Memory system with read threshold estimation and operating method thereof

1. An operating method of a memory system comprising:

performing a symmetric Oversampling (OVS) read with at least an initial read threshold, and creating a symmetric read result;

performing an asymmetric OVS read with at least the initial read threshold, and creating an asymmetric read result;

adjusting the initial read threshold according to at least the symmetric read result and asymmetric read result, and creating an optimal read threshold; and

executing data recovery process with the optimal read threshold.

2. The method of claim 1 wherein the adjusting the initial read threshold includes generating a threshold sense value in accordance with the symmetric read result and asymmetric read result, and creating an adjusted read threshold.

3. The method of claim 2 wherein the adjusting the initial read threshold includes locating a threshold error according to the threshold sense value on a characterization curve.

4. The method of claim 3 wherein the adjusting the initial read threshold includes adjusting the initial read threshold with the threshold error.

5. The method of claim 3 wherein the locating the threshold error on the characterization curve includes locating the threshold error on a linearized characterization curve.

6. The method of claim 1 wherein the performing the symmetric OVS read includes

performing a hard data read with a read threshold, and storing hard data in a hard data buffer; and

performing an erasure data read according a higher threshold and a lower threshold, and storing erasure data in an erasure data buffer, wherein the read threshold is the center of the higher threshold and lower threshold.

7. The method of claim 1 wherein the performing the asymmetric OVS read includes

performing a hard data read with a read threshold, and storing hard data in a hard data buffer; and

performing an erasure data read according a higher threshold and a lower threshold, and storing erasure data in an erasure data buffer, wherein the read threshold is not the center of the higher threshold and lower threshold.

8. The method of claim 1 wherein the adjusting the initial read threshold includes performing primitive 1′s counting, comparing 1′s counting results, and estimating a threshold error.

9. The method of claim 1 further comprising utilizing an Uncorrectable Error Correction code (UECC) recovery algorithm and a proactive background threshold estimation and update algorithm.

10. A memory system comprising:

a processor;

a tangible computer readable storage medium coupled to the processor, embedding the non-transitory computer program product executed by the processor, including computer instructions configured to:

perform a symmetric Oversampling (OVS) read with at least an initial read threshold, and create a symmetric read result;

perform an asymmetric OVS read with at least the initial read threshold, and create an asymmetric read result;

adjust the initial read threshold according to at least the symmetric read result and asymmetric read result, and create an optimal read threshold; and

execute data recovery process with the optimal read threshold.

11. An apparatus of a memory system comprising:

a plurality of memory devices; and

a controller coupled to the plurality of memory devices, wherein the controller is configured to:

perform a symmetric Oversampling (OVS) read with at least an initial read threshold, and create a symmetric read result;

perform an asymmetric OVS read with at least the initial read threshold, and create an asymmetric read result;

adjust the initial read threshold according to at least the symmetric read result and asymmetric read result, and create an optimal read threshold; and

execute data recovery process with the optimal read threshold.

12. The apparatus of claim 11 wherein the controller is further configured to generate a threshold sense value in accordance with the symmetric read result and asymmetric read result, and create an adjusted read threshold.

13. The apparatus of claim 12 wherein the controller is further configured to locate a threshold error according to the threshold sense value on a characterization curve.

14. The apparatus of claim 13 wherein the controller is further configured to adjust the initial read threshold with the threshold error.

15. The apparatus of claim 13 wherein the controller is further configured to locate the threshold error on a linearized characterization curve.

16. The apparatus of claim 11 wherein the controller is further configured to

perform a hard data read with a read threshold, and store hard data in a hard data buffer; and

perform an erasure data read according a higher threshold and a lower threshold, and store erasure data in an erasure data buffer, wherein the read threshold is the center of the higher threshold and lower threshold.

17. The apparatus of claim 11 wherein the controller is further configured to

perform a hard data read with a read threshold, and store hard data in a hard data buffer; and

perform an erasure data read according a higher threshold and a lower threshold, and store erasure data in an erasure data buffer, wherein the read threshold is not the center of the higher threshold and lower threshold.

18. The apparatus of claim 11 wherein the controller is further configured to perform primitive 1′s counting, compare 1′s counting results, and estimate a threshold error.

19. The apparatus of claim 11 the controller is further configured to utilize an Uncorrectable Error Correction Code (UECC) recovery algorithm and a proactive background threshold estimation and update algorithm.