| With the development of the Microwave communication technology, the requirement of the terminal device for communication system has become more and more strict. RF power amplifier is the main device as the terminal of Microwave communication system, which consumes most parts of transmitter'power, its performance has directly affected the normal function of the whole communication system. In order to satisfy transmitting the signal with linearity and non-distortion in the high Peak to Average Ratio (PAR), the power amplifier of the base-station usually work at Class A or Class AB. Traditional design employ the method of power back-off to obtain high linearity at the expense of the efficiency, the efficiency of power amplifier is very low, most of power is consumed. Therefore, in order to maintain the linearity of signal and high Peak to Average Ratio (PAR), how to raise the efficiency of RF power amplifier nowadays has become the popular topic of wireless communication technology study. This paper has done much work on the design of high efficient power amplifier.Firstly, this paper analyzes the key technical indexes of power amplifier, and explains the sense of these technical indexes adequately. The category of power amplifier has been introduced. Through all of them, the design of power amplifier has been recognized. Then, the circuit structure and working principle of Doherty power amplifier have been analyzed in detail. Through introducing the key technology such as the active load pull, the working procedure of Doherty power amplifier has been analyzed in terms of low power, medium power and high power respectively. These analyses show that the output load, output current and output power for main power amplifier and auxiliary power amplifier how to change respectively. Then, the advantage and disadvantage of Doherty power amplifier in practical application have been analyzed.Secondly, a high efficient Doherty power amplifier has been simulated, optimized and designed on the whole. Based on discussing bias circuit design, stability test and match circuit design and so on, this paper optimizes and designs a high efficient Doherty power amplifier combining with the method of double Offset-line. The efficiency of Doherty power amplifier with broadband and high gain is up to 40%, and gain flatness is less than 1dB, and the 1dB compressed output power is more than 50dBm. Compared with Class AB power amplifier, the efficiency of the Doherty power amplifier in this paper has improved obviously.Finally, the Doherty power has been manufactured and tested. The PCB of Doherty power amplifier has been designed, and after manufacturing and welding, the system debugging has been implemented. The test result is close to design target, and it reaches the design aim of this paper. |
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