Importance

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Abstract

To recognize change in the storage characteristics of programmable memory elements, particularly EPROMs, the memory content of an addressed memory element or cell is read out, the first time, at normal design voltage level; the data so read are then again read out at a changed voltage level, for example at a higher or lower read-out voltage, or higher or lower operating voltage of the EPROM, and compared. If the data do not match, the particular memory cell will have the tendency to become defective due to loss or accumulation of charge carriers in due course although, for some time yet, the specific memory cell will function satisfactorily. Detection of errors upon operation under changed voltage conditions provides early warning of failure of a cell.

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First Claim