System, method and computer program product for processing read threshold information and for reading a flash memory module

• US 9,431,118 B1
• Filed: 05/12/2014
• Issued: 08/30/2016
• Est. Priority Date: 05/30/2012
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Bar, Ilan, Weingarten, Hanan
• Primary Examiner(s): Hidalgo, Fernando
• Application Number:
  US14/275,096
• Time in Patent Office: 841 Days
• Field of Search: 365/185.2, 365/185.11, 365/185.12, 365/185.17, 365/185.22, 365/185.23, 365/185.24, 365/185.33, 365/189.011, 365/189.15
• US Class Current: 1/1
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/00 Erasable programmable read-only memories G11C14/00 takes precedence
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 29/021 in voltage or current generators
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters

Abstract

A method comprising: generating or receiving read threshold information indicative of multiple read thresholds values that were applied when reading multiple flash memory cells that belong to multiple rows of a flash memory module; and generating a compressed representation of reference read thresholds to be applied during future read operations of the flash memory cells in response to the read threshold information.

Claims

1. A method comprising:

generating or receiving read threshold information indicative of multiple read thresholds values that were applied when reading multiple flash memory cells that belong to multiple rows of a flash memory module;

generating a compressed representation of reference read thresholds to be applied during future read operations of the flash memory cells in response to the read threshold information;

calculating a group of read thresholds to be applied during a reading operation of a set of flash memory cells that belong to a certain row of the multiple rows of the flash memory module, the calculating is based upon the compressed representation of reference read thresholds; and

reading the set of flash memory cells by applying the group of reference read thresholds to provide read results.

2. The method according to claim 1, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

3. The method according to claim 1, wherein the multiple reference rows form a subset of rows of the flash memory module.

4. The method according to claim 3, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

5. The method according to claim 1, wherein the calculating comprises:

calculating at least one reference read threshold based upon the compressed representation of the reference read thresholds;

estimating read thresholds of the certain row based upon (a) the at least one reference read threshold and (b) estimators that correlate between the at least one reference read threshold and estimated read thresholds of the certain row.

6. The method according to claim 5, comprising calculating the estimators by linear minimum square algorithm or by least squares estimators.

7. The method according to claim 1, comprising updating at least one reference read threshold of a reference row in response to the read results and in response to estimators that correlate between the certain row and the reference row.

8. The method according to claim 1, wherein the generating of the compressed representation comprises clustering rows of the flash memory modules to clusters in response to read threshold information associated with the rows, and selecting a subset of rows from each cluster to provide the multiple reference rows.

9. The method according to claim 1, wherein the generating of the compressed representation comprises:

applying a principle component analysis on read thresholds statistics to provide a group of singular vectors; and

representing each group of read thresholds of a row of the flash memory module by a set of coefficients that map the group of read thresholds to the group of singular vectors.

10. The method according to claim 9, comprising selecting the group of singular vectors out multiple singular vectors that are calculated during the applying of the principle component analysis.

11. The method according to claim 1, wherein the generating of the compressed representation comprises applying a vector quantization algorithm on multiple vectors, each vector represents read thresholds associated with a row of the flesh memory module.

12. The method according to claim 1, wherein the generating of the compressed representation comprises:

partitioning a multi-dimension space to multiple subsets of the multi-dimensional space; and

representing each of the subsets of the multi-dimensional space by a subset representative;

wherein the multi-dimensional space represents read threshold statistics of a plurality of rows of the flash memory module; and

wherein a memory space required for storing all the subset representatives is smaller than a memory space required for storing the read threshold statistics.

13. The method according to claim 12, wherein a subset representative represents a median value of values included in a subset of the multi-dimensional space that is represented by the subset representative.

14. The method according to claim 12, comprising representing the subsets of the multi-dimensional space by a tree.

15. The method according to claim 12, wherein the partitioning comprises applying multiple partitioning iterations.

16. The method according to claim 15, comprising representing the subsets of the multi-dimensional space by a tree that comprises multiple levels, each level comprises a plurality of nodes, wherein each partition iteration is represented by a single level out of the multiple levels.

