Delay locked loop circuit having coarse lock time adaptive to frequency band and semiconductor memory device having the delay locked loop circuit

Abstract

Provided are a DLL circuit having a coarse lock time adaptive to a frequency band of an external clock signal and a semiconductor memory device having the DLL circuit. The DLL circuit includes a delay circuit, a replica circuit, and a phase detector. The phase detector generates a first comparison signal used by the delay circuit to delay an external clock signal in units of a first cell delay time or a second comparison signal used by the delay circuit to delay the external clock signal in units of a second cell delay time. The DLL circuit delays the external clock signal by the cell delay time adaptive to the frequency band of the external clock signal, and thus can perform an accurate and rapid coarse lock operation for the entire frequency band.