A CMOS LC-tank VCO and phase shifting network for direct conversion receiver of IEEE 802.11a

A CMOS LC-tank VCO and phase-shifting network are described for a direct-conversion receiver of IEEE 802.11a. The direct-conversion receiver is configured to have sub-harmonic mixing structure which requires multi-phase local oscillator (LO) signals spaced by 45°. A poly-phase filter with 3and 4-stage RC networks generates multi-phase LO signals whose amplitude imbalance is removed by cascaded limiting amplifiers. The VCO and phase-shifting network were implemented with a 6-metal, 1-poly 0.18-μm CMOS technology. The measured results show the VCO can be tuned from 2.0GHz to 2.7GHz which is sufficient to cover the lower and mid-band of IEEE 802.11a with sub-harmonic mixing direct-conversion architecture. The phase noise of the VCO is -119.68dBc/Hz at 1MHz offset. The phase-shifting network provides multi-phase LO signals with less than 0.75° phase error. The total power consumption of VCO and phase-shifting network is 61mW under 1.8V supply voltage.