| 摘要 |
<p>PROBLEM TO BE SOLVED: To achieve the high speed reading operation and the high speed verification and simplify the control of the reference voltage generation by a method wherein a number of values are judged by using a plurality of reference voltages simultaneously and reference voltages for verification are set by using the judged results. SOLUTION: Quaternary data which are judged by three different thresholds (Vra, Vrb and Vrc) are stored in a memory cell 11. In an ordinary reading operation, reference signal generators 14a-14c output reference signals Vra-Vrc. Stored datum signals read out of the memory cell 11 are compared with the reference signals Vra-Vrc and judgement signals are supplied to an encoder 15. The encoder 15 outputs a four-value code, for instance '10' in accordance with the threshold region in which the stored datum signal exists and the four- value code is latched by a latching circuit 16. A controller 18 controls the reference voltage generators 14a-14c and makes them output reference signals VraH, VrbL and Vrc.</p> |
