I. Introduction
In Wireless communication systems, the power amplifier (PA) is used to accurately amplify and transmit the radio frequency (RF) signals. With the development of wireless communication technology, the high spectral-efficient modulation techniques such as quadrature amplitude modulation and quadrature phase-shift keying are adopted. As a result, the amplitude of the RF signal is no longer constant, and the peak-to-average power ratio (PAPR) is high [1], [2], [3]. When powered by a constant voltage, the PA has large voltage drop, as shown in Fig. 1(a), and thus suffers extremely low efficiency. The envelope tracking (ET) power supply tracks the envelope of the RF signal and dynamically adjusts the PA's supply voltage, as shown in Fig. 1(b). So, the voltage drop on the PA is greatly reduced and the efficiency of the PA is significantly improved [4], [5].
Waveforms of the PA powered by (a) a constant voltage and (b) the ET power supply.