Tuning Methods and Tuning Figures of Merit for LC Oscillators

LC oscillators are used most widely in wireless applications as their resonator can store energy, making its phase noise to carrier ratio given a certain power budget superior to ring oscillators. The tuning range of LC oscillators, especially at high frequencies where parasitic capacitance starts becoming significant, is another important design issue. This paper investigates the influence of tuning methods on the oscillator phase noise. Five tuning methods are compared: varactor tuning, band switching, oscillator switching, active tuning, and phase shift tuning . In addition, for the tuning methods active tuning and phase shift tuning, effective quality factors are introduced as a figure of merit to assess the phase noise performance. Finally, a figure of merit is introduced that makes a comparison between tuning methods possible by normalizing the quality factor of tuning methods for a given tuning range. Keywords— LC oscillators, tuning methods, passive tuning, active tuning, phase noise, figures of merit