A Compact Transformer-Combined Polar/Quadrature Reconfigurable Digital Power Amplifier in 28-nm Logic LP CMOS

This paper presents a transformer-combined dual-mode reconfigurable digital Class-D power amplifier (PA) that supports polar and quadrature transmitters (TXs). Transformer-based load modulation is employed to enhance the efficiency in both modes. The PA is implemented in 28-nm logic LP CMOS and occupies only 0.56 mm
²
active area. The polar mode achieves 28.8-dBm peak power with the PAE of 30.8% at peak power and 22.4% at 6-dB backoff. The quadrature mode obtains 26.3-dBm peak power and 22.9% peak PAE. For 20-MHz 64 Quadrature Amplitude Modulation (QAM) WLAN signals, the PA achieves 23.35-dBm P
_avg
, 23.2% PAE, -25.4-dB error vector magnitude (EVM) in polar mode and 18.50-dBm Pavg, 12.3% PAE, -25.2-dB EVM in quadrature mode.