An amplifying circuit includes a first transistor, a second transistor, and a switching circuit. A control terminal of the first transistor is coupled to an input terminal of the amplifying circuit, and a first terminal of the first transistor is coupled to a first reference end. The input terminal of the amplifying circuit receives a first radio frequency (RF) signal. A first terminal of the second transistor is coupled to a second terminal of the first transistor, and a second terminal of the second transistor is coupled to an output terminal of the amplifying circuit. The output terminal of the amplifying circuit outputs an amplified signal. The first transistor amplifies the first RF signal to generate a second RF signal. The switching circuit performs a switching operation to transmit the second RF signal to one of the first terminal and the control terminal of the second transistor.