Analyzing of Phase Noise in CMOS LC Oscillators

Analyses of phase noise in differential cross coupled inductance-capacitance (LC) oscillators and single-ended Colpitts oscillators are presented. Various noise sources in these oscillators are identified, and then their effects on phase noise are analyzed. To simulate the Impulse Sensitivity and Noise Modulation Factor waveforms of the above mentioned oscillators, the direct impulse response measurement method of is implemented in HSpice. We simulated two different oscillators, using the same tank inductance and are tuned to oscillate at the center frequency of 1.8 GHz with a voltage source of 1.8 V in 0.18 RF CMOS process. The inductors have a quality factor of 5 at 1.8 GHz and operate in the current limited regime.