Phase locked loop and semiconductor device using the same

A driving method of a semiconductor device including a phase locked loop including a loop filter which includes a transistor and a capacitor electrically connected to the transistor, the driving method comprising the steps of:

• inputting a potential to the loop filter;
• turning off the transistor so that the capacitor holds the potential and the phase locked loop becomes a stand-by state;
• and
• turning on the transistor so that the phase locked loop is returned from the stand-by state,
• wherein a channel formation region of the transistor comprises an oxide semiconductor material,
• wherein the phase locked loop includes a voltage controlled oscillator, and
• wherein the transistor is turned off when a cycle of a periodic signal output from the voltage controlled oscillator is constant.

A driving method of a semiconductor device including a phase locked loop, the driving method comprising the steps of:

• converting a phase difference between two periodic signals into a first periodic signal by a phase frequency detector and outputting the first periodic signal into a charge pump;
• converting the first periodic signal into a current signal by the charge pump and outputting the current signal into a loop filter including a transistor;
• converting the current signal into a voltage signal by the loop filter and outputting the voltage signal into a voltage controlled oscillator;
• and
• outputting a second periodic signal from the voltage controlled oscillator wherein the second periodic signal is a signal in accordance with the voltage signal,
• wherein the transistor is configured to be turned off when a cycle of the second periodic signal is constant, and
• wherein a channel formation region of the transistor comprises an oxide semiconductor material.