RF-DAC challenges for mm-Wave transmitter in CMOS process

Abstract

This paper presents a part of the digital concept in the form of a mm-Wave Digital to Analog Radio Frequency Converter design. The mm-Wave transmitter is I/Q Cartesian RFDAC based on all-digital modulator concepts and challenges in the 28 nm CMOS process. Results and ideas presented are based on simulations and design requirements. The RFDAC implementation is a direct Base Band to RF conversion which offers a competitive solution to the classical RF transmitter chain. Final design is a class B current steering RFDAC for improved efficiency. In addition, the linearity vs. efficiency tradeoffs of the IQ Cartesian combining is discussed, assuming the simplified model of IQ interactions presented as well as considerations for beamforming architecture. Expected ENOB limitation before calibration would be of 7 bits reaching an EVM of 30dB.