Non-volatile memory device and read threshold voltage adjustment method for the same

1. An operating method for a data storage device, comprising:

determining a displacement value of a first read voltage, based on a number of memory cells each having a threshold voltage less than the first read voltage;

determining displacement values of second read voltages, when the displacement value is greater than a threshold value;

determining an average of displacement values corresponding to each of a plurality of threshold voltage sections divided by the second read voltages, based on the displacement values;

adjusting at least one reliability value corresponding to at least one threshold voltage section among the threshold voltage sections, based on the average; and

performing an error correction operation on data read from the memory cells based on the first read voltage, using reliability values corresponding to the threshold voltage sections.

2. The operating method of claim 1 , wherein the determining of the displacement value comprises determining a ratio of a difference between the number of memory cells and a reference number with respect to a unit number, as the displacement value, and

wherein the reference number includes a number of memory cells which are expected to have the threshold voltage less than the first read voltage, when threshold voltage distributions of the memory cells are uniform and the first read voltage is an ideal read voltage, and

the unit number includes a number of memory cells which are expected to be positioned in a single threshold voltage distribution, when the threshold voltage distributions are uniform.

3. The operating method of claim 2 , wherein the ideal read voltage includes a read voltage to minimize error bits for the data.

4. The operating method of claim 1 ,

wherein the determining of the average comprises determining the average of displacement values corresponding to each of the threshold voltage sections, based on the displacement value and the displacement values.

5. The operating method of claim 4 , wherein the adjusting of the reliability value among the threshold voltage sections, based on the average comprises adjusting the reliability value by referring to a preset reliability value corresponding to an average section including the average among a plurality of average sections.

6. The operating method of claim 1 , further comprising:

determining an adjustment direction based on the displacement value, when the displacement value is less than the threshold value; and

adjusting the at least one reliability value corresponding to the at least one threshold voltage section positioned in the adjustment direction from the first read voltage among the threshold voltage sections;

wherein the adjustment direction comprises a direction in which the first read voltage is out of an ideal read voltage.

7. The operating method of claim 6 , wherein the ideal read voltage includes a read voltage to minimize error bits for the data.

8. The operating method of claim 6 , wherein the adjusting of the reliability value corresponding to the at least one threshold voltage section positioned in the adjustment direction from the first read voltage among the threshold voltage sections comprises increasing an absolute value of the reliability value.

9. The operating method of claim 1 , wherein the determining of the displacement values comprises determining a ratio of a difference between a number of memory cells each having a threshold voltage less than the second read voltages and a reference number with respect to a unit number, as displacement values of the second read voltages, and

wherein the reference number includes a number of memory cells which are expected to have the threshold voltage less than the first read voltage, when threshold voltage distributions of the memory cells are uniform and the first read voltage is an ideal read voltage, and

wherein the unit number includes a number of memory cells which are expected to be positioned in a single threshold voltage distribution, when the threshold voltage distributions are uniform.

10. A storage device comprising:

a nonvolatile memory device comprising a plurality of memory cells; and

a controller configured to;

determine a displacement value of a first read voltage, based on a number of memory cells each having a threshold voltage less than the first read voltage,

determine displacement values of second read voltages, when the displacement value is greater than a threshold value,

determine an average of displacement values corresponding to each of a plurality of threshold voltage sections divided by the second read voltages, based on the displacement values,

adjust at least one reliability value corresponding to at least one threshold voltage section among the threshold voltage sections, based on the average, and

perform an error correction operation on data read from the memory cells based on the first read voltage, using reliability values corresponding to the threshold voltage sections.

11. The storage device of claim 10 , wherein the controller is configured to determine a ratio of a difference between the number of memory cells and a reference number with respect to a unit number, as the displacement value,

wherein the reference number includes a number of memory cells which are expected to have the threshold voltage less than the first read voltage, when threshold voltage distributions of the memory cells are uniform and the first read voltage is an ideal read voltage, and

the unit number includes a number of memory cells which are expected to be positioned in a single threshold voltage distribution, when the threshold voltage distributions are uniform.

12. The storage device of claim 11 , wherein the ideal read voltage includes a read voltage to minimize error bits for the data.

13. The storage device of claim 10 , wherein the controller is configured to determine the average of displacement values corresponding to each of the threshold voltage sections, based on the displacement value and the displacement values.

14. The storage device of claim 13 , wherein the controller is configured to adjust the reliability value by referring to a preset reliability value corresponding to an average section including the average among a plurality of average sections.

15. The storage device of claim 10 , wherein the controller is further configured to determine an adjustment direction based on the displacement value, when the displacement value is less than the threshold value, and adjust the at least one reliability value corresponding to the at least one threshold voltage section positioned in the adjustment direction from the first read voltage among the threshold voltage sections,

wherein the adjustment direction comprises a direction in which the first read voltage is out of an ideal read voltage.

16. The storage device of claim 15 , wherein the ideal read voltage includes a read voltage to minimize error bits for the data.

17. The storage device of claim 15 , wherein the controller is further configured to increase an absolute value of the reliability value.

18. The storage device of claim 10 , wherein the controller is configured to determine a ratio of a difference between a number of memory cells each having a threshold voltage less than the second read voltages and a reference number with respect to a unit number, as displacement values of the second read voltages, and

wherein the reference number includes a number of memory cells which are expected to have a threshold voltage less than the first read voltage, when threshold voltage distributions of the memory cells are uniform and the first read voltage is an ideal read voltage, and

wherein the unit number includes a number of memory cells which are expected to be positioned in a single threshold voltage distribution, when the threshold voltage distributions are uniform.