Phase locked loop having fast lock function

1. A phase locked loop comprising:

a main voltage-controlled oscillator for which an oscillation frequency is adjusted by an offset current and a control voltage (Vctrl), the offset current being set by an offset current setting code (VCO_CON);

a phase frequency detector configured to adjust the control voltage by comparing an output signal (mCLK) of the main voltage-controlled oscillator and an input data signal (Data); and

an offset current setter configured to generate the offset current setting code for setting the offset current of the main voltage-controlled oscillator,

wherein the offset current setter comprises n sample voltage-controlled oscillators configured to generate n signals with different frequencies, respectively, and n counters configured to compare frequencies of each of the signals (sCLK) output from the n sample voltage-controlled oscillators and the input data signal, and is configured to generate the offset current setting code based on a comparison result of the n counters.

2. The phase locked loop of claim 1 , wherein the offset current setter generates the offset current setting code so that the offset current of the main voltage-controlled oscillator is substantially same as an offset current of a reference sample voltage-controlled oscillator, and

the reference sample voltage-controlled oscillator is a sample voltage-controlled oscillator having a frequency lower than and closest to the frequency of the input data signal among the n sample voltage-controlled oscillators.

3. The phase locked loop of claim 2 , wherein an oscillation frequency of each of the n sample voltage-controlled oscillators is adjusted by an offset current and a control voltage, a same control voltage of the main voltage-controlled oscillator is applied to the n sample voltage-controlled oscillators, and the offset current of each of the n sample voltage-controlled oscillators is set to a different value so that each of the n sample voltage-controlled oscillators oscillates at a different frequency.

4. The phase locked loop of claim 3 , wherein respective offset currents of the n sample voltage-controlled oscillators are determined by preset n sample offset current setting codes (sVCO_CON), and the offset current setting code of the main voltage-controlled oscillator is set to the same value as the sample offset current setting code of the reference sample voltage-controlled oscillator by the offset current setter, so that the offset current of the main voltage-controlled oscillator is set to a value substantially equal to the offset current of the reference sample voltage-controlled oscillator.

5. The phase locked loop of claim 4 , wherein the offset current setting code and the sample offset current setting code are n-bit codes.

6. The phase locked loop of claim 1 , wherein each of the n counters counts in synchronization with the output signal (sCLK) of a corresponding sample voltage-controlled oscillator and is reset by a signal obtained by dividing the input data signal by 2 n-1 .

7. The phase locked loop of claim 6 , wherein each of the n counters outputs an output value that is low or high depending on whether a count of 2 n-1 is completed before being reset by a signal obtained by dividing the input data signal by 2 n-1 , and the offset current setting code is an n-bit code determined by the n output values output from the n counters.

8. The phase locked loop of claim 1 , wherein the main voltage-controlled oscillator and each of the n sample voltage-controlled oscillators include n offset current sources and n offset current sinks, the n offset current sources and the n offset current sinks are each controlled to be turned on and off by corresponding switches, and corresponding pairs of the n offset current sources and the n offset current sinks are controlled to be turned on and off by a same signal.

9. The phase locked loop of claim 8 , wherein the n offset current sources and the n offset current sinks of the main voltage-controlled oscillator are controlled to be turned on and off by respective bits of the offset current setting code.