| 摘要 |
A synchronous memory device having a normal mode and a power down mode includes a power down mode controller for generating a power down mode control signal in response to a clock enable signal, thereby determining onset or termination of a power down mode. A clock buffering unit buffers an external clock signal in response to the power down mode control signal and outputs first and second internal clock signals. A clock selection unit selects one of the first and second internal clock signals based on the power down mode control signal to output the selected signal as an intermediate output clock signal. A phase update unit performs a phase update operation by using the intermediate output clock signal to output a delay locked loop (DLL) clock signal, the first internal clock signal differing in frequency from the second internal clock signal.
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