Providing Reliability Metrics For Decoding Data In Non-Volatile Storage

• US 20130246720A1
• Filed: 05/06/2013
• Published: 09/19/2013
• Est. Priority Date: 03/29/2007
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Mokhlesi, Nima, Chin, Henry, Zhao, Dengtao
• Granted Patent: US 8,966,350 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• 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: 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 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: H03M 13/11 using multiple parity bits
• 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

Abstract

A set of reliability metrics is provided for use by an iterative probabilistic decoding process for non-volatile storage. A plurality of sense operations are performed on at least one set of non-volatile storage elements which are programmed to a plurality of programming states. A set of reliability metrics such as logarithmic likelihood ratios is provided based on the sense operations. The set of reliability metrics is can be used by an iterative probabilistic decoding process in determining a programming state of at least one non-volatile storage element based on at least one subsequent sense operation involving the at least one non-volatile storage element. The plurality of sense operations can be performed at different ages (e.g., number of program/erase cycles) of the at least one set of non-volatile storage elements and the set of reliability metrics can be based on an average over the different ages.

Claims

1. A method for operating non-volatile storage, comprising:

performing a plurality of sense operations on at least one set of non-volatile storage elements which are programmed to a plurality of programming states;

providing a set of reliability metrics based on the sense operations; and

storing the set of reliability metrics for use by an iterative probabilistic decoding process in determining a programming state of at least one non-volatile storage element based on at least one subsequent sense operation involving the at least one non-volatile storage element.

2. The method of claim 1, wherein:

the plurality of sense operations are performed on the at least one set of non-volatile storage elements at different ages of the at least one set of non-volatile storage elements.

3. The method of claim 2, wherein:

the different ages represent different numbers of program/erase cycles of the at least one set of non-volatile storage elements.

4. The method of claim 2, wherein:

the set of reliability metrics is based on an average over the different ages.

5. The method of claim 1, further comprising:

the at least one non-volatile storage element is in the at least one set of non-volatile storage elements.

6. The method of claim 1, further comprising:

obtaining a threshold voltage distribution for each of the plurality of programming states based on the plurality of sense operations; and

providing the set of reliability metrics based on the threshold voltage distributions.

7. The method of claim 1, wherein:

the set of reliability metrics is based on conditional probability functions which are based on the plurality of sense operations.

8. The method of claim 1, wherein:

the set of reliability metrics comprise logarithmic likelihood ratios which are based on the plurality of sense operations.

9. The method of claim 1, wherein the providing the set of reliability metrics comprises:

determining a conditional probability function f1(u|X) based on the plurality of sense operations, where u indicates a sensed threshold voltage and X represents a programmed state of the plurality of programming states; and

determining a probability function f2(v) based on the plurality of sense operations, for each programming state, where v indicates a deviation of a sensed threshold voltage from a threshold voltage free of read noise.

10. The method of claim 9, wherein the providing the set of reliability metrics further comprises:

determining logarithmic likelihood ratios based on the conditional probability function f1(u|X) and the probability function f2(v).

11. A non-volatile storage system, comprising:

a set of non-volatile storage elements; and

one or more control circuits in communication with the set of non-volatile storage elements, the one or more control circuits perform a plurality of sense operations on at least one set of non-volatile storage elements which are programmed to a plurality of programming states, provide a set of reliability metrics based on the sense operations, and store the set of reliability metrics for use by an iterative probabilistic decoding process in determining a programming state of at least one non-volatile storage element based on at least one subsequent sense operations.

12. The non-volatile storage system of claim 11, wherein:

the plurality of sense operations are performed on the at least one set of non-volatile storage elements at different ages of the at least one set of non-volatile storage elements.

13. The non-volatile storage system of claim 12, wherein:

the different ages represent different numbers of program/erase cycles of the at least one set of non-volatile storage elements.

14. The non-volatile storage system of claim 12, wherein:

the set of reliability metrics is based on an average over the different ages.

15. The non-volatile storage system of claim 11, wherein:

the at least one non-volatile storage element is in the at least one set of non-volatile storage elements.

16. The non-volatile storage system of claim 11, wherein one or more control circuits:

obtain a threshold voltage distribution for each of the plurality of programming states based on the plurality of sense operations; and

provide the set of reliability metrics based on the threshold voltage distributions.

17. The non-volatile storage system of claim 11, wherein:

the set of reliability metrics is based on conditional probability functions which are based on the plurality of sense operations.

18. The non-volatile storage system of claim 11, wherein:

the set of reliability metrics comprise logarithmic likelihood ratios which are based on the plurality of sense operations.

19. The non-volatile storage system of claim 11, wherein the one or more control circuits:

determine a conditional probability function f1(u|X) based on the plurality of sense operations, where u indicates a sensed threshold voltage and X represents a programmed state of the plurality of programming states; and

determine a probability function f2(v) based on the plurality of sense operations, for each programming state, where v indicates a deviation of a sensed threshold voltage from a threshold voltage free of read noise.

20. The non-volatile storage system of claim 19, wherein the one or more control circuits:

determine logarithmic likelihood ratios based on the conditional probability function f1(u|X) and the probability function f2(v).