Patent ID: 7288997

Claim:
A phase lock loop capable of operating in a plurality of select states, generating a feedback clock tracing a reference clock, the phase lock loop comprising: a phase/frequency detector comparing phase difference between the feedback clock and the reference clock to generate a comparative signal; a charge pump generating a control voltage according to the comparative signal; a voltage-controlled oscillator operating in one of the select states to generate an oscillating clock according to the control voltage and a select voltage, wherein the ratio of the frequency of the oscillating clock to the frequency of the feedback clock is an integer; and a state select circuit adjusting the select voltage in accordance with the reference clock to select one of the select states, comprising: a highest/lowest clock generator, generating a highest frequency clock and a lowest frequency clock wherein the highest frequency and lowest frequency clocks corresond to the highest frequency oscillating clock and the lowest frequency oscillating clock generated by the voltage-controlled oscillator in one of the select states respectively; a frequency comparator comparing the frequency of the reference clock with the frequency of the highest frequency oscillating clock and the frequency of the lowest frequency oscillating clock and generate a comparison result signal; and a control circuit generating the select voltage according to the comparison result signal to the highest/lowest clock generator and the voltage-controlled oscillator; wherein the voltage-controlled oscillator is a first voltage-controlled oscillator, and the highest/lowest clock generator comprises a second voltage-controlled oscillator and a third voltage-controlled oscillator receiving the select voltage to generate the highest frequency clock and the lowest frequency clock according to a first fixed voltage and a second fixed voltage respectively wherein the first fixed voltage is the maximum control voltage and the second fixed voltage is the minimum control voltage.