Memory system and method of estimating read voltages thereof

Abstract

A memory system includes a nonvolatile memory including a plurality of memory cells, and a controller. The controller is configured to perform a read operation to determine a value of multi-bit data stored in each of the memory cells by using a first plurality of read voltages, and perform an estimation of optimum values of the read voltages. The estimation is performed by applying a second plurality of read voltages to the memory cells and obtaining a first string of bit counts. The estimation is performed further by obtaining a second string of differential bit counts, each of which indicates a difference between adjacent bit counts in the first string of bit counts, extracting a part of the differential bit counts from the second string, and estimating the optimum values of the read voltages using the extracted differential bit counts.