Patent ID: 7701268

Claim:
A clock generation circuit, comprising: a first system comprising a first oscillator controlled by a first control voltage for generating a clock signal according to an output of the first oscillator; and a second system comprising a second oscillator controlled by a second control voltage for generating a clock signal synchronized with said first system according to an output of the second oscillator, wherein said second system detects an amount of frequency fluctuation in said first oscillator, by monitoring a control voltage value that controls said second oscillator such that said second system is synchronized with said first system, according to a phase difference between a reference signal generated by using the output of said first oscillator and the output of said second oscillator, and wherein a correction value of the first control voltage is applied to said first oscillator based on the amount of frequency fluctuation detected in, and reported from, said second system, said amount of frequency fluctuation being reported to said first system independent of the output of said second oscillator.