Recent Progress in Envelope Tracking Power Amplifiers for Mobile Handset Systems

Kenji MUKAI
Hiroshi OKABE
Satoshi TANAKA

Publication
IEICE TRANSACTIONS on Electronics   Vol.E104-C    No.10    pp.516-525
Publication Date: 2021/10/01
Publicized: 2021/03/19
Online ISSN: 1745-1353
DOI: 10.1587/transele.2021MMI0005
Type of Manuscript: Special Section INVITED PAPER (Special Section on Microwave and Millimeter-Wave Technologies)
Category: 
Keyword: 
5G NR,  mobile handset,  power amplifier,  envelope tracking,  

Full Text: FreePDF(2.2MB)

Summary: 
The Fifth-Generation new radio (5G NR) services that started in 2020 in Japan use a higher peak-to-average power ratio (PAPR) of a modulated signal with a maximum bandwidth of up to 100MHz and support multi-input/multi-output (MIMO) systems even in mobile handsets, compared to the Third-Generation (3G) and/or Fourth-Generation (4G) handsets. The 5G NR requires wideband operation for power amplifiers (PAs) used in handsets under a high PAPR signal condition. The 5G NR also requires a number of operating bands for the handsets. These requirements often cause significand degradation of the PA efficiency, consequently. The degradation is due to wideband and/or high PAPR operation as well as additional front-end loss between a PA and an antenna. Thus, the use of an efficiency enhancement technique is indispensable to 5G NR handset PAs. An envelope tracking (ET) is one of the most effective ways to improve the PA efficiency in the handsets. This paper gives recent progress in ET power amplifiers (ETPAs) followed by a brief introduction of ET techniques. The introduction describes a basic operation for an ET modulator that is a key component in the ET techniques and then gives a description of some kinds of ET modulators. In addition, as an example of a 5G NR ETPA, the latest experimental results for a 5G ETPA prototype are demonstrated while comparing overall efficiency of the ET modulator and PA in the ET mode with that in the average power tracking (APT) mode.