Broadband High Back-off Doherty Power Amplifier Research

Doherty power amplifiers are commonly used in communication base stations due to their simple structure and high efficiency at backoff power.However,at present,Doherty power amplifiers still have some shortcomings: for broadband design,their drain efficiency fluctuates greatly at different operating frequencies with different back-off output power,and their performance is unstable in broadband;For designs with a higher output power back-off range,its bandwidth and efficiency of the back-off output power are low.In this thesis,two Doherty power amplifiers have been studied and designed to address the above issues.The specific work of this thesis is as follows:1.Aiming at the problem of large fluctuations in the drain efficiency of Doherty power amplifiers over a wide frequency band,this thesis designs a wideband efficiency consistent Doherty power amplifier,which uses a specific load modulation structure and phase analysis method to achieve broadband design.By combine point load phase control,the stability of the drain efficiency of Doherty power amplifiers in broadband is effectively increased.As a verification,a broadband efficiency consistent Doherty power amplifier has been fabricated through ADS simulation.The physical test performance shows that the drain efficiency is maintained at 44%-52% when the output power is backed off by 6 d B at a working frequency of 1.8 to 2.6 GHz;The drain efficiency is maintained at 51%-59% when the output power is backed off by 4 d B;The drain efficiency is maintained at 54%-62% with an output power backoff of 2 d B;The drain efficiency at saturated output power is maintained at 59%-67%;The maximum output power can reach 43.5-44.5 d Bm.2.Aiming at the low drain efficiency within the power back-off range in the design of a two-way high backoff Doherty power amplifier and the complex design of a threeway broadband Doherty power amplifier,this thesis designs a three-way symmetrical Doherty power amplifier.Based on the design of a three-way symmetrical Doherty power amplifier,the ideal output impedance of the transistor is analyzed to obtain the ideal value of its combine point load at different output power,By designing and implementing a complex combine point load which varies with frequency,the operating bandwidth of a three-way symmetric Doherty power amplifier is effectively expanded when outputting power back.As a verification,this article uses the same type of transistor,and produces a broadband high return Doherty power amplifier through ADS simulation.Actual test performance shows that the power amplifier operates in a frequency band of 1.6-2.2 GHz,with a drain efficiency of 50%-60% at an output power back-off of 9.5 d B;The drain efficiency is 50%-70% at an output power back-off of 6 d B;The drain efficiency and output power at saturated output power are 60%-70% and 45.2-46.3d Bm,respectively.In summary,through theoretical derivation and research on the load modulation structure in Doherty power amplifiers,this thesis has produced broadband efficiency consistent Doherty power amplifiers and broadband high return Doherty power amplifiers and compared the physical test results with the results of recent relevant journal articles,proving that the design method proposed in this article has positive significance in increasing performance stability,bandwidth,and power return range.