Analysis and Design of Open-Loop Multiphase Local-Oscillator Generator for Wireless Applications

Abstract—Multiphase local-oscillator (LO) generators have been widely adopted in modern wireless communication systems. This paper describes the analysis and design of two open-loop multiphase (quadri and octave) LO generators, which can lead to speed relaxation of the phase-locked loop and voltage-controlled oscillator when compared with conventional frequency-division methods. The mathematical model, sizing considerations, and two design examples targeting mobile-TV applications are presented. The first one is an octave-phase LO generator designed in 90-nm CMOS featuring multiple switchable phase correctors in cascade. It covers the VHF-III and UHF bands with an optimized phase precision within 0.8. The second one combines quadri- and octave-phase LO generation to cover the full band of mobile TV from 170 to 1700 MHz. Optimized in 65-nm CMOS, it can be operated in octave-phase mode for image-reject harmonic-reject downconversion or in quadri-phase mode for simple image-reject downconversion. Extensive simulations accounting for process variations show that the achieved phase precisions are within 1.5 (quadri) and 1 (octave). The phase-noise performance is comparable with state-of-the-art solutions. Index Terms—CMOS, harmonic-reject mixer, image-reject mixer, mobile-TV tuner, multiphase local-oscillator (LO) gener-ator, phase-locked loop (PLL), radio frequency (RF), voltage-con-trolled oscillator (VCO). I