This paper presents an analysis of phase noise in differential cross-coupled inductance–capacitance (LC) oscillators. The effect of tail current and tank power dissipation on the voltage amplitude is shown. Various noise sources in the complementary cross-coupled pair are identified, and their effect on phase noise is analyzed. The predictions are in good agreement with measurements over a large range of tail currents and supply voltages. A 1.8-GHz LC oscillator with a phase noise of -121 dBc/Hz at 600 kHz is demonstrated, dissipating 6 mW of power using on-chip spiral inductors. The paper discusses the tank amplitude and its dependence on the tail current and supply voltage. It also analyzes the effect of noise sources in both active and resistive tank loss. The effect of tail-current noise is investigated, and design insights and experimental results are presented. A differential LC oscillator using spiral inductors is demonstrated that dissipates 6 mW of power while running at 1.8 GHz, with a phase noise of -121 dBc/Hz at 600-kHz offset. The paper also discusses the effect of noise sources in the oscillator, including the contribution of the effective series resistance of the inductor. The effect of a tail capacitor is analyzed, and it is shown that the use of an extra tail capacitor can improve the phase-noise behavior of the differential LC oscillator. The paper also discusses the effect of tail current noise, showing that the ISF associated with the tail-current source has a fundamental frequency that is double the oscillation frequency. The effect of the tail capacitor on high-frequency noise components is also discussed. The paper presents experimental results and design insights, showing that the complementary oscillator offers superior phase noise performance compared to an NMOS-only oscillator. The complementary structure offers higher transconductance for a given current, which results in faster switching of the cross-coupled differential pair. It also offers better rise- and fall-time symmetry, which results in a smaller 1/f³ noise corner. The paper concludes that the analysis of phase noise in differential cross-coupled LC oscillators is important for high-frequency circuit design. The predictions made are in good agreement with the measurements for different tail currents and supply voltages. A 1.8-GHz LC oscillator using on-chip spiral inductors exhibits a phase noise of -121 dBc/Hz at 600 kHz while dissipating 6 mW of power.This paper presents an analysis of phase noise in differential cross-coupled inductance–capacitance (LC) oscillators. The effect of tail current and tank power dissipation on the voltage amplitude is shown. Various noise sources in the complementary cross-coupled pair are identified, and their effect on phase noise is analyzed. The predictions are in good agreement with measurements over a large range of tail currents and supply voltages. A 1.8-GHz LC oscillator with a phase noise of -121 dBc/Hz at 600 kHz is demonstrated, dissipating 6 mW of power using on-chip spiral inductors. The paper discusses the tank amplitude and its dependence on the tail current and supply voltage. It also analyzes the effect of noise sources in both active and resistive tank loss. The effect of tail-current noise is investigated, and design insights and experimental results are presented. A differential LC oscillator using spiral inductors is demonstrated that dissipates 6 mW of power while running at 1.8 GHz, with a phase noise of -121 dBc/Hz at 600-kHz offset. The paper also discusses the effect of noise sources in the oscillator, including the contribution of the effective series resistance of the inductor. The effect of a tail capacitor is analyzed, and it is shown that the use of an extra tail capacitor can improve the phase-noise behavior of the differential LC oscillator. The paper also discusses the effect of tail current noise, showing that the ISF associated with the tail-current source has a fundamental frequency that is double the oscillation frequency. The effect of the tail capacitor on high-frequency noise components is also discussed. The paper presents experimental results and design insights, showing that the complementary oscillator offers superior phase noise performance compared to an NMOS-only oscillator. The complementary structure offers higher transconductance for a given current, which results in faster switching of the cross-coupled differential pair. It also offers better rise- and fall-time symmetry, which results in a smaller 1/f³ noise corner. The paper concludes that the analysis of phase noise in differential cross-coupled LC oscillators is important for high-frequency circuit design. The predictions made are in good agreement with the measurements for different tail currents and supply voltages. A 1.8-GHz LC oscillator using on-chip spiral inductors exhibits a phase noise of -121 dBc/Hz at 600 kHz while dissipating 6 mW of power.