System and method for decoder assisted dynamic log-likelihood ratio (LLR) estimation for NAND flash memories

1. A method for performing operations of a flash memory, the method comprising:

estimating slope information of a plurality of threshold voltage samples based on soft decoding errors in connection with a first read operation on the flash memory;

generating estimated soft information based on the estimated slope information; and

decoding a result of a second read operation on the flash memory based on the estimated soft information.

2. The method of claim 1 , wherein estimating slope information comprises:

estimating first soft information based on the first read operation on the flash memory with a first reference voltage;

estimating second soft information based on the soft decoding errors; and

estimating the slope information of the plurality of threshold voltage samples based on the first soft information and the second soft information.

3. The method of claim 2 , wherein the slope information is estimated based on a weighted sum of the first soft information and the second soft information.

4. The method of claim 3 , wherein the weighted sum of the first soft information and the second soft information is calculated using a confidence coefficient as a weight.

5. The method of claim 2 , wherein estimating the second soft information comprises:

detecting a decoding failure;

in response to the detection of the decoding failure, generating an error vector; and

generating log-likelihood ratio (LLR) values as the second soft information based on the error vector.

6. The method of claim 5 , wherein estimating the second soft information further comprises:

generating a histogram from the error vector; and

generating the LLR values as the second soft information based on the histogram.

7. The method of claim 2 , wherein

the estimated soft information includes edge soft information, and

the edge soft information is generated based on the second soft information.

8. The method of claim 2 , wherein the slope information includes first side slope information and second side slope information.

9. The method of claim 8 , wherein

the estimated soft information includes non-edge soft information, and

the non-edge soft information is generated based on the first side slope information and the second side slope information.

10. The method of claim 2 , further comprising:

performing soft decoding on a result of the first read operation such that the soft decoding errors are a result of the soft decoding, wherein

the first soft information is estimated before performing the soft decoding, and

the second soft information is estimated after performing the soft decoding.

11. A flash memory system comprising:

a flash memory; and

a circuit for performing operations of the flash memory, the circuit being configured to:

estimate slope information of a plurality of threshold voltage samples based on soft decoding errors in connection with a first read operation on the flash memory;

generate estimated soft information based on the estimated slope information; and

decode a result of a second read operation on the flash memory based on the estimated soft information.

12. The flash memory system of claim 11 , wherein in estimating slope information, the circuit is further configured to:

estimate first soft information based on the first read operation on the flash memory with a first reference voltage;

estimate second soft information based on the soft decoding errors; and

estimate the slope information of the plurality of threshold voltage samples based on the first soft information and the second soft information.

13. The flash memory system of claim 12 , wherein the slope information is estimated based on a weighted sum of the first soft information and the second soft information.

14. The flash memory system of claim 13 , wherein the weighted sum of the first soft information and the second soft information is calculated using a confidence coefficient as a weight.

15. The flash memory system of claim 12 , wherein in estimating the second soft information, the circuit is further configured to:

detect a decoding failure;

in response to the detection of the decoding failure, generate an error vector; and

generate log-likelihood ratio (LLR) values as the second soft information based on the error vector.

16. The flash memory system of claim 15 , wherein in estimating the second soft information, the circuit is further configured to:

generate a histogram from the error vector; and

generate the LLR values as the second soft information based on the histogram.

17. The flash memory system of claim 12 , wherein

the estimated soft information includes edge soft information, and

the edge soft information is generated based on the second soft information.

18. The flash memory system of claim 12 , wherein the slope information includes first side slope information and second side slope information.

19. The flash memory system of claim 18 , wherein

the estimated soft information includes non-edge soft information, and

the non-edge soft information is generated based on the first side slope information and the second side slope information.

20. The flash memory system of claim 12 , wherein the circuit is further configured to:

perform soft decoding on a result of the first read operation such that the soft decoding errors are a result of the soft decoding,

estimate the first soft information before performing the soft decoding, and

estimate the second soft information after performing the soft decoding.