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 驴m CMOS technology, the VCO consumes 9.52mA current from 1.8V supply voltage and operates with a frequency band from 885MHz to 1.342GHz (41% tuning range). As driving sub-harmonic mixer, the proposed VCO covers three standards: cdma2000 1脳 (1.84 1.87GHz), WCDMA (2.11 2.17GHz), WiBro (2.3 2.4GHz). The simulated phase noise is -107dBc, -133dBc, and -155dBc at 100kHz, 1MHz, and 10MHz offset frequency for cdma2000 1x, WCDMA, and WiBro respectively.
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