CMOS class-C VCO and QVCO for WLAN applications

Abstract

WLAN (Wireless Local Area Network) applications based on 802.11 protocol family have enjoyed a tremendous growth in both home and enterprise market since it was introduced in the market. More modules allowing for versatility are added to the mobile devices, pushing the battery capacity to the limit. Being one of the power hungry modules, wireless transceivers are calling for low power high performance designs so as to preserve or extend the mobile device usage life. The focus of this thesis is voltage controlled oscillator (VCO), one of the critical building blocks in the transceivers. Biased below threshold voltage but offering high figure of merit (FoM), Class-C VCOs are good low-power and high performance candidates. Two Class-C VCOs and one Class-C QVCO are presented, all designed and fabricated in 0.18um process. The designs feature low voltage supply and low power while providing good phase noise, meeting the 5GHz 802.11a standard requirement. The two VCOs use different gate biasing techniques to achieve Class-C biasing, RC network based and transformer based. To overcome the start-up issue associated with Class-C VCO, a dynamic bias scheme is adopted. An amplitude detector is used to provide a high bias for safe startup while a low bias during the steady state for Class-C operation. The two VCOs can cover the required band and consume only 1.7mW from 1V supply. The simulation results show FoM of -187dBc/Hz and -189dBc/Hz, which are among state-of-art designs. The QVCO uses transformer to achieve Class-C bias. A phase advance shifter is introduced for coupling, breaking the trade-off between phase noise and phase error. The phase shifter also provides ‘optimal coupling’ effect to maximize the tank Q to lower the phase noise. The two VCO’s current tails are combined into one to reduce flicker noise. Consuming 5.2mW from a 0.7V supply, the QVCO has a simulated FoM of -184dBc/Hz, which is also among the state-of-art designs.

Date of Award	2013
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology