MULTIVALUE SEMICONDUCTOR MEMORY DEVICE

摘要

PROBLEM TO BE SOLVED: To enable reading by starting up a word line only once and improve an operation speed by a method wherein a memory cell in which one of (n) types of thresholds is stored and reference cells in which (n) types of the thresholds are set respectively are compared with each other and the comparison results are encoded. SOLUTION: One of four thresholds Vt0-Vt3 is stored in a memory cell C1 (106). The thresholds Vt1-Vt3 are set in three reference cells RC1-RC3 (107-109). A voltage dividing circuit 115 supplies a voltage level lower than the voltage level of a word line WOO (121) by a value (Vt1-Vt0)/2 to the reference cells RC1-RC3 (107-109). Differential amplifiers 1-3 (103-105) compare reference voltages from the reference cells RC1-RC3 (107-109) with the voltage level of the memory cell C1 (106) and supply comparison results to an encoder 113 which outputs 2-bit binary data D0 and D1.