Low Phase Noise Voltage-controlled Oscillator Design

Abstract

Two kinds of voltage-controlled oscillators (VCO) - active inductor based VCO and LC cross-coupled VCO - are studied in this work. Although the phase noise performance is not competitive, the proposed active inductor based VCO provide an alternative method to VCO design with very small chip area and large tuning range. The measurement shows a test oscillator based on active inductor topology successfully oscillates near 530MHz band. The phase noise of the widely used LC cross-coupled VCO is extensively investigated in this work. Under the widely used power dissipation and chip area constraints, a novel optimization procedure in LC oscillator design centered on a new inductance selection criterion is proposed. This optimization procedure is based on a physical phase noise model. From it, several closed-form expressions are derived to describe the phase noise generated in the LC oscillators, which indicate that the phase noise is proportional to the L2×gL3 factor. The minimum value of this factor for an area-limited spiral inductor is proven to monotonically decrease with increasing inductance, suggesting a larger inductance is helpful to reduce the phase noise in LC VCO design. The validity of the optimization procedure is proven by simulations. Two test chips are designed and measured.