| 摘要 |
When adjusting reference cells ( 11 ), the first reference unit ( 15 ) and the second reference unit ( 17 ) are used for verification operations of the reference cells ( 11 ). The first reference unit ( 15 ) provides a lower limit current of an allowable current range for currents provided from a nonvolatile transistor of the reference cells ( 11 ), and the second reference unit ( 17 ) provides an upper limit current therefor. An amplification signal REFO of the reference cells ( 11 ), which is outputted from a sense amplifier ( 19 ), is compared with amplification signals LO and HO responsive to the lower and upper limit currents outputted from sense amplifiers ( 21 ) and ( 23 ), respectively, and a verify operation is carried out to see whether or not the current provided from the nonvolatile transistor is between the lower limit current and the upper limit current of the allowable current range.
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