Power amplifier module
A power amplifier module includes an amplifier that amplifies an input signal and outputs an amplified signal, an emitter follower transistor that supplies a bias signal to the amplifier to control a bias point of the amplifier, and a current source that supplies a control current which changes in accordance with a change in control voltage to a collector of the emitter follower transistor. The current source limits the control current to not greater than an upper limit.
1. A power amplifier module comprising:
an emitter follower transistor configured to supply a bias signal to an amplifier; and
a first current source configured to:
supply a control current to a collector of the emitter follower transistor,
change the control current in accordance with a change in a control voltage of the first current source, and
limit the control current to be less than or equal to an upper limit, the upper limit varying in accordance with the control voltage.
2. The power amplifier module according to claim 1 , further comprising:
a second current source configured to supply a constant current to a base of the emitter follower transistor.
3. The power amplifier module according to claim 2 , wherein the control current and the constant current are controlled independently.
4. The power amplifier module according to claim 1 , wherein the control voltage is selected to be one of a constant voltage and a ramp voltage.
5. The power amplifier module according to claim 1 , wherein the first current source comprises:
a voltage-current conversion circuit configured to convert the control voltage into a temperature-independent current,
a temperature compensation circuit configured to generate a temperature-dependent current that compensates for a change in the control current due to a temperature, and
a combining circuit that generates the control current based on the temperature-independent current and the temperature-dependent current.
6. The power amplifier module according to claim 1 , wherein the first current source comprises:
a voltage-current conversion circuit configured to convert the control voltage into a temperature-independent current,
a temperature compensation circuit configured to:
generate a first temperature-dependent current that compensates for a change in the control current due to temperatures equal to or greater than a room temperature, and
generate a second temperature-dependent current that compensates for a change in the control current due to temperatures less than the room temperature, and
a combining circuit that generates the control current based on the temperature-independent current and the temperature-dependent current.
7. The power amplifier module according to claim 4 , wherein the first current source comprises:
a voltage-current conversion circuit configured to convert the control voltage into a temperature-independent current,
a temperature compensation circuit configured to generate a temperature-dependent current that compensates for a change in the control current due to a temperature, and
a combining circuit that generates the control current based on the temperature-independent current and the temperature-dependent current.
8. The power amplifier module according to claim 7 , wherein the first current source further comprises a switch configured to selectively connect one of the constant voltage and the ramp voltage to the voltage-current conversion circuit.
9. The power amplifier module according to claim 5 , wherein the temperature-dependent current has a one-dimensional or a two-dimensional change characteristic.
10. The power amplifier module according to claim 5 , wherein the combining circuit is configured to generate the control current by multiplying the temperature-independent current by a correction coefficient corresponding to the temperature.
11. The power amplifier module according to claim 6 , wherein the combining circuit is configured to generate the control current by multiplying the first temperature-independent current and the second temperature-independent current by correction coefficients corresponding to the temperature.
12. The power amplifier module according to claim 8 , wherein the combining circuit is configured to generate the control current by multiplying the temperature-independent current by a correction coefficient corresponding to the temperature.
13. The power amplifier module according to claim 9 , wherein the combining circuit is configured to generate the control current by multiplying the temperature-independent current by a correction coefficient corresponding to the temperature.
14. The power amplifier module according to claim 5 , wherein the combining circuit is configured to generate the control current by adding the temperature-independent current to a current correction value corresponding to the temperature.
15. The power amplifier module according to claim 6 , wherein the combining circuit is configured to generate the control current by adding the first temperature-independent current and the second temperature-independent current to current correction values corresponding to the temperature.
16. The power amplifier module according to claim 8 , wherein the combining circuit is configured to generate the control current by adding the temperature-independent current to a current correction value corresponding to the temperature.
17. The power amplifier module according to claim 9 , wherein the combining circuit is configured to generate the control current by adding the temperature-independent current to a current correction value corresponding to the temperature.
18. The power amplifier module according to claim 1 , further comprising:
an amplifier configured to amplify an input signal and output an amplified signal.