Research On High Efficiency Inverse Class-F Doherty RF Power Amplifier

Power Amplifier(PA) is a critical component of wireless transmitter system, and its performance has a significant impact on the quality and transmission distance of the output signal generated from the transmitter. Meanwhile, PA is the most power consuming unit in the communication system. Its efficient design can reduce not only the power consumption, but also the design requirements on power supply and cooling devices, thus to improve the stability of the system. LTE system applies OFDM technology to improve the data transfer rate and spectrum utilization, which also ensures high peak-to-average ratio(PAPR) of signals. Efficient linear amplification of high PAPR signals is the key technique of PA design in 4G system.This dissertation mainly discusses the efficiency enhancement of inverse class-F Doherty PA,the main work is divided into four parts:The main performance indicators in PA design are summarized in Part 1. According to different performance requirements on gain, output power and noise figure in the design of RF amplifier, three design principles including double conjugate matching, power matching and noise matching are analyzed correspondingly.Part 2 focuses on the research of the back-off efficiency performance of Doherty structure.According to the load modulation technique, the complete variations of output voltage and current,load impedance and efficiency of the Carrier and Peaking PAs are analyzed. The overall efficiency curve is presented, which confirms the capability of Doherty structure to process high PAPR signals.Part 3 focuses on the research of high efficiency class-F/IF and inverse class-F Doherty PAs.First of all, the operating principle of class-F/IF PAs is introduced, and the influence of transistor parasitic parameters on its switch performance is also analyzed. Later, several structures of inverse class-F output harmonic control network containing parasitic parameter compensation are presented with corresponding theoretical analysis and parameter calculation. Finally, a highefficiency inverse class-F Doherty PA is presented by combining inverse class-F PA with Doherty structure organically. The variations of fundamental and harmonic impedance of the two PAs in the working process are analyzed. Detailed research on the function and length selection of the offset-lines for the carrier and peaking PAs is also carried out.Simulation design, PCB fabrication & debugging as well as pre-distortion linearization of thehigh-efficiency inverse class-F Doherty PA are completed in Part 4. From the measured results for a 930 MHz single tone, the drain efficiency of 64.2% is achieved at 7.5 dB back-off. In the band of910-950 MHz, the drain efficiency is over 50% at 8 dB back-off, and the output power is more than 42.5 dBm. Taking three-carrier WCDMA signal as test signal, the measured ACPRs of output signal are-35.9 dBc(lower) and-35.39 dBc(upper) respectively after pre-distortion linearization.