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Abstract

An improved programming structure for performing a program operation in an array of multiple bits-per-cell flash EEPROM memory cells is provided. A memory core array (12) includes a plurality of memory cells and a reference cell array (22) having a plurality of reference core cells which are selected together with a selected memory core cell. A precharge circuit (36a) is used to precharge all of the array bit lines and the reference bit lines to a predetermined potential prior to a program operation. A reference generator circuit (134) is used for selectively generating one of a plurality of target memory core cell bit line program-verify voltages, each one corresponding to one of a plurality of programmable memory states. A switching circuit (P1,N1) is used to selectively connect a program current source to the selected certain ones of the columns of array bit lines containing the selected memory core cells which are to be programmed. A sensing logic circuit (26,27) continuously compares a potential on one of the selected bit lines and one of the plurality of target program-verify voltages. The sensing logic circuit generates a logic signal which is switched to a low logic level when the potential on the selected bit line falls below the selected one of the plurality of target program-verify voltages. The switching circuit is responsive to the low logic level for disconnecting the program current source so as to inhibit further programming of the selected memory core cells.

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First Claim