Error management for writable tracking storage units

• US 6,678,192 B2
• Filed: 11/02/2001
• Issued: 01/13/2004
• Est. Priority Date: 11/02/2001
• Status: Expired due to Term

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Gongwer, Geoffrey S., Guterman, Daniel C., Khalid, Shahzad B.
• Primary Examiner(s): Elms, Richard
• Assistant Examiner(s): NGUYEN, HIEN N
• Application Number:
  US10/053,339
• Publication Number:
  US 20030086293A1
• Time in Patent Office: 802 Days
• Field of Search: 365/189.07, 365/185.33, 365/185.2, 365/185.24, 365/185.08, 365/185.02, 365/185.09, 365/185.01, 365/185.29
• US Class Current: 365/185.2
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation

Abstract

A memory system (e.g., memory card) having error management for stored levels (e.g., reference levels) used in discrimination of logic levels for data storage units providing data storage is disclosed. The stored levels can be stored in predetermined storage units (e.g., writable tracking storage units) in the memory system. The memory system is typically a non-volatile memory product or device that provides binary or multi-state data storage.

Claims

1. A method for determining discrimination levels for states of storage units of a memory product, said method comprising:

reading stored levels from a plurality of predetermined storage units;

determining whether any of the stored levels are aberrant;

correcting for at least one of the stored levels that said determining determines to be aberrant; and

determining one or more discrimination levels based on the stored levels following said correcting.

2. A method as recited in claim 1, wherein said correcting comprises discarding the at least one of the stored levels that said determining determines to be aberrant.

3. A method as recited in claim 1, wherein said determining of whether any of the stored levels are aberrant comprises:

determining a processed stored level from at least a plurality of the stored levels; and

comparing each of the stored levels to the processed stored level.

4. A method as recited in claim 3, wherein said correcting comprises discarding those of the stored levels that deviate from the processed stored level by more than a predetermined amount.

5. A method as recited in claim 1, wherein said determining of whether any of the stored levels are aberrant comprises:

obtaining an average stored level from the stored levels; and

comparing each of the stored levels to the average stored level.

6. A method as recited in claim 1, wherein the stored levels are reference levels.

7. A method as recited in claim 1, wherein the predetermined storage units are tracking storage units.

8. A method as recited in claim 1, wherein said method further comprises:

thereafter determining states of certain of the data stored in the storage units of the memory product in accordance with the discrimination levels.

9. A method as recited in claim 1, wherein the memory product is a memory card providing non-volatile data storage.

10. In a memory device, a method for managing errors associated with tracking storage units used with data storage units, said method comprising:

reading reference levels from a plurality of tracking storage units;

evaluating a quality for each of the reference levels;

determining whether the quality for any of the reference levels is unacceptable;

correcting for at least one of the reference levels that said determining determines to be unacceptable; and

determining, following said correcting, discrimination levels for data storage units associated with the tracking storage units based on the reference levels.

11. A method as recited in claim 10, wherein said method further comprises:

subsequently using the discrimination levels to determine states of data stored in the data storage units.

12. A method as recited in claim 10, wherein said determining of whether the quality for any of the reference levels is unacceptable comprises:

determining a processed reference level from at least a plurality of the reference levels; and

comparing each of the reference levels to the processed reference level.

13. A method as recited in claim 12, wherein said correcting for at least one of the reference levels that said determining determines to be unacceptable comprises:

removing those of the reference levels that deviate from the processed reference level by more than a predetermined amount.

14. A method as recited in claim 10, wherein the memory device is a memory card providing non-volatile, multi-state data storage.

15. A method for reading data from a memory device having data storage units and associated tracking storage units, said method comprising:

(a) substantially concurrently reading data levels from certain data storage units and reference levels from tracking storage units associated with the certain data storage units;

(b) computing a processed reference level from the reference levels;

(c) determining state discrimination levels based on the processed reference level;

(d) discriminating states of the data levels from the certain data storage units based on the state discrimination levels to acquire read data for a requester;

(e) evaluating, substantially concurrently with said discriminating (d), quality of the reference levels;

(f) determining whether the quality of the reference levels is acceptable;

(g) directing the read data to the requester when said determining (f) determines that the quality of the reference levels is acceptable; and

(h) correcting for at least one of the reference levels when said determining (f) determines that the quality of the reference levels is unacceptable.

