Soft information generation for memory systems

• US 9,058,289 B2
• Filed: 08/31/2012
• Issued: 06/16/2015
• Est. Priority Date: 11/07/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Enterprise IP LLC (Western Digital Corporation)
• Inventors: Tai, Ying Yu, Ma, Yueh Yale
• Primary Examiner(s): MCMAHON, DANIEL F
• Application Number:
  US13/602,047
• Publication Number:
  US 20130117640A1
• Time in Patent Office: 1,019 Days
• Field of Search: None
• US Class Current: 1/1
• 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 11/1048 using arrangements adapted for a specific error detection or correction feature
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits

Abstract

Implementations include systems, methods and/or devices suitable for use in a memory system that use error control codes to improve the reliability with which data can be stored and read. Some implementations include systems, methods and/or devices enabled to generate and utilize soft information for decoding encoded data read from a storage medium. More specifically, some implementations utilize a collection of characterization vectors that include soft information values for bit-tuples that may be read from the storage medium for various combinations of the storage medium characterization parameter values. Some implementations are enabled to determine and utilize read comparison signal values associated with one or more storage medium characterization parameter values. And some implementations are enabled to determine and utilize shifted read comparison signal values associated with one or more storage medium characterization parameter values and an identified error condition.

Claims

1. A method of generating soft information values for data read from a storage medium, the method comprising:

retrieving a characterization vector, of a plurality of distinct characterization vectors that each includes a set of soft information values, wherein the characterization vector retrieved is based on a set of one or more storage medium characterization parameter values for the storage medium including an indicator of a number of previous program/erase cycles of a storage medium location being accessed; and

in response to a read data request;

generating a first plurality of soft information values corresponding to a first plurality of data values read from a first portion of the storage medium and the retrieved characterization vector;

obtaining an error indicator that indicates that the first plurality of soft information values are representative of data that includes at least one uncorrectable error; and

generating a second plurality of soft information values corresponding to a second plurality of data values read from the first portion of the storage medium and the retrieved characterization vector, wherein, the second plurality of soft information values are generated in response to receiving the error indicator, and the second plurality of data values is distinct from the first plurality of data values;

wherein the retrieved characterization vector includes soft information values from which the first plurality of soft information values and the second plurality of soft information values are generated.

2. The method of claim 1, further comprising:

reading, from the first portion of the storage medium, the first plurality of data values using a first read comparison signal value from the retrieved characterization vector; and

reading, from the first portion of the storage medium, the second plurality of data values using a second read comparison signal value from the retrieved characterization vector different from the first read comparison signal.

3. The method of claim 1, further comprising:

generating output data from the second plurality of soft information values or a combination of the second plurality of soft information values and the first plurality of soft information values.

4. The method of claim 1, further comprising:

generating a third plurality of soft information values by combining the first plurality of soft information values and the second plurality of soft information values.

5. The method of claim 4, wherein the third plurality of soft information values is generated in response to receiving an error indicator that indicates that the second plurality of soft information values are representative of data that includes at least one uncorrectable error.

6. The method of claim 1, further comprising retrieving the set of one or more storage medium characterization parameter values in response to receiving the read data request.

7. The method of claim 1, further comprising receiving the set of one or more storage medium characterization parameter values.

8. The method of claim 1, wherein the set of one or more storage medium characterization parameter values provides an indication of at least one of the group consisting of:

a physical characteristic associated with at least a portion of the storage medium, a mode of operation associated with at least a portion of the storage medium, a history of use associated with at least a portion of the storage medium, a condition characteristic associated with at least a portion of the storage medium, a read type associated with at least a portion of the storage medium, and a location associated with at least a portion of the storage medium.

9. The method of claim 1, wherein the set of one or more storage medium characterization parameter values further includes an indicator of the storage medium locations being accessed, and an indicator of a current temperature of the storage medium.

10. The method of claim 1, further comprising:

selecting one or more first read comparison signal values from the retrieved characterization vector;

reading the first plurality of data values by providing the one or more first read comparison signal values to read circuitry associated with the storage medium;

selecting one or more second read comparison signal values from the retrieved characterization vector; and

reading the second plurality of data values by providing the one or more second read comparison signal values to the read circuitry associated with the storage medium.

11. The method of claim 10, wherein the one or more first read comparison signal values and the one or more second read comparison signal values are each representative of voltage values.

12. The method of claim 10, wherein at least one of the one or more second read comparison signal values is offset relative to a corresponding one of the one or more first read comparison signal values according to a transition probability pair.

13. The method of claim 10, wherein the retrieved characterization vector includes at least two read comparison signal values.

14. The method of claim 1, wherein

the retrieved characterization vector includes one or more soft information values for each of one or more bit-tuples;

and

generating the first plurality of soft information values comprises selecting a respective soft information value from the retrieved characterization vector for each bit-tuple in the first plurality of data values.

15. The method of claim 14, wherein the first plurality of data values includes a sequence of single bit bit-tuples, and wherein selecting the respective soft information value includes selecting the soft information value corresponding to either an upper page or a lower page for each bit-tuple.

16. The method of claim 14, wherein the first plurality of data values includes a sequence of bit pair bit-tuples, and wherein selecting the respective soft information value includes selecting the soft information value corresponding to both an upper page and a lower page for each bit-tuple.

