An analysis of 1/f2 phase noise in bipolar colpitts oscillators (With a digression on bipolar differential-pair LC oscillators)

In English This work presents an analysis of phase noise in the 1/f(2) region displayed by both single-ended and differential bipolar Colpitts oscillators. Very accurate and rigorous symbolic phase noise expressions are derived, enabling a deeper insight into the major mechanisms of phase noise generation, and providing new tools for design optimization. Phase noise expressions for the cross-coupled differential-pair LC-tank oscillator are derived as well.
The theoretical analysis is validated on a 3 GHz differential bipolar Colpitts VCO implemented in a 0.35 mu m SiGe process. Measurements show a phase noise of -123 dBc/Hz or less at 1 MHz offset frequency from the 2.8-3.1 GHz carrier, for a phase noise figure-of-merit of at least 183 dBc/Hz across the tuning range. A very good agreement between theory, numerical simulations, and. measurements is observed.