Randomizing for suppressing errors in a flash memory

• US 20080215798A1
• Filed: 06/13/2007
• Published: 09/04/2008
• Est. Priority Date: 12/24/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk IL Ltd. (Western Digital Corporation)
• Inventors: Alrod, Idan, Sharon, Eran
• Granted Patent: US 8,370,561 B2
• Time in Patent Office: Days
• US Class Current: 711/103
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3427 Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation

Abstract

Original data to be stored in a nonvolatile memory are first randomized while preserving the size of the original data, In response for a request for the original data, the randomized data are retrieved, derandomized and exported without authenticating the requesting entity. ECC encoding is applied either before or after randomizing; correspondingly, ECC decoding is applied either after or before derandomizing.

Claims

1. A method of storing data, comprising the steps of:

(a) randomizing original data while preserving a size of said original data, thereby providing randomized data;

(b) storing said randomized data in a nonvolatile memory; and

(c) in response to a request for said original data;

(i) retrieving said randomized data from said memory,

(ii) derandomizing said retrieved randomized data, thereby providing retrieved data substantially identical to said original data, and

(iii) exporting said retrieved data to an entity from which said request is received without authenticating said entity.

2. The method of claim 1, further comprising the steps of:

(d) applying error correction encoding to said original data prior to said randomizing of said original data; and

(e) applying error correction decoding to said retrieved data prior to said exporting of said retrieved data.

3. The method of claim 1, further comprising the steps of:

(d) applying error correction encoding to said randomized data prior to said storing of said randomized data in said memory; and

(e) applying error correction decoding to said retrieved randomized data prior to said derandomizing of said retrieved randomized data.

4. The method of claim 1, wherein said randomizing is effected by steps including summing said original data, modulo 2, with a fixed, random bit sequence, and wherein said derandomizing is effected by steps including summing said retrieved randomized data, modulo 2, with said random bit sequence.

5. The method of claim 1, wherein said randomizing is effected by steps including summing said original data, modulo 2, with a pseudorandom bit sequence, and wherein said derandomizing is effected by steps including summing said retrieved randomized data, modulo 2, with said pseudorandom bit sequence.

6. The method of claim 5, wherein said pseudorandom bit sequence is fixed.

7. The method of claim 5, further comprising the step of:

(d) generating said pseudorandom bit sequence.

8. The method of claim 7, wherein said generating is effected using a linear feedback shift register.

9. The method of claim 8, wherein a seed of said linear feedback shift register is fixed.

10. The method of claim 8, further comprising the step of:

(e) partitioning said memory into units, each said unit having a respective unit number;

and wherein a seed of said linear feedback shift register is a function of said respective unit number of said unit wherein said randomized data are stored.

11. The method of claim 10, wherein said memory is a flash memory and wherein said units are blocks of said flash memory.

12. The method of claim 10, wherein said memory is a flash memory and wherein said units are pages of said flash memory.

13. The method of claim 1, wherein said randomizing is effected by steps including scrambling said original data and wherein said derandomizing is effected by steps including descrambling said retrieved randomized data.

14. The method of claim 13, wherein said scrambling and said descrambling are effected using respective linear feedback shift registers that share a common seed.

15. The method of claim 14, wherein said seed is fixed.

16. The method of claim 14, further comprising the step of:

(d) partitioning said memory into units, each said unit having a respective unit number;

and wherein a seed of said linear feedback shift register is a function of said respective unit number of said unit wherein said randomized data are stored.

17. The method of claim 16, wherein said memory is a flash memory and wherein said units are blocks of said flash memory.

18. The method of claim 16, wherein said memory is a flash memory and wherein said units are pages of said flash memory.

19. A method of storing data, comprising the steps of:

(a) providing a sufficient number of memory cells to store original data by programming said memory cells to a set of corresponding states of said memory cells;

(b) mapping said original data into a set of states of all said memory cells that is randomized relative to said set of corresponding states;

(c) programming said memory cells to said randomized set of states; and

(d) in response to a request for said original data;

(i) reading said memory cells, thereby providing retrieved randomized data,

(ii) derandomizing said retrieved randomized data, thereby providing retrieved data substantially identical to said original data, and

(iii) exporting said retrieved data to an entity from which said request was received without authenticating said entity.