An 18.5W Fully-Digital Transmitter with 60.4% Peak System Efficiency
A high-power digital transmitter (DTX) concept, targeting future low-cost, highly-integrated and energy-efficient mMIMO base stations, is presented. The proposed approach bridges the “historical” gap between low-voltage high-speed digital and high-voltage high-power RF devices. The resulting combination allows for a complete replacement of the traditional TX line-up, which includes signal-generation, up-conversion, and analog pre-drivers and power amplifier (PA), as such, facilitating drastic energy savings. The DTX principles are demonstrated by a dual TX line-up implemented in a dedicated VT -shifted LDMOS technology. Each 11-bit DTX line-up features 15 thermometer and 7 binary-weighted LDMOS output-stage segments, which are individually controlled by digital logic and high-speed drivers implemented in 40 nm CMOS technology. The realized DTX prototype exploits a 2.1 GHz centered class-BE output matching network and provides, at 20 V drain supply, 18.5 W (CW) output power with 66.7% drain and 60.4% system efficiencies. The suitability of the concept to handle modulated signals is demonstrated for a two-tone signal (Δf=80 kHz), yielding an IM3 < -51.4 dBc and a 10 MHz 256-QAM signal, achieving an ACLR of -46.1 dBc and 1.2% EVM.