Method of setting read voltage minimizing read data errors
A method setting a read voltage to minimize data read errors in a semiconductor memory device including multi-bit memory cells. In the method, a read voltage associated with a minimal number of read data error is set based on a statistic value of a voltage distribution corresponding to each one of a plurality of voltage states.
1. A method of setting a read voltage within a memory device, the memory device configured to apply the read voltage to memory cells during a read operation of the memory device, the method comprising:
calculating a first read voltage distinguishing a first voltage state from a second voltage state adjacent to the first voltage state using a first method;
calculating a second read voltage distinguishing the first voltage state from the second voltage state using a second method;
calculating a third read voltage distinguishing the first voltage state from the second voltage state based on the first read voltage and the second read voltage; and
configuring the memory device to set the read voltage of the memory device as the third read voltage.
2. The method of claim 1 , wherein the calculating the third read voltage comprises calculating the third read voltage by performing an offset compensation on at least one of the first and second read voltages.
3. The method of claim 1 , wherein
the first method comprises:
setting the first read voltage to a read voltage level that corresponds to a valley portion of a sum of a voltage distribution corresponding to the first voltage state and a voltage distribution corresponding to the second voltage state; and
the second method comprises:
setting the second read voltage to a read voltage level at which a number of data read errors occurring with respect to the voltage distribution corresponding to the first voltage state is the same as a number of read data errors occurring with respect to the voltage distribution corresponding to the second voltage state.
4. The method of claim 3 , wherein the calculating the third read voltage comprises calculating the third read voltage by performing an offset compensation on at least one of the first and second read voltages.
5. The method of claim 2 , wherein the calculating the third read voltage by performing the offset compensation comprises at least one of:
performing an offset compensation on the first read voltage, such that the first read voltage is shifted toward a voltage state having a smaller variance between the first and second voltage states; and
performing an offset compensation on the second read voltage, such that the second read voltage is shifted toward a voltage state having a greater variance between the first and second voltage states.
6. The method of claim 5 , wherein an offset compensation value used to perform the offset compensation is determined based on the relative difference of the smaller variance and the greater variance.
7. The method of claim 1 , wherein the calculating the third read voltage comprises:
calculating the third read voltage by taking an average of the first read voltage and the second read voltage, wherein the average is one selected from a group consisting of an arithmetic mean, a geometric mean, and a harmonic mean.