Patent ID: 9343163
Filing Date: 2016-05-17
CPC Classification: G11C

Claim Text:
1. A method of operating a semiconductor memory device comprising: determining whether most significant bit (MSB) data is programmed on a selected page; determining whether a moving read mode is selected when the MSB data is programmed; performing a first read operation on the selected page using a default read voltage when the MSB data is not programmed or the moving read mode is not selected; determining whether a randomize mode is selected when the first read operation is performed; counting the number of first reference cells in which least significant bit (LSB) data is programmed on the selected page by an LSB program operation when the moving read mode is selected; counting the number of second reference cells in which the MSB data is programmed by an MSB program operation among the first reference cells; counting the number of first comparison cells in which the LSB data is programmed by performing an LSB read operation based on a second read voltage among first to third read voltages; counting the number of second comparison cells in which the MSB data is programmed by performing an MSB read operation based on the third read voltage; changing the second read voltage according to a difference between the number of first reference cells and the number of first comparison cells; changing the third read voltage according to a difference between the number of second reference cells and the number of second comparison cells; and performing a second read operation on the selected page using the changed second read voltage and the changed third read voltage.