A Low Phase Noise Octa-Phase LC VCO for Multi-band Direct Conversion Receiver

This paper presents an octa-phase LC VCO for a multi-band direct conversion receiver. To obtain the octa-phase signal and low phase noise characteristic, four identical LC VCOs are connected by using series coupling transistors. For a multi-band application, a band tuning circuit that is composed of a switch capacitor circuit and two MOS varactors is proposed. Using two varactors, the VCO can be immune to process variation of the oscillation frequency. Designed in 0.18 mum CMOS technology, the VCO consumes 9.52 mA current from 1.8 V supply voltage and operates with a frequency band from 885 MHz to 1.342 GHz (41% tuning range). As driving sub-harmonic mixer, the proposed VCO covers three standards: cdma2000 1x (1.84 ~ 1.87 GHz), WCDMA (2.11 ~ 2.17 GHz), WiBro (2.3 ~ 2.4 GHz). The simulated phase noise is -107 dBc, -133 dBc, and -155 dBc at 100 kHz, 1 MHz, and 10 MHz offset frequency for cdma2000 1x, WCDMA, and WiBro respectively.