A Study of a Millimeter-Wave Transmitter Architecture Realizing QAM Directly in RF Domain

Abstract

Realization of high-order modulation schemes directly in the RF domain enables the generation of spectrally efficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4^M$</tex-math> </inline-formula> quadrature-amplitude-modulated ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4^M$</tex-math> </inline-formula> QAM) symbols using the vectorial summation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$</tex-math> </inline-formula> quadrature phase-shift keying (QPSK) signals whose amplitudes are progressively scaled by a constant factor of two. Called RF-QAM, this approach leads to numerous advantages including the elimination of power-hungry digital-to-analog converter (DAC) and the mitigation of stringent linearity requirement of the front-end power amplifier (PA). This paper presents a comprehensive comparative study of RF-QAM and conventional transmitters. The design issues associated with the front end and the mixed-signal blocks for both architectures are investigated, and the performance of these two designs is compared. Various circuit-and system-level simulations verify the superior performance of the RF-QAM transmitter compared to the conventional counterpart.