Analysis and Minimization of Flicker Noise Up-Conversion in Voltage-Biased Oscillators

Traditional design of voltage-controlled oscillators (VCOs) can lead to unacceptable degradation of the $1/f^3$ phase-noise component when a broad tuning range is required. In this paper, the flicker noise up-conversion mechanisms in a voltage-biased topology are deeply investigated, providing general design guidelines for its mitigation. An improved VCO architecture is then introduced, where a segmented transconductor tailors the excess gain depending on the operating range to ensure that $1/f$ noise up-conversion remains minimal over the tuning range. The solution covers both fourth-generation and WiMAX 2.5-GHz bands and leads to a 10-dB reduction of the $1/f^3$ phase noise with respect to a traditional design without impairing the $1/f^2$ phase-noise performance.