Power amplifier
A power amplifier includes a first amplifier unit, a second amplifier unit, and an attenuator. The second amplifier receives a signal from the first amplifier unit and amplifies the signal. The attenuator is provided between the first and second amplifier units. The attenuator has arms, including at least one parallel arm and at least one series arm, and has switches connected to the arms to switch the electrical connection states of the arms with respect to the first and second amplifier units. The at least one parallel arm and the at least one series arm are alternately arranged, in the order named, as viewed in the direction from the first amplifier unit to the second amplifier unit.
1. A power amplifier comprising:
a first amplifier unit;
a second amplifier unit for receiving, along a signal connecting path, a signal from the first amplifier unit and amplifying the signal; and
an attenuator connected to the signal connecting path between the first and second amplifier units, wherein
the attenuator comprises
a plurality of arms, including a first parallel arm and a series arm, and
switches connected to the plurality of arms to switch the electrical connection states of the arms with respect to the first and second amplifier units,
the first parallel arm and the series arm are arranged, in that order, as viewed from the first amplifier unit toward the second amplifier unit,
the first parallel arm is the closest arm, with respect to electrical connection, of the arms to the first amplifier unit and is connected at one end to a connection point on the signal connecting path between the first and second amplifier units, and
the series arm follows the first parallel arm, as viewed from the first amplifier unit toward the second amplifier unit, and is connected in series with the signal connecting path between the connection point of the first parallel arm to the signal connecting path and second amplifier unit.
2. The power amplifier according to claim 1 , wherein the power amplifier further comprises a capacitive element connected in series with the series arm in the signal connecting path.
3. The power amplifier according to claim 2 , wherein the capacitive element is a capacitor having a variable capacitance.
4. The power amplifier according to claim 1 , wherein
the first parallel arm includes
a first capacitor connected at a first end to the signal connecting path between the first and second amplifier units,
a first base-collector (BC) diode having an anode and a cathode and connected at the anode to a second end of the first capacitor,
a second BC diode having an anode and a cathode and connected at the anode to the cathode of the first BC diode,
a second capacitor connected at a first end between the first BC diode and the first capacitor and, at a second end, to the cathode of the second BC diode, and
a first control voltage terminal for controlling the voltage at a point between the first capacitor and the first BC diode, and
the series arm includes
a resistance connected at a first end to the first amplifier unit and, at a second end, to the second amplifier unit,
a third BC diode having an anode and a cathode and connected in parallel with the resistance so that the cathode is connected between the first end of the resistance and the first amplifier unit and the anode is connected between the second end of the resistance and the second amplifier unit,
a fourth BC diode having an anode and a cathode and connected at the anode to the cathode of the third BC diode,
a third capacitor connected at a first end to the anode of the third BC diode and, at a second end, to the cathode of the fourth BC diode, and
a second control voltage terminal for controlling the voltage of the anode of the third BC diode.
5. The power amplifier according to claim 1 , wherein the attenuator is an L attenuator.
6. The power amplifier according to claim 1 , wherein:
the attenuator is a Π (pi) attenuator;
the plurality of arms includes the first parallel arm, the series arm, and a second parallel arm; and
the first parallel arm, the series arm, and the second parallel arm are arranged in succession, in that order, as viewed from the first amplifier unit toward the second amplifier unit.
7. The power amplifier according to claim 1 , wherein:
each of the first and second amplifier units includes a heterojunction bipolar transistor;
the switches of the attenuator are field effect transistors; and
the heterojunction bipolar transistors and the field effect transistors are formed on the same semiconductor substrate in a BiFET process.
8. The power amplifier according to claim 2 , wherein the capacitive element is a capacitor.
9. The power amplifier according to claim 1 , wherein the power amplifier further comprises an inductive element connected in series with the series arm in the signal connecting path.
10. The power amplifier according to claim 9 , wherein the inductive element is an inductor having variable inductance.
11. The power amplifier according to claim 2 , wherein the capacitive element is a diode having a cathode and an anode and connected so that the cathode faces the first amplifier unit and the anode faces the second amplifier unit.
12. The power amplifier according to claim 9 , wherein the inductive element is an inductor.
13. The power amplifier according to claim 9 , wherein the inductive element is a diode having a cathode and an anode and connected so that the cathode faces the first amplifier unit and the anode faces the second amplifier unit.