Patent ID: 8519801

Claim:
A digitally controlled oscillator, comprising: a pair of transistors cross-coupled to each other for providing an output signal; a switched capacitor array coupled to the pair of transistors, for tuning a frequency of the output signal; and a plurality of frequency tracking units coupled to the pair of transistors, for tuning the frequency of the output signal to a target frequency, wherein at least one of the frequency tracking units is capable of selectively providing only one of a first capacitance and a second capacitance, and a tuning resolution of the frequency tracking units is determined by a difference between the first and second capacitances, wherein at least one of the frequency tracking units comprises: a first capacitor coupled to one drain of the pair of transistors; a second capacitor coupled between the first capacitor and a ground; and a first switch coupled to the second capacitor in parallel, wherein the first switch is arranged to have only ON and OFF states; wherein the at least one of the frequency tracking units provides only the first capacitance when the first switch is in the ON state and provides the second capacitance when the first switch is in the OFF state.