A delayed locked loop supports increased operation frequency in a semiconductor memory device. An output driver for use in a delay locked loop includes a first driving block for receiving an output from the delay locked loop to generate a first DLL clock for outputting read data corresponding to a read command, and a second driving block for receiving an output from the delay locked loop to generate a second DLL clock for reducing current consumption during a write operation, wherein the first driving block has larger delay amount than the second driving block.