Low-phase-noise CMOS VCO with harmonically tuned LC tank

A low-phase-noise voltage-controlled oscillator (VCO) has been demonstrated using a harmonically tuned LC resonance tank. In this circuit con,figuration, the voltage shape at the differential cell is almost rectangular; thus, the cell is switched effectively and the phase noise is reduced. More importantly, the proposed tank suppresses down-conversion of the noise around 2f(0) to the phase noise, due to the 2(nd) harmonic short of the tank. Therefore, the, phase noise of the VCO based on the tank is improved considerably. The VCO for 1-GHz operation has been realized using a 0.35-mum CMOS process. It shows a phase noise of -111.6 dBc/Hz at 100 KHz offset, which is a 5.7-dB improvement over a comparable standard VCO. (C) 2004 Wiley Periodicals, Inc.