More on the /49/61/102/50Phase Noise Performance of CMOS Differential-Pair LC-Tank Oscillators

Abstract

This paper presents a rigorous phase noise analysis in the /49 /102/50region for the differential CMOSLC-tank oscillator with both nMOS and pMOS switch pairs. A compact, closed-form phase noise equation is obtained, accounting for the noise contributions from both tank losses and transistors currents, which allows a ro- bust comparison between LC oscillators built with either one or two switch pairs. The fabricated oscillator prototype is tunable between 2.15 and 2.35 GHz, and shows a phase noise of 144 dBc/Hz at 3 MHz offset from the 2.3 GHz carrier for a 4 mA bias current. The phase noise figure-of-merit is practically constant across the tuning range, with a minimum of 191.5 dBc/Hz. A reference single-switch-pair oscil- lator has been implemented and tested as well, and the difference between the phase noise levels displayed by the two oscillators is very nearly the one expected from theory.