A 28-GHz DAT-based four-way Doherty power amplifier with 22.6dBm P_sat and 0.48W/mm² power density

This paper presents a 28-GHz four-way differential Doherty power amplifier (PA) implemented in 40-nm CMOS technology. A distributed active transformer (DAT)-based interstage quadrature divider (DIQD) is introduced to minimize insertion loss and enhance power gain. Additionally, a DAT-based single output transformer (DSOT) is proposed to achieve low-loss, compact power combining, and load modulation simultaneously. Measurement results demonstrate a P_sat of 22.6 dBm, an OP1dB of 21.2 dBm, a peak PAE of 20.5%, and 14.2% PAE at 6-dB PBO at 28 GHz. With a 100-MHz 64-QAM modulated OFDM signal, the PA achieves an average output power of 13.5 dBm and an average PAE of 9% at an EVM of -25 dB. With a 400-MHz 64-QAM modulated OFDM signal, it delivers an average output power of 11.3 dBm and an average PAE of 8% at -25 dB EVM.