Research On Three-Way Broadband Doherty Power Amplifier

In the RF front-end and microwave systems,power amplifiers play a vital role in achieving high-performance and low-cost,and with the rapid development of wireless communication systems,a variety of complex signal modulation schemes(WCDMA,OFDM,etc.)have been emerged;signals with new coding require to deal with timevarying envelopes,where the typical peak average power ratio(PAPR)is within the 6-12 dB range.This paper focuses on the requirements of the broadband,high efficiency and large back-off range of the power amplifier imposed by the large PAPR signal,and completes the design of the three-way broadband Doherty power amplifier.On the other hand,the complicated communication frequency bands mean that the bandwidth extension of power amplifiers is also of great significance,thus a continuous class power amplifier based on phase shift parameters is designed in this paper.The main contents of this paper are as follows:1.Aiming at the problem of second harmonic impedance in traditional continuous power amplifiers,by introducing phase shifting parameters to the waveform of output voltages of the conventional continuous class-F power amplifier,the optimal region of the fundamental and the second harmonic impedances can be extended effectively,where the impedance region for the second harmonic extends to the inner part of Smith chart,while the region for the fundamental impedance varies from 1-D to 2-D,thus improving the design degree of broadband power amplifiers.Based on the theoretical analysis,a wideband power amplifier ranging from 0.7 GHz to 3.5 GHz is designed based on the related harmonic impedance regions.The simulation results show that the saturated output power is 40.5 dBm-42 dBm and the drain efficiency is more than 60% over the studied frequency band,and the gain is greater than 10.9 dB.2.Based on a new type of three-way Doherty power amplifier reported recently,and by combining the two-point matching and reverse two-sided matching techniques into the design of broadband three-way Doherty power amplifier,not only the over-saturation issue of the typical three-way Doherty power amplifier is released,but also the bandwidth of the three-way Doherty power amplifier can be greatly extended.With this topology,using three transistors with the same peak power can achieve a power back-off range of 9.5 dB,whereas for the typical three-way Doherty power amplifier,if the same transistor is used,the theoretical power back-off range is only 6 dB.By involving the bandwidth limitation factors of the broadband three-way Doherty power amplifier,the output matching networks of the main power amplifier and two auxiliary power amplifiers are designed by using the methods of two-point matching and reversed two-sided matching.To confirm the study,a broadband three-way Doherty power amplifier,ranging from 1.6 GHz to 2.9 GHz,is developed.The saturation power is between 43 dBm-46.5 dBm,and the drain efficiency with 9.5 dB back-off is greater than 39.5%,while the drain efficiency at the peak power is greater than 48.8%.