A Digital Power Amplifier for 32-QAM

A 500 MHz 3-bit digital power amplifier (DPA) exploiting load modulation is described. Three individual amplifiers are enabled and disabled alternatively by their gate bias to achieve eight unique output power (P
OUT
) amplitude states. A 32-Quadrature Amplitude Modulated (32-QAM) signal is mapped onto five of the DPA's amplitude states from which its phase response can be characterised. With this, the DPA phase response is modelled, and phase corrections applied to each state. When amplifying a phase corrected 32-QAM signal, 38.7% efficiency is achieved at 480 mW (26.8 dBm) P
OUT
with a peak P
OUT
of 30.9 dBm and an error vector magnitude (EVM) of 2.9%.