Storage and retrieval of shaped data

• US 9,135,155 B2
• Filed: 11/30/2012
• Issued: 09/15/2015
• Est. Priority Date: 11/30/2012
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Sharon, Eran, Alrod, Idan, Fainzilber, Omer, Navon, Ariel
• Primary Examiner(s): Alphonse, Fritz
• Application Number:
  US13/690,275
• Publication Number:
  US 20140157086A1
• Time in Patent Office: 1,019 Days
• Field of Search: 714/773, 714/763, 714/770
• US Class Current: 1/1
• CPC Class Codes: G06F 11/08 Error detection or correction by redundancy in data representation, e.g. by using checking codes
• CPC Class Codes: G06F 11/1012 using codes or arrangements adapted for a specific type of error G06F11/1048 takes precedence
• CPC Class Codes: G06F 12/00 Accessing, addressing or allocating within memory systems or architectures digital input from, or digital output to record carriers, e.g. to disk storage units, G06F3/06
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 12/14 Protection against unauthorised use of memory or access to memory

Abstract

Systems and methods of encoding and decoding shaped data include determining a bit representation corresponding to a bit in a representation of a codeword that is read from a non-volatile memory of a data storage device. A soft metric corresponding to the bit representation is determined at least partially based on an amount of shaping of data.

Claims

1. A method comprising:

in a data storage device including a non-volatile memory, performing;

receiving a representation of a codeword that is read from the non-volatile memory;

determining a shaping level of a set of one or more bits of the representation of the codeword;

determining a soft metric of each bit of the one or more bits of the representation of the codeword based on a value of the bit in the received representation and based on the shaping level; and

initiating a decoding operation of the codeword based on the soft metrics.

2. The method of claim 1, wherein the shaping level is determined based on stored side information.

3. The method of claim 1, wherein the shaping level is determined as a function of read values of the representation of the codeword read from the non-volatile memory.

4. The method of claim 3, wherein the shaping level is determined as a function of a number of occurrences of each of the read values within the set of one or more bits.

5. The method of claim 1, wherein determining the soft metric of each bit comprises:

determining an initial soft metric of each bit based on a read value of the bit;

determining a correction value to the initial soft metric of each bit, wherein the correction value is at least partially based on the shaping level; and

generating the soft metric of each bit by applying the correction value to the initial soft metric.

6. The method of claim 5, wherein the correction value is computed further based on received bit reliability information.

7. The method of claim 1, further comprising estimating an error correction capability of decoding the representation of the codeword based on the shaping level.

8. The method of claim 7, further comprising sensing the non-volatile memory to determine additional soft bits in response to the estimated error correction capability being below a threshold.

9. The method of claim 7, further comprising determining the soft metric as a function of the estimated error correction capability.

10. The method of claim 1, wherein the set of one or more bits is determined according to a sliding window of a data stream.

11. The method of claim 1, wherein the soft metric includes a hard value and at least one of a reliability value, a likelihood value, or a probability value.

12. The method of claim 1, wherein the soft metric includes a log likelihood value.

13. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

read a representation of a codeword from the non-volatile memory;

determine a shaping level of a set of one or more bits of the representation of the codeword;

determine a soft metric of each bit of the one or more bits of the representation of the codeword based on a value of the bit in the representation of the codeword and based on the shaping level; and

initiate a decoding operation of the codeword based on the soft metrics.

14. The data storage device of claim 13, wherein the controller is further configured to estimate an error correction capability of decoding the representation of the codeword based on the shaping level.

15. The data storage device of claim 14, wherein the controller is further configured to initiate sensing of the non-volatile memory to determine additional soft hits in response to the estimated error correction capability being below a threshold.

16. The data storage device of claim 14, wherein the controller is further configured to determine the soft metric as a function of the estimated error correction capability.

17. A method comprising:

in a data storage device including a non-volatile memory, performing;

determining a shaping level of data to be written to the non-volatile memory;

selecting at least one programming parameter at least partially based on the shaping level; and

programming the data to the non-volatile memory according to the at least one selected programming parameter.

18. The method of claim 17, wherein the data includes a codeword, wherein the shaping level is determined based on a distribution of bit values in the codeword, and wherein selecting the at least one programming parameter includes:

estimating a correction capability at least partially based on a code rate of the codeword and the distribution of the bit values in the codeword; and

determining the at least one programming parameter based on the estimated correction capability.

19. The method of claim 17, wherein the at least one programming parameter includes a programming step size that is selected based on the shaping level, wherein the selected programming step size is larger than a programming step size corresponding to unshaped data, and wherein using the selected programming step size enables faster programming of the data to the non-volatile memory as compared to using the programming step size corresponding to unshaped data.

