“…Recently, an envelope tracking PA (ET-PA), which can operate in the saturated power region by changing the drain voltage according to the envelope of the modulated RF signal, has been reported to achieve high efficiency. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] An ET-PA based on a III-V semiconductor, which consists of a III-V PA and a CMOS envelope amplifier, has achieved high efficiency, but the reported CMOS ET-PAs have not achieved high efficiency with a sufficient gain and output power. In addition, the reported CMOS ET PAs do not have an integrated driver or transformer in the chip, and they require many external circuits.…”