Abstract: An improved reading structure (110) for performing a read 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, each being previously programmed to one of a plurality of memory conditions defined by memory core threshold voltages. A reference cell array (22) includes a plurality of reference core cells which are selected together with a selected core cell and provides selectively one of a plurality of reference cell bit line voltages defined by reference cell threshold voltages. Each of the reference cells are previously programmed at the same time as when the memory core cells are being programmed. A precharge circuit (36) is used to precharge the array bit lines and the reference bit lines to a predetermined potential. A detector circuit (28) is responsive to the bit line voltages of the reference cells for generating strobe signals.

Abstract: A shift register page buffer for use in an array of multiple bits-per-cell flash EEPROM memory cells so as to render page mode programming and reading is provided. A sensing logic circuit (26,27) is used to selectively and sequentially compare array bit line voltages with each of a plurality of target reference cell bit line voltages. Shift register circuit (300) is responsive to the sensing logic circuit for sequentially storing either a low or high logic level after each comparison of the bit line voltages with one of the plurality of target reference voltages. Each of the shift register circuits is formed of series-connected latch circuits (302-308), each having inputs and outputs. A switching transistor (N5) is interconnected between the sensing logic circuit and the latch circuits and is responsive to a corresponding output of the latch circuits for selectively passing the logic signal from the sensing circuit means to the input of the latch circuits.