Patent ID: 9036412
Filing Date: 2015-05-19
Classification: G11C

Abstract:
1. A method of operating a memory device, comprising: applying an initial read voltage to a selected wordline to perform a read operation on memory cells connected to the selected wordline; determining whether a read failure occurs with respect to one or more of the memory cells; upon determining that a read failure has occurred with respect to some of the memory cells, determining threshold voltage distribution information for distinct groups of the memory cells; and determining a new read voltage to be applied to the selected wordline based on the threshold voltage distribution information, wherein the determining of the threshold voltage distribution information comprises sequentially performing a read operation on the memory cells at a plurality of different voltage levels, performing a first logic operation on data read at two adjacent voltage levels among the different voltage levels, performing a second logic operation on masking patterns indicating some of the memory cells and a result of the first logic operation, and counting a number of memory cells that are present in a plurality of sections divided by the different voltage levels based on a result of the second logic operation.