Adaptive read comparison signal generation for memory systems

• US 8,793,543 B2
• Filed: 08/31/2012
• Issued: 07/29/2014
• 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): Ton, David
• Application Number:
  US13/602,039
• Publication Number:
  US 20130117616A1
• Time in Patent Office: 697 Days
• Field of Search: 386/248, 365/185.18, 714/769, 714/773, 714/718, 714/48
• US Class Current: 714/718
• 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 respective set of one or more storage medium characterization parameter values, and includes a first set of one or more read comparison signal values and a second set of one or more read comparison signal values, the second set corresponding to the first set and a respective pair of transition probabilities associated with the set of one or more storage medium characterization parameter values;

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

a read controller to;

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

provide the second 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 first set of one or more read comparison signal values is provided at one time, and the second set of one or more read comparison signal values is provided at an alternative time.

3. The device of claim 1, wherein the first set of one or more read comparison signal values is provided according to a first condition, and the second set of one or more read comparison signal values is provided according to a second condition.

4. 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.

5. The device of claim 4, 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.

6. The device of claim 4, 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.

7. The device of claim 1, 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 second set of one or more read comparison signal values to the read circuitry in response to obtaining the error indicator.

8. The device of claim 1, wherein each of the second set of one or more read comparison signal values is offset from the corresponding 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.

9. The device of claim 1, wherein each of the second set of one or more read comparison signal values is offset from the corresponding first set of one or more read comparison signal values by a magnitude based on the difference between the respective transition probability pair.

10. 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, 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 a second set of one or more read comparison signal values, the second set corresponding to the first set and a respective pair of transition probabilities associated with the set of one or more storage medium characterization parameter values;

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

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

11. The method of claim 10, wherein the first set of one or more read comparison signal values is provided at one time, and the second set of one or more read comparison signal values is provided at an alternative time.

12. The method of claim 10, wherein the first set of one or more read comparison signal values is provided according to a first condition, and the second set of one or more read comparison signal values is provided according to a second condition.

13. The method of claim 10, 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 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 10, 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.

17. The method of claim 10, wherein, for each characterization vector, the first set of one or more read comparison signal values satisfies a respective threshold error rate associated with one or more statistics.

18. 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 respective set of one or more storage medium characterization parameter values, and includes a second set of one or more read comparison signal values that differs from a first set of one or more read comparison signal values in accordance with a respective pair of transition probabilities associated with the set of one or more storage medium characterization parameter values;

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

a read controller to;

provide the first set of one or more read comparison signal values to read circuitry associated with the storage medium; and

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

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

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

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;

generating transition probabilities from observed reading errors by writing and reading a statistically significant amount of data to and from the at least one portion of the storage medium; and

calculating a shifted read comparison signal value based on a respective pair of transition probabilities.

20. The method of claim 19, wherein the shifted read comparison signal value includes a voltage level.

21. The method of claim 19, wherein the shifted read comparison signal value is an offset relative to a respective base read comparison signal level.

22. The method of claim 21, wherein calculating the shifted read comparison signal value comprises determining a direction of the offset by determining the sign of a difference between the respective pair of transition probabilities.

23. The method of claim 21, wherein calculating the shifted read comparison signal value comprises determining a magnitude of the offset based at least on a difference between the respective pair of transition probabilities.

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

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

26. The method of claim 24, wherein the flash memory comprises at least one of NAND-type flash memory and NOR-type flash memory.

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

28. The method of claim 19, wherein each transition probability comprises the probability of reading a particular bit-tuple value given that a particular bit-tuple value was written to a storage location.