An analysis of phase noise in differential cross-coupled inductance-capacit
ance (LC) oscillators is presented. The effect of tail current and tank pow
er dissipation on the voltage amplitude is shown, Various noise sources in
the complementary cross-coupled pair are identified, and their effect on ph
ase noise is analyzed. The predictions are in good agreement with measureme
nts over a large range of tail currents and supply voltages. A 1.8-GHz LC o
scillator with a phase noise of -121 dBc/Hz at 600 kHz is demonstrated, dis
sipating 6 mW of power using on-chip spiral inductors.