Method of reading memory cells with different threshold voltages without variation of word line voltage and nonvolatile memory device using the same
A soft-decision read method of a nonvolatile memory device includes receiving a soft-decision read command, applying a read voltage to a selected word line, pre-charging bit lines respectively connected to selected memory cells of the selected word line, continuously sensing states of the selected memory cells. The pre-charged voltages of the bit lines and the read voltage supplied to the selected word line are not varied during the sensing states of the selected memory cells.
1. A soft-decision read method of a nonvolatile memory device comprising:
receiving a soft-decision read command;
applying a read voltage to a selected word line;
pre-charging bit lines respectively connected to selected memory cells of the selected word line; and
continuously sensing states of the selected memory cells, wherein the pre-charged voltages of the bit lines and the read voltage supplied to the selected word line are not varied during the sensing states of the selected memory cells.
2. The soft-decision read method of claim 1 , wherein the sensing states of the selected memory cells includes a plurality of sensing operations, each sensing operation being performed by varying voltages of sensing nodes respectively corresponding to the bit lines according to threshold voltages of the selected memory cells, latching voltages of the sensing nodes, and pre-charging the sensing nodes; and
wherein respective develop times of the sensing operations are different from one another.
3. The soft-decision read method of claim 2 , wherein data respectively latched at the sensing operations include hard-decision read data and a plurality of soft-decision read data.
4. The soft-decision read method of claim 2 , wherein data respectively latched at the sensing operations include and a plurality of soft-decision read data.
5. The soft-decision read method of claim 2 , wherein data respectively latched at the sensing operations include hard-decision read data and at least one of a plurality of soft-decision read data.
6. The soft-decision read method of claim 2 , wherein the continuously sensing states of the selected memory cells includes latching voltages of sensing nodes respectively corresponding to the bit lines at least two times as first data and second data.
7. The soft-decision read method of claim 6 , wherein the first data is indicative of a memory cell having a threshold voltage which is higher than the read voltage and a memory cell having a threshold voltage which is lower by a predetermined voltage than the read voltage.
8. The soft-decision read method of claim 7 , wherein the second data is indicative of a memory cell having a threshold voltage which is higher than the read voltage.
9. The soft-decision read method of claim 8 , wherein the latching voltages at least two times data comprises:
varying voltages of the sensing nodes according to threshold voltages of the selected memory cells during a first period of time;
latching the voltages of the sensing nodes as the first data;
pre-charging the sensing nodes;
varying voltages of the sensing nodes according to the threshold voltages of the selected memory cells during a second period of time which is different from the first period of time; and
latching the voltages of the sensing nodes as the second data.
10. The soft-decision read method of claim 9 , wherein the first period of time is shorter than the second period of time.
11. The soft-decision read method of claim 10 , wherein the first period of time is set such that the memory cell having a threshold voltage which is lower by the predetermined voltage than the read voltage is determined to be an off cell.
12. The soft-decision read method of claim 11 , wherein the second time is set such that the memory cell having a threshold voltage which is lower by the predetermined voltage than the read voltage is determined to be an on cell.
13. The soft-decision read method of claim 9 , wherein the bit lines are driven to maintain a pre-charged state until voltages of the sensing nodes are latched as the second data.
14. The soft-decision read method of claim 1 , wherein the read voltage applied to the selected word line is blocked after the sensing operations are completed.
15. A nonvolatile memory device comprising:
a memory cell array having memory cells arranged at intersections of word lines and bit lines;
a row selector circuit configured to drive a selected one of the word lines; and
a read/write circuit having page buffers respectively connected to the bit lines; and
control logic configured to control the read/write circuit and the row selector circuit,
wherein the control logic controls a soft-decision read operation in which bit lines respectively connected to selected memory cells of a selected word line supplied with a read voltage are pre-charged and voltages of sensing nodes respectively corresponding to the bit lines are latched at least two times as first data and second data while the pre-charged voltages of the bit lines and a read voltage supplied to the selected word line are not varied; and
wherein the control logic variably controls respective develop times of continuous sensing operations of the read operation.
16. The nonvolatile memory device of claim 15 , wherein the latching voltages of the sensing nodes at least two times as first data and second data comprises:
varying voltages of the sensing nodes according to threshold voltages of the selected memory cells during a first period of time;
latching the voltages of the sensing nodes as the first data;
pre-charging the sensing nodes;
varying voltages of the sensing nodes according to the threshold voltages of the selected memory cells during a second period of time which is longer than the first period of time; and
latching the voltages of the sensing nodes as the second data.
17. The nonvolatile memory device of claim 15 , wherein data respectively latched at the sensing operations include hard-decision read data and a plurality of soft-decision read data.
18. The nonvolatile memory device of claim 15 , wherein data respectively latched at the sensing operations include a plurality of soft-decision read data.
19. The nonvolatile memory device of claim 15 , wherein data respectively latched at the sensing operations include hard-decision read data and at least one of a plurality of soft-decision read data.
20. The nonvolatile memory device of claim 15 , wherein the read voltage applied to the selected word line is blocked after the sensing operations are completed.