Output driver capable of controlling slew rate of output signal according to operating frequency information or CAS latency information

An output driver that can effectively adjust the slew rate of the output signal is disclosed in accordance with the directly detecting a frequency of an operating clock or according to CAS latency information including the operation frequency information of the semiconductor memory device, the detection frequency information. And the output driver, comprising a driver pull-down to pull-down the pull-up driver and the pull-up output of the output stage. In addition, the output driver is characterized in that the variable to provided, and the pull-up driver and the driving ability of the pull-down driver, the CAS response to the latency information, the mode register set that stores the CAS latency (CAS latency) information of the semiconductor memory device do. The output driver may include a frequency detector for storage by detecting the operating frequency of the semiconductor memory device, in this case, the driving ability of the pull-up driver and the pull-down driver is varied in response to the output signal of the frequency detector.