增強功率效能之多階級LINC系統設計

Abstract

在現今的無線通訊系統中，功率放大器是最消耗功率的元件。而功率放大器又具有非線性特性，因此要設計高效率又高線性度的無線發射機便成了一個相當困難的挑戰。於是多種不同功率放大器的線性化技術被採用來改善無線發射機的線性度及效率。 在這些線性化的技術中，LINC技術可以使用高效率的非線性功率放大器而且可達成線性放大。除此之外，數位信號處理在CMOS製程下具有相對的低成本及其不易受製程變易影響的特性，因此數位化的LINC架構特別適用於當今的製程。 當LINC提高功率放大器效率的同時，LINC需要一個額外的功率合成器來達成線性放大。然而這個低效率的功率合成器會導致整個無線發射機的效率大幅降低。為了改善功率合成器的效率，且同時達到高效率的功率放大器，我們提出了一個多階級系統。基於這個多階級系統，我們提出兩種不同的線性化架構: 增益調整多階級LINC(Gain-adjusting multilevel LINC, GA-MLINC)及包絡調整多階級LINC(Envelope-adjusting multilevel LINC, EA-MLINC)。在WCDMA系統線性度的要求下，三階的增益調整多階級LINC及三階的包絡調整多階級LINC分別可改善LINC系統的輔助功率從16.5%到23.6%及33.4%。

Power amplifiers (PAs) are the most power-hungry devices in modern wireless communication systems. Designing a high linearity and high power efficiency wireless transmitter is a big challenge due to the nonlinear characteristic of the power amplifier. Various PA linearization techniques have been adopted to improve linearity and power efficiency of wireless transmitters. Among them, the linear amplification with nonlinear components (LINC) technique can use high-efficiency nonlinear PAs and achieve a linear amplification. In addition, digital signal processing is widely available at a relatively low cost in nowadays CMOS technology and insensitivity to process variation. Thus, the digital LINC architecture is more suitable for modern process technologies. While LINC increases the efficiency of power amplifiers, LINC requires an extra power combiner to obtain the linearly amplified signal. This low-efficiency power combiner results in low system power efficiency of wireless transmitters. To not only increase power combiner efficiency but also achieve high PA efficiency, we propose a multilevel out-phasing (MOP) scheme and two architectures: gain-adjusting multilevel LINC (GA-MLINC) and envelope-adjusting multilevel LINC (EA-MLINC). Under WCDMA linearity requirements, 3-level GA-MLINC and 3-level EA-MLINC enhance the LINC system power-added efficiency from 16.5% to 23.6% and 33.4%, respectively.