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A novel methodology for reducing the phase noise of a cross-coupled LC tank VCO is presented, verified and measured. The fundamental relationship between the phase noise and the channel length of the cross-coupled MOS transistors is derived, and an optimum channel length of MOS transistors is indicated for a cross-coupled LC tank VCO with the lowest phase noise. A 2 GHz LC tank VCO is designed by this methodology and fabricated by 0.18 μm CMOS technology. The phase noise is -103.3 dBc/Hz at 100 kHz offset frequency and -118.9 dBc/Hz at 600 kHz offset with low-power consumption around 3.15 mW. The best FOM value of 186 is achieved compared to the reported 2 GHz VCO. The tuning range is 14% at a center frequency of 2.05 GHz.
Date of Conference: 23-26 May 2005