Research On High Efficiency Radio Frequency Power Amplifiers

Power amplifier (PA) which is located at the end of the radio transmitter is one of the key components in the RF front end. As the most power consuming and heating unit, its efficiency has a significant impact on the overall power consumption, system stability and the requirement for power supply and cooling system. Efficiency enhancement has always been a critical technique in PA design, especially at the very moment when wireless communication is experiencing a tremendous evolution, raising new demands for PAs. The dissertation is focused on the high efficiency class F/inverse class F(IF) PAs under the new trends.First of all, general principles in PA design are summarized. Commonly used power and efficiency boosting methods including power (gain) match, load-pull contours theory and harmonic tuning approaches are presented, which foreshadows for the following chapters.Chapter3,4and5will introduce separately the single band class F/IF, dual band class F/IF as well as the cooperation of the harmonic tuned PA and the Doherty structure.Chapter3is focused on single band class F/IF harmonic tuned PA. With some theoretical introduction to its operation principle and the analysis of the influence of the parasitic elements of the transistor to the PA’s performance, comparison between class F and IF PAs are carried out in two cases:one given the same drain bias for cellphone use and the other given the same maximum output power for base station use. The classical and state-of-the-art structures to realize class F/IF PAs are overviewed. Then a new structure which employs three-section transmission-line dual band transformer in the harmonic control circuit is proposed. The simple structure is suitable for class F/IF and other harmonic tuned PAs. For demonstration, a PA is designed and fabricated with the proposed method.Researches on dual band class F/IF PAs are carried out in chapter4. First of all, a dual band reconfigurable Class F power amplifier that combines PIN diode switches with harmonic control network is presented. Then, a novel two-section transmission-line (TSTL) based dual band harmonic control network is developed. The TSTL design criterion is investigated for three particular cases and a concurrent dual band class-F harmonic control network adopting all the three kinds of TSTLs is designed. Experimental validation based on the proposed topology is realized by a fabricated PA. After that, a high efficiency concurrent dual-mode dual-band power amplifier is presented to avoid the probable harmonic conflict in dual band class F cases. It simultaneously operates at class-F mode for one band and at inverse class-F mode for the other band. Experimental result shows similar performance as the single band class F/IF PAs.In chapter5, harmonic tuned PA is employed in Doherty structure. Doherty PA is able to keep high efficiency for a wide range of output power back off so it is extremely suitable for the signals with high peak-to-average ratio. But both the harmonic tune PA and the Doherty structure have limited bandwidth. A recently arisen continuous class F/IF PA is believed to have wider bandwidth than the traditional class F/IF PA. So we combine the class IF PA with Doherty structure and achieves good performance in a required bandwidth.