A low power, low phase noise, square wave LC quadrature VCO for ISM band

This paper presents a phase-noise reduction technique for voltage-controlled oscillators (VCOs) using a harmonic tuned (HT) LC tank. The phase-noise suppression is achieved through almost rectangular-shaped VCO oscillating signal maximizing effectively signal slope at zero crossing points and with steering coupling section current transistors by quadrature signals. A comprehensive analysis for frequency and amplitude mismatch as high as 20% for third harmonic and its effect on phase noise improvement will be presented. It will be shown that by tuning the LC tank on fundamental and third harmonic and controlling current transistors, total phase noise improvement will be as high as 9 dB. Designed HT LC quadrature VCO has been implemented using TSMC 0.18 um 1P6M CMOS technology operating at 1.8 V for frequency band of 2.4-2.6 GHz (ISM band) with achieved phase noise of -139 dBc/Hz at frequency offset of 3 MHz. Total current drawn by VCO is 3.9 mA making the power consumption and its figure-of-merit (FOM) as low as 7 mW and -189 dB respectively.