A bias circuit includes a voltage stabilizer connected between a control voltage input terminal through a current limit resistor and a ground, a bias supply emitter follower with a base connected to a node between the current limit resistor and the voltage stabilizer through a resistor, and a current limiter connected between the base and an emitter of the bias supply emitter follower.
1. A bias circuit comprising:
a voltage stabilizer connected between a control voltage input terminal through a current limit resistor and a ground;
a bias supply emitter follower with a base connected to a node between the current limit resistor and the voltage stabilizer through a resistor; and
a current limiter connected between the base and an emitter of the bias supply emitter follower, wherein the current limiter comprises:
a current source having a current value that varies according to a voltage value input through the control voltage input terminal;
a transistor connected between the base of the bias supply emitter follower and the current source and having a base and a collector electrically connected to each other; and
a resistor connected between a node between the transistor and the current source and the emitter of the bias supply emitter follower.
2. The bias circuit according to claim 1 , wherein a base-emitter voltage of the bias supply emitter follower is set by the current limiter.
3. The bias circuit according to claim 1 , wherein a current flowing to the current source of the current limiter is substantially the same as a current flowing to the voltage stabilizer.
4. The bias circuit according to claim 1 , wherein the voltage stabilizer generates a voltage that is set based on a threshold voltage of a power amplifier transistor connected to the bias circuit and a threshold voltage of the bias supply emitter follower.
5. The bias circuit according to claim 1 , wherein the voltage stabilizer generates a voltage that is set based on a voltage that is generated based on temperature characteristics of a threshold voltage of a power amplifier transistor connected to the bias circuit and temperature characteristics of a threshold voltage of the bias supply emitter follower.
6. The bias circuit according to claim 1 , wherein the bias circuit is connected to an input terminal of a power amplifier transistor.
7. The bias circuit according to claim 1 , wherein the voltage stabilizer comprises a diode-connected transistor, and
the current limiter is controlled by a collector voltage of the diode-connected transistor.
8. The bias circuit according to claim 7 , wherein the current limiter comprises a current source transistor, and
the current source transistor and the diode-connected transistor form a current mirror.