| 摘要 |
<P>PROBLEM TO BE SOLVED: To execute refresh operation before errors exceeding a correction limit of an error correcting circuit are generated even when the error correcting circuit receiving soft discrimination information is used, and to suppress error occurrence frequencies exceeding the error correction limit to have no problem practically. <P>SOLUTION: A memory cell array constituting a NAND cell type flash memory has a word line control circuit 2. In this word line control circuit 2, soft value read voltage between the upper limit and the lower limit of respective threshold value distribution are applied to the word line as word line voltage in addition to read voltage between a plurality of threshold value distribution, and soft value data is generated. Likelihood of data of a plurality of bits is calculated by a likelihood calculating circuit 10 based on this soft value. An error correcting circuit 11 performs error correction based on the likelihood. When the repetition of error correction exceeds the prescribed value, the block is refleshed. <P>COPYRIGHT: (C)2008,JPO&INPIT |
