A 6.6 mW 1.25–2.25 GHz low phase noise PLL frequency synthesizer based on wide tuning range Class-C VCO

Abstract

Listen

Translate article

A wide tuning range low phase noise phase-locked loop (PLL) frequency synthesizer based on Class-C voltage-controlled oscillator (VCO) for IEEE 802.11ah is presented. Feedback loop technique is adopted to provide dynamic gate bias to the core transistors of the Class-C VCO, guaranteeing robust start-up against process, voltage and temperature (PVT) variations. Automatic frequency control (AFC) algorithm with tail bias switching scheme is proposed to guarantee start-up condition and maintain optimum oscillation amplitude across the whole tuning range, avoiding the deterioration of figure-of-merit (FoM). Implemented in 65-nm CMOS, the presented frequency synthesizer prototype achieves a tuning range of 57%, from 1.25GHz to 2.25GHz. Drawing 5.5mA current from a 1.2-V power supply, the prototype demonstrates −127.8 dBc/Hz phase noise at 1-MHz offset and −94.6 dBc/Hz in-band phase noise from a carrier of 1.536GHz. With the proposed dynamic gate bias technique and AFC-assisted tail bias switching scheme, the wide tuning range Class-C VCO exhibits a peak FoM of 187.5 dBc/Hz, with only 2.5dB variation across the whole tuning range.