| 摘要 |
First and second memory units store reference values and verification values for generating reference voltages and verification voltages of nonvolatile multilevel memory cells. A reference voltage generator generates the reference voltages and the verification voltages according to the reference values and the verification values stored in the first and second memory units. Since the first and second memory units are rewritable, the reference voltages and the verification voltages can be set after the fabrication of the cell memory in accordance with the characteristics of the memory cells which are dependent on variations of fabrication process. A programming test circuit for obtaining the reference voltages and the verification voltages can also be used to set the reference voltages and the verification voltages after the fabrication of the cell memory. Consequently, it is possible to improve the read margins of data read from the memory cells with an enhancement in fabrication yield.
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