Nonvolatile memory device with multiple references and corresponding control method
View Patent ↗A memory device includes a group of memory cells organized in rows and columns and a first addressing circuit for addressing said memory cells of said group on the basis of a cell address. The device further includes a plurality of sets of reference cells, associated to the group, each of said set having a plurality of reference cells, and a second addressing circuit for addressing one of the reference cells during operations of read and verify of addressed memory cells.
1. A memory device comprising:
a plurality of groups of memory cells organized in rows and columns;
a first addressing circuit for addressing said memory cells of said groups on the basis of a cell address;
a plurality of sets of reference cells associated with respective sets of said memory cells, each set of reference cells including a plurality of reference cells, wherein in each set of reference cells, a read reference cell and a program verify reference cell are connected to a same first reference wordline, and an erase verify reference cell and a depletion verify reference cell are connected to a same second reference wordline, and wherein said read reference cell, said program-verify reference cell, said erase-verify reference cell, and said depletion verify reference cell are connected to respective separate bitlines; and
a second addressing circuit for addressing one of said reference cells through at least one reference wordline and respective bitlines during read and verify operations of addressed memory cells, wherein said second addressing circuit comprises an addressing stage for selecting one of said reference wordlines, and a reference-selection circuit for selecting one of said reference bitlines.
2. The device of claim 1 , wherein a respective plurality of said sets of reference cells is associated with each of said groups of memory cells.
3. The device of claim 2 , wherein memory cells arranged on a same row are connected to a same array wordline, and memory cells arranged on a same column are connected to a same array bitline, and wherein each of said groups is split into a plurality of sectors of memory cells and a respective one of said sets of reference cells is associated with each of said sectors.
4. The device of claim 3 , wherein each of said sectors of memory cells comprises a plurality of said array bitlines.
5. The device of claim 4 , wherein each of said sectors of memory cells comprises one of said array bitlines every N, where N is a number of said sets of reference cells associated with said group.
6. The device according to claim 3 , wherein each of said sets of memory cells comprises the memory cells connected to a plurality of said array wordlines.
7. The device according to claim 6 , wherein each of said sets of memory cells comprises the memory cells connected to Q/N adjacent said array wordlines, where N is a number of said sets of reference cells associated with said partition and Q is the number of array wordlines associated with said partition.
8. The device of claim 1 , wherein said second addressing circuit is configured to address said reference cells on the basis of a column portion of said cell address.
9. The device according to claim 1 , wherein said second addressing circuit is configured to address said reference cells on the basis of a row portion of said cell address.
10. The device of claim 1 , wherein said memory cells are multilevel nonvolatile memory cells.
11. The device of claim 1 , further comprising at least one sense circuit associated with each of said groups of memory cells, each sense circuit having a first sense terminal addressably connectable to one of said memory cells by said first addressing circuit.
12. The device of claim 11 , wherein each of said sets of reference cells comprises M−1 read reference cells, M−1 program-verify reference cells, an erase-verify reference cell, and a depletion-verify reference cell, M being a number of memory levels for each of the memory cells.
13. The device of claim 12 , wherein said sense circuit has a second sense terminal addressably connectable to one of said sets of reference cells by said second addressing circuit.
14. A control method for a memory device, the method comprising the steps of:
addressing, using a first addressing circuit, memory cells organized in rows and columns in a plurality of groups on the basis of a cell address;
associating the at least one sense circuit to each of said groups;
associating a plurality of sets of reference cells with respective groups of memory cells of said array, each set comprising a plurality of reference cells connectable to a second addressing circuit through at least one reference wordline and respective bitlines, wherein in each set of reference cells, a read reference cell and a program verify reference cell are connected to a same first reference wordline, and an erase verify reference cell and a depletion verify reference cell are connected to a same second reference wordline, and wherein said read reference cell, said program-verify reference cell, said erase-verify reference cell, and said depletion-verify reference cell are connected to respective separate bitlines; and
addressing one of said reference cells, during read and verify operations of addressed memory cells by selecting, using an addressing stage of a second addressing circuit, one of said reference wordlines, and selecting, using a reference-selection circuit of the second addressing circuit one of said reference bitlines.
15. The method of claim 14 , wherein said addressing one of said reference cells comprises using a column portion of said cell address.
16. The method according to claim 14 , wherein said step of addressing one of said reference cells comprises using a row portion of said cell address.
17. The method of claim 14 , wherein memory cells arranged on a same row are connected to a same array wordline, and memory cells arranged on a same column are connected to a same array bitline, the method further comprising:
splitting said groups into a plurality of sectors of memory cells; and
associating a respective one of said sets of reference cells with each of said sectors of memory cells.
18. The method of claim 17 , wherein each of said sectors of memory cells comprises a plurality of said array bitlines.
19. The method of claim 18 , wherein each of said sectors of memory cells comprises one of said array bitlines every N, where N is a number of said sets of reference cells associated with said array.
20. The method according to claim 17 , wherein each of said sets of memory cells comprises the memory cells connected to a plurality of said array wordlines.
21. The method according to claim 20 , wherein each of said sets of memory cells comprises the memory cells connected to Q/N adjacent said array wordlines, where N is a number of said sets of reference cells associated to said array and Q is the number of array wordlines in the array.
22. The method of claim 14 , wherein said addressing one of said reference cells comprises addressably connecting, using the first addressing circuit, a first sense terminal of at least one sense circuit to one of said memory cells.
23. The method of claim 22 , further comprising providing M−1 read references cells, M−1 program-verify reference cells, an erase-verify reference cell, and a depletion-verify reference cell in each of said sets of reference cells, M being a number of memory levels for each of the memory cells.
24. The method of claim 23 , further comprising addressably connecting, using the second addressing circuit, a second sense terminal of said sense circuit to one of said sets of reference cells.