Structure and method for detecting errors in a multilevel memory device with improved programming granularity
View Patent ↗An error detection structure is proposed for a multilevel memory device including a plurality of memory cells each one being programmable at more than two levels ordered in a sequence. Each level representsmg a logic value consisting of a plurality of bits, wherein the structure includes components for detecting errors in the values of a selected block of memory cells. The structure further includes components for partitioning the bits of each memory cell of the block into a first subset and a second subset, the bits of the first subset being unchanged in the values of a first and a second ending range in the sequence. The components_for detecting errors only operate on the bits of the second subset of the block.
1. An error detection structure for a multilevel memory device including a plurality of memory cells, each memory cell being programmable at more than two levels and,
wherein the levels have an associated sequence, each level in the sequence corresponding to a respective threshold voltage of the memory cell and each level representing a logic value consisting of a plurality of bits,
wherein the sequence of levels includes a lower range consisting of the first two or more levels in the sequence and an upper range consisting of the last two or more levels in the sequence,
wherein the structure further includes means for partitioning the bits of the levels in the lower range and the bits in the upper range into two subsets,
a first most significant bit subset consisting of bits having the same value for all levels in the lower range and consisting of bits having the same value for all levels in the upper range,
a second least significant bit subset consisting of the remaining bits having different values for levels in the lower range and consisting of bits having different values for levels in the upper range, and
wherein the structure includes means for detecting errors in the values of a selected block of memory cells, and the means for detecting errors operating only on the bits of the second least significant bit subset of the block.
2. The structure according to claim 1 , wherein the second least significant bit subset consists of at least one least significant bit of the logic value.
3. The structure according to claim 1 , further including means for storing an indicator of change of at least one bit of the second least significant bit subset and means for selectively disabling the means for detecting errors according to the indicator of change.
4. The structure according to claim 1 , wherein the bits of the block are organized into a plurality of words partitioned into a first and a second set, each word being suitable to be individually processed in the memory device, and wherein the structure further includes means for associating the words of the first set and the words of the second set with the bits of the first most significant bit subset and the bits of the second least significant bit subset of the block, respectively.
5. The structure according to claim 4 , wherein the second set consists of a plurality of words, the means for detecting errors including a plurality of error detection units each one for detecting errors in a word corresponding to the second set.
6. The structure according to claim 5 , further including, for each word of the second set, means for storing an indicator of change of at least one bit and means for selectively disabling the corresponding error detection unit according to the indicator of change.
7. A multilevel memory device including a plurality of memory cells and the error detection structure according to claim 1 .
8. The multilevel memory device according to claim 7 , further including means for individually programming each memory cell.
9. An error detection method for a multilevel memory device including a plurality of memory cells each one being programmable at more than two levels, the levels having an associated sequence, each level in the sequence representing a logic value consisting of a plurality of bits, the method including the steps of:
detecting errors in the values of a selected block of memory cells comprising partitioning the bits of each memory cell of the block into a first subset and a second subset, the bits of the first subset being unchanged between the first two levels in the sequence and between the last two levels in the sequence, the step of detecting errors only operating on the bits of the second subset of the block.