SEMICONDUCTOR MEMORY DEVICE AND METHOD OF READING THE SAME

摘要

PURPOSE: A semiconductor memory device and a reading method thereof are provided to memorize a plurality of bits on one memory cell by including a memory cell array using a plurality of memory cells to memorize the information on a plurality of bits allocated to a plurality of critical voltage distributions. CONSTITUTION: A memory cell array(1) comprises a plurality of memory cells memorizing the information on a plurality of bits allocated to a plurality of critical voltage distributions. A sensing amplifier circuit(3a) reads the critical voltage information to display the position of the critical voltage of a memory cell on the plurality of critical voltage distributions. A first data retaining circuit retains data read from a memory cell and critical voltage information. A second data retaining circuit retains the critical voltage information and the data read from the memory cell. An operator performs the operation between data retained by the first and second data retaining circuit and the data read from a sensing amplifier. A control circuit(6) controls the read operation, the write operation, and the erase operation about the memory cell array.