Research And Design Of Doherty Power Amplifier For 5G Base Stations

With the rapid development of the information age,people have higher and higher requirements for wireless communication technology and the performance of communication system.In 2019,5G base stations were officially approved by the Ministry of Industry and Information Technology to enter the network,which means the 5G era is officially ushered in.The new generation of communication frequency band requires higher performance of RF transmitter.The power amplifier is located at the end of the transmitter and is used to connect the antenna.Its working performance directly determines the performance of the transmitting link.Therefore,the power amplifier in the5 G base station has become a research hotspot now.Doherty power amplifier is widely used in base station because of its high efficiency in power rollback.In this paper,Doherty power amplifier based on GaAs HBT process is studied and worked as follows:(1)The research status of power amplifiers at home and abroad is investigated according to the background that the current 5G communication frequency band puts forward high requirements for communication system transmitters.The performance index of RF power amplifier and the advantages of GaAs HBT device are analyzed in detail.By means of ADS(Advanced Design System)simulation software and formula derivation,the working principle of traditional Doherty power amplifier is analyzed,and the load modulation effect of Doherty power amplifier is further understood.(2)The technical indexes of Doherty power amplifier are formulated according to the existing technical parameters.Then,the circuit structure of the power amplifier is simulated and designed.The Doherty power amplifier adopts the three-stage cascade structure,in order to ensure that the Doherty power amplifier has high linearity while maintaining high efficiency.In order to ensure that the transistor works in normal state,stabilize the working state of the circuit and improve the performance of the circuit,a kind of adaptive bias circuit is used.In order to keep the power amplifier absolutely stable in the working frequency band,RC parallel network is connected in series in the base of the power amplifier tube to ensure the working performance of the power amplifier.In order to reduce the chip area,a binary power divider is designed by using lumped element instead of 1/4wavelength transmission line.And the use of load traction technology and source traction technology,design the input matching circuit,stage matching circuit and output matching circuit.(3)All levels of power amplifier are designed step by step in the simulation software ADS,and then cascaded simulation optimization is carried out.According to the design of the circuit schematic map to draw the layout,the design of the layout after simulation.The results show that the reflection coefficient S11 of Doherty power amplifier is less than-10 dB in the frequency range of 3.4-3.6 GHz.PAE,power added efficiency(PAE,power added efficiency)reached 28.7% when the power was reduced by 6dB and 28.3% when the power was reduced by 8 dB.At the center frequency of 3.5 GHz,the saturated output power was higher than 33 dBm and the gain was maintained above 27 dB,achieving the desired goal of having greater gain while maintaining high efficiency.