A Current-Switching and $g _{m}$-Enhanced Colpitts Quadrature VCO

This letter presents the design and analysis for a low-phase-noise and low-power Colpitts quadrature voltage-controlled oscillator (QVCO). The Colpitts QVCO employs current switching to lower the phase noise, g
m
enhancement to improve the startup condition in the oscillator core, and device reuse to realize anti-phase injection locking for QVCO operation. The proposed Colpitts QVCO has superior phase noise than cross-coupled LC tank VCO and outperforms conventional QVCO in phase noise, quadrature phase accuracy, and tuning range. The fabricated 0.18 μm CMOS Colpitts QVCO draws 500 μA from a 1.5 V power supply and exhibits a phase noise of -118 dBc/Hz at 1 MHz offset and a quadrature phase error of 0.3° at the center frequency of 488 MHz.