A low-voltage high-frequency CMOS LC-VCO using a transformer feedback

The paper describes a 0.18-mum CMOS 8.5-GHz LC-tank VCO using a technique of reducing parasitic capacitances. Compared to the traditional crossed coupled method with more parasitic capacitances, in this work a symmetry transformer introduced by a transformer on feedback currents from the active components is employed to reduce parasitic capacitances in the VCO. The proposed oscillator can easily arrive at the requirement for high-frequency operation with the tuning range of 8.32 to 8.75 GHz (5%) at 0.7 V supply. With operating at 8.5-GHz frequency, the measured phase noise is -121.6 dBc/Hz at 1-MHz offset under the power dissipation of 6 mW.