a plurality of memory cell blocks each comprising a plurality of memory cells and a plurality of tracking cells for storing expected data;

a reference current generator for outputting a present reference current;

a plurality of sense amplifiers; and

a plurality of comparators, wherein:

in a specific time, the sense amplifiers sense the data stored in the tracking cells as read data according to the present reference current, then the comparators compare the read data with the expected data to obtain a difference, the reference current generator adjusts the present reference current to an adjusted reference current according to the difference so that the sense amplifiers sense the data stored in the tracking cells as the expected data, and then the sense amplifiers read the memory cells according to the adjusted reference current.