Performance Analysis of Envelope Tracking Power Amplifier's Envelope Shaping Methods for LTE Mobile Terminal Application

Envelope tracking (ET) is a significant technique to improve the efficiency of power amplifier (PA) in the power back-off region, especially in modern mobile communication system with a high peak-to-average power ratio (PAPR). Different ET implementation solutions, especially the way of choosing shaping table, have a great impact on the performance of ET system. In this paper, a transistor-level PA and a behavior-level supply modulator are introduced to analyze the performance of ET PA system. The power-added efficiency (PAE), AM-to-AM distortion, AM-to-PM distortion and Adjacent Channel Leakage Ratio (ACLR) are investigated to explain the impacts of different commonly-used shaping methods. Simulation results indicate that adopting ET technology increases the efficiency of RF PA largely, and the shaping methods applied in supply modulation will affect a lot in efficiency and linearity. Consequently, a new dual-mode ET shaping method is proposed in this paper to guarantee high efficiency as far as possible without introducing too much distortions. Besides, it also improves the linearity where the PAE is at a lower level.