Statistical read comparison signal generation for memory systems

• US 8,938,658 B2
• Filed: 08/31/2012
• Issued: 01/20/2015
• Est. Priority Date: 11/07/2011
• Status: Expired due to Fees

• 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): Ton, David
• Application Number:
  US13/602,031
• Publication Number:
  US 20130117613A1
• Time in Patent Office: 872 Days
• Field of Search: 386/248, 365/248, 714/773, 714/769, 714/718, 714/48, 714/774
• US Class Current: 714/769
• 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 may enhance the performance of error control codes used 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 device operable to provide one or more read comparison signal values for reading data 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 storage medium characterization parameter values and includes a first set of one or more read comparison signal values;

a selection module to select a characterization vector based on a specified set of one or more storage medium characterization parameter values for the storage medium, the specified set comprising one or more of;

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 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; and

a read controller to provide the respective first set of one or more read comparison signal values, from the selected characterization vector, to read circuitry associated with the storage medium.

2. The device of claim 1, wherein the read controller is further to receive a read data request and prompt the selection module to select the characterization vector in response to receiving the read data request.

3. The device of claim 2, wherein the read controller is further to receive, in association with the read data request, the specified set of one or more storage medium characterization parameter values.

4. The device of claim 2, wherein the read controller is further to retrieve, in response to receiving the read data request, the specified set of one or more storage medium characterization parameter values.

5. The device of claim 1, wherein the set of one or more storage medium characterization parameter values further comprises an indication of a physical characteristic associated with at least a portion of the storage medium.

6. The device of claim 1, wherein, for each characterization vector, the respective first set of one or more read comparison signal values satisfies a respective threshold error rate associated with one or more statistics.

7. The device of claim 6, wherein:

each characterization vector also includes a second set of one or more read comparison signal values;

the read controller is to provide the respective first set of one or more read comparison signal values, from the selected characterization vector, to read circuitry associated with the storage medium at a first time; and

the read controller is further to, at a second time, provide the respective second set of one or more read comparison signal values, from the selected characterization vector, to the read circuitry associated with the storage medium.

8. The device of claim 7, wherein the read controller is further to:

obtain an error indicator that indicates that the first set of one or more read comparison signal values yields data that includes at least one uncorrectable error; and

provide the respective second set of one or more read comparison signal values to the read circuitry in response to obtaining the error indicator.

9. The device of claim 7, wherein, for each characterization vector, 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 corresponding to the set of one or more storage medium characterization parameter values.

10. The device of claim 9, wherein each of the respective second set of one or more read comparison signal values is offset from the corresponding one of the respective first set of one or more read comparison signal values in a direction determined by the sign of the difference between the respective transition probability pair.

11. The device of claim 9, wherein each of the respective second set of one or more read comparison signal values is offset from the corresponding one of the respective first set of one or more read comparison signal values by a magnitude based on the difference between the respective transition probability pair.

12. A method of providing one or more read comparison signal values for reading data from a storage medium, comprising:

selecting one of a plurality of characterization vectors based on a specified set of one or more storage medium characterization parameter values for the storage medium, the specified set comprising one or more of;

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 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, wherein each of the plurality of characterization vectors corresponds to a set of one or more storage medium characterization parameter values and includes a first set of one or more read comparison signal values; and

providing the respective first set of one or more read comparison signal values, from the selected characterization vector, to read circuitry associated with the storage medium.

13. The method of claim 12, further comprising receiving a read data request, and wherein selection of the characterization vector occurs in response to receiving the read data request.

14. The method of claim 13, further comprising receiving, in association with the read data request, the specified set of one or more storage medium characterization parameter values.

15. The method of claim 13, further comprising retrieving, in response to receiving the read data request, the specified set of one or more storage medium characterization parameter values.

16. The method of claim 12, wherein, for each characterization vector, the respective first set of one or more read comparison signal values satisfies a respective threshold error rate associated with one or more statistics.

17. The method of claim 16, wherein each characterization vector also includes a second set of one or more read comparison signal values, and the method includes:

at a first time, providing the respective first set of one or more read comparison signal values, from the selected characterization vector, to the read circuitry associated with the storage medium; and

at a second time, providing the respective second set of one or more read comparison signal values, from the selected characterization vector, to the read circuitry associated with the storage medium.

18. The method of claim 17, further comprising:

obtaining an error indicator that indicates that the first set of one or more read comparison signal values yields data that includes at least one uncorrectable error, and

wherein the second set of one or more read comparison signal values is provided to the read circuitry in response to obtaining the error indicator.

19. A method of generating read comparison signal values for reading data from a storage medium, the method comprising:

selecting a set of one or more storage medium characterization parameter values, the set comprising one or more of;

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 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;

applying one or more testing conditions associated with the set of one or more storage medium characterization parameter values to at least one portion of the storage medium;

writing and reading a statistically significant amount of data to and from the at least one portion of the storage medium while applying the one or more testing conditions, and recording information comprising reading signal levels corresponding to the read data and information identifying reading errors;

generating statistics associated with the recorded information; and

identifying read comparison signal levels based on the recorded reading signal levels.

20. The method claim 19, wherein the read comparison signal levels include voltage levels.

21. The method claim 19, wherein identifying read comparison signal levels includes identifying the read comparison signal levels in accordance with predefined error minimization criteria.

22. The method of claim 19, wherein the statistics include reading signal level distributions, and the method further comprising:

identifying one of more respective minimum values between adjacent reading signal level distributions;

generating a set of read comparison signal values based the one or more identified minimum values.

23. The method of claim 19, wherein the storage medium comprises flash memory.

24. The method of claim 23, wherein the flash memory is multi-level cell flash memory.

25. The method of claim 23, wherein the flash memory comprises at least one of NAND-type flash memory and NOR-type flash memory.

26. The method of claim 19, wherein the statistically significant amount of data is pseudo-randomly generated.