A 28GHz Compact 3-Way Transformer-Based Parallel-Series Doherty Power Amplifier With 20.4%/14.2% PAE at 6-/12-dB Power Back-off and 25.5dBm PSAT in 55nm Bulk CMOS

The 28GHz band for fifth-generation (5G) millimeter-wave wireless communication supporting high-order QAM, OFDM, and carrier aggregation (CA) requires excellent power and spectrum efficiency for higher data-rate throughput. High-order modulation often forces power amplifiers (PAs) to operate at deep power back-off (PBO) (i.e., 12dB or even higher), where typical PAs always suffer from efficiency degradation. Therefore, efficiency enhancement at deep PBO is critical to improving the average efficiency of transmitters.