Sense amplifier and driving method thereof, and semiconductor memory device having the sense amplifier

A semiconductor memory device, comprising:

• a bank having a cell array and a sense amplifier;
• a back bias voltage generating unit supplying a back bias voltage to the cell array of the bank;
• a negative drive voltage generating unit generating and providing negative driving voltages including a normal pull-up voltage, an overdrive voltage, a normal pull-down voltage, and a negative voltage as a voltage having a voltage level the same as a voltage level of the back bias voltage to the sense amplifier of the bank in accordance with an external command indicating an active mode or a refresh mode;
• and
• a switching unit opening a connection between the back bias voltage generating unit and the negative drive voltage generating unit when in the active mode, and sharing the back bias voltage between the back bias voltage generating unit and the negative drive voltage generating unit when in the refresh mode.