System, method and computer program product for joint search of a read threshold and soft decoding

• US 8,990,665 B1
• Filed: 03/14/2012
• Issued: 03/24/2015
• Est. Priority Date: 04/06/2011
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: DensBits Technologies Ltd. (Broadcom, Inc.)
• Inventors: Steiner, Avi, Weingarten, Hanan, Sabbag, Erez
• Primary Examiner(s): TU, CHRISTINE TRINH LE
• Application Number:
  US13/420,032
• Time in Patent Office: 1,105 Days
• Field of Search: 714/780, 714769-770, 714/773, 714/763, 714799-800, 714/819, 714/746, 714/718, 714/721, 365/189.011, 365/189.04, 365/189.14, 365/189.15, 365/189.07, 365/200, 365/201, 365/220, 365/221
• US Class Current: 714/780
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/04 using variable threshold transistors, e.g. FAMOS
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 7/1006 Data managing, e.g. manipulating data before writing or reading out, data bus switches or control circuits therefor
• CPC Class Codes: H03M 13/152 Bose-Chaudhuri-Hocquenghem [BCH] codes
• CPC Class Codes: H03M 13/2918 with error correction codes in three or more dimensions, e.g. 3-dimensional product code where the bits are arranged in a cube
• CPC Class Codes: H03M 13/2927 Decoding strategies
• CPC Class Codes: H03M 13/37 Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35
• CPC Class Codes: H03M 13/45 Soft decoding, i.e. using symbol reliability information H03M13/41 takes precedence
• CPC Class Codes: H03M 13/451 using a set of candidate code words, e.g. ordered statistics decoding [OSD]
• CPC Class Codes: H03M 13/458 by updating bit probabilities or hard decisions in an iterative fashion for convergence to a final decoding result
• CPC Class Codes: H03M 13/612 Aspects specific to channel or signal-to-noise ratio estimation H03M13/63 takes precedence

Abstract

A flash memory controller, a computer readable medium and a method. The method may include performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results; determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results; and error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results.

Claims

1. A method comprising:

performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results;

error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results; and

evaluating a characteristic of the multiple read results under different assumptions about mapping between the read thresholds and reliability metrics;

wherein an evaluating of the characteristic of the multiple read thresholds under each assumption comprises comparing between (a) a relationship between numbers of first and second read results of the multiple read results and of different values, and (b) an expected relationship between numbers of first and second read results of different numbers.

2. The method according to claim 1 further comprising finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold is selected from the multiple read thresholds.

3. The method according to claim 1, further comprising finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold differs from each one of the multiple read thresholds.

4. The method according to claim 1, wherein the characteristic is a bit error rate metric associated with an outcome of a soft decoding process or a partial soft decoding process applied on the multiple read results.

5. The method according to claim 1, wherein the characteristic is a bit error rate metric associated with an outcome of a hard decoding process or a partial hard decoding process applied on the multiple read results.

6. The method according to claim 1, wherein the different assumptions about the identity of the desired read threshold differ from each other by a reliability associated with each of the multiple read results.

7. The method according to claim 1, comprising evaluating the characteristic of the multiple read thresholds under each assumption by performing a partial decoding process of the multiple read results.

8. The method according to claim 7, wherein the partial decoding is a partial soft decoding.

9. The method according to claim 8, wherein the partial soft decoding involve applying iterations of soft decoding of a lowest decoding complexity.

10. The method according to claim 7, wherein the partial decoding is a partial hard decoding.

11. The method according to claim 1, comprising evaluating the characteristic of the multiple read thresholds by checking a distribution of thresholds voltages of the group of memory cells under the different assumptions.

12. The method according to claim 1, further comprising finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

performing at least one additional read attempt to provide additional read results and determining, based upon the at least one additional read result, a reliability of the at least one additional read result.

13. The method according to claim 1, further comprising soft decoding the multiple read results.

14. The method according to claim 1, comprising finding, based upon the multiple read results, a desired read threshold to be applied during future read attempts;

and performing additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold.

15. The method according to claim 1, wherein the multiple read attempts comprise first and second read attempts and wherein the first and second read attempts are executed before a completion of a determination of a desired read threshold.

16. A method comprising:

performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results;

error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results;

finding, based upon the multiple read results, a desired read threshold to be applied during future read attempts; and

performing additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold;

wherein the additional read thresholds are selected such that there are at least a predefined number of read thresholds that are proximate to the desired read threshold and are positioned at each side of the desired read threshold, as to provide a decoder that performs the error correction decoding of the multiple read results with high resolution sampling for soft information.

17. A flash memory controller, comprising:

a read circuit arranged to perform multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

a reliability circuit arranged to determine, based upon the multiple read results, a reliability metric of each of the multiple read results; and

an error correction decoding circuit arranged to perform error correction decoding of the multiple read results based upon reliability metrics associated with the multiple read results;

wherein the flash memory controller is further arranged to evaluate a characteristic of the multiple read results under different assumptions about mapping between the read thresholds and reliability metrics;

wherein an evaluating of the characteristic of the multiple read thresholds under each assumption comprises comparing between (a) a relationship between numbers of first and second read results of different values, and (b) an expected relationship between numbers of first and second read results of different numbers.

18. The flash memory controller according to claim 17, further comprising a read threshold circuit arranged to find, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold is selected from the multiple read thresholds.

19. The flash memory controller according to claim 17, further comprising a read threshold circuit arranged to find, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold differs from each one of the multiple read thresholds.

20. The flash memory controller according to claim 17, wherein the characteristic is a bit error rate metric associated with an outcome of a soft decoding process or a partial soft decoding process applied on the multiple read results.

