增強效率脈衝式之LINC功率放大器

Abstract

功率放大器在無線通信系統中，扮演著相當重要的角色，因需要更有效率地把信號發射，故功率放大器性能設計的好壞會影響到整個系統，本論文以效率為主要考量。功率放大器效率的提升是發射機中的關鍵，可以使發射機具有較低的能量消耗，而且可使手持裝置的待機時間變長。然而現今的調變技術多以提高頻譜利用率為主，使得信號峰均比(PAR)變大，故線性度亦需要被要求，然而一般來說線性度和效率是互相牴觸的，因此需要利用功率放大器的線性化技術來改善此問題。 LINC (Linear Amplification using Nonlinear Components) 本身是一種線性的架構，再加上脈衝調變來增加效率，故本文所提出的脈衝式之LINC功率放大器發射機架構，為同時提升線性度和效率的發射機架構。 LINC之效率與功率合成器和功率放大器有關，故本論文主要研究是將Wilikinson功率合成器換成Chireix功率合成器後，驗證Chireix功率合成器在脈衝式之LINC功率放大器發射機架構之可行性，根據實驗結果本論文所提出的這種提高效率的架構能將汲極效率提升，對於Wilikinson功率合成器而言，汲極效率由26.4%改善到33.5%；Chireix功率合成器而言，汲極效率由50.7%改善到65.2%。 根據實驗結果可發現，在效率方面確實是有相當的改善，相信本論文所提出的方法是提升效率的一個好的設計方向。然而Chireix 功率合成器所形成之LINC功率放大器不再是線性，若要使用在線性放大器之發射機架構上，則需使用預失真之技術。

In a modern communication system, a power amplifier plays an important role. Because the signal needs to be delivered efficiently, the design of a power amplifier will affect the entire system. In this thesis, we focus on the power efficiency. We conclude that the efficiency of the power amplifier is the key in a transmitter system, because it can reduce the system power consumption, and it can also prolong the standby time of handset devices. In order to improve the spectrum utilization, which increases the peak to average power ratio (PAR), linearity is required. However, for a power amplifier linearity and efficiency are not easy to achieve concurrently. Linearization techniques for power amplifiers can be adopted to improve the problem of linearity and power efficiency. This thesis presents a method for improving the efficiency of LINC (Linear Amplification using Nonlinear Components) by using pulse modulation, which theoretically can improve the linearity and power efficiency of a transmitter at the same time. The efficiency of the LINC power amplifier is related to the efficiency of the power amplifier and the power combiner. To further improve the efficiency of a LINC power amplifier with pulse modulation, replacement of the Wilkinson power combiner with the Chireix power combiner is proposed in this thesis. The experimental results show that the architecture proposed by this thesis does improve the drain efficiency. It can improve the efficiency for Wilkinson power combiner from 26.4% to 33.5%, and improve the Chireix power combiner from 50.7% to 65.2%. According to the experimental results, we know that the efficiency is definitely improved; therefore, this proposed method is a good architecture to enhance the efficiency. Further improvements to the linearity can be achieved through pre-distortion linearization.