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기지국용 RF 전력증폭기의 효율향상에 관한 연구

초록/요약

The main theme of this thesis is efficiency enhancement techniques of RF power amplifier (PA) for base station. The efficiency of the RF PA is very important factor in the transmitter system, because the most of DC power is consumed in the PA. The PA with a low efficiency requires a very bulky cooling system and has a short life time and the maintenance cost is high. 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 as well as a peak power region. There are many types of PA system to enhance the efficiency. Among them, we have studied hybrid-EER / ET transmitter system and bias modulator (BM) which can deliver high efficiency for a high peak-to-average ratio (PAPR) signal. Firstly, we have introduced BM for Hybrid-EER and ET operations which can deliver a high efficiency for a high PAPR signal. The BM is composed of two parts : one is a linear stage which plays an important role as an independent voltage source with good linearity and the other is a switch stage which plays a vital role of a dependent current source with high efficiency. The BM has a high efficiency and linearity because most of the current which is needed to load is supplied from the switch stage. The structure and operation of BM are studied and envelope shaping which is key point of connection between PA and BM is investigated. The proper envelope shaping make it possible to operate the system at optimized linearity, gain and efficiency. Secondly, further improvement of the total efficiency, we have applied the ET operation not only main stage but also drive stage. We use the MATLAB and ADS simulators to validate improvement of the total efficiency. To maximize the drive ET stage effect, the optimum size of the drive PA is needed. The drive PA is designed using the Cree Inc. CGH40006 and the main PA is implemented using the CGH27060, respectively, to optimum ET operation. From the experiment results, this two-stage ET PA delivers the efficiency improvement of 1.5% without size optimization of the bias modulator and 2.5% with size optimization of the bias modulator. We also show a good linearity by appling DPD technique. The problems of the two-stage ET PA with single bias modulator are explained. Finally, we design the integrated circuit of the bias modulator to have high efficiency for ET/HEER transmitter. Furthermore, we introduce the three methods to enhance the efficiency of the BMIC ; Switch efficiency optimization, sinking current reusing, and adaptive Vdd. The simulated results show the efficiency improvement of 8.5% compared to the conventional structure.

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목차

1. Introduction 1

2. Bias Modulator for High Efficiency Hybrid-EER and Envelope Tracking Operation 6
2.1 Introduction 6
2.2 Basic Operation of Bias Modulator 9
2.2.1 Structure of Bias Modulator 9
2.2.2 Operation of Bias Modulator 11
2.3 Envelope Shaping 13
2.4 Summary 16

3. ET with Drive Stage and Main stage 18
3.1 Introduction 18
3.2 Structure of Drive Stage ET 19
3.3 Simulation of ET Operation for Drive PA using MATLAB 21
3.4 Simulation of ET Operation for Drive PA using ADS 23
3.5 Experiment Results 30
3.5.1 Experiment Results of the Drive & Main Stages ( CW Test ) 30
3.5.2 Experiment Overview of ET with Drive and Main Stages 32
3.5.3 Experiment Results of ET with Drive and Main Stages 36
3.6 Summary 44

4. Bias Modulator Efficiency Improvement 46
4.1 Introduction 46
4.2 Switch Efficiency Optimize 47
4.3 Sinking Current Reusing 54
4.5 Adaptive VDD 56
4.6 Summary 59

5. Conclusions 61

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