17. The method of claim 14, wherein a soft information value of the retrieved characterization vector includes at least one of a transition probability and a log-likelihood ratio.

18. The method of claim 14, wherein the retrieved characterization vector further includes a pair of read comparison voltage values.

19. The method of claim 18, wherein the retrieved characterization vector further includes a pair of weighting values associated with the pair of read comparison voltage values.

20. The method of claim 14, wherein the retrieved characterization vector is stored in table form defined by a combination of characterization parameters.

21. The method of claim 1, wherein:

the retrieved characterization vector includes one or more soft information values for each of one or more bit-tuples; and

generating the second plurality of soft information values comprises selecting a respective soft information value from the retrieved characterization vector for each bit-tuple in the second plurality of data values.

22. The method of claim 4, wherein generating the third plurality of soft information values comprises:

comparing a pair of soft information values, the pair of soft information values including one of the first plurality of soft information values and a corresponding one of the second plurality of soft information values;

equating a corresponding one of the third plurality of soft information values to a first combination of the pair of soft information values when the comparison satisfies a first condition; and

equating a corresponding one of the third plurality of soft information values to a second combination of the pair of soft information values when the comparison fails to satisfy the first condition.

23. The method of claim 22, wherein:

each of the pair of the soft information values includes a sign; and

the comparison includes determining whether the signs of the pair of soft information values are equal.

24. The method of claim 22, wherein the first combination of the pair of soft information values comprises only one of the pair of soft information values.

25. The method of claim 22, wherein equating the corresponding one of the third plurality of soft information values to the second combination of the pair of soft information values comprises calculating a weighted sum of the pair of soft information values when the first condition is not satisfied.

26. The method of claim 25, further comprising retrieving respective weights for determining the weighted sum from the retrieved characterization vector.

27. The method of claim 25, further comprising calculating respective weights for determining the weighted sum from the pair of soft information values.

28. The method of claim 1, further comprising transmitting the first plurality of soft information values.

29. The method of claim 1, wherein the data values are error control encoded.

40. The method of claim 1, wherein the retrieved characterization vector includes:

information corresponding to a read comparison signal value for use when reading data from the storage medium in response to receiving an uncorrectable error.

30. A device operable to generate soft information values for data read from a storage medium, the device comprising:

a characterization module including a plurality of characterization vectors,

wherein each characterization vector corresponds to a set of one or more characterization parameter values and includes one or more soft information values for each of one or more bit-tuple combinations;

a selection module to select a characterization vector based on a specified set of one or more characterization parameter values, including an indicator of a number of previous program/erase cycles of a storage medium location being accessed; and

a conversion module to, in response to a read data request;

for a first plurality of data values each comprising one or more bit-tuples, generate a first plurality of soft information values corresponding to the first plurality of data values by associating a respective soft information value from the selected characterization vector with each bit-tuple of the first plurality of data values; and

for a second plurality of data values each comprising one or more bit-tuples, generate a second plurality of soft information values corresponding to the second plurality of data values by associating a respective soft information value from the selected characterization vector with each bit-tuple of the second plurality of data values; and

a read controller to;

read the first plurality of data values from a first portion of the storage medium;

obtain an error indicator that indicates that the first plurality of soft information values corresponding to the first plurality of data values are representative of data that includes at least one uncorrectable error; and

read controller read the second plurality of data values from the first portion of the storage medium in response to obtaining the error indicator,

wherein the selected characterization vector includes soft information values from which the first plurality of soft information values and the second plurality of soft information values are generated.

31. The device of claim 30, further comprising an adjustment module to generate a third plurality of soft information values from a combination of the first plurality of soft information values and the second plurality of soft information values.

32. The device of claim 30, wherein:

reading the first plurality of data values includes, at a first time, providing a first set of one or more read comparison signal values to read circuitry associated with the storage medium, and receiving from the first portion of the storage medium the first plurality of data values; and

reading the second plurality of data values includes, at a second time, provide a second set of one or more read comparison signal values to the read circuitry associated with the storage medium, and receiving from the first portion of the storage medium the second plurality of data values.

33. The device of claim 32, wherein each characterization vector includes the first set of one or more read comparison signal values and the second set of one or more read comparison signal values.

34. The device of claim 33, wherein each of the respective second set of one or more read comparison signal values is associated with a corresponding one of the respective first set of one or more read comparison signal values and a respective transition probability pair.

35. The device of claim 30, wherein the read controller is further to receive the read data request and prompt the selection module to select the characterization vector in response to receiving the read data request.

36. The device of claim 35, wherein the read controller is further to receive, in association with the read data request, the specified set of one or more characterization parameter values.

37. The device of claim 35, wherein the read controller is further to retrieve, in response to receiving the read data request, the specified set of one or more characterization parameter values.

38. The device of claim 31, further comprising a decoder to output data from the second plurality of soft information values or a combination of the second plurality of soft information values and the first plurality of soft information values.

39. The device of claim 31, wherein the third plurality of soft information values is generated in response to receiving an error indicator that indicates that the second plurality of soft information values are representative of data that includes at least one uncorrectable error.

41. The device of claim 32, wherein the selected characterization vector includes information corresponding to the first set of one or more read comparison signal values and the second set of one or more read comparison signal values.