Phase locked loop circuit for semiconductor integrated circuit, has selector which selects voltage controlled oscillation circuit of optimum oscillation frequency band from several oscillation circuits in oscillator

摘要

A low pass filter (2) outputs control voltage signal (S2) based on the phase difference signals (S1) output from phase comparator (1). An oscillator (3) changes the oscillation frequency of each oscillator circuit (4) in it according to the control voltage signal. A selector (5) selects an oscillation circuit (4) of optimum oscillation frequency band from several oscillation circuits in oscillator. A phase comparator (1) compares the phase difference between external clock signal (CK1) and internal clock signal (CK2) and outputs a phase difference signal (S1). A low pass filter outputs control voltage (S2) based on phase difference signal. A voltage controlled oscillators circuit e.g. ring oscillator has several converters which are serially connected to frequency variable invertors to control frequency. INDEPENDENT CLAIM are also included for the following: (a) semiconductor integrated circuit; (b) voltage controlled oscillator