Dynamic detection for flash memory

Patent metadata

Field	Value
Publication number	US-10790860-B2
Application number	US-201816206148-A
Country	US
Kind code	B2
Filing date	Nov 30, 2018
Priority date	Nov 30, 2018
Publication date	Sep 29, 2020
Grant date	Sep 29, 2020

Abstract

A method of decoding data stored in non-volatile memory in which each memory cell stores data by adopting one of a plurality of storage states. The method comprises using a threshold for determining a physical property of the memory cells to distinguish between at least two storage states, reading a data codeword from a plurality of the memory cells using the threshold and determining a bit error rate for the data codeword read using the threshold, repeatedly modifying said threshold and re-reading said data codeword using said modified threshold and determining a modified bit error rate for the data codeword read using the modified threshold, selecting the one of the modified thresholds for which the mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold, determining a log likelihood ratio of a quantisation interval bounded by the threshold and the selected threshold generating soft decoded data by performing soft decoding of the data using said log likelihood ratio and outputting the soft decoding data.

First claim

The invention claimed is:

1. A method of decoding data stored in non-volatile memory, wherein each memory cell stores data by adopting one of a plurality of storage states, the method comprising:
using a threshold for determining a physical property of said memory cells to distinguish between at least two storage states;
reading a data codeword from a plurality of the memory cells using said threshold and determining a bit error rate for the data codeword read using the threshold;
repeatedly modifying said threshold and re-reading said data codeword using said modified threshold and determining a modified bit error rate for the data codeword read using the modified threshold;
selecting one of modified thresholds for which mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold;
determining a log likelihood ratio of a quantisation interval bounded by the said threshold and the selected threshold;
generating soft decoded data by performing soft decoding of the data using said log likelihood ratio; and
outputting said soft decoding data.

2. The method of claim 1 , wherein each of the modified thresholds bounds a quantisation interval, the method further comprising determining a hard bit estimate within the quantisation interval based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold.

3. The method of claim 2 , further comprising:
selecting a second threshold between the selected threshold and the threshold;
repeatedly modifying said second threshold and re-reading said data codeword using said modified second threshold and determining a modified bit error rate for the data codeword read using the modified second threshold; and
selecting the one of the modified second thresholds for which the mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold.

4. The method of claim 3 , wherein the selected modified second threshold and the said threshold define a second quantisation interval, the method further comprising determining a second hard bit estimate for the second quantisation interval and determining a hard bit estimate for a quantisation interval bounded by the selected modified threshold and the selected second modified threshold based on second hard bit estimate and the hard bit estimate.

5. The method of claim 1 , further comprising initially determining said threshold so as to minimise the determined bit error rate.

6. The method of claim 1 , wherein said threshold is an only threshold required to distinguish between the storage states the memory cell is capable of storing to read a stored bit.

7. The method of claim 1 , wherein said threshold is one of a plurality of thresholds required to distinguish between the storage states the memory cell is capable of storing to read a stored bit.

8. The method of claim 7 , further comprising optimising a threshold used for soft decoding for more than one or all of the plurality of thresholds.

9. A non-volatile memory comprising program instructions for execution by a processor, the program instructions, when executed by the processor causing the processor to perform the method of claim 1 .

10. A storage device comprising:
a non-volatile memory configured to store data by adopting one of a plurality of storage states; and
a memory controller configured to:
use a threshold for determining a physical property of memory cells in said memory to distinguish between at least two storage states;
read a data codeword from a plurality of memory cells using said threshold and determine a bit error rate for the data codeword read using the threshold;
repeatedly modify said threshold and re-reading said data codeword using said modified threshold and determine a modified bit error rate for the data codeword read using the modified threshold;
select one of modified thresholds for which mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold;
determine a log likelihood ratio of a quantisation interval bounded by the said threshold and the selected threshold;
generate soft decoded data by performing soft decoding of the data using said log likelihood ratio; and
output said soft decoding data.

11. The device of claim 10 , wherein each of the modified thresholds bounds a quantisation interval, the controller further configured to determine a hard bit estimate within the quantisation interval based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold.

12. The device of claim 10 , the controller further configured to:
select a second threshold between the selected threshold and the threshold;
repeatedly modify said second threshold and re-reading said data codeword using said modified second threshold and determine a modified bit error rate for the data codeword read using the modified second threshold; and
select the one of the modified second thresholds for which the mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold.

13. The device of claim 12 , wherein the selected modified second threshold and the said threshold define a second quantisation interval, the controller further configured to determine a second hard bit estimate for the second quantisation interval and determine a hard bit estimate for a quantisation interval bounded by the selected modified threshold and the selected second modified threshold based on second hard bit estimate and the hard bit estimate.

14. The device of claim 10 , the controller further configured to initially determine said threshold so as to minimise the determined bit error rate.

15. The device of claim 10 , wherein said threshold is an only threshold required to distinguish between the storage states the memory cell is capable of storing to read a stored bit.

16. The device of claim 10 , wherein said threshold is one of a plurality of thresholds required to distinguish between the storage states the memory cell is capable of storing to read a stored bit.

17. The device of claim 16 , the controller further configured to optimise a threshold used for soft decoding for more than one or all of the plurality of thresholds.

Assignees

• Toshiba Kk
• Toshiba Memory Corp

Inventors

• Ismail Amr
• Sandell Magnus Stig Torsten

Classifications

• H03M13/1515

  Reed-Solomon codes · CPC title

• G11C16/3427

  Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written · CPC title

• H03M13/256

  with trellis coding, e.g. with convolutional codes and TCM · CPC title

• H03M13/1111

  Soft-decision decoding, e.g. by means of message passing or belief propagation algorithms · CPC title

• G11C11/5642 Primary

  Sensing or reading circuits; Data output circuits · CPC title