Amplification device with a bias circuit

An amplifier comprising:

• a substrate;
• a high side power supply terminal connected to an external constant-voltage source and maintained at a fixed high potential;
• a low side power supply terminal connected to one of an external constant-voltage source and a ground conductor, and maintained at a fixed low potential;
• an amplifier circuit with a MOSFET input stage that includes an input terminal connected to an external signal source, is embedded on said substrate, receives a signal of said signal source through said input terminal, and amplifies the signal at a predetermined rate;
• and
• a bias circuit embedded on said substrate and comprising:
• a bias voltage generating section that generates a predetermined bias voltage;
• and
• a MOSFET acting as an impedance device including
• a drain and a source, the one of which is connected to one of said high and low side power supply terminals, and the other is connected to the input terminal of said amplifier circuit,
• a gate maintained at the potential to prohibit the channel generation between said drain and said source, and
• a backgate electrically separated from said substrate and maintained at the potential equal to said bias voltage.