| The width of communication channel has been increased with the rapid evolution of mobile communication system.For example,the LTE-Advance technology which is based on the LTE technology had extended its channel width from 20 MHz to 100 MHz.But nowadays,the mobile-telecom spectrum has become quite crowded.The mobile-telecom spectrum that assigned to telecom operators have the feature of fragmentation.It is difficult to provide a continuous channel with 100 MHz width.A solution for this problem is to use multiple frequency bands.Use the carrier aggregation technology we can piece together a 100 MHz wide channel from multiple bands.Based on this technical requirement,more and more scholars begin to research the dual-band or multiband RF transceiver.The technology of Doherty can improve the efficiency of power amplifier in the Back-off area.The dual-band Doherty power amplifier is an extension of single-band Doherty power amplifier and at present it has a significant sense to research.In this article,based on the basic principle of Doherty,we had implemented a Doherty power amplifier working at 1.965 GHz and 2.565 GHz frequencies.The main work content includes the following several parts:(1)The theory of Doherty power amplifier technology was studied.The defect of symmetrical Doherty structure was discussed: due to the peak-power amplifier is a class-C amplifier,under the same drain voltage,its saturated output power is lower than the output power of carrier-power amplifier which was worked as a class-AB amplifier.The current of the peak-power amplifier is lower than the carrier-power amplifier too.So the load impedance on the carrier-power amplifier output side can not pull from100? to 50?,but had pulled to a more than 50? impedance,that caused the carrier-power amplifier did not achieve the best state.According to this design,we use the asymmetric structure to solve that problem.We improved the drain-voltage of the peak-power amplifier,so that more output power can be obtained from the peak-power amplifier.(2)Two kinds of dual-band matching method for power amplifier were discussed.The merits and demerits of the two matching methods were analyzed.For the three-section dual-band matching method,under the condition of some frequency,cannot directly get the accurate solution of the problem.This paper proposes a method that combined with the tuning function of ADS software to complete the corresponding double-frequency matching.(3)During the process of simulation we found that for the same transistor,under different bias voltage,the optimal load impedance value is different.So if the peak power amplifier is just changed its bias voltage based on the carrier-power amplifier,it can not work at the best state.According to that finding,this design makes the carrier-power amplifier and peak-power amplifier match and design respectively,so that both can work in the best state.(4)Combined with the above research and discovery,we simulated a Dual-band Doherty power amplifier which can work at 1.965 GHz and 2.565 GHz frequencies.For this power amplifier,the maximum output power of the two frequencies is 41.6 dBm and 42.03 dBm respectively.The drain efficiency at 5.5 dB output power back-off is36.37% and 45.3% respectively. |
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