Abstract: A method to improve the LCVCOs phase noise characteristic is presented without increasing the power consumption. Based on the structure of conventional LCVCO, a PMOS transistor was used as the tail current source and a LC tank was included to filter the second harmonic. The switching capacitor array was adopted to reduce the VCO gain, thus lower the impact of control voltage disturbance on the output frequency. The developed circuit was implemented under Chartered 0.18 μm RF CMOS processes. The power consumption of the 1.84 GHz LCVCO is 16.6 mW, and the measured phase noises are -105 dB/Hz at 100 kHz and -123 dB/Hz at 1 MHz offset frequencies, respectively.