Controller and operating method thereof

1. A controller that controls a memory device, comprising:

a processor suitable for controlling the memory device to perform a first soft read operation by using first soft read voltages; and

an error correction code (ECC) codec suitable for performing a first soft decision decoding operation based on first soft read data obtained through the first soft read operation,

wherein the processor controls the memory device to perform a second soft read operation with an additional read voltage, of second soft read voltages, that is different than any of the first soft read voltages and which is determined based on the first soft read data, according to whether the first soft decision decoding operation failed,

wherein the ECC codec performs a second soft decision decoding operation based on the first soft read data and second soft read data obtained through the second soft read operation,

wherein the processor performs a first operation of controlling the memory device to perform the first soft read operation by using any one of the first soft read voltages,

wherein the ECC codec performs a second operation of performing the first soft decision decoding operation based on the first soft read data obtained through performance of the first soft read operation, and

wherein the processor and the ECC codec repeatedly perform the first and second operations until the first soft decision decoding operation is successfully performed or reaches a set number of iterations.

2. The controller of claim 1 , wherein the processor determines the first soft read voltages as having respective offsets from a first reference read voltage.

3. The controller of claim 2 , wherein the processor determines, as the first reference read voltage, a voltage between average threshold voltages of two adjacent logic states within a threshold voltage distribution of memory cells in the memory device based on a Gaussian modeling technique applied to the distribution.

4. The controller of claim 3 ,

wherein the processor controls the memory device to perform a first hard read operation by using a first reference voltage, and

wherein the ECC codec performs a first hard decision decoding operation based on first hard read data obtained through the first hard read operation before performing the first soft decision decoding operation.

5. The controller of claim 2 , wherein the processor determines the second soft read voltages as having respective offsets from a second reference read voltage.

6. The controller of claim 5 , wherein the processor determines, as the second reference read voltage, a center threshold voltage of a bin label, to which the smallest number of memory cells belong, among bin labels determined according to the first soft read voltages.

7. The controller of claim 1 , further comprising a memory suitable for storing the first and second soft read data.

8. An operating method of a controller that controls a memory device, the operating method comprising:

controlling the memory device to perform a first soft read operation by using first soft read voltages;

performing a first soft decision decoding operation based on first soft read data obtained through the first soft read operation;

controlling the memory device to perform a second soft read operation with an additional read voltage, of second soft read voltages, that is different than any of the first soft read voltages and which is determined based on the first soft read data, according to whether the first soft decision decoding operation failed;

performing a second soft decision decoding operation based on the first soft read data and second soft read data obtained through the second soft read operation;

determining the first soft read voltages as having respective offsets from a first reference read voltage; and

determining, as the first reference read voltage, a voltage between average threshold voltages of two adjacent logic states within a threshold voltage distribution of memory cells in the memory device based on a Gaussian modeling technique applied to the distribution.

9. The operating method of claim 8 , further comprising:

controlling the memory device to perform a first hard read operation by using a first reference voltage; and

performing a first hard decision decoding operation based on first hard read data obtained through the first hard read operation before performing the first soft decision decoding operation.

10. The operating method of claim 8 , further comprising determining the second soft read voltages as having respective offsets from a second reference read voltage.

11. The operating method of claim 10 , further comprising determining, as the second reference read voltage, a center threshold voltage of a bin label, to which the smallest number of memory cells belong, among bin labels determined according to the first soft read voltages.

12. The operating method of claim 8 ,

wherein the controlling of the memory device to perform the first soft read operation by using the first soft read voltages includes a first operation of controlling the memory device to perform the first soft read operation by using any one of the first soft read voltages, and

wherein the performing of the first soft decision decoding operation based on the first soft read data obtained through the first soft read operation includes a second operation of performing the first soft decision decoding operation based on the first soft read data obtained through performance of the first soft read operation, and

further comprising repeatedly performing the first and second operations until the first soft decision decoding operation is successfully performed or reaches a set number of iterations.

13. An error correcting method of a controller, the method comprising:

performing a first soft decision decoding operation on first data read using different first read voltages; and

performing, when the first decision decoding operation fails, a second soft decision decoding operation on second data according to second read voltages determined on a basis of the first data, the second read voltages,

wherein the second read voltages includes one or more of the first read voltages and one or more third read voltages different from the first read voltages, and

wherein the second data includes one or more pieces of the first data read by first read voltages during the first soft decision decoding operation and third data read by the one or more third read voltages during the second soft decision decoding operation.