A technique to reduce flicker noise up-conversion in CMOS LC voltage-controlled oscillators

This work presents a technique for reducing the flicker noise up-conversion to phase noise in CMOS LC voltage-controlled oscillators (VCOs). The technique is a modification to a standard VCO, which can achieve about 6 dB of improvement in phase noise at close frequency offsets to the radio frequency (RF) carrier. The same technique has been applied to a differential Colpitts oscillator and achieved the same level of improvement compared to a standard VCO. A reference VCO, a modified VCO and a differential Colpitts VCO were designed to have the same bias current, the same fundamental frequency, the same frequency tuning range, the same gain, the same inductor value and the same output voltage swing to allow for a fair comparison between the oscillator architectures. The VCOs were fabricated using the CMOS part of a 0.35 μm BiCMOS process. Measurement results validate the simulations.