Radio-frequency power amplifier

1. A radio-frequency multistage power amplifier using hetero bipolar transistors of which emitters are connected to ground, the radio-frequency multistage power amplifier comprising:

a first amplification stage including a first hetero bipolar transistor of which collector output is detected;

a second amplification stage which is prior to the first amplification stage and includes a second hetero bipolar transistor in which the detection result is reflected;

a first resistor provided between a collector of the second hetero bipolar transistor and a power supply; and

a protection circuit which is connected between a collector of the first hetero bipolar transistor and the collector of the second hetero bipolar transistor, detects output from the collector of the first hetero bipolar transistor, and reduces a voltage of the collector of the second hetero bipolar transistor in accordance with the detected output.

2. The radio-frequency multistage power amplifier according to claim 1 ,

wherein the protection circuit includes:

a diode circuit having an anode terminal connected to the collector of the first hetero bipolar transistor and also having a cathode terminal; and

a third hetero bipolar transistor of which a base is connected to the cathode terminal, a collector is connected to the collector of the second hetero bipolar transistor, and an emitter is connected to ground, and

wherein the protection circuit detects a voltage of the collector of the first hetero bipolar transistor.

3. The radio-frequency multistage power amplifier according to claim 2 ,

wherein the diode circuit has a plurality of diodes series-connected therein.

4. The radio-frequency multistage power amplifier according to claim 2 ,

wherein the protection circuit further includes:

a second resistor provided between the anode terminal and the collector of the first hetero bipolar transistor; and

a third resistor provided between the collector of the third hetero bipolar transistor and the collector of the second hetero bipolar transistor.

5. The radio-frequency multistage power amplifier according to claim 2 ,

wherein the protection circuit further includes

a capacitor of which one end is connected to the base or the collector of the third hetero bipolar transistor and the other end is connected to ground.

6. The radio-frequency multistage power amplifier according to claim 4 ,

wherein the protection circuit further includes

an inductor provided between the second resistor and the collector of the first hetero bipolar transistor or between the third resistor and the collector of the second hetero bipolar transistor.

7. The radio-frequency multistage power amplifier according to claim 2 ,

wherein the protection circuit further includes

a resistor of which one end is connected to the base of the third hetero bipolar transistor and the other end is connected to ground.

8. The radio-frequency multistage power amplifier according to claim 3 ,

wherein an anode and a cathode of any one of the plurality of diodes included in the diode circuit are connected by a resistor.

9. The radio-frequency multistage power amplifier according to claim 1 , further comprising a second resistor provided between a base of the second hetero bipolar transistor and a bias power supply,

wherein the protection circuit is further connected to the base of the second hetero bipolar transistor and further reduces a voltage of the base of the second hetero bipolar transistor in accordance with the collector output.

10. The radio-frequency multistage power amplifier according to claim 9 ,

wherein the protection circuit includes:

a diode circuit having an anode terminal connected to the collector of the first hetero bipolar transistor and also having a cathode terminal;

a third hetero bipolar transistor of which a base is connected to the cathode terminal, a collector is connected to the collector of the second hetero bipolar transistor, and an emitter is connected to ground; and

a fourth hetero bipolar transistor of which a base is connected to the cathode terminal, a collector is connected to the base of the second hetero bipolar transistor, and an emitter is connected to ground, and

wherein the protection circuit detects a voltage of the collector of the first hetero bipolar transistor.

11. The radio-frequency multistage power amplifier according to claim 1 ,

wherein the protection circuit includes:

a first capacitor of which one end is connected to the collector of the first hetero bipolar transistor;

a diode detector circuit having an input terminal connected to the other end of the first capacitor and also having an output terminal, thereby converting power inputted from the input terminal into a voltage and outputting the voltage from the output terminal;

a third hetero bipolar transistor of which a base is connected to the output terminal of the diode detector circuit, a collector is connected to the collector of the second hetero bipolar transistor, and an emitter is connected to ground; and

a second resistor which is parallel-connected between the first capacitor and the input terminal of the diode detector circuit and of which one end is connected to ground, and

wherein the protection circuit detects power of the collector of the first hetero bipolar transistor.

12. The radio-frequency multistage power amplifier according to claim 11 ,

wherein the diode detector circuit includes:

a diode of which an anode is connected to the input terminal and a cathode is connected to the output terminal; and

a third resistor and a second capacitor, each of which is parallel-connected between the cathode of the diode and the output terminal and of each of which one end is connected to ground.

13. The radio-frequency multistage power amplifier according to claim 12 ,

wherein the protection circuit further includes a fourth resistor between the collector of the third hetero bipolar transistor and the collector of the second hetero bipolar transistor.