RF power amplifier, The Load-pull test platform and the ADS software can simplify design process of power amplifier, and improves design technology of power amplifier.The linearization technology is the main method to improve the linearity and efficiency, this article analysis some popular linearization techniques. Considering the cost and complexity of circuits, the analog pre-distortion techniques is used to improve the design RF power amplifier linearity. The article firstly designs a coupler with 90 degree, uses it with some non-linear devices to design a simple third-order intermodulation signal generator to improve the linearity, and at the same time, designes a branch to compensate the undesired fundamental frequency signal to achieve the best results, and finally simulation and debug the module in actual circuit. By simulation and verification, the results achieve the original design requirements. This analog predistorter has a simple structure, easy implementation, low cost, good performance characteristics.Another way to improve power amplifier efficiency is to suppress the harmonics of power amplifier, the traditional method is to use various filters, but this method is high cost, and increases the space of the power amplifier. DGS (Defects ground structure) can be used to suppress the output harmonics and the method is lossless, costly, and need occupied area. The artical has done a lot of research and analysis on DGS and raises a new type DGS, the structure have a big improvement compared with the previous structure. This paper used the new type DGS in the final stage power amplifier, the simulation and test results show that the new DGS without increasing the cost and size of amplifier, The new structure is applied to the RF power amplifier, not only can suppress the harmonics and solve the problem that bias line is too narrow.