Patent ID: 7417512
Filing Date: 2008-08-26
Classification: H03B,H03L

Abstract:
1. A dual mode tuning digitally controlled crystal oscillator comprising: a crystal resonator that resonates at substantially a predetermined resonance frequency; an oscillation circuit, coupled to the crystal resonator, generating an oscillation frequency based on the predetermined resonance frequency to output the oscillation frequency; a coarse mode tuning unit performing a coarse mode tuning operation on the oscillation frequency by controlling the oscillation circuit in response to one of a coarse mode tuning signal and a controlled coarse mode tuning signal; a fine mode tuning unit performing a fine mode tuning operation on the oscillation frequency by controlling the oscillation circuit in response to a fine mode tuning signal; and a tuning control unit controlling the coarse mode tuning signal to output the controlled coarse mode tuning signal to the coarse mode tuning unit in response to the fine mode tuning signal, wherein the tuning control unit comprises: a signal comparison unit determining whether the fine mode tuning signal approaches an upper or a lower limit of the fine mode tuning signal; and a coarse mode tuning control unit controlling the coarse mode tuning signal based on a determination of the signal comparison unit to output the internal coarse mode signal to the coarse mode tuning unit.