| As all know, traditional power amplifier decreases significantly in the regression of power efficiency, increasing the power consume of expensive cooling equipments, which deviate to the green energy theory and could not satisfy with the modulated signal with higher peak to average power ratio in modern communication system. In order to improve the efficiency at back-off, Doherty power amplifier technology is widely used in base station. In the article, efficiency at back-off and bandwidth extension technology of Doherty power amplifier are researched based on gallium nitride(GaN) power amplifier tube. Main contents are as follows:Firstly, to meet the requirement of Doherty active load modulation, we propose a new method called dual impedance matching through theoretically analyzing the factors that limit the efficiency and bandwidth of traditional Doherty power amplifier. The proposed method can be used for designing the output matching network which simplifies the load modulation network. Moreover, it ensures high efficiency at back-off and expands the working bandwidth significantly.Secondly, through the anslysis of the impedance of carrier and peaking amplifier, S parameters of output matching network can be obtained based on dual impedance matching method and used in actual circuit design. The 2.3-2.8GHz symmetric Doherty power amplifier can achieve 50% and 43% efficiency at 6dB and 9dB back-off respectively.Finally, through theoretically analyzing the optimal phase of ouput matching network, we simplify the load modulation network structure of Doherty power amplifier by eliminating the use of traditional quarter wavelength impedance transformation line, which broadens the bandwidth of amplifier further. To validate the proposed method, the 1.6-2.2GHz asymmetrical Doherty power amplifier has been designed with different types of power amplifiers. It can achieve 31% relative bandwidth and 50% efficiency at 10 dB power back-off. The efficiency and output power have good consistency among the interested bandwidth.In this paper, the designed symmetric and asymmetric Doherty amplifier meet the requirements of the signal with high PAPR for back-off efficiency in modern communication system and the demand of carrier aggregation technique for bandwidth. The amplifier’s bandwidth can be expanded effectively while maintaining high efficiency at back-off. And the results of simulation and testing have verified the method mentioned. The proposed method could provide tech-nical reference for the power amplifier designed in next generation mobile communication system. |
PDF Full Text Request