Patent ID: 6683812
Filing Date: 2004-01-27
Classification: G11C

Abstract:
A multilevel memory device, comprising:an input/output control circuit controlling inputting/outputting of data to/from an external device; a memory including a plurality of nonvolatile semiconductor memory cells which are electrically rewritable; and a control circuit controlling writing data in said memory and reading data from said memory, wherein said plurality of nonvolatile semiconductor memory cells are capable of storing two-bit data based on first, second, third or fourth levels; wherein said control circuit compares a level of data read out of a memory cell with a first reference level which is set between said second and third levels to discriminate whether said level of data read out of said memory cell corresponds to a first group of said first and second levels or a second group of said third and fourth levels, compares said level of data read out of said memory cell with a second reference level which is set between said first and second levels to discriminate whether said level of data read out of said memory cell corresponds to said first or second level when said level of data read out of said memory cell is discriminated to be in said first group, and compares said level of data read out of said memory cell with a third reference level which is set between said third and fourth levels to discriminate whether said level of data read out of said memory cell corresponds to said third or fourth level when said level of data read out of said memory cell is discriminated to be in said second group.