16. A method as recited in claim 15, wherein said method further comprises:

(i) following said correcting (h), repeating at least said computing (b) through said discriminating (d) one or more times when said determining (f) determines that the quality of the reference levels is unacceptable.

17. A method as recited in claim 15, wherein said determining (f) of whether the quality of the reference levels is acceptable comprises:

comparing each of the reference levels to the processed reference level.

18. A method as recited in claim 15,

wherein the reference levels being read by said reading (a) pertain to first and second reference levels,

wherein said computing (b) computes a first processed reference level from the reference levels pertaining to the first reference level, and computes a second processed reference level from the reference levels pertaining to the second reference level, and

wherein said determining (c) determines the state discrimination levels based on the first and second processed reference levels.

19. A method as recited in claim 18, wherein said determining (f) of whether the quality of the reference levels is acceptable comprises:

comparing each of the reference levels pertaining to the first reference level to the first processed reference level, and

comparing each of the reference levels pertaining to the second reference level to the second processed reference level.

20. A method as recited in claim 15, wherein the memory device is a memory card providing non-volatile, multi-state data storage.

21. A method as recited in claim 15, wherein said computing (b) operates to average the reference levels to compute the processed reference level.

22. A method as recited in claim 15, wherein said computing (b) performs at least one of a minimum, maximum, Root-Mean-Square (RMS), peak, average, median, modulus, and linear regression with respect to the reference signals in computing the processed reference level.

23. A method as recited in claim 15, wherein said computing (b) computes a plurality of processed reference levels from the reference levels, and

wherein said determining (c) operates to determine the state discrimination levels based on the processed reference levels.

24. A method for reading data from a memory device having data storage units and associated tracking storage units, said method comprising:

(a) substantially concurrently reading data levels from certain data storage units and reference levels from tracking storage units associated with the certain data storage units;

(b) computing a processed reference level from the reference levels;

(c) determining state discrimination levels based on the processed reference level;

(d) discriminating states of the data levels from the certain data storage units based on the state discrimination levels to acquire read data for a requester;

(e) evaluating quality of the reference levels;

(f) determining whether the quality of the reference levels is acceptable;

(g) sending the read data to the requester when said determining (f) determines that the quality of the reference levels is acceptable;

(h) halting said sending (g) when said determining (f) determines that the quality of the reference levels is unacceptable; and

(i) correcting for at least one of the reference levels when said determining (f) determines that the quality of the reference levels is unacceptable.

25. A method as recited in claim 24, wherein said method further comprises:

(j) following said correcting (i), repeating said computing (b) through said correcting (i) one or more times when said determining (f) determines that the quality of the reference levels is unacceptable.

26. A method as recited in claim 25, wherein said halting (h) comprises canceling any read data that has been received by the requester prior to said halting (h).

27. A method as recited in claim 24, wherein said halting (h) comprises canceling any read data that has been received by the requestor prior to said halting (h).

28. A method as recited in claim 24, wherein said determining (f) of whether the quality of the reference levels is acceptable comprises:

comparing each of the reference levels to the processed reference level.

29. A method as recited in claim 24,

wherein the reference levels being read by said reading (a) pertain to first and second reference levels,

wherein said computing (b) computes a first processed reference level from the reference levels pertaining to the first reference level, and computes a second processed reference level from the reference levels pertaining to the second reference level, and

wherein said determining (c) determines the state discrimination levels based on the first and second processed reference levels.

30. A method as recited in claim 29, wherein said determining (f) of whether the quality of the reference levels is acceptable comprises:

comparing each of the reference levels pertaining to the first reference level to the first processed reference level, and

comparing each of the reference levels pertaining to the second reference level to the second processed reference level.

31. A method as recited in claim 24, wherein the memory device is a memory card providing non-volatile, multi-state data storage.

32. A method as recited in claim 24, wherein said computing (b) operates to average the reference levels to compute the processed reference level.

33. A method as recited in claim 24, wherein said computing (b) performs at least one of a minimum, maximum, Root-Mean-Square (RMS), peak, average, median, and modulus with respect to the reference signals in computing the processed reference level.

