Dual band vco with improved phase noise.

摘要

A dual band VCO selects between the oscillator output frequencies by switching the resonant circuit elements in the active circuit. For each output frequency selected, the oscillator produces a single frequency signal and additional energy in the form of phase noise. This phase noise may be from sideband noise produced by modulation of the single frequency or produced by the active device in the oscillator as flicker noise, or the noise figure of the active device under large signal conditions or the filtering effect or the resonant circuit. Phase noise is reduced by shifting the bias point for the active device to the level where phase noise is minimum for each output frequency. At the time the output frequency is selectively switched, the bias to the active device is selectively switched to an optimum bias level for minimum phase noise for each respective selected frequency.