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이동통신용 RF 전력증폭기의 효율 향상에 관한 연구

Title
이동통신용 RF 전력증폭기의 효율 향상에 관한 연구
Authors
손정환
Date Issued
2014
Publisher
포항공과대학교
Abstract
The efficiency and linearity enhancement techniques of RF power amplifier (PA) for mobile communication have been studied. Those characteristics are very important design parameters for a base-station transmitter. However, it is difficult to simultaneously achieve these two characteristics because the PA should be operated in a large back-off region for the linearity, resulting in a low efficiency. In addition, recent modern mobile communication system requires broadband operation for multimode/multiband application. The digital pre-distortion (DPD), which is the most cost-effective solution for linearization, has been extensively studied. In this dissertation, the various techniques to improve efficiency, linearity, and bandwidth characteristics of the PA are presented. In detail, the broadband saturated PA with harmonic control circuits has been investigated. This saturated PA achieves the broadband operation characteristic as well as high efficiency. In addition, due to the modulated signal with a high peak-to-average ratio (PAPR), the PA should be highly efficiency in an average power region. For this purpose, this dissertation considers the Doherty PA and envelope tracking (ET) technique. The sequential DPD is explored to compensate the strong nonlinearity from the ET operation.Firstly, for the broadband transmitter with high efficiency, the broadband PA based on the saturated PA is proposed. The saturated PA has advantages for broadband operation with high efficiency due to large tolerance for the second harmonic tuning. However, it is difficult to achieve high efficiency across a wide bandwidth. To solve the problem, the harmonic control circuits are placed at the input and output of the device’s die. The saturated PA with the harmonic control circuit is designed using 120W GaN device, achieving a high efficiency and wide bandwidth characteristics simultaneously. This broadband saturated PA with the harmonic control circuits can be a promising candidate for PAs of the next generation multimode/multiband wireless communication systems.Secondly, in order to achieve the high efficiency in average output power region, Doherty PA, which is the most popular efficiency enhancement technique, is studied. In this dissertation, a new output combining circuit for asymmetric Doherty PA (ADPA) is proposed. The new combining circuit has an advantage for easy of implementation with a large matching tolerance, compared to the conventional output combining circuits.The ADPA has been implemented using the Cree Inc. CGH27060 and CGH40120 GaN HEMT devices and tested using WiMAX signal with 8.3 dB PAPR at 2.6GHz and achieves excellent performances.Thirdly, ET technique, the other promising candidate to enhance the efficiency at an average output power, is also investigated. We have proposed high frequency ET transmitter system using optimized supply modulator and the average PA in this dissertation. The average PA is optimized at the average power generation region for enhanced ET operation. The PA has been implemented using the Cree Inc. CGH35060 GaN HEMT device at 3.5 GHz. The improved supply modulator and proper ET shaping functions are applied. In the interlock experiment, the ET transmitter has delivered excellent performance. This proposed ET system provides a good linearity and high efficiency at the high frequency.Finally, we have proposed a two-stage ET PA operation and introduced a new sequential DPD architecture to linearize it. The ET technique is applied to both the drive and main power amplifiers to improve efficiency of the drive amplifier. In addition, to overcome a serious non-linearity due to the dual envelope tracking operation, a new sequential DPD architecture is also proposed. To validate the proposed two-stage ET PA and the sequential DPD operation, a drive PA using a Cree Inc. CGH40010 GaN HEMT and a main PA using a CGH27060 GaN HEMT are designed at 2.6-GHz. The two-stage ET PA is functions as expected and a very attractive architecture when the gain of the main stage is relatively low due to the ET operation.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001673612
https://oasis.postech.ac.kr/handle/2014.oak/2049
Article Type
Thesis
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