Patent ID: 7733729

Claim:
A non volatile memory device comprising: a series of memory cells for providing data signals representative of a stored series of data values; at least one reference cell for generating a reference signal; a reader capable of determining the series of data values from the signals read from the series of memory cells and from the at least one reference cell; a reference degrade detector capable of determining when the reference signal is degraded; and a reference rewriter capable of rewriting the reference cell in response to the reference degrade detector determining that the reference signal is degraded, wherein the reference cell has a given degradation susceptibility, wherein the reference degrade detector comprises: a reference test cell having a susceptibility greater than said given susceptibility of the reference cell; a reference test cell read circuit for reading the values of the reference test cell; and a reference test cell error detector capable of detecting test errors in the read values of the reference test cell, and wherein the reference cell detector determines the reference signal is degraded based on said detecting test errors in the read values of the reference test cell.