Memory system

A memory system, comprising:

• a nonvolatile memory including a plurality of memory cells;
• and
• a memory controller configured to control the nonvolatile memory,
• wherein in read operation for the memory cells, the memory controller is configured to:
• perform tracking including a plurality of reads in which a read voltage is shifted;
• determine a hard bit read voltage based on results of the tracking;
• calculate a soft bit read voltage based on the determined hard bit read voltage;
• perform soft bit read using the calculated soft bit read voltage;
• and
• perform a soft bit decoding process using a result of the soft bit read and a log-likelihood ratio table associated with the calculated soft bit read voltage,
• wherein:
• the memory controller includes a storage circuit configured to store a first table that stores a set value of the soft bit read voltage and a second table that stores a set limit value of the read voltage;
• and
• the memory controller is configured to:
• calculate a difference between the determined hard bit read voltage and a set limit value corresponding to the determined hard bit read voltage in the second table;
• and
• calculate a soft bit read voltage using a reference value corresponding to the difference in the first table.