SEMICONDUCTOR MEMORY SYSTEM USING REGRESSION ALALYSIS AND READ METHOD THEREOF

摘要

A method of reading used in a nonvolatile memory device according to the present invention includes the steps of: reading selected memory cells by different read voltages; counting the number of the memory cells corresponding to each of the multiple threshold voltages by referencing the data read by the different read voltages; determining the coordinate values of a probability density function for the threshold voltages of the selected memory cells by referencing the result of the counting; calculating the coefficients of the probability density function by referencing the coordinate values; and determining a threshold voltage of a coordinate value which has a slope of zero for the probability density function as a read voltage of the selected memory cells.