Research And Design Of Broadband High Back-off Doherty Power Amplifier Based On GaN Transistor

In order to meet the needs of large capacity and high transmission rate,high-order digital modulation technology is widely used in wireless communication,which makes the peak to average power ratio of signal rising.At the same time,with the continuous development of spectrum resources and the gradual increase of radio frequency band,the bandwidth of RF front-end power amplifier module is required to be very wide.Doherty power amplifier relies on the simple and easy structure And is widely used in base station equipment because it can maintain high efficiency in power back-off,but the bandwidth of traditional Doherty power amplifier is narrow and the back-off range is only 6d B,which can not meet the requirements of communication system.This paper studies Doherty power amplifier in two aspects of bandwidth and back-off range expansion.Aiming at the problem that the phase delay of the actual impedance inversion network is steeper than the ideal ?/4 line,the phase delay slope parameter is introduced into the output matching of carrier power amplifier and peak power amplifier respectively,and its influence on the bandwidth of Doherty power amplifier is analyzed in depth.The significance of reducing the phase delay slope of the impedance inversion network for improving the bandwidth of Doherty power amplifier is explained,and then an eight step impedance short circuit is designed.A broadband Doherty power amplifier is designed with this structure.The measured saturation output power is 42.7-44.5d Bm in the range of 1.4GHz-2.5 GHz,the 6d B back-off efficiency is 40.5%-57.5%,and the saturation gain is greater than 8d B.The asymmetric Doherty power amplifier is deeply studied.By selecting the drain bias ratio and saturation output current ratio reasonably,the required amount of back-off can be achieved.A broadband matching network is designed by using load pull method.After combining the matching structure,a 1.6GHz-2.4GHz broadband asymmetric Doherty power amplifier is designed and implemented,The output power is 42.5-43.3 d Bm,the 9d B back-off efficiency is 41.3%-52.2%,and the saturated gain is more than 8.4 d B.The peaking reactance is introduced into the asymmetric Doherty structure,and its influence on the back-off range is deeply analyzed.Under the condition of fixed two drain bias ratio and saturated output current ratio,the back-off range of the asymmetric Doherty power amplifier is increased from 9d B to 11 d B by using the peaking reactance,and an asymmetric Doherty power amplifier operating at 2.1GHz-2.2GHz is designed.The measured saturated output power reaches 43 d Bm,The drain efficiency is more than 46% at 11 d B backoff point and the saturation gain is more than 9.3d B.Aiming at the bandwidth problem of high back-off Doherty power amplifier based on peaking reactance,the solution based on variable combining load is adopted to expand its bandwidth,and a wideband high back-off Doherty power amplifier operating at 1.9GHz-2.4GHz with efficiency of 47.0%-54.4% at 11 d B backoff point is designed by simulation.