Method and apparatus for reference cell adjusting in a storage device

Abstract

When adjusting the reference cells (11), the first reference unit (15) and the second reference unit (17) are used for a verify operation of the reference cells (11). The first reference unit (15) provides the lower limit current of the allowable current range, which is caused to flow by a nonvolatile transistor of the reference cells (11), and the second reference unit (17) provides the upper limit current thereof. 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), and a verify operation is carried out to see whether or not the current caused to flow by the nonvolatile transistor is between the lower limit current and the upper limit current of the allowable current range.

Dependencies are inferred from the claim text.