Phase locked loop and semiconductor device using the same

摘要

It is an object of the present invention to provide a phase locked loop in which a voltage signal input to a voltage controlled oscillator after a return from a stand-by state becomes constant in a short time and power consumption is reduced. A transistor including a semiconductor layer formed using an oxide semiconductor material is provided between an input terminal of a voltage controlled oscillator and a capacitor of a loop filter. The transistor is turned on in a normal operation state and turned off in a stand-by state.

主权项

1. A driving method of a semiconductor device including a voltage controlled oscillator and 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; and turning off the transistor when a cycle of a periodic signal output from the voltage controlled oscillator is constant so that the capacitor holds the potential, wherein a channel formation region of the transistor comprises an oxide semiconductor material.