| In the third generation mobile communication systems, it concludes some complex modulation methods, which makes the PAPR of the modulation signal increases, that's lead to the RF power amplifier which is the most important modules in the wireless communication must have higher linear level. Now several methods can be used to realize the linearity of the modulation requires, but all of them cost efficiency of the RF power amplifier. As we all know, RF amplifier is the main energy-consuming module in communication systems. The efficiency of it affects the energy-consuming and the stability of the whole communication system. At the same time, the efficiency of RF power amplifier affects the use time of the battery. High-efficiency power amplifier can not only economize electricity, but also reduce the energy dissipated as heat of device .This paper describes the structure of the Doherty power amplifier, which can provide high efficiency at 6dB back-off range, so this can solve the efficiency decrease by the power return technology. If the linearization technique can be combined with Doherty power amplifier, the power amplifier can provide high efficiency and advantage linearity. There are a variety of linear technology, such as, feed forward technology and digit pre-distortion technique.In this paper, MRF281s 4-W LDMOS FETs of Freescale is used in the design of Doherty power amplifier. Bias circuit, matching circuit, stability analysis and the theory of Doherty power amplifier were introduced in detail. Tradition AB power amplifier was compared with Doherty power amplifier, the result show that the Doherty power amplifier has good characteristics. At the same time we proposed two methods of optimal design, one is optimum design of Doherty power amplifiers based on average power efficiency, which can determine the best back-off point. The other is optimization design of wideband Doherty RF power amplifiers.The paper is organized in the following way. The first part is Introduction. The RF power amplifiers fundamental is described in the second part. The third section describes the principle of the Doherty power amplifier. The fourth section describes the process of design and results of Doherty power amplifier. A method of optimum design of Doherty power amplifiers is presented in fifth Section, the method based on average power efficiency. The Sixth part describes the method of optimization design of wideband Doherty RF power amplifiers. The seventh part summarizes the paper. |
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