Determining read thresholds based upon read error direction statistics

摘要

There is provided a method for setting read thresholds to be used for reading multiple bits per cell flash memory cells, the method may include reading, by a read circuit, the flash memory cells using a set of current read thresholds to provide current read results; finding, by an error evaluation circuit, current read errors direction statistics associated with the current read results; determining multiple read threshold changes based upon the current read error direction statistics, without determining a contribution of each current read threshold to the current read error direction statistics; and altering multiple current read thresholds, by the multiple read threshold updates, to provide a set of next read thresholds.

主权项

1. A method for setting read thresholds to be used for reading multiple bits per cell flash memory cells, the method comprises:
reading, by a read circuit, the flash memory cells using a set of current read thresholds to provide current read results; finding, by an error evaluation circuit, current read errors direction statistics associated with the current read results; determining multiple read threshold changes based upon the current read error direction statistics, without determining a contribution of each current read threshold to the current read error direction statistics; and altering multiple current read thresholds, by the multiple read threshold updates, to provide a set of next read thresholds; wherein at least one of the following is true: (i) the method further comprises receiving or calculating old read errors direction statistics associated with multiple previously obtained read results, and wherein the determining is further responsive to the old read error direction statistics; (ii) each of the multiple read threshold changes does not exceed a smallest change amount allowable by the read circuit; (iii) the determining of the multiple read threshold changes comprises determining, for each current read threshold, a read threshold change; (iv) the determining of the multiple read threshold changes is further responsive to at least one physical characteristic of the flash memory cells; (v) the determining of the multiple read threshold changes comprises finding a maximal margin estimator to the set of next read thresholds; (vi) the determining of the multiple read threshold changes comprises applying a Kalman filter on the current read error direction statistics and on old read errors direction statistics associated with multiple previously obtained read results; (vii) the method further comprises finding a set of optimal read thresholds; and (viii) the determining the multiple read threshold changes is responsive to optimal and sub-optimal read thresholds.