Power amplification circuit
A power amplification circuit includes an amplification transistor, a variable voltage power supply that supplies a variable voltage to a collector of the amplification transistor, a bias circuit that has a constant current amplification transistor outputting a DC bias current to a base of the amplifier transistor, and a current limiting circuit that limits the DC bias current. The current limiting circuit includes a current limiting transistor, a resistor element connected to a collector of the current limiting transistor and the variable voltage power supply, and a resistor element connected to a base of the current limiting transistor and a base of the constant current amplifying transistor.
1. A power amplification circuit, comprising:
a first amplification transistor that has a first terminal, a second terminal, and a first control terminal, that is configured to perform power amplification on a high-frequency signal input from the first control terminal, and that is configured to output the high-frequency signal on which the power amplification has been performed from the first terminal;
a variable voltage power supply configured to supply a variable voltage to the first terminal;
a bias circuit configured to output a direct current (DC) bias current; and
a current limiting circuit configured to limit the DC bias current,
wherein the bias circuit comprises a constant current amplification transistor that has a third terminal, a fourth terminal, and a second control terminal and that is configured to output the DC bias current from the fourth terminal to the first control terminal, and
wherein the current limiting circuit comprises:
a current limiting transistor that has a fifth terminal, a sixth terminal, and a third control terminal, the sixth terminal being connected to the fourth terminal;
a first resistance element having a first end connected to the fifth terminal and having a second end connected to the variable voltage power supply; and
a second resistance element having a first end connected to the third control terminal and having a second end connected to the second control terminal.
2. The power amplification circuit according to claim 1 , wherein when the variable voltage becomes less than a reference voltage, as a potential difference between the reference voltage and the variable voltage increases, the current limiting circuit is configured to increase a DC limiting current flowing from the second control terminal to the fifth terminal and through the third control terminal.
3. The power amplification circuit according to claim 1 , wherein:
the first resistance element includes a first split resistor and a second split resistor connected in series, and
the current limiting circuit further comprises:
a first capacitive element connected in parallel to the first split resistor; and
a second capacitive element connected between the third control terminal and the fifth terminal.
4. The power amplification circuit according to claim 2 , wherein:
the first resistance element includes a first split resistor and a second split resistor connected in series, and
the current limiting circuit further comprises:
a first capacitive element connected in parallel to the first split resistor; and
a second capacitive element connected between the third control terminal and the fifth terminal.
5. The power amplification circuit according to claim 1 , wherein:
the first resistance element comprises a first split resistor and a second split resistor connected in series, and
the current limiting circuit further comprises:
a first capacitive element connected between the sixth terminal and a node between first split resistor and the second split resistor; and
a second capacitive element connected between the third control terminal and the fifth terminal.
6. The power amplification circuit according to claim 2 , wherein:
the first resistance element comprises a first split resistor and a second split resistor connected in series, and
the current limiting circuit further comprises:
a first capacitive element connected between the sixth terminal and a node between first split resistor and the second split resistor; and
a second capacitive element connected between the third control terminal and the fifth terminal.
7. The power amplification circuit according to claim 1 , wherein the power amplification circuit comprises a plurality of amplification transistors connected in cascade, the first amplification transistor being one of the plurality of amplification transistors.
8. The power amplification circuit according to claim 2 , wherein the power amplification circuit comprises a plurality of amplification transistors connected in cascade, the first amplification transistor being one of the plurality of amplification transistors.
9. The power amplification circuit according to claim 3 , wherein the power amplification circuit comprises a plurality of amplification transistors connected in cascade, the first amplification transistor being one of the plurality of amplification transistors.
10. The power amplification circuit according to claim 5 , wherein the power amplification circuit comprises a plurality of amplification transistors connected in cascade, the first amplification transistor being one of the plurality of amplification transistors.
11. The power amplification circuit according to claim 7 , wherein the first amplification transistor is a final stage transistor closest to an output terminal of the power amplification circuit.
12. The power amplification circuit according to claim 7 , wherein the first amplification transistor is a transistor of at least one stage anterior to a final stage transistor closest to an output terminal of the power amplification circuit.
13. The power amplification circuit according to claim 11 , wherein the first amplification transistor is a transistor of at least one anterior stage relative to a final stage transistor closest to an output terminal of the power amplification circuit.
14. The power amplification circuit according to claim 1 , further comprising a power supply control circuit configured to control the variable voltage in accordance with a high-frequency power amplitude of a high-frequency input signal input to the power amplification circuit.
15. The power amplification circuit according to claim 14 , wherein the power supply control circuit is configured to control the variable voltage such that the variable voltage is a linear function of the high-frequency power amplitude.