A phase locked loop capable of improving stability without addition of chip area is provided, in which an integral part comprises a first phase frequency detector providing a phase error signal, a first charge pump circuit generating a control signal according to the phase error signal, a controllable oscillator providing an output clock according to the control signal, and a sampling adjustment unit decreasing the number of times the control signal is updated according to the phase error signal. A proportional part is coupled between the controllable oscillator and a reference clock and operated in a fraction mode.