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, gm 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.