Patent ID: 8797805

Claim:
A method for determining threshold voltage shift in memory cells, comprising: determining changes in threshold voltage for memory cells at each data state of a first number of data states by searching threshold voltage data of memory cells programmed to the first number of data states having threshold voltages within a first range of threshold voltages, wherein the threshold voltage data includes data associated with the memory cells at each data state of the first number of data states during a first time period and during a second time period; and determining changes in threshold voltage for memory cells at each data state of a second number of data states by searching threshold voltage data of memory cells programmed to the second number of data states having threshold voltages within a second range of threshold voltages, wherein the threshold voltage data includes data associated with the memory cells at each data state of the second number of data states during the first time period and during the second time period, and wherein the second range is shifted from a previous range based on the changes in threshold voltage for memory cells programmed to the first number of data states and wherein the first number of data states are different data states than the second number of data states.