DATA SENSING SYSTEM FOR MULTIPLE BIT MEMORY CELL

摘要

PROBLEM TO BE SOLVED: To improve the reliability of sensing by comparing a quantization voltage with a narrower width than a voltage in a threshold voltage distribution of a memory cell on the basis of a current flowing through the memory cell optionally selected in a memory cell array section having a plurality of threshold voltage levels with a plurality of reference voltages. SOLUTION: Each branch of a multi-step circumferential source section 25 sequentially repeats a process that each branch prevents current flowing through the multi-step circumferential source section 25 when a voltage across the multi-step circumferential source section 25 is constant and flows a current stepwise when the voltage across the multi-step circumferential source section 25 increases. A bit line selection section 22 selects an optional bit line of a memory cell array section 21 and a current the same as a current flowing to the bit line is delivered to a sensing node SN. A voltage equivalent to the current is respectively compared with reference voltages Vref1-Vref3 at 1st-3rd voltage comparison sections 27a-27c, and a decoding logic section 28 outputs signals at terminals A, B.