US Patent 7821334 Amplification circuit

The present invention is aimed at realizing an amplifying circuit whose chip size is prevented from being significantly increased even if the number of compatible frequencies increases, and which has a wide dynamic range when it operates under a low voltage. The amplifying circuit includes a plurality of impedance converting circuits connected to each other by a switching circuit of a first type having a signal cutting-off function, a switching circuit of a second type connected to a path branched from an input side of the switching circuit of the first type, the switching circuit of the second type having a signal cutting-off function, amplifiers connected respectively to an output side of one of the impedance converting circuits in a final stage and to an output side of the switching circuit of the second type, and a control signal generating circuit for controlling connection/disconnection between said switching circuit of the first type and said switching circuit of the second type; wherein either one of the paths is selected to input a signal to one of the amplifiers.