High-frequency power amplifier
View Patent ↗In a base-bias-control-type high-frequency power amplifier with a plural stage configuration, a rising voltage of a base bias current supplied to an initial stage transistor is made lower than a rising voltage of a base bias current supplied to a second stage transistor by a bias circuit, and a difference between the both voltages is set to be smaller than a base-emitter voltage of an amplifying stage transistor. Also, a rising voltage of a base bias current supplied to a third stage transistor is made equal to the rising voltage of the base bias current supplied to an initial stage transistor. Accordingly, a technology capable of improving the power control linearity can be provided in a high-frequency power amplifier used in a polar-loop transmitter or the like.
1. A high-frequency power amplifier comprising:
a plurality of amplifying stage transistors; and
a bias circuit which supplies a base bias current to each amplifying stage transistor of said plurality of amplifying stage transistors,
wherein said base bias current supplied to each amplifying stage transistor varies linearly to a control voltage inputted into said bias circuit,
wherein a first control voltage at which a first base bias current supplied to a first amplifying stage transistor in an initial stage of said plurality of amplifying stage transistors rises is lower than a second control voltage at which a second base bias current supplied to a second amplifying stage transistor other than the initial stage rises, and
wherein a difference between said second control voltage and said first control voltage is smaller than a base-emitter voltage of said amplifying stage transistor.
2. The high-frequency power amplifier according to claim 1 ,
wherein the difference between said second control voltage and said first control voltage is larger than 0 V and equal to or less than 0.1 time the base-emitter voltage of said amplifying stage transistor.
3. The high-frequency power amplifier according to claim 1 ,
wherein the difference between said second control voltage and said first control voltage is larger than 0 V and equal to or smaller than 200 mV.
4. The high-frequency power amplifier according to claim 1 ,
wherein said bias circuit has a circuit for adjusting the difference between said second control voltage and said first control voltage.
5. The high-frequency power amplifier according to claim 4 ,
wherein the circuit for adjusting the difference between said second control voltage and said first control voltage is stabilized by a current mirror circuit.
6. The high-frequency power amplifier according to claim 1 ,
wherein said bias circuit comprises:
a voltage-current conversion circuit which converts a control voltage inputted to said bias circuit to a current;
a constant current circuit which adds an offset current to the current converted by said voltage-current conversion circuit; and
a constant voltage circuit which receives the current converted by said voltage-current conversion circuit to output said base bias current.
7. The high-frequency power amplifier according to claim 6 ,
wherein said constant current circuit includes a current mirror circuit and is stabilized by said current mirror circuit.
8. The high-frequency power amplifier according to claim 1 ,
wherein said plurality of amplifying stage transistors have three-stage configuration,
wherein said second amplifying stage transistor is an amplifying stage transistor in a second stage, and
wherein a third control voltage at which a third base bias current supplied to a third amplifying stage transistor in a third stage rises is equal to said first control voltage in the initial stage.
9. The high-frequency power amplifier according to claim 1 ,
wherein said plurality of amplifying stage transistors have three-stage configuration,
wherein said second amplifying stage transistor is an amplifying stage transistor in a third stage, and
wherein a third control voltage at which a third base bias current supplied to a third amplifying stage transistor in a second stage rises is equal to said first control voltage in the initial stage.
10. The high-frequency power amplifier according to claim 1 ,
wherein said plurality of amplifying stage transistors are heterojunction bipolar transistors.