Input circuitry for transistor power amplifier and method for designing such circuitry

1. A circuit, comprising:

an input impedance matching network;

a transistor coupled to an output of the impedance matching network; and

wherein the input matching network has a first input impedance when such input matching network is fed with an input signal having a relatively low power level and wherein the input matching network has an input impedance different from the first input impedance when such input matching network is fed with an input signal having a relatively high power level.

2. The circuit recited in claim 1 wherein the transistor has a field plate.

3. The circuit recited in claim 1 wherein the transistor is a gallium nitride transistor.

4. The circuit recited in claim 3 wherein the transistor has a field plate.

5. A circuit, comprising;

a transistor having an input electrode;

an input matching network having an input fed by an input signal and having an output connected to the input electrode of the transistors;

a power level sensing circuit fed by the input signal; and

wherein the input matching network is responsive to the power level sensing circuit to: configure the input matching network with a first input impedance when such power level sensing circuit senses the input signal has a relatively low power level; and configure the input matching network with an input impedance different from the first input impedance when such power level sensing circuit senses the input signal has a relatively high power level.

6. The circuit recited in claim 5 wherein the transistor has a field plate.

7. The circuit recited in claim 5 wherein the transistor is a gallium nitride transistor.

8. The circuit recited in claim 7 wherein the transistor has a field plate.

9. A circuit, comprising;

a transistor having an input electrode;

an input matching network having an input fed by an input signal and having an output connected to the input electrode of the transistors;

a power level sensing circuit fed by the input signal;

wherein the input matching network is responsive to the power level sensing circuit to: configure the input matching network with a first input impedance when such power level sensing circuit senses the input signal has a relatively low power level; and configure the input matching network with an input impedance different from the first input impedance when such power level sensing circuit senses the input signal has a relatively high power level; and

wherein the input matching network has a first inductor serially coupled between the input signal and the input electrode of the transistor when such power level sensing circuit senses the input signal has the relatively high power level and wherein the input matching network has a second inductor serially coupled between the input signal and the input electrode of the transistor when such power level sensing circuit senses the input signal has the relatively low power level.

10. The circuit recited in claim 9 wherein the transistor has a field plate.

11. The circuit recited in claim 9 wherein the transistor is a gallium nitride transistor.

12. The circuit recited in claim 11 wherein the transistor has a field plate.

13. The circuit recited in claim 9 wherein the transistor is a field effect transistor and wherein the input electrode is a gate electrode of such transistor.

14. The circuit recited in claim 13 wherein the transistor has a field plate.

15. The circuit recited in claim 13 wherein the transistor is a gallium nitride transistor.

16. The circuit recited in claim 15 wherein the transistor has a field plate.

17. A circuit, comprising;

a transistor having an input electrode;

an input matching network having an input fed by an input signal and having an output connected to the input electrode of the transistors;

a power level sensing circuit fed by the input signal; and

wherein the input matching network is responsive to the power level sensing circuit to: configure the input matching network with a first input impedance when such power level sensing circuit senses the input signal has a relatively low power level; and configure the input matching network with an input impedance different from the first input impedance when such power level sensing circuit senses the input signal has a relatively high power level;

wherein the input matching network includes:

a pair of electrical components; and

at least one switch, and

wherein the at least one switch operates in response to the power level sensing circuit to electrically decouple one of the pair of electrical components from the input matching network at one of the relatively high or relatively low power levels and operates to electrically couple said one of the pair of electrical components to the input matching network at the other one of the relatively high or relatively low power levels.

18. The circuit recited in claim 17 wherein the electrical components are inductors having different inductances.

19. The circuit recited in claim 1 wherein the input matching network includes:

a pair of reactive electrical components; and

at least one switch, and

wherein the at least one switch operates in response to the power level sensing circuit to electrically decouple one of the pair of reactive electrical components from the input matching network at one of the relatively high or relatively low power levels and operates to electrically couple said one of the pair of reactive electrical components to the input matching network at the other one of the relatively high or relatively low power levels.