An apparatus includes an amplifying circuit configured to include stacked first and second transistors, and to amplify a signal input from an input terminal during an operation in an amplifying mode, and provide the amplified signal to an output terminal, and a negative feedback circuit comprising first to nth sub-negative feedback circuits, each corresponding to a separate gain mode included in the amplifying mode, wherein the negative feedback circuit is configured to provide a variable resistance value to determine a negative feedback gain based on each of the separate gain modes.