17. The method according to claim 16, wherein each node comprises location information indicative of a location of the node in the tree, and partition information indicative of a partition value of a partition iteration that corresponds to the level of the node.

18. A non-transitory computer readable medium that stores instructions for:

generating or receiving read threshold information indicative of multiple read thresholds values that were applied when reading multiple flash memory cells that belong to multiple rows of a flash memory module;

generating a compressed representation of reference read thresholds to be applied during future read operations of the flash memory cells in response to the read threshold information;

calculating a group of read thresholds to be applied during a reading operation of a set of flash memory cells that belong to a certain row of the multiple rows of the flash memory module, the calculating is based upon the compressed representation of reference read thresholds; and

reading the set of flash memory cells by applying the group of reference read thresholds to provide read results.

36. The non-transitory computer readable medium according to claim 18, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

37. The non-transitory computer readable medium according to claim 18, wherein the multiple reference rows form a subset of rows of the flash memory module.

38. The non-transitory computer readable medium according to claim 37, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

39. The non-transitory computer readable medium according to claim 18, wherein the calculating comprises:

calculating the at least one reference read threshold based upon the compressed representation of the reference read thresholds;

estimating read thresholds of the certain row based upon (a) the at least one reference read threshold and (b) the estimators that correlate between the at least one reference read threshold and estimated read thresholds of the certain row.

40. The non-transitory computer readable medium according to claim 39, that stores instructions for calculating the estimators by linear minimum square algorithm or by least squares estimators.

41. The non-transitory computer readable medium according to claim 18, that stores instructions for updating the at least one reference read threshold of the reference row in response to the read results and in response to the estimators that correlate between the certain row and the reference row.

42. The non-transitory computer readable medium according to claim 18, wherein the generating of the compressed representation comprises clustering rows of the flash memory modules to clusters in response to read threshold information associated with the rows, and selecting a subset of rows from each cluster to provide the multiple reference rows.

43. The non-transitory computer readable medium according to claim 18, that stores instructions for applying the principle component analysis on the read thresholds statistics to provide group of singular vectors;

and representing each group of read thresholds of the row of the flash memory module by the set of coefficients that map the group of read thresholds to the group of singular vectors.

44. The non-transitory computer readable medium according to claim 43, that stores instructions for selecting the group of singular vectors out multiple singular vectors that are calculated during the applying of the principle component analysis.

45. The non-transitory computer readable medium according to claim 18, that stores instructions for applying a vector quantization algorithm on multiple vectors, each vector represents read thresholds associated with a row of the flesh memory module.

46. The non-transitory computer readable medium according to claim 18, that stores instructions for partitioning the multi-dimension space to multiple subsets of the multi-dimensional space;

and representing each of the subsets of the multi-dimensional space by the subset representative;

wherein the multi-dimensional space represents read threshold statistics of the plurality of rows of the flash memory module; and

wherein the memory space required for storing all the subset representatives is smaller than the memory space required for storing the read threshold statistics.

47. The non-transitory computer readable medium according to claim 46, wherein a subset representative represents a median value of values included in a subset of the multi-dimensional space that is represented by the subset representative.

48. The non-transitory computer readable medium according to claim 46, that stores instructions for representing the subsets of the multi-dimensional space by a tree.

49. The non-transitory computer readable medium according to claim 46, wherein the partitioning comprises applying multiple partitioning iterations.

50. The non-transitory computer readable medium according to claim 49, that stores instructions for representing the subsets of the multi-dimensional space by a tree that comprises multiple levels, each level comprises a plurality of nodes, wherein each partition iteration is represented by a single level out of the multiple levels.

51. The non-transitory computer readable medium according to claim 50, wherein each node comprises location information indicative of a location of the node in the tree, and partition information indicative of a partition value of a partition iteration that corresponds to the level of the node.

