Abstract: A VCO includes N delay stages that each contribute 180°/N phase shift at the VCO frequency of interest and provide a tunable selection of at least a fast delay and a slow delay path. Each delay stage includes a delay interpolator that smoothly interpolates between the delay paths within the stage. Each delay stage is coupled to a bandpass frequency selective network that acts as a load and helps filter phase noise. Feedback from the Nth delay stage to the first delay stage is via a phase shifter that provides a fixed phase at the frequency of interest of 180° or 0° that is required to sustain oscillation. VCO frequency is determined by the various stage delays and by the load circuit phase response. Individual stage delays are varied by interpolation such that overall VCO frequency control and phase noise performance are enhanced. Multiphase signals are available from the N delay stages.

Abstract: A VCO includes N delay stages that each contribute 180°/N phase shift at the VCO frequency of interest and provide a tunable selection of at least a fast delay and a slow delay path. Each delay stage includes a delay interpolator that smoothly interpolates between the delay paths within the stage. Each delay stage is coupled to a bandpass frequency selective network that acts as a load and helps filter phase noise. Feedback from the Nth delay stage to the first delay stage is via a phase shifter that provides a fixed phase at the frequency of interest of 180° or 0° that is required to sustain oscillation. VCO frequency is determined by the various stage delays and by the load circuit phase response. Individual stage delays are varied by interpolation such that overall VCO frequency control and phase noise performance are enhanced. Multiphase signals are available from the N delay stages.