Patent ID: 7489757

Claim:
A clock data recovery circuit comprising: a voltage control oscillator that generates a clock; a data identifier that identifies input data based on the clock generated by the voltage control oscillator; a frequency divider that divides a frequency of the input data; a duty ratio detector that determines a duty ratio of the input data; a variable delaying unit that generates a delay clock, which is obtained by delaying the clock generated by the voltage control oscillator based on the duty ratio of the input data; and a phase comparator that detects a phase difference between a phase of the delay clock generated by the variable delaying unit and a phase of the input data of which frequency is divided by the frequency divider, and generates a phase difference signal to eliminate the detected phase difference, wherein the voltage control oscillator generates the clock by adjusting an oscillation frequency based on the phase difference signal, and outputs the clock to both the data identifier and the variable delaying unit.