19. A flash memory controller that is coupled to flash memory cells of a flash memory module,

the flash memory comprises a read threshold processing circuit arranged to generate or receive read threshold information indicative of multiple read thresholds values that were applied when reading multiple flash memory cells that belong to multiple rows of a flash memory module;

and generate a compressed representation of reference read thresholds to be applied during future read operations of the flash memory cells in response to the read threshold information;

wherein the read threshold processing circuit is further arranged to calculate a group of read thresholds to be applied during a reading operation of a set of flash memory cells that belong to a certain row of the multiple rows of the flash memory module based upon the compressed representation of reference read thresholds; and

wherein the flash memory controller further comprises a read circuit arranged to read the set of flash memory cells by applying the group of reference read thresholds to provide read results.

20. The flash memory controller according to claim 19, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

21. The flash memory controller according to claim 19, wherein the multiple reference rows form a subset of rows of the flash memory module.

22. The flash memory controller according to claim 21, wherein values of the reference read thresholds form a subset of possible values of actual read thresholds to be applied when reading the flash memory module.

23. The flash memory controller according to claim 19, wherein the flash memory controller is configured to calculate at least one reference read threshold based upon the compressed representation of the reference read thresholds;

estimating read thresholds of the certain row based upon (a) at least one reference read threshold and (b) the estimators that correlate between the at least one reference read threshold and estimated read thresholds of the certain row.

24. The flash memory controller according to claim 23, wherein the flash memory controller is configured to calculate the estimators by linear minimum square algorithm or by least squares estimators.

25. The flash memory controller according to claim 19, wherein the flash memory controller is configured to update at least one reference read threshold of a reference row in response to the read results and in response to estimators that correlate between the certain row and the reference row.

26. The flash memory controller according to claim 19, wherein the flash memory controller is configured to cluster rows of the flash memory modules to clusters in response to read threshold information associated with the rows, and selecting a subset of rows from each cluster to provide the multiple reference rows.

27. The flash memory controller according to claim 19, wherein the flash memory controller is configured to apply a principle component analysis on the read thresholds statistics to provide group of singular vectors;

and representing each group of read thresholds of a row of the flash memory module by a set of coefficients that map the group of read thresholds to the group of singular vectors.

28. The flash memory controller according to claim 27, wherein the flash memory controller is configured to select the group of singular vectors out multiple singular vectors that are calculated during the applying of the principle component analysis.

29. The flash memory controller according to claim 19, wherein the flash memory controller is configured to apply a vector quantization algorithm on multiple vectors, each vector represents read thresholds associated with a row of the flesh memory module.

30. The flash memory controller according to claim 19, wherein the flash memory controller is configured to partition a multi-dimension space to multiple subsets of the multi-dimensional space;

and represent each of the subsets of the multi-dimensional space by a subset representative;

wherein the multi-dimensional space represents read threshold statistics of a plurality of rows of the flash memory module; and

wherein a memory space required for storing all the subset representatives is smaller than a memory space required for storing the read threshold statistics.

31. The flash memory controller according to claim 30, wherein a subset representative represents a median value of values included in a subset of the multi-dimensional space that is represented by the subset representative.

32. The flash memory controller according to claim 30, wherein the flash memory controller is configured to representing the subsets of the multi-dimensional space by a tree.

33. The flash memory controller according to claim 30, wherein the flash memory controller is configured to applying multiple partitioning iterations during the partitioning.

34. The flash memory controller according to claim 33, wherein the flash memory controller is configured to represent the subsets of the multi-dimensional space by a tree that comprises multiple levels, each level comprises a plurality of nodes, wherein each partition iteration is represented by a single level out of the multiple levels.

35. The flash memory controller according to claim 34, wherein each node comprises location information indicative of a location of the node in the tree, and partition information indicative of a partition value of a partition iteration that corresponds to the level of the node.