Amplifier circuit
According to embodiments of the present invention, an over-input signal may be limited to be within a range between adjustable upper limit voltage and lower limit voltage while suppressing deterioration of a noise figure. An amplifier circuit includes an input transistor; an input transistor; a resistor element having a first terminal connected to a gate of the input transistor and a second terminal connected to a bias voltage; and a protective circuit connected to the gate of the input transistor and limiting an input to the gate of the input transistor to be within a range between an upper limit voltage and lower limit voltage adjustable based on the bias voltage.
1. An amplifier circuit, comprising:
an input transistor;
a resistor element having a first terminal connected to a gate of the input transistor and a second terminal connected to a bias voltage; and
a protective circuit connected to the gate of the input transistor and limiting an input to the gate of the input transistor to be within a range between an upper limit voltage and lower limit voltage adjustable based on the bias voltage,
wherein the protective circuit includes:
a first MOS transistor that is diode-connected, and
a second MOS transistor disposed in parallel with the first MOS transistor and diode-connected in a reverse direction with respect to the first MOS transistor,
wherein a source of the first MOS transistor and a drain of the second MOS transistor are connected to the bias voltage, and
a body terminal of the first MOS transistor and a body terminal of the second MOS transistor are connected to a variable bias voltage.
2. An amplifier circuit, comprising:
an input transistor;
a resistor element having a first terminal connected to a gate of the input transistor and a second terminal connected to a bias voltage; and
a protective circuit connected to the gate of the input transistor and limiting an input to the gate of the input transistor to be within a range between an upper limit voltage and lower limit voltage adjustable based on the bias voltage,
wherein the protective circuit includes:
a first MOS transistor group including a plurality of MOS transistors disposed in series, respective MOS transistors being diode-connected in the same direction,
a second MOS transistor group disposed in parallel with the first MOS transistor group and including a plurality of MOS transistors disposed in series, respective MOS transistors being diode-connected in a reverse direction with respect to the respective MOS transistors included in the first MOS transistor group, and
a connection control unit controlling a short-circuit of sources and drains of the respective MOS transistors included in the first MOS transistor group and the second MOS transistor group.