21. The flash memory controller according to claim 17, wherein the characteristic is a bit error rate metric associated with an outcome of a hard decoding process or a partial hard decoding process applied on the multiple read results.

22. The flash memory controller according to claim 17, wherein the different assumptions about the identity of the desired read threshold differ from each other by a reliability associated with each of the multiple read results.

23. The flash memory controller according to claim 17 that is arranged to evaluate the characteristic of the multiple read thresholds under each assumption by performing a partial decoding process of the multiple read results.

24. The flash memory controller according to claim 23, wherein the partial decoding is a partial soft decoding.

25. The flash memory controller according to claim 24, wherein the partial soft decoding involve applying iterations of soft decoding of a lowest decoding complexity.

26. The flash memory controller according to claim 23, wherein the partial decoding is a partial hard decoding.

27. The flash memory controller according to claim 17 that is arranged to evaluate the characteristic of the multiple read thresholds by checking a distribution of thresholds voltages of the group of memory cells under the different assumptions.

28. The flash memory controller according to claim 17 that is arranged to find, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

perform at least one additional read attempt to provide additional read results and determine, based upon the at least one additional read result, a reliability of the at least one additional read result.

29. The flash memory controller according to claim 17 that is arranged to soft decode the multiple read results.

30. The flash memory controller according to claim 17 that is arranged to find, based upon the multiple read results, a desired read threshold to be applied during future read attempts;

and perform additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold.

31. The flash memory controller according to claim 17, wherein the multiple read attempts comprise first and second read attempts and wherein the first and second read attempts are executed before a completion of a determination of a desired read threshold.

32. A non-transitory computer readable medium that stores instructions for performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results;

error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results;

evaluating a characteristic of the multiple read results under different assumptions about mapping between the read thresholds and reliability metrics;

wherein an evaluating of the characteristic of the multiple read thresholds under each assumption comprises comparing between (a) a relationship between numbers of first and second read results of different values, and (b) an expected relationship between numbers of first and second read results of different numbers.

33. The non-transitory computer readable medium according to claim 32 that stores instructions for finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold is selected from the multiple read thresholds.

34. The non-transitory computer readable medium according to claim 32 that stores instructions for finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

wherein one or more desired read threshold out of the at least one desired read threshold differs from each one of the multiple read thresholds.

35. The non-transitory computer readable medium according to claim 32, wherein the characteristic is a bit error rate metric associated with an outcome of a soft decoding process or a partial soft decoding process applied on the multiple read results.

36. The non-transitory computer readable medium according to claim 32, wherein the characteristic is a bit error rate metric associated with an outcome of a hard decoding process or a partial hard decoding process applied on the multiple read results.

37. The non-transitory computer readable medium according to claim 32, wherein the different assumptions about the identity of the desired read threshold differ from each other by a reliability associated with each of the multiple read results.

38. The non-transitory computer readable medium according to claim 32 that stores instructions for evaluating the characteristic of the multiple read thresholds under each assumption by performing a partial decoding process of the multiple read results.

39. The non-transitory computer readable medium according to claim 38, wherein the partial decoding is a partial soft decoding.

40. The non-transitory computer readable medium according to claim 39, wherein the partial soft decoding involve applying iterations of soft decoding of a lowest decoding complexity.

41. The non-transitory computer readable medium according to claim 38, wherein the partial decoding is a partial hard decoding.

42. The non-transitory computer readable medium according to claim 32 that stores instructions for evaluating the characteristic of the multiple read thresholds by checking a distribution of thresholds voltages of the group of memory cells under the different assumptions.

43. The non-transitory computer readable medium according to claim 32 that stores instructions for finding, based upon the multiple read results, at least one desired read threshold to be applied during future read attempts;

performing at least one additional read attempt to provide additional read results and determining, based upon the at least one additional read result, a reliability of the at least one additional read result.

44. The non-transitory computer readable medium according to claim 32 that stores instructions for soft decoding the multiple read results.

45. The non-transitory computer readable medium according to claim 32 that stores instructions for finding, based upon the multiple read results, a desired read threshold to be applied during future read attempts;

and performing additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold.

46. The non-transitory computer readable medium according to claim 32, wherein the multiple read attempts comprise first and second read attempts and wherein the first and second read attempts are executed before a completion of a determination of a desired read threshold.

47. A non-transitory computer readable medium that stores instructions for performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results;

error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results;

finding, based upon the multiple read results, a desired read threshold to be applied during future read attempts; and

performing additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold;

wherein the additional read thresholds are selected such that there are at least a predefined number of read thresholds that are proximate to the desired read threshold and are positioned at each side of the desired read threshold, as to provide a decoder that performs the error correction decoding of the multiple read results with high resolution sampling for soft information.

48. A flash memory controller, comprising:

a read circuit arranged to perform multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results;

a reliability circuit arranged to determine, based upon the multiple read results, a reliability metric of each of the multiple read results; and

an error correction decoding circuit arranged to perform error correction decoding of the multiple read results based upon reliability metrics associated with the multiple read results;

wherein the flash memory controller is further arranged to find, based upon the multiple read results, a desired read threshold to be applied during future read attempts; and

perform additional read results using additional read thresholds, after finding the desired read threshold, wherein the additional read thresholds are proximate to the desired read threshold;

wherein the additional read thresholds are selected such that there are at least a predefined number of read thresholds that are proximate to the desired read threshold and are positioned at each side of the desired read threshold, as to provide a decoder that performs the error correction decoding of the multiple read results with high resolution sampling for soft information.