Amplifier

1. An amplifier comprising:

a first FET including a first back-gate end;

a second FET including a second back-gate end;

a third FET including a third back-gate end;

a first power supply terminal configured to apply a first voltage to the first back-gate end;

a second power supply terminal configured to apply a second voltage to the second back-gate end; and

a third power supply terminal configured to apply a third voltage to the third back-gate end,

wherein gate ends of the first through third FETs are connected in common with one another,

source ends of the first through third FETs are connected in common with one another,

drain ends of the first through third FETs are connected in common with one another,

the first through third power supply terminals are configured such that different voltages are set to the first through third power supply terminals,

wherein the source ends of the first through third FETs are grounded in a direct current way, and at least one power supply terminal among the first through third power supply terminals has a negative voltage relative to the ground.

2. The amplifier according to claim 1 ,

wherein the first power supply terminal has a positive voltage relative to the ground, the second power supply terminal has the same voltage as the ground, and the third power supply terminal has the negative voltage.

3. An amplifier comprising:

a first FET including a first back-gate end;

a second FET including a second back-gate end;

a third FET including a third back-gate end;

a first power supply terminal configured to apply a voltage to the first back-gate end;

a second power supply terminal configured to apply a voltage to the second back-gate end;

a third power supply terminal configured to apply a voltage to the third back-gate end; and

a negative voltage generation circuit configured to supply the negative voltage to the at least one power supply terminal among the first through third power supply terminals, wherein:

gate ends of the first through third FETs are connected in common with one another,

source ends of the first through third FETs are connected in common with one another,

drain ends of the first through third FETs are connected in common with one another,

the first through third power supply terminals are configured such that different voltages are set to the first through third power supply terminals,

the source ends of the first through third FETs are grounded in a direct current way, and

at least one power supply terminal among the first through third power supply terminals has a negative voltage relative to the ground.

4. An amplifier comprising:

a first FET including a first back-gate end;

a second FET including a second back-gate end;

a third FET including a third back-gate end;

a first power supply terminal configured to apply a voltage to the first back-gate end;

a second power supply terminal configured to apply a voltage to the second back-gate end;

a third power supply terminal configured to apply a voltage to the third back-gate end; and

a cascode connection FET connected with all of the first through third FETs in a cascode connection manner, wherein:

gate ends of the first through third FETs are connected in common with one another,

source ends of the first through third FETs are connected in common with one another,

drain ends of the first through third FETs are connected in common with one another,

the first through third power supply terminals are configured such that different voltages are set to the first through third power supply terminals,

the cascode connection FET includes a source end for supplying a voltage and a current to the drain ends of the first through third FETs,

high frequency power is inputted in common to the gate ends of the first through third FETs, and

the amplifier amplifies the high frequency power and outputs the amplified high frequency power from a drain end of a fourth FET.

5. An amplifier comprising:

a first FET including a first back-gate end;

a second FET including a second back-gate end;

a third FET including a third back-gate end;

a first power supply terminal configured to apply a voltage to the first back-gate end;

a second power supply terminal configured to apply a voltage to the second back-gate end;

a third power supply terminal configured to apply a voltage to the third back-gate end; and

a cascode connection FET connected with all of the first through third FETs in a cascode connection manner, wherein:

the cascode connection FET includes a source end for supplying a voltage and a current to the drain ends of the first through third FETs,

high frequency power is inputted in common to the gate ends of the first through third FETs,

the amplifier amplifies the high frequency power and outputs the amplified high frequency power from a drain end of a fourth FET,

the source ends of the first through third FETs are grounded in a direct current way,

at least one power supply terminal among the first through third power supply terminals has a negative voltage relative to the ground, and

the first power supply terminal has a positive voltage relative to the ground, the second power supply terminal has the same voltage as the ground, and the third power supply terminal has the negative voltage.

6. The amplifier according to claim 3 , further comprising:

a cascode connection FET connected with all of the first through third FETs in a cascode connection manner,

wherein the cascode connection FET includes a source end for supplying a voltage and a current to the drain ends of the first through third FETs,

high frequency power is inputted in common to the gate ends of the first through third FETs, and

the amplifier amplifies the high frequency power and outputs the amplified high frequency power from a drain end of a fourth FET.

7. The amplifier according to claim 1 , wherein the source ends of the first through third FETs are grounded through an inductance.