A phase locked loop is provided. The phase locked loop includes a detector, a controlled oscillator and a filtering unit coupled between the detector and the controlled oscillator. The detector generates a phase difference signal according to a reference frequency and an oscillation signal. The controlled oscillator generates the oscillation signal according to a filtered signal. The filtering unit filters the phase difference signal to generate the filtered signal, and the filtering unit has a high frequency filter of which a pole is greater than the reference frequency and less than a frequency of the oscillation signal.