Methods of generating internal clock signals from external clock signals and of measuring the frequency of external clock signals and related frequency measuring circuits and semiconductor memory devices

摘要

Pursuant to certain embodiments of the present invention, methods of generating an internal clock signal in a semiconductor memory device are provided in which the frequency of an external clock signal is measured. A CAS latency value of the semiconductor memory device is automatically set based at least in part on the measured frequency of the external clock signal. The automatically set CAS latency value is then used to generate the internal clock signal from the external clock signal. In these methods, the delay of a delay lock loop of the semiconductor memory device may be based at least in part on the automatically set CAS latency value. The internal clock signal may be generated from the external clock signal using the delay lock loop. Circuits and methods for measuring the frequency of the external clock signal are also provided.