Device of phase locked-loop and the method using the same

A device of phase-locked loop, comprising:

• a phase frequency detector, receiving a reference clock and a dividing clock, and generating a control signal according to the reference clock and the dividing clock;
• and
• a charge pump, coupled to the phase frequency detector, having an adjustable current source, wherein the charge pump controls current output according to the control signal and regulates the adjustable current source to output a first current according to a first parameter and a second current according to a second parameter, wherein the first current is larger than the second current;
• a switch, coupled to the charge pump and a preset voltage;
• a low pass filter, coupled to the switch, for filtering the first current or the second current to generate a reference voltage while the switch is connecting the low pass filter and the charge pump, and sustaining a voltage level to the preset voltage while the switch is connecting the low pass filter and the preset voltage;
• a voltage controlled oscillator, coupled to the low pass filter, for generating an output clock according to a reference voltage;
• a frequency divider, coupled to the voltage controlled oscillator and the phase frequency detector, for receiving the output clock to generate the dividing clock;
• and
• a controller, coupled to the charge pump and the switch, for controlling the switch to connect the preset voltage and the low pass filter under an energy saving mode, controlling the switch to connect the charge pump and low pass filter while leaving the energy saving mode, directing the charge pump to output the first current according to the first parameter, and directing the charge pump to output the second current according to the second parameter after a preset time.