Gm- and Swing-Enhanced Colpitts VCO by Optimization of Capacitance Ratio

This letter presents a negative conductance (G_m)and swing-enhanced Colpitts voltage-controlled oscillator (VCO) based on optimization of the capacitance ratio. In the proposed VCO structure, a current source typically used in conventional VCOs is replaced with an inductor to increase the output voltage swing. A current-reuse configuration is also adopted to decrease power consumption. Theoretical analyses and simulations show that the devised VCO with an optimized capacitance ratio exhibits enhanced G_m and swing when compared to a conventional VCO. Measurements revealed a phase noise of -129.67 dBc/Hz at a 1-MHz offset frequency from the 2.2-GHz carrier, while power consumption was 2.2 mW from a 1.2-V supply voltage. This resulted in a figure-of-merit of -193.1 dBc/Hz. The proposed device was implemented using a 65-nm CMOS process.