| The explosive growth of mobile data services has driven the rapid development of mobile communication systems.The fifth-generation mobile communication system can reach a peak downlink transmission rate of 10 Gbps.Complex modulated signals with high peak-to-average ratio and high bandwidth are used to improve the spectrum utilization and achieve a higher data transmission rate.Power amplifier is an important part of wireless communication transmitter,and its bandwidth,efficiency and linearity characteristics will determine the overall performance of the transmitter.This paper focuses on the designs of supply modulator and class-J power amplifier to enhance efficiency in a back-off region.Firstly,according to the characteristics of the wideband of the envelope signal,a constant current source parallel hybrid structure supply modulator is developed based on the classic parallel hybrid topology.The main feature is that a constant current source and a linear amplifier are used to separate voltage and current components for benefits.High-efficiency buck switcher is replaced to reduce static losses and improve the bandwidth and efficiency of the supply modulator.The supply modulator with 500 m W of the maximum output power is measured to have 61.2% efficiency.The Q-band power amplifier module with TGA4521 chip is produced with a saturated output power of 23 d Bm,which is combined with the supply modulator to form an ET power amplifier.For a 20 MHz OFDM with PAPR of 9.1d B,measured drain efficiency of the ET power amplifier of 2.7% is reported,which is 1.5 times the efficiency of power amplifier under constant supply.-46.4d Bc and-45.4d Bc for ACLR are achieved after digital predistortion,with an improvement of 13 d B.Secondly,a digitally controlled series hybrid topology ET power amplifier is developed,which include a digitally controlled series hybrid structure supply modulator and a class-J power amplifier.From the power spectral density analysis,multilevel converter is optimized to improve the efficiency of the supply modulator,with maximum output power of 30 W and maximum output voltage of 28 V.Efficiency of the supply modulator measured is 70.3%.ClassJ power amplifier using quarter-wave line as the drain feed network is developed,which is suitable for ET power amplifier for its low frequency response characteristics.A class-J power amplifier over 3.4-3.6GHz is designed,with saturation output power ranging from 41.75-41.9d Bm,saturation efficiency ranging from 68.3-71.8%.For a 20 MHz OFDM signal with PAPR of 8.6d B,the efficiency of the ET power amplifier reaches 32.2%,with an improvement of 4.9% over the efficiency of power amplifier under constant supply.After digital predistortion,ACLR reaches-46.4d Bc and-46.2d Bc. |
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