Power amplifier device

A power amplifier device comprising:

• a first power supply terminal for inputting a first power supply voltage;
• a first transistor for power amplification that includes a first drain supplied with power from the first power supply terminal, a first source that is grounded, and a first gate for inputting a radio-frequency signal;
• a second power supply terminal for inputting a second power supply voltage lower than the first power supply voltage;
• and
• a bias circuit that applies a bias voltage to the first gate of the first transistor,
• wherein the bias circuit includes:
• a second transistor for monitoring that (i) includes a second drain supplied with power from the second power supply terminal, a second source that is grounded, and a second gate electrically connected to the first gate, and (ii) causes a second drain current to flow through the second drain, the second drain current corresponding to a first drain current flowing through the first drain;
• and
• a bias adjustment circuit that is supplied with the power from the second power supply terminal and adjusts the bias voltage according to the second drain current.

A power amplifier device comprising:

• a first power supply terminal for inputting a first power supply voltage;
• a first transistor for power amplification that includes a first drain supplied with power from the first power supply terminal, a first source that is grounded, and a first gate for inputting a radio-frequency signal;
• a second power supply terminal for inputting a second power supply voltage lower than the first power supply voltage;
• and
• a bias circuit that applies a bias voltage to the first gate of the first transistor,
• wherein the bias circuit includes:
• a second transistor for monitoring that (i) includes a second drain supplied with power from the first power supply terminal or the second power supply terminal, a second source that is substantially grounded, and a second gate electrically connected to the first gate, and (ii) causes a source current to flow through the second source, the source current corresponding to a drain current of the first transistor;
• and
• a bias adjustment circuit that is supplied with power from the second power supply terminal and adjusts the bias voltage according to the source current of the second transistor.