Flash memories with adaptive reference voltages
View Patent ↗Cells of a flash memory are read by determining respective adaptive reference voltages for the cells and comparing the cells' threshold voltages to their respective reference voltages. The adaptive reference voltages are determined either from analog measurements of the threshold voltages of the cells' neighbors or from preliminary estimates of the cells' threshold voltages based on comparisons of the cells' threshold voltages with integral or fractional reference voltages common to all the cells. Cells of a flash memory also are read by comparing the cells' threshold voltages to integral reference voltages, comparing the threshold voltages of cells that share a common bit pattern to a fractional reference voltage, and adjusting the reference voltages in accordance with the comparisons.
1. A flash memory comprising:
(a) a plurality of cells; and
(b) for each cell: a circuit for:
(i) reading a threshold voltage of at least one other cell that is sufficiently close to said each cell that said threshold voltage of said other cell affects a threshold voltage of said each cell, and
(ii) setting at least one respective reference voltage of said each cell based on said threshold voltage of said at least one other cell, said at least one respective reference voltage being specific to said each cell.
2. The flash memory of claim 1 , wherein, for each cell, said circuit is an analog circuit.
3. A flash memory comprising:
(a) a plurality of cells; and
(b) for each cell: a circuit for:
(i) for a set of said cells that includes at least one member, at least one of said at least one member being sufficiently close to said each cell that a threshold voltage of said at least one of said at least one member affects a threshold voltage of said each cell: reading a threshold voltage of each member of said set, and
(ii) setting at least one respective reference voltage for said each cell based on said threshold voltage of every said at least one member of said set;
wherein said set is different for each said cell.