A sensing amplifier, coupled to at least one memory cell, includes an output terminal and a reference terminal, a multiplexer circuit, and a plurality of reference cells having equal value. An output terminal of the multiplexer circuit is coupled to the reference terminal of the sensing amplifier. Each of the reference cell is coupled to each input node of the multiplexer circuit. The multiplexer circuit is controlled by a control signal to select one of the reference cells as a selected reference cell to couple to the reference terminal of the sensing amplifier when each read operation to the at least one memory cell is performed. The plurality of reference cells are selected sequentially and repeatedly, and the one of the reference cells is selected for one read operation to the at least one memory cell.