Method and apparatus for emulating an electrically erasable programmable read only memory (EEPROM) using non-volatile floating gate memory cells
View Patent ↗An emulated EEPROM memory array is disclosed based on non-volatile floating gate memory cells, such as Flash cells, where a small group of bits share a common source line and common row lines, so that the small group of bits may be treated as a group during program and erase modes to control the issues of program disturb and effective endurance. The bits common to the shared source line make up the emulated EEPROM page which is the smallest unit that can be erased and reprogrammed, without disturbing other bits. The memory array is physically divided up into groups of columns. One embodiment employs four memory arrays, each consisting of 32 columns and 512 page rows (all four arrays providing a total of 1024 pages with each page having 8 bytes or 64 bits). A global row decoder decodes the major rows and a page row driver and a page source driver enable the individual rows and sources that make up a given array. The page row drivers and page source drivers are decoded by a page row/source supply decoder, based on the addresses to be accessed and the access mode (erase, program or read).
1. An array of non-volatile floating gate memory cells arranged in a plurality of rows and columns, a plurality of said memory cells electrically coupled to form a plurality of pages, said array comprising:
a plurality of page row lines, each of said page row lines connected to a gate of one or more of said memory cells in one of said rows;
a plurality of page source lines, each of said page source lines connected to a source of one or more of said memory cells in one of said pages, wherein each of said pages includes each of said plurality of non-volatile floating gate memory cells that are subject to program disturb voltages when at least one of said plurality of non-volatile floating gate memory cells within a same page is programmed;
a plurality of column lines, each of said column lines connected to a drain of all of said memory cells in one of said columns; and
a global row decoder to decode major rows in said memory array.
2. The array of claim 1 , wherein said non-volatile floating gate memory cells are flash cells.
3. The array of claim 1 , wherein each of said pages of memory cells sharing a common source line includes at least two rows of said memory cells in said page.
4. The array of claim 1 , wherein said columns in said array are further divided into a plurality of sub-arrays comprised of one or more groups of columns to reduce a size of said pages, said group of columns consists of one or more of said columns, each column in said group connects to a drain of all said non-volatile floating gate memory cells in a column of each page.
5. The array of claim 4 , further comprising:
a plurality of page row drivers, each of said page row drivers selectively couples signals to said page row lines,
a plurality of page source drivers, each of said page source drivers selectively couples signals to said page source lines,
a plurality of word lines, one or more of said word lines connect to said page row drivers, said plurality of word lines are selectively coupled to said page row lines,
a plurality of source lines, one or more of said source lines connect to said page source drivers, said plurality of source lines are selectively coupled to said page source lines.
6. The array of claim 1 , wherein said page row lines associated with each of said memory cells in one of said pages must be selected during an erase operation.
7. The array of claim 1 , further comprising a set of page row drivers that are decoded by said global row decoder and a page row supply decoder, based on said memory cells to be accessed and an indication of an access mode to enable individual rows of said array.
8. The array of claim 1 , further comprising a set of page source drivers that are decoded by said global row decoder and a page source supply decoder, based on said memory cells to be accessed and an indication of an access mode to enable the individual sources of said array.
9. The array of claim 1 , further comprising a decoder for decoding page rows and page sources in said memory array.
10. A method for programming a memory array comprised of a plurality of non-volatile floating gate memory cells arranged in a plurality of one or more rows and columns, each of said memory cells having a drain, gate and source terminal, a plurality of said memory cells electrically coupled to form a plurality of pages, said method comprising:
applying a voltage to at least one page source line connected to a source of each of said memory cells in one of said pages, wherein each of said pages includes each of said plurality of non-volatile floating gate memory cells that are subject to program disturb voltages when at least one of said plurality of non-volatile floating gate memory cells within a same page is programmed; and
decoding major rows in said memory array using a global row decoder.
11. The method of claim 10 , wherein said non-volatile floating gate memory cells are flash cells.
12. The method of claim 10 , wherein each of said pages of memory cells sharing a common source line includes at least two rows of said memory cells in said page.
13. The method of claim 10 , wherein said columns in said array are further divided into a plurality of sub-arrays comprised of one or more groups of columns to reduce a size of said pages, said group of columns consists of one or more of said columns, each column in said group connects to a drain of all said non-volatile floating gate memory cells in a column of each page.
14. The method of claim 10 , wherein said page row lines associated with each of said memory cells in one of said pages must be selected during an erase operation.
15. The method of claim 10 , further comprising the step of decoding page rows and page sources in said memory array.
16. An array of non-volatile floating gate memory cells arranged in a plurality of rows and columns, a plurality of said memory cells electrically coupled to form a plurality of pages, said array comprising:
a plurality of page row lines, each of said page row lines connected to a gate of one or more of said memory cells in one of said rows;
a plurality of page source lines, each of said page source lines connected to a source of one or more of said memory cells in one of said pages, wherein each of said pages includes each of said plurality of non-volatile floating gate memory cells that are subject to erase conditions when at least one of said plurality of said non-volatile floating gate memory cells is erased within said same page;
a plurality of column lines, each of said column lines connected to a drain of all of said memory cells in one of said columns; and
a global row decoder to decoder major rows in said memory array.
17. An array of non-volatile floating gate memory cells arranged in a plurality of rows and columns, a plurality of said memory cells electrically coupled to form a plurality of pages, said array comprising:
a plurality of page row lines, each of said page row lines connected to a gate of one or more of said memory cells in one of said rows;
a plurality of page source lines, each of said page source lines connected to a source of one or more of said memory cells in one of said pages, wherein each of said non-volatile floating gate memory cells within each of said pages is erased when one of said non-volatile floating gate memory cells within each of said pages is erased;
a plurality of column lines, each of said column lines connected to a drain of all of said memory cells in one of said columns; and
a global row decoder to decode major rows in said memory array.