A device includes a first reference storage unit, a second reference storage unit, a first reference switch, and a second reference switch. The first reference switch includes a first terminal coupled to a first reference bit line, a second terminal coupled to the first reference storage unit, and a control terminal coupled a reference word line. The second reference switch includes a first terminal coupled to a second reference bit line, a second terminal coupled to the second reference storage unit, and a control terminal coupled the reference word line. The first reference storage unit is configured to receive a bit data through the first reference switch, and to generate a first signal having a first logic state.