Delay locked loop and locking method thereof

摘要

The present invention provides a delay locked loop of a semiconductor memory device for preventing a stuck fail. The DLL of the present invention includes: a buffer for outputting a first clock corresponding to an in-phase of an external clock and outputting a second clock corresponding to an out-of-phase of the external clock; a phase comparator for outputting a control signal to increase/decrease a delay amount after comparing the first clock with a phase of a feedback clock; a shift register for outputting a shift signal in accordance with the control signal; a multiplexing unit for selecting one between the first and the second clocks by using the output of the phase comparator and the output of the shift register.