34. A method for reading data from a memory device having data storage units and associated tracking storage units, said method comprising:

(a) substantially concurrently reading data levels from certain data storage units and reference levels from tracking storage units associated with the certain data storage units;

(b) computing a processed reference level from the reference levels;

(c) determining state discrimination levels based on the processed reference level;

(d) discriminating states of the data levels from the certain data storage units based on the state discrimination levels to acquire read data for a requester;

(e) evaluating quality of the reference levels;

(f) determining whether the quality of the reference levels is acceptable;

(g) sending the read data to the requester when said determining (f) determines that the quality of the reference levels is acceptable;

(h) canceling the read data that has been received by the requester when said determining (f) determines that the quality of the reference levels is unacceptable; and

(i) correcting for at least one of the reference levels when said determining (f) determines that the quality of the reference levels is unacceptable.

35. A method for reading data from a memory device having data storage units and associated tracking storage units, said method comprising:

(a) substantially concurrently reading data levels from certain data storage units and reference levels from tracking storage units associated with the certain data storage units;

(b) computing a processed reference level from the reference levels;

(c) determining state discrimination levels based on the processed reference level;

(d) determining read data from the data levels using the state discrimination levels and error correction code processing;

(e) determining whether a data error is indicated by the error code processing; and

(f) evaluating quality of the reference levels and correcting for at least one of the reference levels having poor quality when said determining (e) detects the data error.

36. A method as recited in claim 35, wherein said method comprises:

(g) repeating said computing (b), said determining (c) and said determining (d) following said correcting of at least one of the reference levels.

37. A method for reading data from a memory device having data storage units and associated tracking storage units, said method comprising:

(a) initiating a count;

(b) reading data levels from certain data storage units and reference levels from tracking storage units associated with the certain data storage units;

(c) computing a processed reference level from the reference levels;

(d) determining state discrimination levels based on the processed reference level;

(e) discriminating states of the data levels from the certain data storage units based on the state discrimination levels to acquire read data for a requester;

(f) evaluating quality of the reference levels;

(g) determining whether the quality of the reference levels is acceptable;

(h) comparing the count with a count limit;

(i) correcting for at least one of the reference levels when said determining (g) determines that the quality of the reference levels is unacceptable and said comparing (h) determines that the count does not exceed the count limit;

(j) updating the count;

(k) repeating at least said computing (b) through said comparing (h) one or more times when said determining (g) determines that the quality of the reference levels is unacceptable and said comparing (h) determines that the count does not exceed the count limit; and

(l) directing the read data to the requester when said determining (g) determines that the quality of the reference levels is acceptable or when said comparing (h) determines that the count does exceed the count limit.

38. A memory system, comprising:

a plurality of data storage units, each of the data storage units providing multi-state data storage in a non-volatile manner;

a plurality of tracking storage units, the tracking storage units providing storage for reference levels in a non-volatile manner;

a reference level error manager operatively connected to receive the reference levels from said tracking storage units, said reference level error manager evaluates quality of the reference levels; and

a memory controller operatively connected to said data storage units and said tracking storage units, said memory controller operates to control read, write and erase operations with respect to said data storage units and said tracking storage units, said memory controller using state discrimination levels to determine the state of the data storage elements being read.

39. A memory system as recited in claim 38, wherein said memory system further comprises:

state discrimination level circuitry operatively connected to said tracking storage units, said reference level error manager and said memory controller, said state discrimination level circuitry operates to determine the state discrimination levels for use by said memory controller based on a plurality of the reference levels.

40. A memory system as recited in claim 39, wherein said reference level error manager corrects for one or more of the reference levels having an unacceptable quality.

41. A memory system as recited in claim 40, wherein said memory system is a memory card.

42. A memory system as recited in claim 39, wherein at least one of said reference level error manager and state discrimination level circuitry are provided within said memory controller.

43. A memory system as recited in claim 38, wherein said reference level error manager corrects for one or more of the reference levels having an unacceptable quality.

44. A memory system as recited in claim 38,

wherein said memory controller causes data to be written to a block of said data storage units, and

wherein a set of said tracking storage units associated with the block of said data storage units are written with predetermined reference levels whenever the block of said data storage units are written.

45. A memory system as recited in claim 38, wherein the set of said tracking storage units is read whenever the block of said data storage units is read.

46. A memory system as recited in claim 38, wherein said memory system further comprises:

an error correction unit that assists in determination of the state of the data storage elements being read.