Read commands for reading interfering memory cells

• US 8,694,853 B1
• Filed: 04/17/2011
• Issued: 04/08/2014
• Est. Priority Date: 05/04/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Sommer, Naftali
• Primary Examiner(s): Decady, Albert
• Assistant Examiner(s): Ahmed, Enam
• Application Number:
  US13/088,361
• Time in Patent Office: 1,087 Days
• Field of Search: 714/763
• US Class Current: 714/763
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 29/42 using error correcting codes [ECC] or parity check
• CPC Class Codes: G11C 29/52 Protection of memory contents; Detection of errors in memory contents

Abstract

A method for data storage includes, in a memory system that stores data by programming analog memory cells to respective programming states selected from a predefined set, providing a first read command that retrieves the data stored in target memory cells, and a second read command that identifies at least one potentially-interfering memory cell that is programmed to a programming state in a predefined subset of programming states expected to cause interference. Given data is stored in a first group of the memory cells. After storing the given data, the given data is retrieved by reading the first group using the first read command, reading a second group of the memory cells using the second read command, and compensating for the interference caused to the first group by the memory cells in the second group that were identified by the second read command.

Claims

1. A method comprising:

storing data in a group of target memory cells of a memory system by programming analog memory cells to respective programming states selected from a predefined set;

issuing a first read command that addresses one or more target memory cells and retrieves the data stored in the target memory cells;

issuing a second read command that addresses one or more memory cells neighboring the target memory cells, wherein the second read command identifies at least one of the neighboring memory cells as being programmed to a programming state in a predefined subset of the programming states that are expected to cause interference to the target memory cells; and

compensating for the interference caused to the target memory cells based upon the programming state of the neighboring memory cells that were identified by the second read command;

wherein storing the data comprises encoding the data with an Error Correction Code (ECC), and wherein reading the data using the first read command comprises computing soft decoding metrics for the data read from the target memory cells based on the neighboring memory cells that were identified by the second read command, and decoding the ECC of the target memory cells using the soft decoding metrics.

2. The method according to claim 1, wherein the second read command does not produce output that is unambiguously indicative of the data stored in the neighboring memory cells.

3. The method according to claim 1, wherein computing the soft decoding metrics comprises assigning a low soft decoding metric to the data read from a given target memory cell, if at least one neighboring memory cell was identified by the second read command.

4. The method according to claim 1, wherein the first read command compares respective analog storage values of the target memory cells to one or more first sets of read thresholds, and wherein the second read command compares the respective analog storage values of the neighboring memory cells to a second set of read thresholds, different from any of the first sets.

5. The method according to claim 1, wherein the second read command specifies one or more ranges of analog storage values that are expected to cause the interference, and identifies the neighboring memory cells having the analog storage values falling in the ranges.

6. The method according to claim 1, wherein the predefined subset of the programming states includes the programming states in which a change in analog storage value during programming from a previous programming state is larger than a predefined value.

7. The method according to claim 1, wherein reading the data comprises sending the first and second read commands from a memory controller to the memory cells, returning results of the first and second read commands to the memory controller, and compensating for the interference in the memory controller.

8. The method according to claim 1, wherein reading the target memory cells comprises reading a first word line, and wherein reading the neighboring memory cells comprises reading a second word line that neighbors the first word line.

9. A data storage apparatus, comprising:

a memory comprising multiple analog memory cells; and

circuitry coupled to the memory and configured to;

store data in the memory by programming the analog memory cells to respective programming states selected from a predefined set;

provide a first read command that addresses one or more target memory cells and retrieves the data stored in the target memory cells;

provide a second read command that addresses one or more potentially-interfering memory cells and identifies at least one of the potentially-interfering memory cells that is programmed to a programming state in a predefined subset of the programming states that are expected to cause interference;

store given data in a first group of the memory cells; and

after storing the given data, retrieve the given data by;

reading the first group using the first read command;

reading a second group of the memory cells using the second read command; and

compensating for the interference caused to the first group by the memory cells in the second group that were identified by the second read command;

wherein the circuitry is configured to encode the given data with an Error Correction Code (ECC), and to retrieve the given data by computing soft decoding metrics for the data read from the first group depending on the memory cells in the second group that were identified by the second read command, and decoding the ECC using the soft decoding metrics.

10. The apparatus according to claim 9, wherein the second read command does not produce output that is unambiguously indicative of the data stored in the potentially-interfering memory cells.

11. The apparatus according to claim 9, wherein the circuitry is configured to assign a low soft decoding metric to the data read from a given memory cell in the first group, if at least one memory cell in the second group, which neighbors the given memory cell, was identified by the second read command.

13. The apparatus according to claim 9, wherein the second read command specifies one or more ranges of analog storage values that are expected to cause the interference, and identifies the potentially-interfering memory cells having the analog storage values falling in the ranges.

14. The apparatus according to claim 9, wherein the predefined subset of the programming states includes the programming states in which a change in analog storage value during programming from a previous programming state is larger than a predefined value.

15. The apparatus according to claim 9, wherein the circuitry comprises a Read/Write (R/W) unit that is coupled to the memory and a controller that communicates with the R/W unit over an interface, wherein the controller is configured to send the first and second read commands over the interface to the R/W unit and to compensate for the interference based on results of the first and second read commands, and wherein the R/W unit is configured to execute the first and second read commands in the memory cells and to return the results over the interface to the controller.

16. The apparatus according to claim 9, wherein the circuitry is configured to read the first group by reading a first word line, and to read the second group by reading a second word line that neighbors the first word line.

12. A data storage apparatus comprising:

a memory comprising multiple analog memory cells; and

circuitry coupled to the memory and configured to;

store data in the memory by programming the analog memory cells to respective programming states selected from a predefined set;

provide a first read command that addresses one or more target memory cells and retrieves the data stored in the target memory cells;

provide a second read command that addresses one or more potentially-interfering memory cells and identifies at least one of the potentially-interfering memory cells that is programmed to a programming state in a predefined subset of the programming states that are expected to cause interference;

store given data in a first group of the memory cells; and

subsequent to storing the given data the circuitry is configured to;

read the first group using the first read command and;

read a second group of the memory cells using the second read command; and

compensate for the interference caused to the first group by the memory cells in the second group that were identified by the second read command;

wherein the first read command compares respective analog storage values of the target memory cells to one or more first sets of read thresholds, and wherein the second read command compares the respective analog storage values of the potentially-interfering memory cells to a second set of read thresholds, different from any of the first sets.