50% Drain Efficiency Doherty Amplifier with Optimized Power Range for W-CDMA Signal

A novel high-efficiency Doherty amplifier is presented. A carrier amplifier and a peak amplifier in the Doherty amplifier are set to asymmetrical drain voltages to extend the power range where a high drain efficiency of the Doherty amplifier is maintained. Matching circuits of the carrier amplifier and the peak amplifier are designed for each drain voltage so that the drain efficiency and signal linearity of the Doherty amplifier at a 9 dB backoff point from its saturated output power (Psat) become higher than those of a conventional Doherty amplifier. These simple steps optimize the power range of the Doherty amplifier for a wideband code-division multiple-access (W-CDMA) signal that has a peak-to-average power ratio (PAR) of 9 dB. A Doherty amplifier containing gallium nitride (GaN) high-electron-mobility transistors (HEMTs) achieves an adjacent channel leakage power ratio (ACLR) of -38 dBc and a drain efficiency of 50% at an output power of 45 dBm. This is the highest drain efficiency of a Doherty amplifier for a W-CDMA signal to the best of the authors´ knowledge.