Amplifier circuit and wireless communication device

1. An amplifier circuit comprising:

a current conversion circuit that receives a high frequency signal and produces a signal current according to the high frequency signal;

a gain control circuit that includes a control signal input for receiving a control signal, a first output, and a second output, and produces the signal current from said first output or said second output according to the control signal;

an impedance circuit that includes a first node connected to said first output, a second node connected to said second output, and a third node, said impedance circuit presenting a predetermined impedance between said nodes;

a switch circuit that is inserted between said first output and said first node; and

a load impedance unit that is connected to said first output and produces a gain signal representing an amplified high frequency signal, wherein the amplifier circuit changes a level of the gain signal according to the control signal.

2. The amplifier circuit described in claim 1 , wherein said switch circuit is switched off when said gain control circuit produces the signal current from said first output, and is switched on when said gain control circuit produces the signal current from said second output.

3. The amplifier circuit described in claim 1 , wherein said third node is connected to a power supply supplying a power to said gain control circuit.

4. The amplifier circuit described in claim 1 , further comprising a variable impedance circuit connected to said first output.

5. The amplifier circuit described in claim 4 , wherein said variable impedance circuit includes an impedance device and a switch, and wherein said impedance device has a predetermined impedance and is serially connected to said switch.

6. The amplifier circuit described in claim 5 , wherein said impedance device includes at least one of a resistor, a capacitor, and an inductor.

7. The amplifier circuit described in claim 1 , wherein:

said impedance circuit includes a first transistor and a second transistor;

said first transistor is inserted between said first node and said second node; and

said second transistor is inserted between said second node and said third node.

8. The amplifier circuit described in claim 7 , wherein each of said first transistor and said second transistor is a metal oxide semiconductor transistor.

9. The amplifier circuit described in claim 1 , wherein said current conversion circuit includes a high frequency signal input for receiving the high frequency signal, and wherein the amplifier circuit further comprising a switch inserted between said high frequency signal input and said first output.

10. The amplifier circuit described in claim 9 , wherein said switch is switched on when the gain signal is smaller than the high frequency signal.

11. A wireless communication device comprising the amplifier circuit described in claim 1 .