US Patent 7450455 Semiconductor memory device and driving method thereof

A semiconductor memory device prevents deterioration of refresh operation caused by sensing noise and a driving method thereof. First pull-down and second pull-down voltages which are different from each other are as a pull-down voltage of a bit line sense amplifier. The first and the second pull-down voltages are used in different driving periods to protect data from noises caused by another memory bank. A driving period can be separated into an initial sensing period, wherein large currents are consumed and significant noise is generated, and a subsequent stable period. The driving period can be separated into a pre-precharge period and a post-precharge period.