Aspects of the disclosure provide a circuit that includes a detector, a loop filter and a controller. The detector is configured to generate a first signal indicative a timing difference between a reference clock signal and a feedback clock signal. The feedback clock signal is generated based on an oscillating signal from an oscillator. The oscillator includes a first tuning circuit and a second tuning circuit to tune a frequency of the oscillating signal. The loop filter is configured to filter out a portion of frequency components from the first signal to generate a second signal for tuning the first tuning circuit of the oscillator. The controller is configured to tune the second tuning circuit based on the first signal and the second signal.