a delay locked loop is disclosed which is less responsive to noise so as to improve an ac parameter tac . the delay locked loop generally includes : a phase detector , a shift register , and a noise determining circuit which is enabled when the delay locked loop is locked for controlling driving of the shift register by determining whether a phase comparison signal from the phase detector is produced by noise . the noise determining circuit drives the shift register when the phase comparison signal has information for driving the shift register at least three times sequentially .