Oscillator tuning for phase-locked loop circuit

摘要

In one example, a method of tuning an oscillator of a phase-locked loop (PLL) circuit includes adjusting a coarse control signal to select one of a plurality of frequency tuning curves of the oscillator. The method includes adjusting a fine control signal to select a position on the selected frequency tuning curve. A frequency of the oscillator is determined by the coarse control signal and the fine control signal. The method includes attempting to detect a lock between a feedback signal and a reference signal. A frequency of the feedback signal is determined by the frequency of the oscillator. The method includes comparing the fine control signal to a reference value if the lock is detected. The method includes adjusting the coarse control signal to select a different one of the frequency tuning curves if the selected position on the selected frequency tuning curve is outside a desired tuning range.