Page buffer for multi-level NAND programmable memories

摘要

A page buffer (130) for an electrically programmable memory (100) is provided. The electrically programmable memory includes a plurality of memory cells (110) arranged in a plurality of bit lines (BLe,BLo) of memory cells and forming a plurality of individually-selectable memory sets. The electrically programmable memory includes a plurality of distinct programming states defined for each memory cell, corresponding to a number N>=2 of data bits storable in each memory cell. The data bits include at least a first data bits group (MSB) and a second data bits group (LSB), the first data bits groups and, respectively, the second data bits groups stored in the memory cells of one of said individually-selectable memory cell sets forming at least a first memory page and a second memory page, respectively. The first and second memory pages are individually addressable in reading and writing. The page buffer comprises at least one read/program unit (205) having a coupling line (SO) operatively associable with at least one of said bit lines and adapted to at least temporarily storing data bits read from or to be written into either one of the first or second memory page stored in the memory cells of a selected memory cells sets. The read/program unit comprises enabling means (230-1, 230-2, 252, 254, 256, 258, 272, 274, 276, 278) for selectively enabling a change in programming state of a selected memory cell by causing the coupling line to take one among a program enabling potential and a program inhibition potential, conditioned to a target data value to be stored in the first group of data bits (MSB) of the selected memory cell, and an existing data value already stored in the second group of data bits (LSB) of the selected memory cell. The enabling means comprise reading means (256, 258, 260, 230-2) for retrieving the existing data value; means (252, 254, 230-1) for receiving an indication of the target data value; combining means (272, 274, 276, 278) for combining the received target data value with the retrieved existing data value, thereby modifying said indication of the target data value so as to obtain a modified indication; and conditioning means (272, 274) included in the combining means for conditioning a potential of the coupling line based on the existing data value and the modified indication, so as to cause the coupling line to take the program enabling potential or the program inhibition potential.