Page buffer and memory device including the same
A page buffer includes a charging circuit, first and second storage circuits, and a selection circuit. The charging circuit charges a bit line during a precharging period. The first storage circuit determines and stores data corresponding to a state of a selected memory cell among memory cells connected to the bit line while the charging circuit charges the bit line. The second storage circuit, which is a circuit separate from the first storage circuit, determines and stores data corresponding to a state of the selected memory cell after the precharging period. The selection circuit outputs a control voltage controlling a switch element connected between the bit line and the charging circuit, and determines a magnitude of the control voltage during the precharging period, based on the data stored in the first storage circuit.
1. A memory device comprising:
a memory cell array including a plurality of memory cells, and a plurality of bit lines connected to the plurality of memory cells; and
a memory controller configured to read data corresponding to a threshold voltage of a selected memory cell connected to a selected bit line among the plurality of bit lines, input a first charging current to the selected bit line during a first period of time, and input a second charging current lower than the first charging current to the selected bit line during a second period of time, after the first period of time, when the threshold voltage of the selected memory cell is higher than a reference voltage.
2. The memory device of claim 1 , wherein, when the threshold voltage of the selected memory cell is lower than the reference voltage, the first charging current is input to the selected bit line during the second period of time.
3. The memory device of claim 1 , wherein the memory controller comprises:
a charging circuit connected to the selected bit line by a switch element;
a storage circuit configured to read and store data of the selected memory cell; and
a selection circuit configured to determine a current of the switch element as one of the first charging current and the second charging current, based on data stored in the storage circuit.
4. The memory device of claim 3 , wherein the storage circuit comprises a first storage circuit configured to read and store data corresponding to a first threshold voltage of the selected memory cell during the first period of time, and a second storage circuit configured to read and store data corresponding to a second threshold voltage of the selected memory cell during the second period of time, and
wherein the selection circuit is further configured to determine the current of the switch element as one of the first charging current and the second charging current during the second period of time, based on data stored in the first storage circuit.
5. The memory device of claim 1 , wherein the reference voltage has a first reference voltage, and a second reference voltage higher than the first reference voltage.
6. The memory device of claim 5 , wherein the memory controller is further configured to:
when the threshold voltage of the selected memory cell is higher than the first reference voltage and lower than the second reference voltage, input the second charging current to the selected bit line during the second period of time, and
when the threshold voltage of the selected memory cell is higher than the second reference voltage, input a third charging current lower than the second charging current to the selected bit line during the second period of time.
7. The memory device of claim 1 , wherein the selected bit line comprises a first selected bit line and a second selected bit line, and the selected memory cell comprises a first selected memory cell connected to the first selected bit line and a second selected memory cell connected to the second selected bit line; and
the memory controller is further configured to simultaneously charge the first selected bit line and the second selected bit line.
8. The memory device of claim 7 , wherein the memory controller is further configured to determine a charging current input to each of the first selected bit line and the second selected bit line during the second period of time, based on a first threshold voltage of the first selected memory cell and a second threshold voltage of the second selected memory cell.