S-band High Efficiency Study Doherty Power Amplifier

With the development of the modern mobile communications technology, muchhigher performance of the power amplifiers is required to deal with signal which hasthe wide frequency band, multiple carriers, large capacity and high peak to averageratio. Operators pay more and more attention to the efficiency of the mobile basestation as the popularization of a new concept--“green base”. How to improve theefficiency of the power amplifier has become very significant. The Doherty amplifierbecomes the focus of current research for its advantages of simple structure, low cost,high efficiency. In this paper, our purpose is aiming at how to improve the efficiency ofthe Doherty amplifier. The major achievements are listed as follows:1. The structure and operational principles of the Doherty amplifier is studied andthe state of art is also analyzed.2. The effect of input power dividing ratio on the Power-added efficiency ofDoherty amplifier is emphasized in this paper. A new self-adapting power divider isproposed. With the aid of the divider, the main input power is allocated to the mainamplifier when PA operates in small signal condition, and more and more input poweris allocated to the auxiliary amplifier when the auxiliary amplifier is turned on. Thetheoretical analysis and simulation verification is also carried out.3. The effect of main and auxiliary amplifiers’ operational state on the PA’sperformance is researched.4. With the help of ADS simulation tools, by utilizing the Freescale’sLDMOSMRF8P26080H, two power amplifiers based on the self-adapting powerdivider have been developed. The main and auxiliary amplifiers work at different drainvoltages. The simulation result shows that the PAE of modified Doherty amplifier hasan improvement of2.5%-3.5%with power back-off.5. Eventually, two modified Doherty amplifiers have been fabricated and testedbased on the simulated model. The test result shows that the modified Dohertyamplifier with different drain voltage has a higher efficiency and wider back-off rangethan that with same drain voltage, with the exception of little degeneration in gain and IMD3.It has a good agreement between the result of experimentation and simulation.The research production of this dissertation has reference values to engineeringapplications.