Patent ID: 8782495

Claim:
A method of reading a cell of a non-volatile memory, the cell having a threshold window demarcated by a first set of (L−1) reference thresholds into a first set of L bands, with L being an integer >1, and the cell having being programmed with a threshold among one of the L bands, said method comprising: setting a first portion of a second set of reference thresholds, the first portion having L−1 reference thresholds that corresponds to the first set; setting a second portion of additional M reference thresholds for the second set, with M being an integer, the additional M reference thresholds being distributed non-uniformly in the threshold window with a higher density clustering asymmetrically around each of the second set of L−1 demarcation thresholds; the first and second portions of the second set of L+M−1 reference thresholds demarcating the threshold window into L+M bands; and reading the cell by locating a band containing the programmed threshold among the L+M bands of the second set.