Recent Progress in Envelope Tracking Power Amplifiers for Mobile Handset Systems

Abstract

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.

Evolution of Power Amplifiers for Mobile Phone Terminals from the 2nd Generation to the 5th Generation

“…Since V CC is changed according to the envelope of the modulated signal, the minimum operating voltage is in the vicinity of V knee regardless of the magnitude of the amplitude of the modulated signal, and power loss can be reduced. Figure 10 shows an example of the characteristics of PA for ET [3]. Figure 10 (a) shows examples of the table used in Fig.…”

“…Therefore, it can also be used for NR. The details of the ET method are described in the paper [3], and please refer to that as well.…”

“…Copyright c 2022 The Institute of Electronics, Information and Communication Engineers Due to the multi-value modulation, the PAPR of the modulated signal increases to 4.0-6.5 dB, which is larger than that of W-CDMA [3]. The modulation bandwidth is 5-40 MHz.…”

“…There are two types of multiple access methods on the transmitting side: CP (cyclic prefix)-OFDM (orthogonal frequency division multiplexing) and DFTS (discrete Fourier transform spreading)-OFDM. 256QAM is added as the modulation signal, and the maximum PAPR is about 8.5 dB [3].…”

A review of different structures of power amplifiers to improve linearity and efficiency

“…This type usually has low bandwidth and linearity. Especially, in CMOS technology, the bandwidth is not wide because of the limiting of switching speed, though, the switching modulator is efficient [30,32,33]. The block diagram of the switching modulator is shown in Figure 7c.…”