Efficiency and Linearity of Digital Class-C like Transmitters

Abstract

An energy-efficient, intrinsically linear, digital class-C like operation-mode is investigated for use in high-power digital transmitters (DTXs), which target next generation mMIMO base stations that offer lower costs, higher integration, and improved system efficiency. The proposed operation utilizes class-B/C output matching in combination with duty-cycle reduction and current-mode operation of a segmented output stage. Its performance in terms of efficiency, output power, and linearity is benchmarked with analog class-B/C operation. The proposed digital class-C like operation has been experimentally verified using a fully-digital, dual TX line-up with VT-shifted segmented LDMOS output stages. All output stage segments are individually controlled by high-speed digital drivers implemented in 40 nm CMOS technology. The realized prototype provides 25.9 W (CW) output power with 75.7 % drain and 72.9 % system efficiencies, at 930 MHz and at 28 V drain supply.