Digital doherty transmitter with envelope ΔΣ modulated class-D GaN power amplifier for 800 MHz band

Abstract

This paper presents a novel transmitter (Tx) architecture combining voltage-mode class-D power amplifiers (PAs) with an efficient 1-bit envelope delta-sigma modulation scheme for the 800 MHz band. By digitally processing the input 1-bit codes, the proposed Tx operates as a digital Doherty Tx. The proposed Tx architecture is realized with a GaN H-bridge class-D PA module and CMOS modulator ICs and delivers a CW power of 35.9 dBm at 860 MHz with a final-stage drain efficiency of 75.6% at the saturation point. The drain efficiency at 6-dB BO is still 73.4% which corresponds to an improvement of 23.9 points compared to balanced operation. Using a CDMA signal of 1-MHz bandwidth and 6.5-dB peak-to-average power ratio, the digital Doherty Tx achieves an average output power of 28.6 dBm with a drain efficiency of 56.5%.