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 9dB. Designed HT LC Quadrature VCO has been implemented using TSMC 0.18um 1P6M CMOS technology operating at 1.8V for frequency band of 2.4-2.6GHz (ISM band) with achieved phase noise of -139dBc/Hz at frequency offset of 3MHz. Total current drawn by VCO is 3.9mA making the power consumption and its Figure-of-Merit (FOM) as low as 7mW and -189dB respectively.
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