Patent ID: 7577036

Claim:
A method for operating an array of non-volatile multilevel memory cells, comprising: programming at least one data cell of a number of data cells coupled to a selected word line to a target data threshold voltage (Vt) level corresponding to a target state; programming at least one reference cell of a number of reference cells coupled to the selected word line to a target reference Vt level, the number of reference cells interleaved with the number of data cells; determining a reference state based on a data read of the at least one reference cell; and changing a state read from the at least one data cell based on a change of the at least one reference cell, wherein the reference state is obtained, based on a reference Vt level determined from the data read of the at least one reference cell, by comparing the reference Vt level with the target reference Vt level, and wherein the reference Vt level is an average Vt level of the at least one reference cell.