Doherty Power Amplifier

The current wireless communication systems have made significant progress toward increased bandwidth and number of carriers for high-data-rate applications. Memory effects, however, make it very difficult to design a high-power amplifier with a wide instantaneous bandwidth. In addition to bandwidth concerns, the instantaneous transmit powers of the wireless communication systems, such as CDMA-2000, wide-band code division multiple access (WCDMA), orthogonal frequency division multiplexity (OFDM) and so on, vary widely and rapidly, carrying high peak-to-average ratio (PAR) signals. The base station power amplifiers for the systems require a high linearity to amplify the high PAR signal source without distortion. To satisfy linearity requirements, the power amplifiers are usually biased at class A or AB mode and must operate at a large amount of back-off from the peak output power.Meanwhile, a very requirement of the base station power amplifier for the modern wireless communication systems is high efficiency. As the communication systems are reduced in both size and cost, the cooling system should be simple and small, requiring a power amplifier with high efficiency. Because the base station power amplifiers have a low efficiency due to the back-off operation, efficiency enhancement techniques become very important. The design technique of the base station power amplifiers with high efficiency and linearity across a wide instantaneous bandwidth has become a hot issue.This issue begins with a brief introduction about the relative technology and principles in design of PA's. Furthermore, some efficiency enhancement techniques were introduced in the article, such as LINC, EER, Doherty and so on. Using load-pull technique, detailed discussion was made in the field of PA design and matched network to realize the optimum design:--at 43dBm output power, PAE reached 35% which at least 10% higher than normal amplifier. Then DGS was import to Doherty PA to improve the performance of harmonics and PAE.This thesis includes seven chanters. The first chapter is the requirement which was derived from wireless communication system, and necessary to make this research. Chanter two present some classification of PA and some major index. Chapter three present some high efficiency techniques. In the fourth chapter the Doherty PA will be designed and simulated on the ADS bench, including the drive PA MW4IC2230. In the fifth chapter, the principle of DGS was introduced and the model was also drawn. Chapter six give the designed and simulated results about the Doherty PA using DGS. The final chapter make a summarize for the whole paper.