Study, Based On The The Doherty Theory Of L-band 40w Amplifier

The power amplifiers (PA) are the one of most important blocks in wireless communication systems. The wireless communication technology development needs the better and better performances of PA. In the present-day wireless communication systems, spectrum is expensive, and newer technologies demand transmission of maximum amount of data with minimum spectrum usage. This requires complicated modulation techniques, for example, WCDMA, it lead to wide, dynamic signals that require linear PA. Although linear amplification is achievable, efficiency such as PAE is always sacrificed by the linearity improvement. Most of the modern wireless applications are used of non-constant envelope modulation techniques with a high peak to average ratio. Linearity is a critical issue, power amplifiers implemented in such applications are forced to operate at a backed off region from saturation. Therefore, in order to overcome the battery lifetime limitation and PA's MTBF, a design of a high efficiency power amplifier is necessary. The Doherty technique can be good for resolving these problems.A 40W L Band Doherty PA will be introduced in this thesis. The techniques related to the PA design such as match theory, Doherty theory, load pull theory and the bias theory will be argued and researched. And the way which uses the load pull theory and the Freescale's LDMOS PA software pack in the ADS will be stressed. In this way, the match can be changed by difference demand to come to an optimal design. At the same time, Use a novel theory to settle the question some amplifier can't be used in the Doherty circuit and test this theory by ADS simulation.The thesis includes six chapters. The first chapter is exordium. In the second chapter the classes of PA operation and the characteristics will be introduced. In the third chapter the Doherty theory and the related RF theory will be analyzed in detail. In the fourth chapter the Doherty PA will be designed and simulated on the ADS bench, and the load pull theory will be used in this chapter. In the fifth chapter the way which can settle the question some amplifier can't be used in the Doherty circuit will be introduced and tested, and infection of auxiliary PA's bias grid voltage to linearity, PAE and gain will be analyzed. At the same time, envelope track theory will be used to improve the linearity of DPA. Sixth chapter is conclusion.