포락선 추적방식을 이용한 기지국용 고효율 RF 전력증폭기에 대한 연구
- 포락선 추적방식을 이용한 기지국용 고효율 RF 전력증폭기에 대한 연구
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- The main purpose of the thesis is to study Envelope Tracking(ET) RF Power Amplifier(PA) which is considered as a future PA technology with high efficiency and broadband characteristic. There have been lots of efforts to improve the efficiency of RF PA for it is the most power consuming block in wireless transmitter system. Among those efforts, ET PA is most likely to take the first place because it has not only high efficiency structure, but broadband characteristic.
At first, theoretical ET PA operation is described. Because of their fundamental current amplitude, Class-A, Class-AB, Class-B and Class-C PAs theoretically have different efficiency curves and Envelope Shaping Function(ESF). And non-ideal effects like knee voltage effect or gain expanding curve are explained to help to understand real operation of ET PA.
Secondly, simulation method to design and analysis ET PA is suggested. ET simulation program developed with MATLAB makes it possible to anticipate ET PA operation Harmonic balance 3D data. Furthermore, various RF PA modeling is suggested to calculate correct efficiency of supply modulator. As RF PA model varies with ESF, supply modulator efficiency has different value depending on various ESFs. Because the total efficiency of ET PA is the product of supply modulator efficiency and PA efficiency, the optimum ESFs which have maximum efficiency can be calculated by sweeping compression order (n) and voltage offset of ESF. In ‘n=1.5, voltage offset = 9V’ case, it shows the best AM-AM curve among the optimum ESFs, which means that it has the best linearity. It has 72% of PA efficiency, 79.3% of supply modulator efficiency and 57.1% of total efficiency.
At last, highly efficient supply modulator circuit is suggested. Through the structural analysis for efficiency enhancement, additional circuit is attached to Hybrid Switching Amplifier (HSA) structure which consists of switching stage and linear amplifier. By reducing voltage difference in buffer transistors, it can save power which consumes in buffer linear stage. It improves efficiency by about 3% and it achieves 82.5% of supply modulator efficiency in simulation.
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