| The radio-frequency (RF) power amplifier(PA) as an important part of mobile communication base-station system, its performance directly affects the entire mobile communication base-station system linearity and power consumption, thereby increasing the frequency band, linearity and efficiency of RF power amplifier have an great significance for improving the entire performance of mobile communication base-station system. Due to the superiority of linear and efficiency improvement of Doherty PA, making it become the current research focus.This paper mainly studies the Doherty amplifier theory, and on this basis using LDMOS and GaN tubes to complete the Doherty amplifier design. The principal contributions and innovation of this paper include:1)The conduction angle and active load-pull theories are used to study and analyze the Doherty power amplifier theory, on this basis a classification of the Doherty power amplifier has been done, and in the last the actual Doherty power amplifier design features have been analyzed, in particular, the impedance matching and offset-line theories have been detailed analysis.2) On the basis of the theoretical analysis, and according to design specifications requirement:center frequency of 2.65 GHz,100 MHz bandwidth, the drain efficiency is above 40% when the output power is 40 dBm, and the peak to average ratio(PAR) of the output signal is above 7 dB, to complete the LDMOS-based Doherty power amplifier system design and tuning. The finally tuning result is the drain efficiency is 40% at the 42 dBm (6dB back-off) output and 33.6% at the 40 dBm (8dB back-off) output. 3) Due to the LDMOS-based Doherty power amplifier can not meet the design specifications requirement, then the GaN tube is used to design the Doherty power amplifier system. Base on the corresponding design, the tuning result is the drain efficiency is above 45.8% at 40 dBm (7.4dB back-off) output.4) According to the previous design, a comparison has been done about the LDMOS-based Doherty power amplifier and GaN-based Doherty power amplifier considering the performance, design difficulty and so on. |
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