20. The method of claim 17, wherein the non-volatile memory includes a multi-level cell (MLC) partition, wherein the shaping of the data causes a state of the MLC partition to be more highly populated than a less-populated state of the MLC partition when the data is programmed to the MLC partition, and wherein the at least one programming parameter is selected to reduce an error rate associated with the more highly populated state.

21. The method of claim 20, wherein the at least one programming parameter includes a programming step size and wherein a programming step size for the more highly populated state is smaller than a programming step size for the less-populated state.

22. The method of claim 20, wherein the at Least one programming parameter includes a verify level.

23. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

determine a shaping level of bit values in data to be written to the non-volatile memory;

select at least one programming parameter at least partially based on the shaping level; and

program the data to the non-volatile memory according to the at least one selected programming parameter.

24. The data storage device of claim 23, wherein the data includes a codeword, wherein the shaping level is determined based on a distribution of bit values in the codeword, and wherein the controller is configured to:

estimate a correction capability at least partially based on a code rate of the codeword and the distribution of the bit values in the codeword; and

determine the at least one programming parameter based on the estimated correction capability.

25. The data storage device of claim 23, wherein the data includes a codeword, wherein the shaping level is determined based on a distribution of bit values in the codeword, and wherein the controller is configured to:

estimate a correction capability at least partially based on a code rate of the codeword and the distribution of the bit values in the codeword; and

determine a plurality of verify levels based on the estimated correction capability.

26. The data storage device of claim 25, wherein verify levels of the plurality of verify levels corresponding to a more highly populated state of storage elements in the non-volatile memory are spaced farther apart than verify levels corresponding to a less-populated state of the storage elements.

27. A method comprising:

in a data storage device including a controller and a non-volatile memory, performing;

descrambling scrambled data that is read from the non-volatile memory to generate a representation of a codeword;

determining a shaping level of the representation of the codeword; and

determining a soft metric for decoding based on the representation of the codeword and based on the shaping level.

28. The method of claim 27, further comprising estimating an error correction capability of decoding the representation of the codeword based on the shaping level.

29. The method of claim 28, further comprising sensing the non-volatile memory to determine additional soft bits in response to the estimated error correction capability being below a threshold.

30. The method of claim 27, wherein the shaping level corresponds to a global distribution of hard values.

31. The method of claim 27, wherein the shaping level corresponds to a local distribution of hard values.

32. The method of claim 31, wherein the local distribution is determined according to a sliding window of a data stream.

33. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

descramble scrambled data that is read from the non-volatile memory to generate a representation of a codeword;

determine a shaping level of the representation of the codeword; and

determine a soft metric for decoding based on the representation of the codeword and based on the shaping level.

34. The data storage device of claim 33, wherein the controller is further configured to estimate an error correction capability of decoding the representation of the codeword based on the shaping level.

35. The data storage device of claim 34, wherein the non-volatile memory is sensed to determine additional soft bits in response to the estimated error correction capability being below a threshold.

36. A method comprising:

in a data storage device including a controller and a non-volatile memory, performing;

determining a shaping level of data to be stored in the non-volatile memory;

scrambling the data prior to storing the data in the non-volatile memory in response to the shaping level being less than a threshold; and

storing the data in the non-volatile memory as unscrambled data in response to the shaping level satisfying the threshold.

37. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

determine a shaping level of data to be stored in the non-volatile memory;

set an indicator to have a first value to cause scrambling of the data prior to storing the data in the non-volatile memory in response to the shaping level being less than a threshold; and

set the indicator to have a second value to cause the data to be stored in the non-volatile memory as unscrambled data in response to the shaping level satisfying the threshold.

38. A method comprising:

in a data storage device including a non-volatile memory, performing;

determining a bit representation corresponding to a bit in a representation of a codeword that is read from the non-volatile memory;

determining a soft metric corresponding to the bit representation, wherein the soft metric is at least partially based on a shaping level of data stored in the non-volatile memory; and

initiating a decoding operation of the soft metric.

39. The method of claim 38, wherein, determining the soft metric includes:

determining an estimated amount of shaping of at least a portion of the representation of the codeword; and

sending an indication of the estimated amount of shaping to a soft decoder.

40. The method of claim 38, wherein determining the soft metric includes:

determining an initial soft metric corresponding to the bit representation at least partially based on a table lookup operation;

determining a soft metric correction value corresponding to the hit representation; and

updating the initial soft metric according to the soft metric correction value.

41. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

determine a hit representation corresponding to a bit in a representation of a codeword that is read from the non-volatile memory;

determine a soft metric corresponding to the bit representation, wherein the soft metric is at least partially based on a shaping level of data stored in the non-volatile memory; and

initiate a decoding operation of the soft metric.

42. A data storage device comprising:

a non-volatile memory; and

a controller configured to;

determine a shaping level of bit values in data to be written to the non-volatile memory;

select a storage location of the data within the non-volatile memory at least partially based on the shaping level; and

program the data to the selected storage location within the non-volatile memory.

43. The data storage device of claim 42, wherein the controller is further configured to determine programming parameters used for programming the data into the storage location within the non-volatile memory at least partially based on the shaping level.

44. The data storage device of claim 42, wherein the controller is further configured to determine a ratio of write/erase cycles directed into the storage location within the non-volatile memory at least partially based on the shaping level.

45. A method comprising:

in a data storage device including a non-volatile memory, performing;

determining a shaping level of bit values in data to be written to the non-volatile memory;

selecting a storage location of the data within the non-volatile memory at least partially based on the shaping level; and

programming the data to the selected storage location within the non-volatile memory.

46. A method comprising:

in a data storage device including a controller and a flash memory, performing;

shaping data to be stored to the flash memory to generate shaped data;

encoding the shaped data to generate encoded shaped data;

scrambling the encoded shaped data to generate scrambled data;

programming the scrambled data into the flash memory;

reading the scrambled data from the flash memory;

descrambling the scrambled data that is read from the flash memory to generate a representation of a codeword;

determining a shaping level of the representation of the codeword; and

determining a soft metric for decoding based on the representation of the codeword and based on the shaping level.

47. The method of claim 46, farther comprising, prior to scrambling the encoded shaped data:

programming the encoded shaped data into a single level cell (SLC) portion of the flash memory; and

reading the encoded shaped data from the SLC portion; and

providing the encoded shaped data to a scrambler,

wherein the scrambled data is programmed into a multi-level cell (MLC) portion of the flash memory.

48. The method of claim 46, wherein the shaped data has a same number of bits as the data.

49. The method of claim 48, wherein shaping the data is performed via a block transformation.

50. The method of claim 46, wherein scrambling the encoded shaped data includes providing the encoded shaped data to an input of a scrambler and wherein the scrambled data is provided at an output of the scrambler.

51. The method of claim 50, wherein the scrambler is in a controller external to a die that includes the flash memory.

52. The method of claim 50, wherein the scrambler is in a die that includes the flash memory.

53. The method of claim 46, wherein the scrambled data is programmed into a multi-level cell (MLC) portion of the flash memory, and wherein each logical page of the MLC portion is associated with a distinct scrambling word.

54. The method of claim 46, wherein the scrambled data is programmed into a multi-level cell (MLC) portion of the flash memory, and wherein multiple logical pages within a same word line of the MLC portion are associated with a common scrambling word.

55. A data storage device comprising:

a flash memory; and

a controller configured to;

shape data to be stored to the flash memory to generate shaped data;

encode the shaped data to generate encoded shaped data;

program scrambled data into the flash memory, wherein the encoded shaped data is scrambled to generate the scrambled data;

read the scrambled data from the flash memory;

descramble scrambled data that is read from the flash memory to generate a representation of a codeword;

determine a shaping level of the representation of the codeword; and

determine a soft metric for decoding based on the representation of the codeword and based on the shaping level.

56. The data storage device of claim 55, wherein the flash memory includes a single level cell (SLC) portion and a multi-level cell (MLC) portion, wherein the controller is configured to program the encoded shaped data into the SLC portion, wherein the encoded shaped data is read from the SLC portion and scrambled to generate the scrambled data, and wherein the scrambled data is programmed into the MLC portion.

57. The data storage device of claim 55, wherein the shaped data has a same number of bits as the data.

58. The data storage device of claim 57, wherein shaping the data is performed via a block transformation.

59. The data storage device of claim 55, wherein scrambling the encoded shaped data includes providing the encoded shaped data to an input of a scrambler, and wherein the scrambled data is provided at an output of the scrambler.

60. The data storage device of claim 59, wherein the scrambler is in the controller and external to a die that includes the flash memory.

61. The data storage device of claim 59, wherein the scrambler is in a die that includes the flash memory.

62. The data storage device of claim 55, wherein the scrambled data is stored to a multi-level cell (MLC) portion of the flash memory, and wherein each logical page of the MLC portion is associated with a distinct scrambling word.

63. The data storage device of claim 55, wherein the scrambled data is stored to a multi-level cell (MLC) portion of the flash memory, and wherein multiple logical pages within a same word line of the MLC portion are associated with a common scrambling word.