Abidi, “A filtering technique to lower LC oscillator phase noise

Abstract—Based on a physical understanding of phase-noise mechanisms, a passive LC filter is found to lower the phase-noise factor in a differential oscillator to its fundamental minimum. Three fully integrated LC voltage-controlled oscillators (VCOs) serve as a proof of concept. Two 1.1-GHz VCOs achieve 153 dBc/Hz at 3 MHz offset, biased at 3.7 mA from 2.5 V. A 2.1-GHz VCO achieves 148 dBc/Hz at 15 MHz offset, taking 4 mA from a 2.7-V supply. All oscillators use fully integrated resonators, and the first two exceed discrete transistor modules in figure of merit. Practical aspects and repercussions of the technique are discussed. Index Terms—Analog integrated circuits, CMOS oscillators, noise filtering, optimization, phase noise, radio frequency, spiral inductors, voltage-controlled oscillators. I