Envelope delta-sigma-modulated voltage-mode class-S PA

This paper reports on a digital transmitter architecture for the 450 MHz band using an envelope delta-sigma modulator realized in CMOS and a voltage-mode class-S PA based on GaN MMICs. The class-S PA is characterized with narrowband single-tone signals and a single-carrier downlink WCDMA signal with a peak-to-average power ratio of 7.5 dB. Using single-tone excitation the PA shows a maximum drain efficiency of 86% and a peak output power of 4.4 W. At 6 dB and 10 dB back-off, 59% and 36% efficiency are achieved, respectively. With the WCDMA input signal a maximum drain efficiency of 64% and an output power of 0.7 W is reached. The ACLR shows values of about -34 dBc (5 MHz) and -38 dBc (10 MHz). This is the first complete voltage-mode class-S PA chain characterized with standard communication signals.