A cycle control circuit may include a judgement pulse generation circuit, a detection signal generation circuit or a flag generation circuit. The judgement pulse generation circuit may be configured to set a predetermined value based on an initialization signal and a period signal, and to generate a judgment pulse. The detection signal generation circuit may be configured to generate a detection signal from a reference flag. The flag generation circuit may be configured to generate a reference flag based on a reference signal. A cycle of the reference signal may be maintained or adjusted based on the reference flag.