Delay-locked loop (DLL) circuit apparatus and method for locking thereof

1. A delay-locked loop (DLL) circuit apparatus comprising:

a storage configured to store a control signal voltage value corresponding to a DLL locking state as a reference voltage value;

a lock detector configured to determine when a DLL unlocking state occurs using an external clock signal and a feedback internal clock signal;

a level determiner configured to determine when a DLL unlocking state occurs using a level of a control signal voltage value; and

an initializer configured to receive a reset signal from at least one of the lock detector and the level determiner in response to determining that the DLL unlocking state occurs, and configured to reset a control signal voltage value of the DLL circuit apparatus to the reference voltage value as stored in the storage in response to receiving the reset signal.

2. The DLL circuit apparatus of claim 1 , wherein the lock detector is configured to detect a phase difference between the external clock signal and the feedback internal clock signal, and configured to determine that the DLL unlocking state occurs in response to detecting the phase difference.

3. The DLL circuit apparatus of claim 2 , wherein the lock detector comprises:

a plurality of flip-flops configured to receive the external clock signal and the feedback internal clock signal; and

an AND gate configured to calculate an AND operation of output signals received from the flip-flops and output the result of the AND operation as a high logic signal or a low logic signal.

4. The DLL circuit apparatus of claim 3 , wherein the plurality of flip-flops are DQ flip-flops.

5. The DLL circuit apparatus of claim 3 , wherein the result of the AND operation is transmitted to the initializer as a reset signal.

6. The DLL circuit apparatus of claim 1 , wherein the level determiner comprises:

a first comparator configured to compare the control signal voltage value with a minimum DLL locking voltage value;

a second comparator configured to compare the control signal voltage value with a maximum DLL locking voltage value; and

an OR gate configured to output the reset signal to the initializer in response to the control signal voltage value being less than the minimum DLL locking voltage value or greater than the maximum DLL locking voltage value.

7. The DLL circuit apparatus of claim 2 , wherein the storage comprises:

a sampler configured to sample the control signal voltage value in synchronization with the external clock signal, when the DLL circuit apparatus is in a locking state; and

a hold unit configured to store the sampled control signal voltage value.

8. The DLL circuit apparatus of claim 7 , wherein at least one of the sampler and the hold unit further comprises an amplifier.

9. The DLL circuit apparatus of claim 7 , wherein the hold unit is configured to provide the stored control signal voltage value to the initializer as the reference voltage value.

10. A delay-locked loop (DLL) locking method, comprising:

storing a control signal voltage value corresponding to a DLL locking state as a reference voltage value;

determining when a DLL unlocking state occurs by comparing an external clock signal and a feedback internal clock signal, or by detecting a change in level of the control signal voltage value; and

performing DLL locking by resetting the control signal voltage value in the DLL unlocking to the stored reference voltage value in response to detecting the DLL unlocking.

11. The DLL locking method of claim 10 , wherein determining when a DLL unlocking state occurs comprises comparing phases of the external clock signal and the feedback internal clock signal.

12. The DLL locking method of claim 11 , wherein the detecting when the DLL unlocking state further comprises determining that the DLL unlocking occurs in response to the phases being different.

13. The DLL locking method of claim 10 , wherein the detecting that the DLL unlocking occurs comprises determining that the DLL unlocking occurs in response to the control signal voltage value deviating from a normal operation range.

14. The DLL locking method of claim 13 , wherein the normal operation range is a normal operation range of a voltage controlled delay line for receiving the control signal voltage value and generating an internal clock signal.

15. The DLL locking method of claim 10 , wherein resetting the control signal voltage value in the DLL comprises changing a setting of a charge pump of the DLL.

16. A delay-locked loop (DLL) circuit apparatus comprising:

a lock detector configured to generate a reset signal in response to a DLL unlocking state being determined to occur using an external clock signal and a feedback internal clock signal;

a level determiner configured to generate a reset signal in response to a DLL unlocking state being determined to occur using a level of a control signal voltage value; and

an initializer configured to reset a control signal voltage value of the DLL circuit apparatus to a stored reference voltage value corresponding to a DLL locking state in response to the reset signal being generated.

17. The DLL circuit apparatus of claim 16 , wherein the lock detector is configured to detect a phase difference between the external clock signal and the feedback internal clock signal, and configured to generate the reset signal in response to detecting the phase difference.

18. The DLL circuit apparatus of claim 16 , further comprising a storage configured to store a control signal voltage value corresponding to a DLL locking state as the reference voltage value.

19. The DLL circuit apparatus of claim 16 , wherein the level determiner comprises:

a first comparator configured to compare the control signal voltage value with a minimum DLL locking voltage value;

a second comparator configured to compare the control signal voltage value with a maximum DLL locking voltage value; and

an OR gate configured to generate the reset signal in response to the control signal voltage value being less than the minimum DLL locking voltage value or greater than the maximum DLL locking voltage value.