A device includes memory cells, a first reference switch, a second reference switch, a first reference storage unit, a second reference storage unit, and an average current circuit. The memory cells are each configured to store corresponding bit data. The first reference switch and the second reference switch are turned on when a word line is activated. The first reference storage unit generates a first signal having a first logic state when the first reference switch is turned on. The second reference storage unit generates a second signal having a second logic state when the second reference switch is turned on. The average current circuit averages the first signal and the second signal to generate a reference signal to be compared with a current indicating the bit data of one memory cell, in order to determine a logic state of the bit data of the memory cell.